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CHAPTER 4: STRONG MOTION OBSERVATIONS

GENERAL ASPECTS OF STRONG-MOTION OBSERVATIONS DURING THE EARTHQUAKE Peng Kezhong, Yu Shuangjiu and Guo Yuxue*

The main shock accelerograms were recorded at most of the stations of the strong-motion accelerograph network in North during the Tangshan earthquake of magnitude 7.8. Strong-motion records were also recorded at some of the stations during the Luanxian earth- quake of magnitude 7.1 and the Ninghe earthquake of magnitude 6.9. After the main shock of the Tangshan earthquake occurred some mobile observation stations were quickly deployed in Tangshan City and its nearby regions, and a number of near-source records from the aftershocks were obtained thereafter.

I. Strong-Motion Accelerograph Network in North China After the 1966 earthquake in Province a strong-motion accelerograph net- work of China was first established and developed slowly in North China. Prior to the July 28, a total of 23 accelerographs had been installed. Among them, 18 accelerographs (Model RDZ1-12-66) were operated by the Institute of Engineering Mechanics, Academia Sinica (IEM), 3 accelerographs (Model RDZ1-12-66) were operated by the Institute of Earthquake Engineering, Chinese Academy of Building Research (IEE), one accelerograph (Model SG-4-12) by the Institute of Scientific Research, Ministry of Water Conservancy and Electric Power (ISR), and one accelerograph (Model SMAC-B2) by the Institute of Geophysics, State Seismological Bureau (IGP). After the Tangshan earth- quake of magnitude 7.8 another accelerograph was supplemented at Baliqiao in Tongxian County by IEE. The total of 24 accelerographs was deployed. The distribution of the strong- motion accelerograph stations in North China is shown in Figure 1. The basic information on stations of the network is given in Table 1.

II. Instrumentation There were 3 types of strong-motion accelerographs used in the permanent network and the mobile stations: Models RDZ1-12-66, SG-4-12 and SMAC-B2.

* Institute of Engineering Mechanics, State Seismological Bureau 340

(1) RDZ1-12-66 strong-motion accelerograph The RDZ1-12-66 is a multi-channel instrument with galvanometer registrations. It con- sists of one electromagnetic optical oscillograph of Model RDZ1, eight horizontal trans- ducers of Model RPS1, four vertical transducers of Model RZS1, two mechanical triggers of Model RCF1 and one protective support for the oscillograph (see Photos 1–4). They were designed by IEM and produced by the Geological Instrument Factory (Huang Zhen- ping et al., 1977). The RDZ1-12-66 is used with external batteries. Both the horizontal and vertical transducers were velocity sensing pendulum. While the coils of the transducer move in the magnetic field during an event, the current generated in the coils is directly proportional to the acceleration of the measured point and the current would drive the high-frequency galvanometer coupled with the transducer to record the acceleration. To connect the transducer with the galvanometer for a recording channel, a dual T-shaped network of resistance coupling shown in Fig. 2 is adopted. In this figure, Rs was the interior resistance of a sensor coil, R1 the damping resistance of the sensor, R2 an adjustable resistor for changing the sensitivity of the recording channel, rg is the interior resistance of a galvanometer coil, rd and R3 represent a matched resistance for adjusting the sensitivity of the recording channel and the damping resistor of the galvanometer respec- tively. The primary technical specifications of the transducer, galvanometer and trigger are given in Tables 2 to 4. The technical specifications of the accelerograph are as follows: 1. Flat frequency response: 0.5 to 35 Hz (Fig. 3). 2. Recording sensitivity: 0.5 to 10 gal/mm (with Model FC6-120 galvanometer), adjust- able. 5 to 100 gal/mm (with Model FC6-400 galvanometer), adjustable. 3. Triggering sensitivity: minimal triggering level of 1 gal, adjustable. 4. Start-up time: full operation within 0.2 to 0.25 Sec. 5. Optical arm length of oscillograph: 308.38 mm. 6. Recording medium: photographic paper, width of 200 mm, length of 20 m. 7. Paper speed: 2.1, 4.8, and 11.3 cm/s, selectable, paper speed variations less than 3% within 1 m. 8. Hold-on time: 2 to 3 Sec. Continuous running is possible when acceleration is larger than triggering level.

9. Timing mark: 20 ±0.1 Hz. 10. Power: DC 25 volts (nominal), rechargeable batteries.

11. Size of oscillograph: 490 ×358 ×353 mm. 341

12. Weight of oscillograph: 35 kilograms.

13. Operating temperature: 0°C to 40°C for oscillograph, −20°C to +40°C for transducer.

(2) Model SG-4-12 strong-motion accelerograph** The SG-4-12 is a multi-channel galvanometer recording system designed to record strong earthquake motion. It consists of an electromagnetic optical oscillograph of Model SG-4-12, developed by the Institute of Scientific Research, Ministry of Water Conservancy and Elec- tric Power, and DJ651-B seismic detectors manufactured by the Xian Chemical Instrument Factory. The natural frequency of the sensor is about 26 Hz and the damping constant is 0.35 to 0.5. The sensor is considered as an acceleration transducer for recording strong ground motion, because the output current of the sensor is directly proportional to derivative of acceleration at a measured point. Integral galvanometers or low frequency galvanometers with the natural frequency, f2 , of 10 Hz and the damping constant of 0.15 to 0.2 were used to respond to the sensor's current and then to record the acceleration at the measured point. Two types of triggers were used in this accelerograph. One was the electromagnetic type and the other was the mechanical trigger. The former consisted of a DJ651-B sensor, an elec- tronic amplifier and a control circuit and the latter consisted of a horizontal pendulum, a ver- tical pendulum, a set of contact switches and a control circuit. The appearance of the SG-4-12 is shown in Photo 5. A resistance coupling network shown in Fig. 4 was used to couple a sensor with a galvanometer. In this figure, Rs is the interior resistance of the sensor coil, R1 is the damping resistance of the sensor, R2 is a vari- able resistor for changing the sensitivity, and rg is the interior resistance of a galvanometer. Rd is a matched resistance to adjust the damping of the galvanometer. The primary technical specifications of the sensor and the galvanometer for the SG-4-12 strong-motion accel- erograph are given in Table 5 and Table 6. The technical specifications of the SG-4-12 accelerograph are as follows: 1. Flat frequency response: 0.5 to 20 Hz. 2. Dynamic range: 1 to 200 gal. 3. Triggering sensitivity: from 1 gal, adjustable, for the mechanical trigger. Four levels (1, 2.5, 5, 10) are available for the electromagnetic trigger. 4. Hold-on time: 3 to 60 Sec., adjustable. 5. Optical arm length: 0.32 m. 6. Photographic paper: width of 120 mm, sensitivity of 140 DIN.

** The specifications of SG-4-12 is provided by Mr. Su Kezhong of ISR.

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7. Paper speed: 5 cm/sec. 8. Number of channels: a total of 12, 10 channels for recording, 2 channels for timing marks. 9. Timing mark: 10 Hz. 10. Power : AC 220 volts; DC 12 or 24 volts. (3) Model SMAC-B2 strong-motion accelerograph The SMAC-B2 strong-motion accelerograph is a direct mechanical scratch recording sys- tem, which is manufactured by AKASHI SEISAKUSHO, LTD., Japan (Photo 6). Three torsional type accelerometers with the natural frequency of 7.14 Hz in an orthogo- nal position were fixed in the accelerograph. The air piston damper is used for critical damping. The recording system was operated by a mechanical spiral spring. Both the hori- zontal and vertical triggers were available: the former is a horizontal one controlled by a mechanical fall-ball system and the latter is a vertical electric pendulum. Its technical specifications are as follows: 1. Flat frequency response: 0 to 7 Hz. 2. Sensitivity: 12.5 gal/mm. 3. Dynamic range: 6 to 500 gal. 4. Timing mark: 1 Hz. 5. Recording speed: 10 mm/sec. 6. Recording medium: wax paper, width of 280 mm and length of 10 m. 7. Number of channels: a total of 4, 3 channels for recording, l channel for timing mark. 8. Triggering sensitivity: 100 gal. for the fall-ball type trigger; 10 gal. for the vertical pendulum starter, adjustable. 9. Single recording duration: 3 minutes, up to 5 times of recording. 10. Power: DC 6 volts.

11. Size: 540 ×540×370 mm. 12. Weight: 100 kilograms. 343

III. Strong-Motion Data Acquisition of the Tangshan Earthquake (1) Records from the main shock of magnitude 7.8 During the Tangshan earthquake of magnitude 7.8 a total of 58 well recorded accelera- tion traces were recorded at 7 stations (8 accelerographs) of the strong-motion network in North China: the Beijing Hotel Station (2 accelerographs), the Hujialou Building Station, the Miyun Reservoir Dam Station, the Sanlihe Building Station, the Guanting Reservoir Dam Station, the Fengcun Bridge Station and the Hongshan Ground Station (see Table 7). In addition, 6 accelerographs installed at the Friendship Hotel Station, the Fensiting Station, the Babaoshan Subway Station, the Baijiatan Station, the Hospital Station and the Secondary Dam Station of Huangbizhuang were triggered, but records were not transferred due to some faults. The other 9 accelerographs were not triggered because of environmental reasons or the distance from the epicenter. (2) Records from the Luanxian earthquake of magnitude 7.1 and the Ninghe earthquake of magnitude 6.9 During the Luanxian earthquake of magnitude 7.1, which occurred at 18 h 45 m, July 28, 1976, 45 acceleration traces were recorded at 5 stations: the Beijing Diplomatic Apartment Station, the Hujialou Station, the Fengcun Bridge Station of Hebei Province, the Huangbiz- huang Reservoir Emergency Spillway Station and the Normal Spillway Station (Table 8). During the Ninghe earthquake of magnitude 6.9 which occurred at 21 h 53 m, November 15, 1976, 72 acceleration traces were recorded at 9 stations: the Tianjin Hospital Station, the Tongxian Dongguan Bridge Station, the Tongxian Baliqiao Station, the Beijing Hotel Station, the Zhoungguancun Station, the Babaoshan Subway Station, the Zhoukoudian Station, the Guanting Reservoir Station and the Fengcun Bridge Station (Table 9). During this earthquake an excellent accelerogram with the maximum ground acceleration of 0.15 g was obtained at the Tianjin Hospital building, a 9-story reinforced concrete frame structure which is 56.5 kilometers from the epicenter. (3) Near source accelerograms recorded during the aftershocks After the main shock, four mobile stations were immediately deployed at the Tangshan Airport, the Tangshan Cement Factory, the Qianan Luanhe Bridge and the Changli Fen- ghuangshan Seismic Station by IEM. In addition, a mobile station was installed at the Yutian Guest House by IEE. The instruments operated at the five mobile stations were all RDZ1-12-66 accelerograph. The locations of the mobile stations is shown in Figure 1. The aftershocks occurred very frequently. As of October 1, 1976, 163 strong-motion accelerograms had been recorded at the five mobile stations from 134 aftershocks. The after- shock magnitudes ranged from 3.1 to 5.8. The epicentral distances varied from 2.0 to 72.5 kilometers. The observed objects and relevant records for each mobile station are given in Table 10. 344

IV. Data Processing and Analysis The strong-motion accelerograms from the Tangshan earthquake were all recorded on photographic paper except for the accelerogram obtained at the Sanlihe Station, which was recorded on wax paper by the SMAC-B2 accelerograph. There were several acceleration traces and two timing mark traces on each record. The timing mark traces were placed at the top and bottom of the record, respectively. The zero trace sections at the beginning of the acceleration curves before the triggering of the accel- erograph could be used as reference zero traces. Generally, a record contains also a fixed trace named as zero baseline, which is produced by a fixed galvanometer mirror in the accel- erograph. Based on the integrity, acceleration amplitudes and usefulness of records the accelero- grams were processed and analyzed in the following three phases. (1) Preliminary analysis

As the preliminary results the maximum acceleration value Am, the length T1 and the primary period Tp corresponding to the Am, were directly measured with a steel ruler on the original records. First, measuring the distance between the reference zero trace of an accel- eration trace and the fixed zero baseline of the record, then, measuring the distance between the point corresponding to the maximum acceleration of the acceleration trace and the fixed zero baseline, then the peak acceleration value, Am, was scaled according to the sensitivity. The period corresponding to the Am, was obtained according to the given paper speed. The length of a record was read out from the beginning to the end of the record by the reference timing mark. The peak ground accelerations and the durations are given in Table 7 to Table 9. All preliminary analysis results of the accelerograms from the strong-motion net- work in North China and the mobile stations will be given in the following paragraphs of this chapter. (2) Digitizing processing For further analysis the accelerograms were also digitized on a manually operated DT- 206 digitizer made in Japan (see Photo 7). The maximum length of the unit for each digitizing was 740 mm. In case the recording length of an accelerogram was longer than 740 mm the digitization of the accelerogram had to be divided into several sections and then the record was digitized section by section. The sensitivity of the digitizer may be adjusted from 1 to 10 digital counts per millimeter in the X axis and from 1 to 50 digital counts per millimeter in the Y axis. The acceleration traces were digitized on an unequal time space. All significant peaks and points of inflection had been digitized along with as many intermediate points as was needed for an accurate definition of shape. The average number of digitized points per second was about 40 to 50. The digitizing interval of fixed traces was approximately 0.25 Sec.. The digitizing interval of timing marks was 0.2 Sec. The digitization of the strong-motion accelerograms had been carried out in accordance with the standard programs (Zhou Yongnian, 1979). Because timing marks are digitized and 345 smoothed by a weighted averaging method, accurate time for all picked points may be calcu- lated by using the programs, and the effects of paper speed variation could then be elimi- nated. The digitized data of fixed traces were also smoothed by a weighted averaging. Acceleration digitizing data are obtained by subtracting the corresponding smoothed digitized samples of the fixed baseline from the acceleration trace samples, so long period distortion caused by placing the record on the table of the digitizing system, by irregular transversal motions of the paper due to misalignment could be automatically eliminated. Finally, the zero axis of an acceleration trace should be translated to make the integral of the digitized acceleration curve over the length of the record equal to zero. This would mean physically that the variation in velocity from the beginning to the end of a record is zero. Then, the zero baseline of the digitized acceleration curve is preliminarily determined. Obvi- ously, the digitized data may be considered to be a reasonable representation of the original record, as long as the number of digitized points was enough. (3) Routine analysis Corrected accelerograms, integrated velocity and displacement curves, calculated response spectra and Fourier spectra, and so on, were all performed in the routine analysis. The instrumental and baseline corrections to the digitized accelerograms were performed according to the differential-integral method (Xie Li-Li et al., 1981), and then the corrected accelerograms were obtained. The digital filtering methods were used to restrain the long period digitizing noise in the baseline correction and calculation of velocity and displacement (Trifunic, M. D. 1971). Cut-off frequency of 35 Hz was selected for low-pass filters. Cut-off frequency for high-pass filters was selected based on the length of a digitized record, Tl, and the digitizing noise characteristics. Usually, 2/Tl to 4/Tl was selected as the cut-off frequency for high-pass filters (Xie Li-Li). In the following paragraphs of this chapter, the corrected accelerograms are presented for some typical structures and from aftershocks in which the strong-motion accelerograms were simultaneously obtained at several mobile stations. All corrected data from routine analysis were published in the Report on Strong Earthquake Motion Records in China, Vol. 1, No. 1 to 4, by the Seismological Press. References Huang Zhenping, "RDZ1 Strong-motion Accelerograph and its Field Calibration Method," Research Reports on Earthquake Engineering, Vol. 3, 1977, Science Press. State Seismological Bureau, "The Code of Seismological Observation (trial edition)," Seismological Press, 1978, (in Chinese). Zhou Yongnian, "Digitizing Method and Computing Procedures of Strong-motion Accelero- gram," Research Report, IEM, Academia Sinica, 1979, (in Chinese) Xie Lili, Li Shabai and Qian Qukang, "Study on the Instrument Correction of Accelerograms Recorded by Accelerograph Coupled with Galvanometers," Earthquake Engineering and Engineering Vibration, Vol. 1, No. 1, 1981, (in Chinese). Trifunic, M. D., "Zero Baseline Correction of Strong-Motion Accelerograms," BSSA, Vol. 61, pp. 1201–1211, 1971. 346

