EERI SPECIAL EARTIf1U~KE REPORT

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TABLE 1

Uncorrected peak accelerations

North Earthquake -March 5. 1987

Station Coordinates Coaponent PGA(g) Si te Geology

s w

Taltal 25.50° 70.53° N40°W 0.44 Alluvium Vertical 0.15 S50oW 0.26

Antofagasta 23.63° 70.43° NS no record Rock VertIcal no record EW 0.086

Calama 22.48° 68.95° N70 ow 0.029 Stiff Alluvium Ver tical 0.038 N20 oE 0.038

(( The event has special impor- The principal shock was felt STRONG MOTION tance in that, for the first with the following Modified time, the accelerograph network Mercalli intensities: Antofa- RECORDING recorded an important event in gasta V-Vl, Taltal V, Calama V, During the March 5 earthquake, the north of Chile. IV-V, Chanaral IV, 3 strong-motion records were 1quique 111, Arica 11-111, obtained with DG2 accelero- SEISMOLOG ICAL Vallenar 11-111 and La Serena meters (Saragoni (I), Bolt CHARACTERISTICS 1-11. (2)). The preliminary peak The mainshock of the earthquake accelerations and station All the reported intensities occurred at 6: 17 a.m. local geology are listed in Table I. are lower than VII reflecting time on Friday, March 5, 1987 the nondamaging character of (09: 17: 02.4 GMT). The epicen- the earthquake. ter was located off the coast, 90 km south of A portion of the accelerogram The maximum horizontal ground (Fig. 1). The magnitude calcu- recorded at Taltal in the N40°W lated by U8GS is M8 = 7.3. The acceleration was 0.44 9 recor- direction is shown in Fig. 3. ded in Taltal at 100 km from Of particular interest is the epicenter coordinates were es- the epicenter. Most of the timated as 24.44°8 and 70.62°W amplitude of 0.44 9 and the houses of Taltal are made of with a focal depth of 30 km. high frequency content. The wood. One instance of non- (Department of Geology and Geo- amplitude of 0.44 9 is very structural damage was reported. physics, University of Chile, high considering that this Pardo personal communication). station is loo km from the In Antofagasta a maximum hori- epicenter. zontal ground acceleration of 0.086 9 was recorded. Only NONDAMAGING nonstructural damage was repor- The record obtained at Taltal ted, with the exception of the EARTHQUAKE exhibits a strong directivity collapse of a wall of an old in the NS direction which is Despite the large magnitude of cinema and the settlement of common to the records obtained the earthquake no structural about one inch of the fill at at coast stations in Chile damage was observed. Antofagasta harbor (see Fig.2). (Saragoni et al. (3». £ERI SPECIAL EARTHOUAKE REPORT

Ii ,

~0.449.

5 S~C

Fig. 3 Tracing of a portion of the Taltal accelerogram, N40W component.

The maximum ground acceleration (0.44 g) no structural damage 4. Saragoni, G. R., J. Crempien formulas proposed by Saragoni was observed. and R. Araya, "Carac.teristic.as et al. (4) are in agreement Experimentales de los Movimi- with the values obtained in This low ability to produce entos sismic.os Sudameric.anos", Calama. damage of subduction Chilean Revista del IDIEM, Vol. 21, No. earthquakes has been observed 2, September 1982, , The lower value recorded in already (Fresard and Saragoni Chile. Antofagasta (0.086 g), compared (5». and it may be associated with Taltal, may be due to the with their low destructiveness 5. Fresard, M. and G. R. Doppler effect of the fault potential factor (Araya and Saragoni, "Analisis de los rupture starting from the epi- Saragoni (6». Acelerogramas de los Sismos de center and moving from north to 1981 en la Zona Central de south, to the site effects, and REFERENCES Chile" , Seccion Ingenieria to the directivity (the station Estructura1, Departmento de at Antofagasta has only the EW 1. Saragoni, G. R. 1 "Earthquake Ingenieria Civil, Universidad component). Engineering Research Program in de Chile, Publicacion SES I Chile", Earthquake Information 3/85 (198), December 1985. CONCLUSIONS Bulletin, January-February 1982. 6. Araya, R. and G. R. For the first time an important Saragoni, "Earthquake event was recorded in the north 2. Bolt, B., "The Chile Earth- Accelerogram Destructiveness of Chile. The characteristics quake of March 3, 1985- Seis- Potential Factor", 8th World of the recorded accelerograms mological Features", Earthquake Conference on Earthquake confirm the observed charac- Spectra, Vol. 2, No.2, 1986. Engineering, San Francisco, teristics of the subduction California, 1984. Chilean earthquakes i.e. high 3. Saragoni, G., P. Gonzalez Note to reader: Copy as desired amplitude, high frequency and M. Fresard, "Analisis de for unlimited distribution. content, strong directivity and los acelerogramas del Terremoto Doppler effect. del 3 de Marzo de 1985", Chapter 3 in "El Sismo del 3 de Metric Conversions Despite the large magnitude of Marzo 1985- Chile", Facultad 1 Mile = 1.6 km this earthquake and large de Ciencias Fisicas y 1 km = 0.62 mile acceleration amplitude recorded Matematicas, Universidad de 1 cm = 0.4 in at 100 km from the epicenter Chile. 1 in. = 2.54 cm

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