Xie Lili, Li Shabai, Qian Qukang and Hu Chengxian, "Some Features of Strong-motion Data Processing Procedure in IEM," Proceedings of US-PRC Workshop on Earthquake Engineering, August 27–30, 1982, Harbin, China. (Translator: Li Shabai, Xie Li-Li) 347

Table 1. Summary of stations of the strong-motion network in North China. Instrument No. of Installatio Station Name Location Observed Object Owner Model Channels n Date Hongshan , Ground (Rock) RDZ 1 9 December IEM Hebei Province l966 Secondary dam of Huolu County, Earth dam RDZ 1 9 May IEM Huang Bizhuang Hebei Province 1966 Reservoir Emergency spillway Houlu County, Sluice pier of the RDZ 1 12 September IEM of Huangbizhuang Hebei Province spillway 1967 Reservoir Normal spillway of Huolu County, Interface of sluice RDZ 1 9 July IEM Huangbizhuang Hebei Province with earth dam, 1971 Reservoir ground (rock) 13th Institute , Building of Heating RDZ 1 12 May IEM Hebei Province Power Station 1966 CAAC Dongcheng 13-story building RDZ 1 12 September IEM , Beijing R.C. frame 1967 Hujialou Chaoyang 6-story building RDZ 1 12 April IEM District, Beijing brick structure 1967 Friendship Hotel Haidian District, 7-story building RDZ 1 12 October IEM Beijing brick structure 1967 Miyun Reservoir Miyun County, Earth dam RDZ 1 12 November IEM Beijing 1967 Tianjin Hospital Tianjin 9-story building RDZ 1 12 April IEM R.C. frame 1967 Tongxian Dongguan Tongxian Highway bridge RDZ 1 12 March IEM Bridge County, Beijing 1968 Shunyi Bridge Shunyi County, Highway bridge RDZ 1 12 February IEM Beijing 1969 Fengcun Bridge Longyao County, Railway bridge RDZ 1 12 September IEM Hebei Province 1969 Zhongguancun Haidian District, Ground (soil) RDZ 1 6 October IEM Beijing 1973 Beijing Hotel Dongcheng 17 story building 2-RDZ 1 21 August IEM District, Beijing R.C. frame 1974 Baijiatuan Haidian District, Ground (soil) RDZ 1 6 May IEM Beijing 1976 Zhoukoudian Fangshan Ground (rock) RDZ 1 6 May IEM County, Beijing 1976 Sanlihe Haidian District, Basement ground SMAC-B2 3 1969 IGP Beijing (soil) Guanting Reservoir Yanqing County, Earth dam SG-4-12 8 1968 ISR Beijing Babaoshan Subway Shijingshan, Underground RDZ 1 12 December CABR District. Beijing engineering 1975 Fensiting Dongcheng Ground (soil) RDZ 1 6 June CABR District, Beijing 1974 Diplomatic flat Dongcheng 16-story building RDZ 1 12 April CABR District, Beijing R.C. frame 1975 Baliqiao Tongxian Ground (soil) RDZ 1 12 August CABR County, Beijing 1976 348

Table 2. Specifications of RPS 1 and RZS 1 sensors.

Value Term Symbol RPS 1-66 RZS 1-66 Unit

Natural frequency f1 4.0±0.2 4.0±0.2 Hz Mechanical electrical Bl ≥57 ≥57 volt. sec /m coupling coefficient 3 Rotatory inertia K 36. × 10−4 36. × 10−4 volt. amp. sec Reduced pendulum length Lo 48± 56± mm

Indicated pendulum length Lk 100 100 mm

Interior resistance Rs 150±10 150±10 ohm

Damping resistance R1 43±10 43±10 ohm

Intensity of magnetic B 6000 6000 Gauss* induction Size 268×108×150 287×126×144 mm3 Weight 5.6 6.5 Kilogram

Table 3. Specifications of FC6 galvanometer.

Value Term Symbol FC6-120 FC6-400 Unit

Natural frequency f2 120 400 Hz

Operating frequency fw 60 200 Hz

Sensitivity vg 2700 220 mm/Am/m

Interior resistance rg 50±10 50±10 ohm External resistance critical rd 180±10 20±10 ohm damping of 0.6 to 0.7

Max. current Im 0.2 2 milliampere Max. deflection, within ±100 ±100 mm given linearity Balance 1 1 349

Table 4. Specifications of RCF1 mechanical trigger.

Term Symbol Value Unit

Natural frequency f3 1.5-2 Hz

Damping constant D3 0.1

Static magnification V3 10 Size 293×136×152 mm Weight 6.2 Kilogram

Table 5. Specifications of DJ651-B sensor.

Term Symbol Value Unit

Natural frequency f1 26±1 Hz

Damping constant D1 0.35-0.5

Mechanical electrical B >12 volt. sec/m coupling coefficient l

Interior resistance Rs 270±7% ohm Weight W 74 gram

Table 6. Specifications of galvanometer.

Term Symbol Value Unit

Natural frequency f1 10 Hz

Sensitivity Vg 43×103 ±20% mm/Am/0.32m

Interior resistance rg 110 ohm

Critical damping r 750 ohm resistance d 350

Table 7. Summary of the M7.8 Tangshan main shock records.

No. of Maximum Ground Acceleration (gal) Station Recording Traces Record Epicenter Name Length Distance Ground Structure Location E–W N–S U–D (Sec.) (Km) Beijing 3 16 Basement 64.1 53.0 36.2 150 154 Hotel Hujialou 1 5 First floor 55.3 135 149.5 Miyun Ground 3 9 95.3 56.6 48.7 114 148 Reservoir (soil) Basement Sanlihe 3 102.5 112.5 36.3 34.7 160.5 ground Guanting Toe of 1 4 5.0 130 229 Reservoir dam Fengcun Ground 3 7 13.8 16.7 10.2 138 397.5 Bridge (soil) Hongsha Ground 3 14.1 7.0 4.6 250 385.5 n (rock) Total 17 41 58

Table 8. Summary of records from the Luanxian earthquake of magnitude 7.1.

No. of Maximum Ground Acceleration (gal) Recording Traces Record Epicenter Station Name Length Distance Ground Structure Location E–W N–S U–D (Sec.) (km)

Hujialou 1 5 First floor 27.6 124 186 Diplomatic flats 3 9 First floor 26.7 23.2 13.4 43 187 Ground Fengcun Bridge 3 4 3.4 2.0 1.2 18 442.5 (soil) Emergency Spillway spillway of 3 9 gate base 1.6 1.5 2.1 413 Huangbizhuang plate Normal Ground spillway of 3 5 (rock) 1.8 1.2 1.4 68.5 413 Huangbizhuang Total 13 32 45 351

Table 9. Summary of records from the Ninghe earthquake of magnitude 6.9.

No. of Maximum Ground Acceleration (gal) Recording Traces Record Epicenter Station Name Length Distance Ground Structure Location E–W N–S U–D (Sec.) (Km) Tianjin 3 5 First floor 104.4 147.1 73.4 170 56.5 Hospital Tongxian Ground Dongguan 3 42.7 51.4 62.6 70 120 (soil) Bridge Tongxian Ground 12 51.4 57.8 23.5 51.1 124.5 Baliqiao (soil) Beijing Hotel 2 15 Basement 24.7 30.8 65 139.5 Ground Zhongguancun 3 40.0 57.0 20.8 42.5 150.5 (soil) Babaoshan Tunnel 3 7 16.0 8.6 4.8 152.5 Subway base plate Ground Zhoukoudian 5 10.6 10.7 8.2 44.1 186.5 (rock) Guanting Bottom of 2 5 6.8 2.8 72.3 217 Reservoir toe Fengcun Bridge Ground 3 4 8.0 6.2 3.8 64 351 (soil) Total 36 36 72

Table 10. Summary of the aftershock records.

Station Observed No. of No. of Recording Traces* Name Object Records Ground Structure

Tangshan Airfield Ground, soil, 42 126 Classified II Tangshan Cement Ground, 18 48 Factory limestone Qianan Ground, quartz 89 267 sandstone Changli Ground, granite 11 33 Yutian 5-story brick 3 9 17 building Total 163 483 17 500

*This means the number of the original record traces which are available for the preliminary analysis. 352

Figure 1. The distribution of the strong motion network in North China.

Figure 2. Duralt Shape resistance coupling network for the RDZI accelerograph.

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Figure 3. Amplitude Frequency characteristic curve of RDZ1 accelerograph.

Figure 4. Coupling network of the sensor with the galvanometer for SG-4-12 accelerograph.

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Photo 1. RDZ1-12-66 accelerograph.

Photo 2. RPS1-horizontal transducer. Photo 3. RPS1-vertical transducer.

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Photo 4. RCF1 mechanical trigger.

Photo 5. SG-4-12 accelerograph. Photo 6. SMAC-B2 accelerograph.

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Photo 7. DT-206 Data reducer Unit.

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THE STRONG MOTION RECORDS OF PERMANENT ACCELEROGRAPH NETWORK

Shuangjiu Yu, Chenxiang Hu, Kezhong Peng and Yuxue Guo*

I. Acquiring Records In this chapter the collected significant strong motion records of the main shock (Ms=7.8) and two strong aftershocks (Ms=7.1 and 6.9) from the permanent accelerograph network of North China (HBNW) are described. The are listed in Table 1 and the details of the accelerograms obtained in HBNW are summarized in Table 2. In Table 2 a total of 175 recording traces from 16 stations are listed. Among them, there are 71 ground motion traces and 104 structure response traces. The records of the Beijing Hotel, the Beijing Diplomatic Apartments and the Tianjin Hospital were the most significant.

II. Description of the Stations

1. Baihe Dam, Miyun An accelerograph was installed on the Baihe Main dam (Photo 1). The detailed informa- tion on structure, site and damage of the Baihe Main dam are described in Chapter 12 of Volume III. This station was first operated on November 17, 1967. The objectives were to study the acceleration response of the profile of the earth dam and the influence of the dam on ground motion during earthquakes. The accelerograph installed here was Type RDZ1-12-66 which had 12 channels. A total of 6 measuring points were distributed on the ground surface of the downstream and Section 0+720 of the Baihe Main dam (Fig. 1), and the information about measuring points and instruments are listed in Table 3. For the main shock (Ms=7.8), the local intensity was VI and the water level of the Miyun Reservoir was 138.4 m. The stone facing of the upstream slope was damaged from Section 0+50 to Section 0+950 of the main dam. 2. Hujialou Apartments An accelerograph had been installed on Building No. 19 in the Hujialou residential dis- trict in Beijing and began operation on April 8, 1967. This building was a 5-story masonry structure. Its structural layout, site geology and the position of measuring points are shown in Fig. 2.

* Institute of Engineering Mechanics, State Seismological Bureau 358 The Strong Motion Records of Permanent Accelerograph Network

The type of instrument used was an RDZ1-12-66 accelerograph. The transducers were installed on the floors of each story of this building; a total of 9 channels for studying the earthquake response of this conventionally used multistory masonry building (see Table 4 and Fig. 2). This building suffered slight damage during the Tangshan Earthquakes and only small cracks were occasionally found at connections of prefabricated components. 3. Beijing Hotel The accelerographs were installed in Part III of the Eastern Building of the Beijing Hotel and began operation on August 6, 1974. The Eastern Building of the Beijing Hotel is located in the Wangfujing commercial quar- ter in Beijing. It was a 17-story cast-in-place reinforced concrete frame structure, which was built in 1974 (Photo 2). The elevation of the site is 43 meters above sea level. There are two stories of basement and one story of reinforced concrete caisson foundation. The foundation is built on natural firm site soil. The column layout of Part III of the Eastern Building of the Beijing Hotel was rectangular in shape. The layout of this building is regular and simple and the seismic joint between Part III and Part II of this building is 90 cm wide. The structural diagram and site geology conditions are shown in Fig. 3. The aseismic intensity design for this building was VIII, and anti-seismic reinforced concrete shear walls were constructed on each story of this building along two axes. Two sets of accelerographs (Type RDZ1-12-66) had been installed in Part III of the Eastern Building of the Beijing Hotel and began operation at August 6, 1974. A total of 10 measuring points (19 sensors) were distributed on several floors and on the top floor of the building (Fig. 3) for studying earthquake response of this multistory R.C. frame structure. Information on measuring points and instruments is listed in Table 5. No site could be used as a free-field instrument location around the building so a three instrument (Point 1) was deployed in the basement for recording the input ground motion. Two central recorders (oscillographs) and the triggers were installed on the first floor and the cables were preset during the construction procedure. During the Tangshan main shock, the Beijing area was affected by intensity VI and the infill walls of this frame structure were apparently damaged. Many suspension mounts on ceilings were cracked and many ornamental materials were damaged but no damage to the frame structure was found. 4. Sanlihe office building An accelerograph was installed in the basement of the branch office building of the Insti- tute of Geophysics at Sanlihe area in Beijing. The branch office building was a 5-story masonry structure built in 1954 and the constructional quality was very good; the site soil was classified as Type II soil. A Japanese accelerograph of Type SMAC-B2 was installed. The sensitivity of all 3 com- ponents was 0.08 mm/gal. 359

Some of the load bearing walls of this building cracked during the Tangshan main shock: the building damages in this region were heavier than those in the adjacent regions and in this region the damages to the 4-story or taller masonry buildings were heavier than those to the 3-story or shorter masonry buildings. 5. Guanting main dam The Guanting Reservoir is located about 80 km north-west of Beijing. The main dam was built in 1954 (Photo 3). The basic intensity in the Guanting Reservoir region was scaled as VIII. The seismic evaluation of the main dam was done in 1975 and it had been consid- ered that the main dam was safe for intensity VIII. The capacity of this reservoir is 2.27 million m3. The main dam is an earth dam with a thick heart-wall, the maximum dam height is 45 m and dam length is 290 m. The basement rock of the dam site is limestone of the Sinian Period of the Proterozoic Era, which is over 300 m deep. The overburden under the dam foundation is an alluvium layer of 20 m deep, which consists of sand and grit. One set of instruments, of Type SG4-12, was installed on the main dam it had 8 channels; the positions of measuring points on the dam are shown in Fig. 4 and the information about the measuring points and instruments are listed in Table 6. 6. Hongshan The Hongshan strong-motion instrument was located in a single-story wood house in the Hongshan Seismographical Station located about 6 km north-west of Longyao City in Hebei Province (Fig. 5). One set of accelerographs, Type RDZ1-12-66 with 9 channels, was installed in this sta- tion on December 9, 1966. Nine sensors were equally divided into 3 groups for recording NS, EW and vertical com- ponents of ground motion, respectively. The instrument foundation laid on fresh quartzite. Two groups of pick-ups with different sensitivities were installed on the concrete foundation. In order to compare the differences of ground motions between the base rock and the shallow soil deposits (less than 10 m), the third group of pick-ups was installed on the soil ground in a room, which was about 20 m from the other instruments. Table 7 lists the information about measuring points and instruments. 7. Fengchun Bridge The instruments were installed on the Fengchun railway bridge of the Beidishui River and on the ground of the north bank. This bridge was located at about 1 km south of the Fengchun Railway Station of the Jing-Han Railway. The observation began on September 28, 1969. This bridge is a deck type multi-span railway bridge with a simple-support plate girder with a thin web and has 15 bridge-openings, among which the first opening has a span of 32.84 m and each of the remaining openings has a span of 20.70 m and the total length of the bridge is 336.55 m. The bridge abutments are T-shaped and the piers have semicircular 360 The Strong Motion Records of Permanent Accelerograph Network shapes at both ends, and they were built with mortar-bonded stone blocks. Sink-wells were used for the abutment and pier foundations except for the south abutment which was built on a spread foundation. The type of accelerograph used was RDZ1-12-66, which had 12 channels. Three pick-ups were respectively installed on the ground surface (Type II soil) of the north bank, north abutment, the top of the sink-well foundation of Pier 4, and at the top of Pier 4. The layout of measuring points is shown in Fig. 6. The parameters of measuring points and instruments are shown in Table 8. 8. Beijing Diplomatic Apartments The Beijing Diplomatic Apartments (Qijiayuan Apartment No. 10) built in 1973 is located at Jianguomenwai in Beijing. It is an 18-story reinforced concrete framed tower structure with type with shear wall. The building is 59 m above ground with a basement underground and has a caisson foundation (see Fig. 7 and Photo 4). The building site is on the alluvial plain in Beijing. The site soil consisted of alluvial deposits of the Quaternary Period with a thickness of up to 100 m. The soil was classified as grade II. The soil profile of the site and corresponding shear wave velocity are shown in Fig. 8. The installation of accelerograph Type RDZ1-12-66 was completed in July 1975. The recorder and mechanical triggers were fastened to the floor of the basement. Twelve pick- ups were divided into 4 groups which were installed at 4 measuring points on the ground of the basement (base slab of caisson foundation), 5th floor, 10th floor and 17th floor respec- tively. The positions of measuring points in plane were close to the centroid of the building in plane (see Fig. 7) and 3 pick-ups were installed at each measuring point. The parameters of measuring points and instruments are listed in Table 9. During the Tangshan Earthquake the affected intensity in the area was VI. From the 6th story to the 8th story of this building light infilled-walls were slightly cracked and separated from columns, a few pieces of veneer on the exterior wall fell. All of these damages were slight. 9. Strong-motion instrument array of the Huangbichuang Reservoir The Huangbizhuang Reservoir is located at the middle reach of the Hutuo River in Hebei Province, about 30 km northwest of Shijiazhuang City. It is a large water conservancy project for flood control, irrigation, electric generation and water supply for the city. The reservoir engineering project consisted of the main dam, secondary dam, regular spillway, emergency spillway, gravity dam for the hydro-electric power station of Shi-Jin Channel and the hydroelectric power station of Ling-Zheng Channel, etc. The major struc- tural engineering was completed before the flood season of 1968 (Huangbizhuang Reservoir Engineering Bureau of Ministry of Electric Power and Water Conservancy, 1970). The Institute of Engineering Mechanics of Academia Sinica in cooperation with the Huangbizhuang Reservoir Administrative Department of Hebei Province deployed 3 accel- 361 erographs on the secondary dam (Section 2+610), emergency spillway gate, the joining part of the main dam with the regular spillway (Photo 5), and the bedrock outcrop of Maanshan Hill one after the other and thus, the Huangbizhuang Reservoir Strong Motion Accelerograph Array was formed (Fig. 9). An accelerograph, RDZ1-12-66, was used for the emergency spillway and 12 pick-ups were installed on 5 measuring points, respectively, (Fig. 10) for measuring the seismic response of gate-pier structure with high trestle and tower-structure of the bridge. The meas- uring points and instrument parameters are listed in Table 10. The installation of a strong-motion observation station at the regular spillway aimed at: (1) during the Xingtai Earthquake of 1966 the joining part of the gate-pier of the regular spillway of the main dam suffered moderate damage and therefore 2 groups of pick-ups were deployed at both shoulders of the joining parts of main dam and at the top of the gate-pier respectively for the sake of further understanding of the seismic behaviors of joining parts during future earthquakes; and (2) on the hill-slope at one side of Maanshan Hill close to the regular spillway gate a measuring point was selected on the bedrock outcrop as the reference point for ground motion in the reservoir area. A set of accelerographs, RDZ1-12-66, was used for this station. A total of 9 pick-ups were divided into 3 groups which were installed on the above 3 measuring points and are listed in Table 11. 10. Tianjin Hospital The Tianjin Hospital is located in the vicinity of the intersection of Jiefangnan Road and Weidi Road in the Hexi District of Tianjin. The main building which was used as the ward is a 9-story reinforced concrete framed structure with a mat foundation built directly on a base of soft soil. The construction of this building was completed in December 1965. A set of accelerographs, RDZ1-12-66, was installed in Part A and C of the main building. A total of 8 pick-ups were set up on the main building (Fig. 11). Four measuring points (MP1 to MP4) were deployed on the floors of the 1st story, 3rd story and 5th story and the berm above the ventilating duct outside the north wall of the 7th story in Part C of the build- ing respectively, and the points were on the same transverse section for observing the seismic response of the multistory frame structure on a weak base. Besides, on Part A symmetrical to MP4 the MP5 was set up for observing and comparing the different responses of the two parts of the building to earthquakes. The measuring points and instrument parameters are listed in Table 12. This building experienced the Xingtai Earthquake (1966), the Earthquake (1967), the Bohai Earthquake (1969), and the Haicheng Earthquake (1975) and sustained no damage. During the Tangshan Earthquake the location of this building was affected by seismic inten- sity VII and the building incurred slight damage. A more detailed description can be found in Volume 2 of this report. 11. Dongguanqiao, Tongxian The strong-motion instrument station of Dongguanqiao in Tongxian (Fig. 12) was installed in March 1968. There was only one instrument with 3 components deployed on the 362 The Strong Motion Records of Permanent Accelerograph Network ground of the west bank of the North Channel and it recorded ground motion during the Tangshan Earthquake. The ground measuring point of the station is set on soil ground (site classification II), mixed with lime-slag from the ground surface to a depth of 2.5 m and filled soil from 2.5 m to a depth of 4.20 m and a stratum of medium-light sandy clay up to a depth of 10 m. The type of accelerograph installed was an RDZ1-12-66. The relevant information about measuring points and the instrument are described in Table 13. 12. Baliqiao, Tongxian The Baliqiao (Tongxian) Station was located at the Baliqiao Seismographical Station in the western part of Tongxian (Fig. 14). The type of accelerograph was RDZ1-12-66. Four measuring points were selected in the courtyard of the seismographical station (Fig. 14) for investigating the differences in ground motions within a small area. A descrip- tion of measuring points and instrument parameters are given in Table 14. 13. Zhongguancun, BSMOC The Zhongguancun Station is located at the courtyard of the Beijing Strong Motion Observation Center of the Institute of Engineering Mechanics, State Seismological Bureau (BSMOC of IEM, SSB) in the Haidian District of Beijing. The instrument was installed on the ground floor in a room of a single-story masonry building with a flat roof for measuring the ground motion of the soil site (site classification II). The location of Zhongguancun, BSMOC and the condition of the soil property are shown in Fig. 15. Detailed information on measuring points and instrument parameters are listed in Table 15. 14. Babaoshan Subway Station The Babaoshan Subway Station is located in the neighborhood of Lugu Village on Shijinshan Road in the Fengtai District of Beijing. The instruments were installed in the Babaoshan Subway Station and fully operated in December 1975. The objective of this station is to observe the seismic response of underground engineer- ing structures. An accelerograph of RDZ1-12-66 was used and 12 pick-ups were divided into 4 groups which were respectively set at the tunnel base, station platform and in the crawl space for vent conduit in the tunnel top-board. Each group containing 3 pick-ups was used for measuring the motion in the east-west (along the tunnel) direction, north-south (across the tunnel) direction and vertical direction. The layout of measuring points and condition of soil property are shown in Fig. 16. The measuring points and instruments are listed in Table 16. 15. Zhoukoudian The Zhoukoudian Station was located in the yard of the Beijing Apeman Exhibition Hall on the north slope of Longgu Hill in Fangshan County of Beijing (Fig. 17). This station was established for obtaining information on ground motion of bedrock outcrop in the south-west part of Beijing and put into operation on May 27, 1976. 363

An accelerograph RDZ1-12-66 was adopted and 6 pick-ups were divided into 2 groups, one was set on bedrock outcrop and the other on the ground of the nearby instrument room for comparing the effects of two different site conditions. Measuring points and instrument parameters are listed in Table 17. The rock at the station site is sedimentary pure limestone with great thickness. (Translators: Peng Kezhong, Xie Li-Li and Zhou Yongnian)

III. Results of Observation

1. Results of preliminary analysis

According to the method presented above, the maximum acceleration Am, corresponding peak period Tp and duration T1 of ground motion are given by preliminary visual analysis of records listed in Table 2. All the Am, Tp , and T1 are summarized in Table 18. Seventy-one components of them are obtained on grounds; 11 components on bedrock, and 60 compo- nents on overlying soils or bottoms of structures. The maximum accelerations obtained from the strong motion network of North China during 3 earthquakes are shown in Fig. 18. The digit at the upper left of the acceleration values in Fig. 18 represents the earthquake number [(1) for earthquake M=7.8, (2) for earthquake M=7.1 and (3) for earthquake M=6.9]. The attenuation of strong ground motion recorded during the 3 earthquakes is clearly shown in this figure. It can be seen from the peak period and duration in Table 18 that longer peak period and longer duration were the characteristics of ground motion in the Beijing area during the Tangshan Earthquake with magnitude 7.8. In this earthquake the maximum acceleration on the ground or base of the structure in Beijing is 112.5 gal (Sanlihe), the maximum accelera- tion of structure response is 240.1 gal (Beijing Hotel). In the earthquake of November 15, 1976 (M=6.9), the maximum acceleration of the first floor of the Tianjin Hospital was 147.1 gal with a maximum acceleration of structure response of 560.7 gal. 2. Uncorrected digitized accelerograms Routine computer processing of strong-motion accelerograms recorded during the 3 earthquakes was carried out for the following stations: Hujialou, Guanting Reservoir, Hong- shan, Fengchun Railway Bridge and the Diplomatic Apartments. Figures 19-28 show only the uncorrected accelerograms. Corrected accelerograms of the Tangshan main shock (M=7.8) obtained at the Beijing Hotel and those of the aftershock (M=6.9) at Tianjin Hospital are analyzed as examples. 3. Routine analysis of typical records

(1) Beijing Hotel Station The two instruments installed in the Beijing Hotel were triggered and perfect records were obtained during the Tangshan main shock of magnitude 7.8. Good records were also 364 The Strong Motion Records of Permanent Accelerograph Network obtained during the aftershock of magnitude 6.9. Routine analysis of records of the earth- quake of magnitude 7.8 were carried out for convenient application. Its main results, includ- ing corrected maximum acceleration Am, calculated peak velocity and displacement (Vm and Dm), and corresponding peak periods TpA , TpV , TpD, are listed in Table 19. They are obtained from corrected accelerograms with respect to instrument response and baseline, thus slightly different from those in Table 18. The data in Table 19 can be considered as the real motion of measurement points in a band-pass filtered frequency range. Figures 29-36 show the corrected acceleration histories of the Beijing Hotel Station in the Tangshan Earthquake with magnitude 7.8. The data are at equal intervals of 0.01 sec. and band-pass filtered between 0.1 and 35 Hz. The peak value of accelerations (unit: gal) are also shown. The distributions of peak accelerations along the height of the Beijing Hotel during the earthquakes of magnitude 7.8 and 6.9 are shown in Fig. 37. The ratio of EW component accelerations on the top to that on the base are 2.25 for the M=7.8 earthquake and 4.36 for M=6.9; the ratio of the NS accelerations is 2.84 for the former and 2.9 for the latter. (2) Tianjin Hospital Station In the North China Strong Motion Network, Tianjin Hospital is the nearest station to the epicenter of the Tangshan Earthquake (M=7.8). Unfortunately, because the sensitivities of channels were very high, the traces of the record overlapped and went off-scale so that it is difficult for digitizing and application. However, in the earthquake of November 15, 1976 (M=6.9), valuable records were obtained from this station. The epicenter distance is about 56 km. At present, it is an important and unique record having larger magnitude and shorter epicentral distance than any other in China. To make full use of the record, corrected peak acceleration Am, computed velocity Vm and displacement Dm, and peak period TpA , TpV , TpD are listed in Table 20. Corrected accelerograms of the Tainjin Hospital Station are shown in Figs. 38-40. The data was sampled at equal intervals of 0.01 sec. and band-pass filtered between 0.15 and 35 Hz. (Translators: Guo Yuxue and Zhou Yongnian) 365

Table 1. Earthquake parameters.

Earthquake Time of Earthquake Epicenter Coordinate Depth Magnitude No. y.m.d h-m-s Northern Eastern (km) Ms Note Latitude Longitude

1 1976.7.28 03-42-56 39°38' 118°11' 11 7.8 Tangshan main shock

2 1976.7.28 18-45-37 39°50' 118°39' 10 7.1 Luanxian earthquake

3 1976.11.15 21-53-0139°17' 117°50' 17 6.9 Ninghe earthquake

Table 2. The quantity of useful traces of accelerograms obtained in the SMA Network of North China (HBNW).

Earthquake Name of Station 1 2 3 (M7.8) (M7.1) (M6.9) Miyun Reservoir 12 Hujialou Apt. 6 6 Beijing Hotel 19 17 Sanlihe 3 Guanting Main Dam 5 7 Hongshan 3 Fengcun Bridge 10 7 7 Diplomatic Apt., Beijing 12 Huangbizhuang Reservoir, ES 12 Huangbizhuang Reservoir, RS 8 Tianjin Hospital 8 Dongguanqiao, Tongxian 3 Baliqiao, Tongxian 12 Zhongguancun, BSMOC 3 Babaoshan Subway 10 Zhoukoudian 5 Total 58 45 72 Sum 175

Note: There are 2 RDZ1 in the Beijing Hotel. 366 The Strong Motion Records of Permanent Accelerograph Network

Table 3. Information of measuring points and instruments of Baihe Dam, Miyun.

Measuring Point Component Sensitivity (mm /gal) No. Position Elevation (m)

Along river 1.597 1 Ground 100 Dam -axial 1.894 Vertical 0.854 Along river 1.295 2 Dam toe 100.24 Dam-axial 1.525 Vertical 1.496 3 Berm 121.22 Along river 0.785

4 Upper slope of 139.62 Along river 0.915 dam Along river 0.273 5 Shoulder 158.67 Dam-axial 0.927 Vertical 0.985 6 Upstream slope 154 Vertical 0.734

Note: Measuring section is 0+72.

Table 4. Information of measuring points and instruments of Hujialou Apartments.

No. Position Component* Sensitivity (mm/gal)

U-D 0.192 1 Ground floor E-W 0.233 N-S 0.210 2 2nd floor N-S 0.236 3 3rd floor N-S 0.205 4 4th floor N-S 0.208 N-S 0.231 5 5th floor E-W 0.226 U-D 0.248

*E-W is the long axis of bldg., N-S is the short axis of bldg. 367

Table 5. Information of measuring points and instruments in the Beijing Hotel.

Measuring Points Sensitivity (mm/gal) No. Elevation (m)* Position Component** M=7.8 M=6.9

1 -8.20 Underground room U-D 0.392 0.0810 1 -8.20 Underground room N-S 0.497 0.1680 2 +0.00 1st floor N-S 0.370 0.1475 3 +15.60 4th floor N-S 0.386 0.1101 4 +31.20 8th floor N-S 0.272 0.0994 5 +46.80 12th floor N-S 0.304 0.0708 6 +62.40 16th floor N-S 0.232 0.0720 7 +68.20 17th floor, cabinet #1 N-S 0.193 0.0913 7 +68.20 17th floor, cabinet #2 U-D 0.184 0.0704 10 +68.20 17th floor, cabinet #4 N-S 0.156 0.1007 1 -8.20 Underground room E-W 0.344 0.1316 2 +0.00 1st floor E-W 0.384 0.1560 3 +15.60 4th floor E-W 0.307 0.1132 4 +31.20 8th floor E-W 0.296 0.0878 5 +46.80 12th floor E-W 0.184 0.0639 6 +62.40 16th floor E-W 0.197 0.0736 7 +68.20 17th floor, cabinet #1 E-W 0.144 0.0636 8 +68.20 17th floor, cabinet #2 E-W 0.144 0.0900 9 +68.20 17th floor, cabinet #3 E-W 0.147 0.0720

*The relative elevation of the 1st floor is +0.00m. **N-S is the long axis of the building, E-W is the short axis of the building.

368 The Strong Motion Records of Permanent Accelerograph Network

Table 6. Information of measuring points and instruments of the Guanting Main Dam.

Measuring Points Sensitivity No. Position Section Elevation (m) Component* (mm/gal)

1 Right bank at 0+170 460 Along river 2.86 downstream (rock) 2 Berm of dam 0+230 444 Along river 1.28 toe Vertical 1.28 3 Berm of dam 0+190 462 Along river 2.86 toe Vertical 1.28 4 Crest 0+160 485 Along river 2.86 Vertical 2.86 5 Crest 0+220 485 Along river 2.86

*The direction of the river is N10 °E.

Table 7. Information of measuring points and instruments of Hongshan S.S.

Position Component Sensitivity (mm/gal)

Instrument foundation in E-W 0.925 pick-up room (rock) N-S 0.820 U-D 1.013 Instrument foundation in E-W 2.10 pick-up room (rock) N-S 2.47 U-D 1.69 Ground in recorder room E-W 1.40 (soil) N-S 1.216 U-D 1.64 369

Table 8. Information of measuring points and instruments of Fengcun Bridge.

Measuring Point Component* Sensitivity (mm/gal) No. Position 1 North bank of river E-W 2.860 (ground) N-S 2.530 U-D 1.700 2 North abutment E-W 1.725 N-S 2.630 U-D 1.655 3 Top of foundation of E-W 2.500 Pier #4 N-S 2.185 U-D 2.250 4 Top of Pier #4 E-W 1.580 N-S 2.600 U-D 1.760

*The direction of the river is E-W, and the axis of the bridge is N-S.

Table 9. Information of measuring points and instruments of the Diplomatic Apartments in Beijing.

Measuring Point Sensitivity No. Position Elevation (m)* Component (mm /gal)

1 Underground -4.30 U-D 0.698 room E-W 0.649 N-S 0.808 2 5th floor +13.50 U-D 0.348 E-W 0.507 N-S 0.360 3 10th floor +30.00 U-D 0.373 E-W 0.365 N-S 0.426 4 17th floor +51.59 U-D 0.440 E-W 0.386 N-S 0.415

*The elevation of the 1st floor is +0.00 m. 370 The Strong Motion Records of Permanent Accelerograph Network

Table 10. Information of measuring points and instruments of Huangbizhuang Reservoir, ES.

Measuring Point Sensitivity No. Position Elevation (m) Component* (mm/gal)

1 Bottom of 108 U-D 1.49 north pier of E-W 1.40 gate # 6 N-S 1.25 2 Top of north 124 U-D 1.650 pier of gate #6 E-W 1.540 N-S 0.853 3 Middle of 130 E-W 1.78 north pier of gate #6 4 Top of frame 136 U-D 0.490 of north pier E-W 0.513 of gate #6 N-S 0.593 5 Top of north 137.6 E-W 0.620 bridge tower U-D 0.620

*The direction of the spillway is E-W, upstream is west; and the sluice axis is N-S.

Table 11. Information of measuring points and instruments of Huangbizhuang Reservoir, ES.

Measuring Point Sensitivity No. Position Elevation (m)* Component* (mm/gal)

1 Sluice-pier of 128 N-S 1.020 regular spill- E-W 1.292 way U-D 0.691 2 Shoulder of 128 N-S 1.490 Main Dam E-W 1.480 U-D 0.805 3 Base rock of 130 N-S 1.287 Maanshan E-W 1.584 U-D 1.096

*The direction of the spillway is E-W, upstream is west; and the sluice axis is N-S. 371

Table 12. Information of measuring points and instruments of Tianjin Hospital.

Measuring Point Component** Sensitivity (mm/gal) No. Position Elevation (m)* M=7.8 M=6.9 1 1st floor on +0.00 N-S 1.202 0.093 part C of bldg. E-W 1.073 0.097 U-D 1.214 0.080 2 3rd floor on +7.65 N-S 1.022 0.087 part C of bldg. 3 5th floor on +15.15 N-S 0.919 0.093 part C of bldg. 4 7th floor on +23.90 N-S 0.869 0.097 part C of bldg. U-D 0.656 0.091 5 7th floor on +23.90 N-S 0.580 0.090 part A of bldg.

*The absolute elevation of the 1st floor of the building is +5.75 m. **N-S is the short axis of the building, and E-W is the long axis of the building.

Table 13. Information of measuring points and instruments of Dongguangiao, TongXian.

Measuring Point Component Sensitivity (mm/gal) No. Position 75.1.30-76.7.30 76.7.30-77.4.23 1 Ground on west N-S 0.400 0.117 bank E-W 0.517 0.111 U-D 0.456 0.107 372 The Strong Motion Records of Permanent Accelerograph Network

Table 14. Information of measuring points and instruments of Baliqiao, TongXian.

Measuring Point Component Sensitivity (mm/gal) No. Position 1 Foundation(-1.2 m) in N-S 0.169 room E-W 0.178 U-D 0.167

2 Ground floor in room N-S 0.159 E-W 0.175 U-D 0.170

3 Ground floor in room N-S 0.188 E-W 0.175 U-D 0.175

4 Ground floor in room N-S 0.176 E-W 0.171 U-D 0.183

Table 15. Information of measuring points and instruments of Zhongguancun, BSMOC.

Channel No. Component Sensitivity (mm/gal)

1 N-S 0.220 2 E-W 0.140 3 U-D 0.106 4 U-D 0.181

373

Table 16. Information of measuring points and instruments of the Babaoshan Subway Station.

Measuring Point Component Sensitivity (mm/gal) No. Position 1 Bottom of tunnel E-W 0.488 N-S 0.527 U-D 0.518

2 Bottom of tunnel E-W 0.507 N-S 0.241 U-D 0.484

3 Platform E-W 0.476 N-S 0.224 U-D 0.491

4 Roof of tunnel E-W 0.140 N-S 0.167 U-D 0.436

Table 17. Information of measuring points and instruments of Zhoukoudian Station.

Measuring Point Component Sensitivity (mm/gal) No. Position 1 Outcrop of basement rock U-D 0.181 N-S 0.325 E-W 0.310

2 Ground in room (shallow U-D 0.273 covered basement rock) N-S 0.270 E-W 0.312 374

Table 18. Results of preliminary analysis of accelerograms obtained from the North China strong-motion network during the Tangshan earthquakes.

Epicentral Maximum Acceleration Am (gals) Peak Station earthquake Distance Component Period Duration Name (km) (sec.) T (sec.) Point Point 2 Point 3 Point 4 Point 5 Point 6 Point 7 Point 8 Point 9 Point 10 1

Miyun NS 56.6∆ 57.8+ 130.9 132.6 169.7 114 Reservoir 7.8 148 EW 95.3∆ 35.4+ 169.4 114 + (Baihe River UD 48.7∆ 48.2 127.7 59.0 114 Dam) Hujialou 7.8 149.5 NS 173.2 183.0 219.7 135 EW 55.3 145.8 0.54 135 UD 88.1 135 7.1 186 NS 27.6+ 95.2 74.4 92.2 0.27 124 EW 68.7 124 UD 28.2 124 Beijing 7.8 154 NS 53.0+ 71.8 91.6 102.3 93.2 143.8 165.9 240.1 1.00 150 Hotel EW 64.1+ 64.8 79.0 107.9 107.4 143.3 204.4 194.5 216.4 0.59 150 UD 36.2+ 111.2 0.29 150 6.9 139.5 NS 30.8+ 38.5 37.5 50.3 70.5 87.0 89.3 91.1 0.98 65 EW 24.7+ 27.5 45.4 59.5 76.3 105.9 107.7 157.5 129.8 0.90 65 UD 65 Sanlihe 7.8 160.5 NS 112.5 0.48 34.7 EW +02.5 0.37 34.7 UD +26.3 0.23 34.7 Guanting 7.8 229 Along river 21.5 36.3 130 Reservoir UD 5.0+ 9.6 34.3 0.16 130 217 Along river 6.8+ 13.2 19.7 18.0 0.25 72.3 6.9 UD 2.8+ 7.7 11.7 0.15 72.3 Hongshan 7.8 385.5 NS 7.0* 0.95 250 EW 14.1* 0.49 250 UD 4.6* 0.80 250

Table 18 (continued)

Epicentra Maximum Acceleration Am (gals) Peak Station earthquake l Distance Component Period Duration Name (km) (sec.) T (sec.) Point 1 Point 2 Point 3 Point 4 Point 5 Point 6 Point 7 Point 8 Point 9 Point 10

Fengcun 7.8 397.5 NS 16.7∆ 13.9 23.6 15.3 0.23 138 Railway EW 13.8∆ 15.7 15.6 0.30 138 Bridge UD 10.2∆ 8.3 7.2 0.64 138 7.1 442.5 NS 2.0∆ 2.4 1.5 0.27 18 EW 3.4∆ 2.6 2.6 0.27 18 UD 1.2∆ 0.19 18 6.9 351 NS 6.2∆ 8.5 7.3 0.26 64 EW 8.0∆ 7.0 0.18 64

UD 3.8∆ 3.3 0.24 64 Diplomatic 7.1 187 NS 23.2+ 33.2 40.9 66.1 0.60 43 Apartments EW 26.7+ 52.1 65.3 92.6 1.20 43 UD 13.4+ 21.0 23.0 25.7 0.35 43 Huan- 7.1 413 NS 1.5+ 4.6 31.2 0.13 bizuang EW 1.6+ 2.0 2.4 24.3 28.6 0.16 Reservoir UD 2.1+ 2.3 2.9 0.16 unusual spillway Huan- 7.1 413 NS 2.3 8.1 1.2* 0.24 68.5 bizuang EW 7.7 1.8* 0.24 68.5 Reservoir UD 2.1 9.0 1.4* 0.21 68.5 normal spillway Tianjin 6.9 56.5 NS 147.1+ 193.6 257.4 514.6 560.7 0.92 170 Hospital EW 104.4+ 1.01 170 UD 73.4+ 166.0 0.14 170

375 376

Table 18 (continued)

Maximum Acceleration Am (gals)

Epicentral Peak Station Distance Point Point Point Point Point Point Point Point Point Point Period Duration Name earthquake (km) Componen 1 2 3 4 5 6 7 8 9 10 (sec.) T (sec.) t Dongguan 6.9 120 NS 51.4∆ 0.77 70 Bridge EW 42.7∆ 0.14 70 UD 62.6∆ 0.40 70 Bali Bridge 6.9 124.5 NS 57.8∆ 62.7∆ 63.7∆ 56.8∆ 0.48 51.1 EW 51.4∆ 45.0∆ 53.7∆ 57.4∆ 0.86 51.1 UD 23.5∆ 22.8∆ 21.8∆ 14.7∆ 0.20 51.1 Zhong- 6.9 150.5 NS 57.0∆ 8.99 0.74 42.5 guancun EW 40.0∆ 13.4++ 9.66 17.84 0.89 42.5 ++ UD 20.8∆ 5.16 5.06 3.44 0.81 42.5 Babaosham 6.9 152.2 NS 8.55+ 0.32 23 Subway EW 15.99+ 0.40 23 UD 4.825+ 0.24 23 Zhoukoudi 6.9 186.5 NS 10.7* 14.8* 0.16 44.1 an EW 10.6* 0.13 44.1 UD 8.2* 7.2* 0.08 44.1

Note: * Measuring point on bedrock ∆ Measuring point of free ground + Measuring point on first floor of structure ++ There are two accelerographs 377

Table 19. Main results of routine analysis on records obtained from the Beijing Hotel during the Tangshan Earthquake (M=7.8).

Acceleration Velocity Displacement Measuring Component Am TPA Vm TPA Dm TPD Point (gals) (sec) (cm/sec) (sec) (cm) (sec)

Basement EW 66.2 1.39 7.79 1.43 3.38 8.33 NS 55.6 0.77 10.39 1.39 5.61 5.55 UD 35.9 5.60 3.10

1st floor EW 65.2 1.43 7.27 1.43 3.08 4.35 NS 74.5 1.28 12.67 10.89 9.52

4th floor EW 78.1 1.67 9.50 1.33 4.78 8.33 NS 89.4 1.18 15.56 6.80 5.00

8th floor EW 119.1 1.39 15.21 1.39 5.61 5.55 NS 108.4 1.32 24.7 1.30 7.64

12th floor EW 101.4 1.39 18.69 1.39 7.97 NS 95.9 1.32 29.66 1.30 10.80

16th floor EW 138.5 1.43 23.54 1.41 6.07 NS 148.8 1.28 68.74 7.69 58.69 8.33

17th floor-1 EW 196.4 1.41 25.22 1.37 6.90 NS 157.9 1.28 42.03 1.30 13.69 5.00 UD 104.6 1.43 10.08 5.15 8.00

17th floor-2 EW 186.3 1.43 27.81 1.43 8.80 8.33

17th floor-3 EW 217.3 30.20 7.22

17th floor-4 NS 235.8 1.32 54.12 1.39 18.73 3.85

378

Table 20. Main results of routine analysis on records obtained from the Tienjin Hotel during the Tangshan Earthquake (M=6.9).

Acceleration Velocity Displacement Measuring Component Am TPA Vm TPA Dm TPD Point (gals) (sec) (cm /sec) (sec) (cm) (sec)

1st floor EW 149.98 29.22 0.90 NS 101.49 19.64 7.52 UD 75.76 5.64 1.91

3rd floor NS 189.00 0.68 37.00 0.68 9.96 0.68

5th floor NS 272.9 0.68 45.2 0.68 12.02 0.68 -0.70

7th floor NS 530.0 0.68 75.2 0.68 16.6 UD 160.0 18.1 4.44

7th floor NS 590.5 0.68 78.29 0.68 19.17 0.68 (section A) -0.72 379

Figure 1. The distribution of measuring points on Baihe River Main Dam Of Miyun Reservoir.

380

Figure 2. The distribution of measuring points on Hujialou Apt. 19.

Figure 3. The distribution of measuring points on part III of eastern building of Beijing Hotel. 381

Figure 4. The distribution of measuring points on Guanting Main dam.

382

Figure 5. The Location of Hongshan Station, Longyao County.

Figure 6. The distribution of measuring points on Fengcun Bridge. 383

Figure 7. The distribution of measuring points on Diplomatic Apartment, Beijing.

384

Figure 8. The Boring Log of Diplomatic Apartment, Beijing.

385

Figure 9. The distribution of measuring points of Huangbizhuang Reservoir.

Figure 10. The distribution of measuring points of Huangbizhuang Reservoir, ES.

386

Figure 11. The distribution of measuring points of Tianjin Hospital (measuring points #5 is located on part A of bldg., it is symmetrical with Mp #4 on part C).

387

Figure 12. Station of Dongguanqiao, Tongxian.

Figure 13. Station of Baliqiao, Tongxian. Figure 14. The distribution of measuring points on Baliqiao, Tongxian. 388

Figure 15. Zhongguancun Station.

Figure 16. Babaoshan Subway.

389

Figure 17. Location of Zhoukoudian station.

Figure 18. Distribution of peak ground accelerations for Tangshan mainshock and strong aftershocks.

390

Figure 19. Uncorrected accelerograms of Hujialou station in Tangshan earthquake (M=7.8) (unit: gal).

Figure 20. Uncorrected accelerograms of Guanting Reservoir station in Tangshan earthquake (M=7.8). 391

Figure 21. Uncorrected accelerograms of Hongshan station in Tangshan earthquake (M=7.8).

Figure 22. Uncorrected accelerograms of Fengcun Railway Bridge (ground) in Tangshan earthquake (M=7.8).

392

Figure 23. Uncorrected accelerograms of Fengcun Railway Bridge (North abutment) in Tangshan earthquake (M=7.8).

Figure 24. Uncorrected accelerograms of Fengcun Railway Bridge (pier) in Tangshan earthquake (M=7.8).

393

Figure 25. Uncorrected accelerograms of Diplomatic apartment, Beijing, in Luanxian earthquake (M=7.1) (Basement).

Figure 26. Uncorrected accelerograms of Diplomatic apartment, Beijing, in Luanxian earthquake (M=7.1 (5th floor)).

394

Figure 27. Uncorrected accelerograms of Diplomtic apartment, Beijing, In Luanxian earthquake (M=7.1 (10th floor).

Figure 28. Uncorrected accelerograms of Diplomatic apartment, Beijing, in Luanxian earthquake (M=7.1(17th floor).

395

Figure 29. Corrected accelerograms on basement of Beijing Hotel in Tangshan main shock (M=7.8).

Figure 30. Corrected accelerograms on 1st floor of Beijing Hotel in Tangshan main shock (M=7.8).

396

Figure 31. Corrected accelerograms on 4th floor of Beijing Hotel in Tangshan main shock (M=7.8).

Figure 32. Corrected accelerograms on 8th floor of Beijing Hotel in Tangshan main shock (M=7.8).

397

Figure 33. Corrected accelerograms on 12th floor of Beijing Hotel in Tangshan main shock (M=7.8).

Figure 34. Corrected accelerograms on 16th floor of Beijing Hotel in Tangshan main shock (M=7.8).

398

Figure 35. Corrected accelerograms on 17th floor(top 1) of Beijing Hotel in Tangshan Main shock (M=7.8).

Figure 36. Corrected accelerograms on 17th floor(top 2,3, 4) of Beijing Hotel in Tangshan mainshock (M=7.8). 399

Figure 37. Ratio of accelerograms on top to that on bottom of Beijing Hotel in Tangshan main shock (M=7.8) and Ninghe shock (M=6.9).

Figure 38. Corrected accelerograms on 1st floor of Tianjin Hospital in Ninghe earthquake (M=6.9). 400

Figure 39. Corrected accelerograms on 3rd and 5th floor of Tianjin Hospital in Ninghe earthquake (M=6.9).

Figure 40. Corrected accelerograms on 7th floor of Tianjin Hospital in Ninghe earthquake (M=6.9).

401

Photo 1. Baihe River Main Dam of Miyun Reservoir.

Photo 2. Beijing Hotel. 402

Photo 3. The main dam of Guanting reservoir.

Photo 4. Diplomatic Apartment. 403

Photo 5. Regular Spillway of Huangbizhuang Reservoir (upstream).

Photo 6. Appearance of the main building of Tianjin Hospital (by Information Station of Tianjin Hospital.)

404

MOBILE OBSERVATIONS OF AFTERSHOCKS

Shabai Li, Yuxue Guo and Azeng Song*

I. Introduction There was no strong motion accelerograph deployed in the Tangshan area when the great Tangshan earthquake of magnitude 7.8 occurred on 28 July 1976. In order to record near- source ground motion accelerograms generated by strong aftershocks, a mobile observation team was organized and sent into the field by the Institute of Engineering Mechanics as soon as the great earthquake occurred. Four mobile observation stations were set up at the Tangshan Air Field (Station AF), Tangshan Cement Mill (Station CM), Fenghuangshan of (Station CL) and the Luanhe Highway Bridge of Qianan County (Station QA) successively. Later, another mobile station was also set up at the Guest House of Yutian County (Station YT) by the Institute of Earthquake Engineering, China Academy of Building Research. The locations of the above 5 stations are shown in Fig. 1. All the instruments used in these stations were RDZ1-12-66 strong motion accelerographs. At Stations AF, CM, CL and QA the instruments were deployed on the ground for collection of strong ground motions during aftershocks and at Station YT the instrument was deployed on a three-story brick mixed structure to study seismic response of structures. After the main shock a series of strong aftershocks occurred frequently in the area. By the first of October 1976 the 5 accelerographs were triggered over 200 times. Because no pre-event memory system was used in the instruments, the triggering of an instrument caused recorded accelerograms to miss some information (about 0.2 second). Particularly for some accelerograms which were obtained at the field near the source not only P waves but also part of S waves were missing. Excluding these missing S wave records, a total of 134 ≥ aftershocks with magnitude ML 3 were recorded at the 5 stations. Figure 1 shows the locations of the epicenters of 134 aftershocks. It can be seen that the epicenters of aftershocks are distributed along the north-easterly belt with about 110 km in length and 40 km in width from Tangshan to Lulong.

The earthquake parameters of the 134 events, including time of occurrence (Beijing time), epicentral distance, local magnitude ML and depth of focus are listed in Table 1 (Seismological Bureau of Hebei Province, 1980).

163 well-recorded accelerograms, in which 42 were obtained at Station AF, 18 at CM, 11 at CL, 89 at QA and 3 at YT have been obtained during the 134 aftershocks. For the earth- quake of 19:09, 8 August 1976, ML=5.5 and the earthquake of 06:41, 9 August 1976,

* Institute of Engineering Mechanics, State Seismological Bureau 405

ML=5.7, all 5 stations recorded accelerograms. For the three events, 15 August 1976 (ML=4.8), 31 August 1976 (ML=5.8) and 31 August 1976 (ML=5.7), accelerograms were obtained at three stations simultaneously. For another 15 events accelerograms were obtained at two of the five stations. For the others, only one instrument recorded well.

The range of magnitudes of the 134 aftershocks were ML=3.1-5.8, in which there were ≤ ≤ ≤ ≤ 28 events of magnitude ML 4.0, 87 for 4.0 M<5.0, and 19 of 5.0 ML 5.8. The epicentral distances were from 2 to 72.5 km. The maximum value of peak acceleration was 159 gal.

II. Deployment of Measuring Points and Parameters of Instruments

1. Station AF It was located at the Tangshan Airfield (39.659°N, 118.138°E) in the north-western suburb of Tangshan City. The instrument operated from 23 hours on 28 July 1976 to 23 April 1978. Before 16 hours on 16 August 1976, the transducers were deployed on free ground surface 30 meters from the house of the ground crews and were then moved into the house because they were submerged by heavy rain. Based on the boring data obtained by the First Coal Geological Prospecting Team of Hebei Province in 1974, the Quaternary Period overburden of about 100 meters in depth overlies on the limestone of the Sinian Period. Figure 2 shows the boring log and the distri- bution of shear wave velocity at this station site. Two sets of transducers were put on the same observation point and each set consisted of 3 transducers which were used to record NS, EW and UD components of ground motion, respectively. Corresponding sensitivities were adjusted so that the first set was used for recording smaller ground motion and the second for stronger motion.

2. Station CM Station CM was installed at the Tangshan Cement Mill (39.642°N, 118.191°E) which was located on the west side of Dachengshan Mountain. It was operated from 13 hours on 29 July 1976 and removed on 3 September of the same year. The transducers were deployed on an outcropping of limestone of the Middle Ordovician Period. Similar to Station AF, two sets of transducers were put on the same site and each set consisted of three transducers recording NS, EW and UD components of ground motion, respectively. The sensitivities of the instrument were also adjusted to two different levels. The parameters of the instrument are listed in Table 3.

3. Station CL The instrument was installed at the Changli Seismic Station which was located at the foot of Fenghuangshan Hill 10 km north-west from the town of Changli. The location of the station was 39.758°N, 119.095°E. The instrument operated from 31 July 1976 to 4 September 1976. The station was located on bedrock (granite). 406

A set of transducers were deployed on the cement block in the pendulum room and another set was installed in the observation room (a flat building), which is about 30 meters from the former. Table 4 shows the parameters of the instrument.

4. Station QA The instrument was installed in the guardroom of the Luanhe Highway Bridge at the south bank of the Luanhe River, about 10 km south-east from the town of Qianan. The loca- tion was 39.956°N, 118.731°E. The operating duration was from 10:00, 2 August 1976 to 10 December of the same year. Five transducers were deployed on the ground in the guard- room which was located on bedrock. The parameters are shown in Table 5.

5. Station YT** The instrument was deployed on a three-story mixed construction building, the Enter- tainment House of Yutian County. The location of the station was 39.884°N, 117.748°E. It operated from 3 August to 28 August 1976. Figure 3 shows the distribution of the three observation points at the station. At each point there were three transducers corresponding to the three components of motion. Point 1 was on the free ground 13 meters from the building, Point 2 was set on the first floor and Point 3 on the third floor. Figure 3 shows the locations of the three instruments. Table 6 lists the parameters of the instruments. Yutian County was located in the abnormal lower intensity area in which the local inten- sity was VI. The building which was sited on an alluvial plain was undamaged. Figure 4 shows the boring log as well as the distribution of shear wave velocity.

III. Preliminary Analysis of the Accelerograms of Aftershocks

The maximum acceleration Am and the corresponding primary periods Tp of the 163 accelerograms obtained at the 5 stations are listed in Tables 7, 8, 9, 10 and 11, respectively. The epicentral distance was measured from 1:500000 map, with the accuracy of about ±0.5 km. Besides, all of the accelerograms in which the P waves were recorded are denoted by the symbol "*".

1. Maximum acceleration Am It is shown by the data of earthquakes obtained in China and other countries that differ- ences between the various empirical formulas on the relation of maximum acceleration Am, ∆ magnitude ML and epicentral distance are large and the scatter is also large. The 163 accelerograms of aftershocks may be used for determining the empirical formula of the local attenuation relationship of ground motion. Provided that the effect of site conditions on ground motion is negligible when the magnitude is definite the relationship between the

** The station data, instrument parameters and accelerograms of Station YT were provided by Mr. Li Fumin of the Institute of Earthquake Engineering, Chinese Academy of Building Research. 407

maximum horizontal acceleration Am and the epicentral distance ∆ can be assumed as follows: =×α ∆−β Am where a and b are coefficients determined by regression analysis of observed data shown in Tables 7-11. In the regression analysis the data were classified into 3 sets according to the ≤ ≤ magnitude ML, i.e. the first set for 3.0 M<4.0, the second for 4.0 ML<5.0, and the third for ≤ 5.0 ML<6.0. The corresponding numbers of samples are 27, 101 and 35 respectively, but only the larger of the every two horizontal components was used. The resulting relationships are =×∆−031. σ = ≤< AMmL22.4 , 111 .b 3 . 0 4 . 0g =×∆−049. σ = ≤< AMmL50.,... 2 12 8bg 4 0 5 0 =×∆−136. σ = ≤< AMmL1932.,... 0 29 8b 5 0 6 0g ∆ Figure 5 shows the relationships between Am, ML and . As shown in Tables 7-11 it is not consistent which of the two horizontal components is larger. Most of the maximum vertical accelerations Amv are smaller than the corresponding maximum horizontal accelerations Amh. The mean ratios RAA= mv/ mh and the standard deviations s are R ==066.,s 020 . (Station AF), R ==050.,s 018 . (Station CM), R ==090.,s 018 . (Station CL) and R ==040.,s 010 . (Station QA) respectively. Figures 6 and 7 show the distribution of the ratio AAmv/ mh for Station AF and Station QA, respec- tively.

The strongest ground motion was recorded at Station QA during the ML=5.7 aftershock which occurred at 6:41 on 9 August 1976. The epicentral distance was about 7 km. The maximum accelerations of NS, EW and UD components were 159.0 gal, 150 gal and 79.5 gal, respectively. The guardroom in which the instrument was installed was damaged once more by a cross crack "X" on the west wall. The local intensity was stronger than VII (Chinese scale).

2. The primary period Tp

The primary period Tp with which the peak acceleration occurred can be considered approximately as the predominant period of the spectrum of ground motion. Figures 8-11 ∆ show the relationships of Tp , ML and for Stations AP, CM, CL and QA, respectively. It ∆ can be seen that the correlations between Tp , and ML or are poor. The mean value Tp and the standard deviation σ of the four stations are listed in Table 12. Generally speaking, the periods Tp of the vertical components are smaller than those of the horizontal components and the Tp Tp on the bedrock sites are smaller than those on the soil sites. 408

3. The comparison of observation results between Station AF and Station CM The distance between stations AF and CM was only about 7 km. However, the site con- ditions were quite different in that the depth of the soil layers was about 100 meters at Station AF and Station CM was located on bedrock. Ten accelerograms of aftershocks (Nos. 15, 16, 45, 58, 61, 66, 86, 87, 88 and 92), which are valuable for studying the effects of site conditions on ground motion, were obtained simultaneously at both stations. It can be seen from Tables 7 and 8 that the effects of overlying soils on ground motion are complicated. In the instance of the No. 66 aftershock the ground motion was markedly amplified by the overlying soil layers so that the amplification constants of NS, EW and UD components were 3.02, 2.66 and 2.36, respectively. For aftershock Nos. 15, 16, 86 and 88, most components of ground motion were also amplified, while for other events such as Nos. 61, 87 and 92 the acceleration of some components on overlying soils were reduced. For the above 10 events the mean ratios of accelerations on soil site (Station AF) to those on rock site (Station CM) were 1.23 for the NS component, 1.22 for the EW component and 1.76 for the UD component, respectively. It can be concluded that the soil amplification was not consistent. The field exploration and the calculation of response of the soil layer made by IEM in 1979 showed that there was a soft clay layer with high plasticity directly overlying the bed- rock at Station AF (Fig. 2), and the incident vibration was isolated in some degree by this layer so that the ground motion was not obviously amplified.

IV. Some Typical Accelerograms Some typical accelerograms of aftershocks with a magnitude over 5 are shown in this section. During the aftershocks of No. 58 (M=5.5) and No. 66 (M =5.7), the accelerograms were obtained on all 5 stations and for the aftershocks of No. 108 (M=5.8) and No. 109 (M=5.7), the accelerograms were obtained from two of the five stations. These records have been digitized and corrected for the frequency characteristics of instrument and zero baseline, and the velocity and displacement have been integrated. The maximum corrected acceleration (absolute) Am, maximum velocity (absolute) Vm , maximum displacement (absolute) Dm, calculating duration of accelerogram Td, and the effective frequency band, etc. are listed in Table 13. Figures 12-25 show the corrected accelerograms of the events of Nos. 58, 66, 108 and 109, the step of calculation was 0.01 seconds. (Translators: Zhou Yongnian, Xie Li-Li) 409

Table 1. The parameters of aftershocks.

Time of Location of Epicenter Depth of No. Occurrence Latitude Longitude Reference Place Magnitude Focus M. D. H. M. H (km) 001 7 30 23 32 39°44' 118°32' 4.5 <5 002 7 31 01 02 39°42' 118°26' 4.5 10 003 7 31 02 39 39°27' 118°05' 4.1 16 004 7 31 04 06 39°41' 118°41' 4.8 005 7 31 05 23 39°41' 118°27' Luannan Tatuo 5.4 006 7 31 05 55 39°41' 118°22' 3.6 12 007 7 31 06 26 39°39' 118°30' Luannan Tatuo 4.8 008 7 31 10 15 39°39' 118°23' 3.4 20 009 7 31 10 27 39°38' 118°20' Wulitun, Tangshan 4.3 <5 010 7 31 15 23 39°43' 118°43' Luanxian 4.9 17 011 7 31 15 35 39°40' 118°17' Kaiping Town 4.4 8 012 7 31 15 42 39°39' 118°29' Luannan Tatuo 4.6 <5 013 7 31 19 28 39°21' 118°07' Jianzigu, Fengnan 4.6 <5 014 7 31 21 08 39°36' 118°12' Tangshan 4.3 21 015 7 31 21 22 39°51' 118°26' Longtuo 4.2 10 016 8.1 02 01 39°33' 118°16' Daqigezhuang 4.7 017 8 1 06 26 39°25' 118°03' Wanglanzhuang 5.1 018 8 1 07 47 39°27' 118°06' Wanglanzhuang 4.3 13 019 8 1 18 32 39°34' 118°15' Daqigezhuang 4.3 14 020 8 1 18 48 39°26' 118°09' 4.5 14 021 8 2 10 05 39°43' 118°21' Guye 4.0 <5 022 8 2 15 32 39°45' 118°34' 3.5 10 023 8 2 16 38 39°58' 118°40' Qianan 4.6 024 8 2 17 15 39°21' 118°05' Fengnan Xihe 5.0 025 8 2 18 26 39°55' 118°54' Shigezhuang, Lulong 4.6 10 026 8 2 18 49 39°37' 118°23' Fangezhuang 4.5 027 8 2 19 20 39°36' 118°18' 3.4 8 410

Table 1 Continued.

Time of Location of Epicenter Depth of No. Occurrence Latitude Longitude Reference Place Magnitude Focus M. D. H. M. H (km) 028 8 2 19 50 39°50’ 118°36’ 3.2 18 029 8 2 20 01 39°56’ 118°51’ 3.1 12 030 8 2 20 29 39°48’ 118°48’ Mazhuangzi 4.0 5 031 8 2 20 46 39°54’ 118°50’ Pengdianzi 4.3 5 032 8 2 21 18 39°45’ 118°45’ 3.4 16 033 8 3 00 25 39°58’ 118°40’ 3.4 14 034 8 3 04 27 39°51’ 118°47’ Xifangezhuang 4.1 5 035 8 3 13 55 39°43’ 118°31’ Xilin 4.7 036 8 3 14 54 39°45’ 118°27’ Zhaogezhuang 4.5 18 037 8 3 15 40 40°00’ 118°48’ Chenguangying 4.7 038 8 3 17 33 40°04’ 118°43’ Shangzhuang, Qianan 4.2 <5 039 8 3 18 16 39°38’ 118°04’ Hancheng Town 5.0 10 040 8 3 20 40 39°59’ 118°51’ Dahenghe 4.8 <5 041 8 4 09 24 39°53’ 118°43’ Hejiazhuang 4.9 042 8 4 09 29 39°50’ 118°46’ Xifangezhuang 4.3 043 8 4 11 29 39°59’ 118°54’ Dahenghe 4.0 12 044 8 5 07 37 39°50’ 118°50’ Mataizi 4.2 <5 045 8 5 23 31 39°38’ 118°20’ Wulitun 4.6 046 8 6 03 38 39°55’ 118°49’ Pengdian 4.3 047 8 6 12 28 39°36’ 118°10’ Tangshan 3.1 7 048 8 6 15 35 39°38’ 118°15’ 3.5 12 049 8 6 18 51 39°54’ 118°46’ Hejiazhuang 4.1 11 050 8 6 19 49 39°30’ 118°12’ Liutangbao 4.6 10 051 8 6 21 17 39°44’ 118°16’ Shuangqiao 4.6 10 052 8 7 04 20 39°39’ 118°09’ 3.5 13 053 8 7 11 07 39°51’ 118°44’ Xifangezhuang 4.1 5 054 8 7 13 18 39°45’ 118°38’ Zhenzhuang 4.7 5 411

Table 1 Continued.

Time of Location of Epicenter Depth of No. Occurrence Latitude Longitude Reference Place Magnitude Focus M. D. H. M. H (km) 055 8 7 14 45 39°45’ 118°36’ Leizhuang 4.5 056 8 8 12 26 39°53’ 118°50’ Lulong 4.5 8 057 8 8 16 53 39°52’ 118°48’ Lulong 4.0 058 8 8 19 09 39°48’ 118°32’ Jiubaihu 5.5 5 059 8 8 20 07 39°50’ 118°49’ Tangshan 3.4 5 060 8 8 21 53 39°53’ 118°52’ 3.6 5 061 8 8 22 33 39°40’ 118°06’ 4.3 062 8 8 22 44 39°50’ 118°50’ Mataizi 3.6 063 8 9 03 02 39°53’ 118°51’ Yashang 3.1 5 064 8 9 04 10 39°51’ 118°50’ Pengdian 4.0 7 065 8 9 06 18 39°34’ 118°55’ 4.0 7 066 8 9 06 41 39°57’ 118°49’ Dahenghe 5.7 14 067 8 9 06 45 39°53’ 118°50’ Jiubaihu 3.8 8 068 8 9 07 36 39°58’ 118°52’ Songjiaying 4.5 8 069 8 9 09 28 39°49’ 118°28’ 5.1 12 070 8 9 10 10 39°25’ 118°15’ Zhaogezhuang 5.1 071 8 9 12 29 39°54’ 118°49’ 3.6 6 072 8 9 15 58 39°45’ 118°26’ Pengdian 4.7 073 8 10 03 45 39°50’ 118°49’ Jiubaihu 3.6 17 074 8 10 22 23 39°55’ 118°51’ Shigezhuang 4.8 075 8 11 09 36 39°51’ 118°30’ Lulong 4.8 15 076 8 13 07 56 39°55’ 118°59’ Lulong 4.3 13 077 8 13 08 28 39°54’ 118°51’ Lulong 4.1 6 978 8 13 12 51 39°55’ 118°48’ 3.3 8 079 8 13 20 52 39°54’ 118°52’ Shuangqiao 4.0 7 080 8 14 03 44 39°53’ 118°47’ Lulong 3.5 9 081 8 14 10 32 39°47’ 118°21’ Lulong 4.5 11 412

Table 1 Continued

Time of Location of Epicenter Depth of No. Occurrence Latitude Longitude Reference Place Magnitude Focus M. D. H. M. H (km) 082 8 14 13 26 39°53' 118°49' 4.1 17 083 8 14 13 40 39°53' 118°52' Xifangezhuang 4.6 10 084 8 14 15 10 39°52' 118°46' Shuangqiao 4.5 085 8 15 00 02 39°51' 118°42' Zhaogezhuang 5.0 12 086 8 15 18 21 39°44' 118°20' 4.8 087 8 15 18 28 39°46' 118°23' Shigezhuang 4.8 088 8 15 18 53 39°42' 118°23' Jianzigu 4.6 089 8 16 05 27 39°55' 118°58' 4.8 13 090 8 17 00 42 39°23' 118° 07' 4.6 <5 091 8 17 08 10 39°33' 118°02' Kuazizhuang 4.4 14 092 8 18 23 37 39°38' 118°17' Wulitun 4.4 28 093 8 21 03 06 39°35' 118°11' 3.3 5 094 8 23 09 50 39°58' 118°55' Dahenghe 4.1 11 095 8 23 12 57 40°00' 119°00' 3.3 5 096 8 23 15 45 39°57' 118°52' 3.6 5 097 8 24 01 15 39°39' 118°20' Wulitun 4.6 16 098 8 25 06 08 39°41' 118°55' Danggezhuang 4.1 5 099 8 25 12 01 39°41' 118°28' Luannantatuo 4.4 100 8 26 01 31 39°39' 118°10' Tangshan 4.9 12 101 8 26 16 55 39°50' 118°45' Xifanggezhuang 3.5 16 102 8 27 17 32 39°55' 118°46' Xifanggezhuang 4.0 10 103 8 28 03 50 39°50' 118°31' Jiubaihu 4.2 9 104 8 28 12 34 39°55' 118°54' Shigezhuang 4.2 5 105 8 28 14 34 29°58' 118°55' Dahenghe 5.0 15 106 8 29 22 51 39°59' 118°50' Xiaguanying 4.1 18 107 8 30 15 31 39°53' 118°50' 3.5 5 108 8 31 11 25 39°50' 118°42' Xifanggezhuang 5.8 413

Table 1 Continued.

Time of Location of Epicenter Depth of No. Occurrence Latitude Longitude Reference Place Magnitude Focus M. D. H. M. H (km) 109 8 31 11 27 39°53' 118°53' Lulong 5.7 10 110 8 31 11 49 39°49' 118°49' 3.5 7 111 8 31 11 56 39°49' 118°53' Mataizi 5.1 11 112 8 31 12 03 39°53' 118°50' Lulong 4.2 13 113 8 31 12 21 39°53' 118°52' Lulong 4.0 13 114 8 31 13 05 39°52' 118°47' Hejiazhuang 4.3 9 115 8 31 14 30 39°48' 118°46' Mazhuangzi 4.2 12 116 9 1 03 29 39°58' 118°52' Dahenghe 4.2 12 117 9 1 10 26 39°20' 118°02' Xihe 4.6 14 118 9 1 16 15 39°57' 118°48' 3.2 5 119 9 2 05 31 39°49' 118°50' Mataizi 4.4 <5 120 9 2 16 49 40°00' 118°57' Daliuzhuang 5.0 9 121 9 5 14 11 39°51' 118°51' 3.4 <5 122 9 5 18 59 39°41' 118°15' Kaiping Town 4.2 11 123 9 6 13 24 39°53' 118°50' Lulong 4.3 13 124 9 6 23 46 39°55' 118°55' Shigezhuang 4.4 18 125 9 7 01 01 39°58' 119°00' Chenguanzhuang 5.0 15 126 9 7 04 02 39°57' 119°03' Shanzhuang 4.5 127 9 9 03 43 39°52' 118°49' 4.3 23 128 9 15 14 08 39°42' 118°52' Shimen 4.8 20 129 9 19 03 14 39°43' 118°48' Zhugezhuang 5.1 11 130 9 25 19 50 39°43' 118°24' Shuangqiao 5.4 7 131 9 27 04 11 39°53' 118°54' Lulong 4.2 13 132 9 28 09 15 39°53' 118°53' Lulong 4.4 133 9 29 07 12 39°52' 119°01' Yinggezhuang 5.3 <5 134 10 1 04 05 39°49' 118°41' Xifanggezhuang 5.0 414

Table 2. Specifications of accelerograph used at Station AF (No. 073 oscillograph).

Sensitivity Electromechanical (mm/gal) No. of No. of Natural Rotation Inertia Coupling Coil Damping Critical Channel Component Transducer Frequency 10-4 (V A sec) Coefficient Resistance Resistance Damping Before After (Hz) (V sec/m) (Ω¸) (Ω¸) Ratio 17:10 17:10 Aug. 3 Aug. 3 1 EW 081 3.97 3.597 59.24 156.6 44.0 9.75 0.833 0.435 2 NS 413 3.92 3.303 59.00 147.0 43.0 11.25 0.709 0.709 3 UD 255 4.52 3.650 58.85 148.4 42.8 8.73 0.730 0.730 4 EW 411 3.91 3.263 60.50 155.0 42.4 11.56 0.124 0.142 5 NS 412 3.92 3.340 61.25 150.4 43.5 11.75 0.136 0.158 6 UD 082 4.40 3.631 61.13 153.4 44.4 9.41 0.111 0.122

Table 3. Specifications of accelerograph used at Station CM (No. 046 oscillograph).

Sensitivity Electromechanical (mm/gal) No. of No. of Natural Rotation Inertia Coupling Coil Damping Critical Channel Component Transducer Frequency 10-4 (V A sec) Coefficient Resistance Resistance Damping Before After (Hz) (V sec/m) (Ω¸) (Ω¸) Ratio 14:45 14:45 Aug. 3 Aug. 3 1 EW 115 3.90 3.569 62.10 153.7 43.5 11.18 0.746 0.741 2 NS 407 4.01 3.329 59.90 150.9 42.4 11.08 0.694 0.699 3 UD 252 4.53 3.546 57.20 156.8 42.8 8.13 0.671 0.671 4 EW 088 3.95 3.478 59.66 154.2 43.0 10.45 0.144 0.265 5 NS 086 4.00 3.596 61.74 152.0 43.4 10.79 0.123 0.270 6 UD 083 4.50 3.941 59.81 152.7 42.3 8.23 0.172 0.270

Table 4. Specifications of accelerograph used at Station CL (No. 042 oscillograph).

Electromechanical Natural Coil Damping Critical No. of No. of Rotation Inertia Coupling Sensitivity Component Frequency Resistance Resistance Damping Channel Transducer 10-4 (V A sec) Coefficient (mm/gal) (Hz) (Ω¸) (Ω¸) Ratio (V sec/m)

1 NS 374 4.00 3.452 63.10 146.6 45.1 11.97 0.213 2 EW 190 3.96 3.593 58.40 148.1 42.2 10.02 0.308 3 UD 071 4.40 3.568 62.21 152.3 43.3 10.03 0.218 4 NS 245 4.01 3.743 59.30 148.0 44.0 9.71 0.196 5 EW 239 4.00 3.741 57.50 146.9 45.0 9.16 0.230 6 UD 312 4.50 3.600 60.20 151.8 43.2 9.13 0.207

Table 5. Specifications of accelerograph used at Station CL (No. 042 oscillograph).

Sensitivity Electromechanical (mm/gal) No. of No. of Natural Rotation Inertia Coupling Coil Damping Critical Channel Component Transducer Frequency 10-4 (V A sec) Coefficient Resistance Resistance Damping Before After (Hz) (V sec/m) (Ω¸) (Ω¸) Ratio 14:45 14:45 Aug. 3 Aug. 3 1 UD 310 4.50 3.770 58.00 149.9 42.2 8.21 0.549 0.549 2 NS 089 4.04 3.575 58.80 156.9 42.2 9.57 0.629 0.629 3 EW 090 4.02 3.595 60.80 155.9 42.2 10.28 0.654 0.654 4 NS 095 4.00 3.564 60.00 157.4 43.1 10.02 0.399 0.158 5 EW 293 3.96 3.659 59.94 149.7 42.1 10.29 0.336 0.161 415 416

Table 6. Specifications of accelerograph used at Station YT (No. 015 oscillograph).

Electromechanical Natural Coil Damping Critical No. of No. of Rotation Inertia Coupling Sensitivity Component Frequency Resistance Resistance Damping Channel Transducer 10-4 (V A sec) Coefficient (mm/gal) (Hz) (Ω¸) (Ω¸) Ratio (V sec/m)

1 Point I EW 112 4.05 3.495 61.50 157.3 43.5 10.59 0.690 2 Point I NS 118 3.99 3.570 59.40 153.1 43.1 10.05 0.671 3 Point I UD 088 4.59 3.830 57.69 159.5 44.8 7.37 0.588 4 Point II EW 116 3.97 3.720 63.90 152.1 42.7 11.30 0.755 5 Point II NS 114 3.94 3.660 57.90 153.0 44.3 9.38 0.765 6 Point II UD 090 4.56 3.750 59.06 155.3 45.9 8.07 0.724 7 Point III EW 120 4.02 3.412 62.50 152.8 42.3 11.62 0.624 8 Point III NS 117 4.06 3.680 63.10 161.3 44.4 10.31 0.674 9 Point III UD 087 4.51 3.840 60.19 157.0 44.2 8.27 0.740

417

Table 7. Results of preliminary analysis of accelerograms obtained at Station AF.

NS EW UD Epicentral No. of Magnitud Distance Duration Remarks A T A T A T Aftershock e M (km) (sec) m n m n m n L (gal) (sec) (gal) (sec) (gal) (sec)

001 4.5 34.0 5.3 4.1 0.07 2.9 0.08 2.7 0.07 002 4.5 25.0 5.3 3.5 0.09 2.4 0.11 2.7 0.07 003 4.1 24.5 14.1 4.4 0.10 3.0 0.11 2.7 0.06 004 4.8 45.5 5.4 4.2 0.11 3.1 0.09 3.0 0.08 005 5.4 26.0 38.0 28.0 0.11 33.2 0.23 27.9 0.08 * 006 3.6 19.0 11.3 3.1 0.10 2.4 0.11 2.1 0.06 007 4.8 30.5 19.5 7.8 0.10 6.7 0.17 4.1 0.08 008 3.4 20.5 14.1 6.4 0.13 5.3 0.12 3.4 0.06 009 4.3 16.5 17.2 7.1 0.08 4.9 0.11 7.5 0.07 010 4.9 50.0 17.0 4.2 0.26 3.2 0.31 3.6 0.07 011 4.4 11.5 17.1 8.5 0.23 5.4 0.27 5.9 0.08 012 4.6 29.5 17.0 5.4 0.11 7.9 0.13 4.8 0.06 013 4.6 35.5 17.0 4.7 0.10 3.6 0.12 2.7 0.06 014 4.3 8.5 14.1 13.3 0.09 12.6 0.11 12.3 0.06 * 015 4.2 32.5 18.1 12.0 0.13 12.7 0.08 17.8 0.08 * 016 4.7 17.0 17.1 13.1 0.08 21.0 0.09 12.9 0.09 017 5.1 27.5 15.6 10.0 0.16 6.6 0.11 8.2 0.07 * 018 4.3 24.5 4.4 8.6 0.11 6.0 0.10 6.2 0.08 019 4.3 14.5 17.6 19.0 0.17 18.5 0.10 11.0 0.06 020 4.5 25.0 11.6 4.1 0.09 3.7 0.10 1.4 0.06 021 4.0 19.0 13.6 12.7 0.10 8.2 0.14 9.6 0.08 024 5.0 36.0 17.7 5.4 0.22 4.1 0.22 2.7 0.07 026 4.5 21.5 17.8 4.9 0.13 6.5 0.11 4.3 0.08 027 3.4 16.0 5.5 9.9 0.08 7.7 0.10 7.5 0.08 039 5.0 6.5 15.2 46.1 0.09 39.3 0.10 21.9 0.08 * 045 4.6 16.5 24.0 17.5 0.12 10.6 0.16 13.7 0.10 047 3.1 7.5 7.6 9.2 0.11 5.8 0.10 7.1 0.07 048 3.5 10.5 5.0 7.9 0.11 7.1 0.10 2.1 0.08 050 4.6 18.0 20.8 12.0 0.17 7.4 0.14 5.5 0.09 * 418

Table 7 Continued.

NS EW UD Epicentral No. of Magnitud Distance Duration Remarks A T A T A T Aftershock e M (km) (sec) m n m n m n L (gal) (sec) (gal) (sec) (gal) (sec)

051 4.6 14.5 25.0 6.6 0.10 4.6 0.07 5.2 0.07 * 052 3.5 2.0 7.6 9.2 0.09 13.8 0.10 5.5 0.07 058 5.5 37.0 5.0 21.2 0.12 13.5 0.08 11.1 0.06 061 4.3 3.5 5.0 9.2 0.09 5.5 0.11 5.9 0.08 066 5.7 66.0 7.8 13.6 0.26 12.5 0.25 7.8 0.08 * 086 4.8 18.0 16.0 20.8 0.19 22.0 0.18 11.8 0.13 * 087 4.8 24.0 16.0 11.7 0.10 14.7 0.12 7.7 0.07 088 4.6 21.5 10.5 11.3 0.11 12.6 0.13 5.3 0.11 091 4.4 15.5 5.1 9.2 0.09 7.0 0.09 4.3 0.07 092 4.4 13.5 13.3 14.7 0.14 10.1 0.11 11.7 0.08 117 4.6 38.0 8.0 9.2 0.09 11.9 0.09 7.8 0.07 122 4.2 9.5 5.3 9.9 0.11 7.7 0.09 6.4 0.06 130 5.4 24.0 9.0 5.8 0.12 6.3 0.13 4.2 0.07

* P waves were recorded. 419

Table 8. Results of preliminary analysis of accelerograms obtained at Station CM.

NS EW UD Epicentral No. of Magnitud Distance Duration Remarks A T A T A T Aftershock e M (km) (sec) m n m n m n L (gal) (sec) (gal) (sec) (gal) (sec)

015 4.2 31.5 5.0 14.8 0.07 8.9 0.08 4.9 0.08 016 4.7 11.5 2.3 9.6 0.07 8.3 0.06 3.7 0.05 045 4.6 12.0 2.4 23.6 0.09 17.0 0.09 058 5.5 35.0 30.0 19.6 0.12 14.4 0.10 12.0 0.11 061 4.3 8.0 10.7 11.0 0.07 16.2 0.07 4.1 0.07 066 5.7 64.0 19.5 4.5 0.10 4.7 0.10 3.3 0.09 072 4.7 24.5 5.2 2.9 0.09 4.1 0.09 081 4.5 21.0 5.2 6.4 0.06 4.7 0.06 086 4.8 16.0 10.8 11.6 0.10 20.3 0.10 13.3 0.08 * 087 4.8 22.5 10.8 18.0 0.12 16.2 0.12 8.9 0.15 * 088 4.6 18.0 13.6 8.3 0.10 9.5 0.10 5.2 0.11 * 090 4.6 29.0 5.3 4.3 0.07 10.8 0.08 3.7 0.08 * 092 4.4 8.5 5.4 22.8 0.09 27.2 0.14 9.7 0.10 * 093 3.3 6.5 2.4 1.9 0.08 4.6 0.08 4.0 0.06 097 4.6 12.5 8.0 5.2 0.09 4.1 0.10 2.6 0.07 100 4.9 2.0 8.2 76.6 0.07 55.4 0.07 * 108 5.8 49.5 13.7 1.9 0.07 2.7 0.09 109 5.7 64.5 13.6 1.9 0.08 2.7 0.08

* P waves were recorded. 420

Table 9. Results of preliminary analysis of accelerograms obtained at Station CL.

NS EW UD Epicentral No. of Magnitud Distance Duration Remarks A T A T A T Aftershock e M (km) (sec) m n m n m n L (gal) (sec) (gal) (sec) (gal) (sec)

037 4.7 36.5 5.2 4.6 0.06 4.4 0.05 4.4 0.06 040 4.8 32.0 5.1 5.6 0.05 8.7 0.05 6.3 0.05 058 5.5 47.5 19.0 10.4 0.06 11.9 0.07 10.3 0.04 * 066 5.7 31.0 27.4 35.1 0.05 31.7 0.06 30.5 0.05 * 074 4.8 26.5 2.5 3.1 0.06 6.5 0.06 4.4 0.06 076 4.3 19.5 5.3 5.1 0.06 7.0 0.06 5.8 0.08 077 4.1 25.5 5.3 9.2 0.06 9.6 0.07 7.3 0.04 105 5.0 27.5 8.1 10.2 0.05 10.9 0.06 14.0 0.05 * 108 5.8 34.0 24.8 35.3 0.12 30.8 0.07 28.6 0.04 * 109 5.7 22.0 22.0 30.0 0.07 30.1 0.07 31.8 0.04 * 113 5.0 28.5 5.3 7.6 0.05 7.8 0.06 8.7 0.06

* P waves were recorded. 421

Table 10. Results of preliminary analysis of accelerograms obtained at Station QA.

NS EW UD Epicentral No. of Magnitud Distance Duration Remarks A T A T A T Aftershock e M (km) (sec) m n m n m n L (gal) (sec) (gal) (sec) (gal) (sec)

022 3.5 26.0 2.6 2.1 0.07 2.3 0.06 0.9 0.04 023 4.6 6.0 5.5 18.3 0.07 18.4 0.07 9.3 0.04 025 4.6 14.0 5.4 21.3 0.05 17.9 0.07 8.5 0.07 028 3.2 17.0 5.5 4.8 0.08 5.1 0.08 1.8 0.07 029 3.1 10.0 5.5 8.0 0.07 7.7 0.08 4.6 0.09 030 4.0 18.0 5.5 15.0 0.07 11.6 0.07 4.6 0.09 031 4.3 10.0 5.6 22.4 0.06 13.8 0.10 6.4 0.09 032 3.4 22.5 5.4 11.5 0.07 8.4 0.06 3.5 0.08 033 3.4 6.0 5.4 3.5 0.08 4.6 0.09 1.8 0.04 034 4.1 12.0 2.5 13.5 0.07 16.1 0.11 5.5 0.09 035 4.7 32.0 5.4 7.3 0.09 5.4 0.09 2.6 0.06 036 4.5 33.0 5.5 20.0 0.05 19.9 0.04 8.4 0.04 037 4.7 7.5 5.5 8.8 0.07 11.5 0.07 6.4 0.05 038 4.2 13.5 5.4 58.2 0.06 51.0 0.06 18.2 0.05 040 4.8 11.0 8.2 23.1 0.14 21.2 0.15 7.9 0.12 041 4.9 8.0 2.6 8.0 0.06 7.7 0.05 2.7 0.04 * 042 4.3 13.5 2.6 7.2 0.05 7.7 0.06 4.4 0.06 043 4.0 14.5 2.6 3.5 0.07 6.1 0.06 2.7 0.04 044 4.2 16.0 5.4 23.5 0.05 15.9 0.06 7.7 0.04 046 4.3 8.0 5.5 10.3 0.06 7.0 0.06 2.7 0.05 049 4.1 6.5 2.5 11.1 0.06 16.4 0.06 4.6 0.05 051 4.6 46.0 2.6 4.8 0.06 6.1 0.06 1.8 0.04 053 4.1 11.5 5.4 21.5 0.08 24.5 0.10 8.0 0.05 054 4.7 24.0 5.5 8.8 0.11 14.1 0.08 3.6 0.06 055 4.5 25.0 5.6 8.3 0.07 9.2 0.07 3.6 0.06 056 4.5 11.5 5.6 12.4 0.06 10.0 0.08 4.2 0.04 057 4.0 11.0 5.6 410.3 0.09 12.5 0.07 6.7 0.12 058 5.5 23.5 11.6 54.7 0.10 44.2 0.11 18.8 0.12 059 3.4 15.0 2.6 7.2 0.10 3.8 0.10 3.6 0.10 060 3.6 14.0 5.7 20.7 0.06 22.5 0.07 10.2 0.06 422

Table 10 Continued.

NS EW UD Epicentral No. of Magnitud Distance Duration Remarks A T A T A T Aftershock e M (km) (sec) m n m n m n L (gal) (sec) (gal) (sec) (gal) (sec)

062 3.6 16.0 2.6 5.7 0.05 4.6 0.06 3.6 0.04 063 3.1 12.5 5.6 10.3 0.07 17.4 0.07 5.5 0.05 064 4.0 14.5 5.6 15.3 0.07 16.1 0.08 5.5 0.04 065 4.0 45.5 5.6 10.2 0.09 9.5 0.06 5.5 0.11 066 5.7 7.0 23.4 177.1 0.06 162.6 0.07 89.3 0.04 * 067 3.8 11.5 2.6 16.9 0.08 19.1 0.06 6.4 0.08 068 4.5 11.5 2.6 11.1 0.06 9.2 0.06 3.6 0.06 069 5.1 27.0 5.6 16.7 0.14 17.4 0.07 11.1 0.16 070 5.1 72.5 8.6 4.8 0.10 4.1 0.10 2.7 0.09 071 3.6 9.0 5.7 15.9 0.05 18.4 0.07 6.4 0.05 073 3.6 15.0 5.7 12.4 0.07 12.2 0.06 4.6 0.10 075 4.8 22.5 3.2 12.4 0.11 12.2 0.07 5.6 0.06 077 3.3 7.0 5.3 18.3 0.06 16.1 0.05 8.4 0.05 079 4.0 12.5 2.5 9.7 0.06 9.2 0.05 3.4 0.05 080 3.5 9.0 5.4 13.5 0.07 11.0 0.07 3.8 0.04 082 4.1 10.5 5.4 67.6 0.10 32.6 0.10 14.9 0.06 083 4.6 14.0 5.2 30.5 0.07 27.4 0.07 17.1 0.05 084 4.5 9.5 8.1 93.3 0.11 64.3 0.11 35.5 0.05 085 5.0 11.0 8.0 61.9 0.06 40.4 0.05 35.0 0.05 087 4.8 36.0 5.4 12.1 0.08 10.1 0.07 4.0 0.07 089 4.8 20.0 5.4 27.7 0.09 36.7 0.10 13.5 0.10 094 4.1 15.5 2.6 15.0 0.06 19.1 0.06 10.9 0.08 095 3.3 22.5 2.6 10.0 0.06 7.7 0.09 3.6 0.11 096 3.6 11.0 5.5 57.2 0.06 39.2 0.08 16.4 0.07 098 4.1 33.5 2.6 11.1 0.05 9.0 0.07 3.8 0.04 099 4.4 37.5 5.5 10.0 0.08 11.6 0.06 4.4 0.05 100 4.9 58.0 5.5 10.0 0.08 7.8 0.08 3.6 0.04 101 3.5 13.0 5.4 28.1 0.05 23.6 0.05 16.2 0.05 102 4.0 5.0 5.5 10.8 0.06 12.4 0.08 4.4 0.04 103 4.2 22.0 5.5 29.4 0.09 24.0 0.07 7.5 0.08 423

Table 10 Continued.

NS EW UD Epicentral No. of Magnitud Distance Duration Remarks A T A T A T Aftershock e M (km) (sec) m n m n m n L (gal) (sec) (gal) (sec) (gal) (sec)

104 4.2 15.5 4.8 8.6 0.06 8.7 0.06 3.6 0.06 105 5.0 15.5 8.4 56.5 0.07 29.8 0.06 18.4 0.04 106 4.1 9.0 5.5 11.1 0.10 11.8 0.09 5.5 0.08 107 3.5 11.5 2.6 9.5 0.07 10.3 0.06 4.7 0.08 108 5.8 13.5 22.4 146.3 0.10 110.2 0.08 54.4 0.06 109 5.7 15.0 22.0 119.0 0.14 115.5 0.09 63.2 0.04 110 3.5 16.0 5.3 11.9 0.06 15.9 0.06 5.3 0.07 111 5.1 19.0 5.3 52.5 0.10 28.2 0.06 20.0 0.11 * 112 4.2 11.5 5.3 19.9 0.06 12.9 0.05 6.6 0.04 * 113 4.0 14.0 2.5 15.0 0.06 15.9 0.06 4.9 0.07 114 4.3 10.5 5.4 19.9 0.06 19.9 0.07 9.8 0.06 115 4.2 16.5 5.4 15.9 0.07 16.8 0.07 5.5 0.05 116 4.2 11.5 5.4 15.6 0.21 13.9 0.17 8.7 0.17 118 3.2 6.0 5.4 13.4 0.08 15.6 0.09 5.6 0.04 119 4.4 16.5 5.4 12.7 0.07 13.8 0.08 6.2 0.05 120 5.0 18.5 5.4 40.5 0.07 47.9 0.08 21.8 0.15 121 3.4 15.0 2.6 11.9 0.07 15.3 0.06 5.6 0.05 123 4.3 11.5 5.5 10.7 0.08 6.7 0.09 3.6 0.09 124 4.4 16.0 5.5 19.2 0.06 15.3 0.08 6.4 0.08 125 5.0 22.5 5.5 36.4 0.06 28.9 0.07 11.8 0.08 126 4.5 27.0 5.5 20.0 0.06 17.6 0.06 9.7 0.06 127 4.3 12.0 5.5 13.5 0.06 13.0 0.06 4.4 0.06 128 4.8 30.0 5.5 11.8 0.05 11.0 0.13 4.9 0.07 129 5.1 26.5 5.5 16.7 0.05 23.0 0.08 13.7 0.08 130 5.4 38.5 15.0 35.7 0.06 41.1 0.28 18.0 0.39 131 4.2 16.0 2.6 18.0 0.08 13.8 0.09 4.9 0.04 132 4.4 15.0 5.5 20.0 0.08 14.4 0.08 7.8 0.08 133 5.3 25.5 8.5 34.0 0.10 23.7 0.12 14.2 0.19 134 5.0 15.0 5.6 37.4 0.14 38.6 0.17 16.9 0.21

* P waves were recorded 424

Table 11. Results of preliminary analysis of accelerograms obtained at Station YT.

NS EW UD Epicentral No. of Magnitud Distance Duration Remarks A T A T A T Aftershock e M (km) (sec) m n m n m n L (gal) (sec) (gal) (sec) (gal) (sec)

1 5.9 0.15 8.4 0.15 3.5 0.10 point 1 058 5.5 67.5 3.0 3.1 0.15 7.5 0.15 2.9 0.15 point 2 4.7 0.17 11.2 0.15 3.8 0.15 point 3 4.7 0.16 6.2 0.22 3.2 0.12 point 1 066 5.7 91.5 21.0 4.1 0.34 5.2 0.22 2.8 0.16 point 2 6.6 0.20 7.7 0.26 2.6 0.08 point 3 7.2 0.16 6.7 0.17 2.6 0.13 point 1 069 5.1 61.5 8.0 2.8 0.25 3.3 0.17 2.4 0.15 point 2 5.7 0.25 8.6 0.17 point 3

Table 12. Mean values of primary periods.

Component NS EW UD

T T T Primary Period Station p p p (sec) σ(sec) (sec) σ(sec) (sec) σ(sec)

AF 0.12 0.05 0.13 0.05 0.08 0.01 CM 0.09 0.02 0.09 0.02 0.09 0.03 CL 0.06 0.02 0.06 0.01 0.05 0.01 QA 0.08 0.03 0.08 0.03 0.07 0.05

425

Table 13. Analytical results of typical accelerograms.

No. of Epicentral A V D T F Station Component m m m d e Aftershock Distance (gal) (cm/sec) (cm) (sec) (Hz)

058 NS 20.5 0.80 0.12 4.9 0.3-35 AF 37.0 EW 12.0 0.48 0.08 5.0 0.3-35 UD 9.8 0.26 0.05 4.9 0.3-35 NS 20.2 0.68 0.08 9.0 0.25-35 CM 35.0 EW 13.2 0.22 0.04 9.0 0.25-35 UD 12.4 0.46 0.14 8.9 0.25-35 NS 9.3 0.37 0.10 10.6 0.2-35 CL 47.5 EW 9.7 0.48 0.19 10.5 0.2-35 UD 9.4 0.43 0.21 10.6 0.2-35 NS 54.8 1.14 0.12 11.1 0.2-35 QA 23.5 EW 42.7 1.20 0.11 11.1 0.2-35 UD 18.4 0.40 0.11 11.1 0.2-35 NS 6.1 0.23 0.06 12.6 0.2-35 YT 67.5 EW 8.2 0.23 0.06 12.6 0.2-35 Point 1 UD 3.6 0.23 0.09 12.6 0.2-35 066 NS 13.4 0.62 0.07 6.4 0.3-35 AF 66.0 EW 13.0 0.53 0.09 6.4 0.3-35 UD 7.4 0.23 0.03 6.4 0.3-35 NS 4.2 0.20 0.04 6.6 0.3-35 CM 64.0 EW 4.8 0.16 0.03 6.6 0.3-35 UD 3.2 0.33 0.11 6.5 0.3-35 NS 34.2 1.88 0.22 7.1 0.3-35 CL 31.0 EW 29.7 1.22 0.13 7.1 0.3-35 UD 27.2 0.74 0.13 7.1 0.3-35 NS 159.0 9.74 3.22 23.4 0.15-35 QA 7.0 EW 150.3 3.48 0.70 23.3 0.15-35 UD 79.5 2.11 0.42 23.4 0.15-35 NS 4.5 0.19 0.05 11.8 0.2-35 YT EW 6.1 0.29 0.03 11.8 0.2-35 Point 1 UD 3.1 0.14 0.04 11.8 0.2-35 108 NS 34.0 1.30 0.28 16.2 0.2-35 CL 34.0 EW 27.3 1.09 0.20 16.1 0.2-35 UD 26.3 0.91 0.22 16.2 0.2-35 NS 135.3 2.64 0.75 22.2 0.15-35 QA 13.5 EW 99.2 3.44 0.95 22.1 0.15-35 UD 49.5 2.25 0.68 22.2 0.15-35 109 NS 25.3 0.95 0.36 13.5 0.2-35 CL 22.0 EW 26.7 0.64 0.27 13.5 0.2-35 UD 27.1 0.82 0.24 13.5 0.2-35 NS 115.7 2.84 0.44 21.7 0.15-35 QA 15.0 EW 121.3 2.97 0.71 21.7 0.15-35 UD 59.2 2.30 0.63 21.7 0.15-35 426

Figure 1. The locations of mobile observation stations and the epicenters of aftershocks.

427

Figure 2. The boring log and the distribution of shear wabe velocity of station AF.

428

Figure 3. The distribution of observation points of station YT.

Figure 4. The boring log and distribution of shear wave velocity of station YT.

429

Figure 5. The relationship of maximum acceleration Am, magnitude ML and epicentral distance ∆.

Figure 6. The frequency distribution of Amv/ A mh for station AF.

430

Figure 7. The frequency distribution of Amv/ A mh for station QA.

Figure 8. The relationship of Tp , ML and ∆ for station AF.

431

Figure 9. The relationship of Tp , ML and ∆ for station MC.

Figure 10. The relationship of Tp , ML and ∆ for station CL.

Figure 11. The relationship of Tp ML and ∆ for station QA.

432

Figure 12. The corrected accelerogram of No. 58 aftershock obtained on station AF.

Figure 13. The corrected accelerogram of No. 66 aftershock obtained on station AF.

433

Figure 14. The corrected accelerogram of No. 58 aftershock obtained on station CM.

Figure 15. The corrected accelerogram of No. 66 aftershock obtained on station CM. 434

Figure 16. The corrected accelerogram of No. 58 aftershock obtained on station YT.

Figure 17. The corrected accelerogram of No. 66 aftershock obtained on station YT. 435

Figure 18. The corrected accelerogram of No. 58 aftershock obtained on station QA.

Figure 19. The corrected accelerogram of No. 66 aftershock obtained on station QA. 436

Figure 20. The corrected accelerogram of No. 108 aftershock obtained on station QA.

Figure 21. The corrected accelerogram of No. 109 aftershock obtained on station QA. 437

Figure 22. The corrected accelerogram of No. 58 aftershock obtained on station CL.

Figure 23. The corrected accelerogram of No. 66 aftershock obtained on station CL.

438

Figure 24. The corrected accelerogram of No. 108 aftershock obtained on station CL.

Figure 25. The corrected accelerogram of No. 109 aftershock obtained on station CL.