Soils and Foundations 2012;52(5):769–779

The Japanese Geotechnical Society

Soils and Foundations

www.sciencedirect.com journal homepage: www.elsevier.com/locate/sandf

Ground motion characteristics during the 2011 off the Pacific Coast of Tohoku Earthquake

Hiroyuki Gotoa,n, Hitoshi Morikawab

aDisaster Prevention Research Institute, Kyoto University, bDepartment of Built Environment, Tokyo Institute of Technology, Japan

Received 12 January 2012; received in revised form 9 May 2012; accepted 20 June 2012 Available online 20 December 2012

Abstract

The 2011 off the Pacific Coast of Tohoku Earthquake ðMW 9:0Þ caused severe damage not only because of the great tsunami, but also because of the ground motions. In the present paper, we report some details of the source mechanism and the ground motions during the earthquake, and discuss the ground motion characteristics related to the damage in the Tsukidate and Furukawa areas. Damage grades in Tsukidate, where the largest peak ground accelerations were observed, are not severe in comparison to those in Furukawa. The pseudo-velocity response spectrum for the ground motions observed in the Furukawa area is similar to that in the JR Takatori records for the 1995 Kobe earthquake. & 2012 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. Open access under CC BY-NC-ND license.

Keywords: The 2011 off the Pacific Coast of Tohoku Earthquake; Earthquake; Ground motion; Peak ground acceleration; Pseudo velocity response spectrum; Frequency contents (IGC: A-01, C-00)

1. Introduction accelerations of over 980 cm=s2, and two stations observed seismic intensities of over 6.5 on the Japan Meteorological On 11 March 2011, a large earthquake hit the eastern Agency (JMA) scale. It should be noted that the damaged part of mainland Japan. The earthquake, and particularly areas do not correspond to the locations for which the the great tsunami caused by it, resulted in the death of observing the large accelerations and intensities. more than ten thousand persons. Structures were also Residential damage, due to the ground motions, was damaged not only due to the tsunami, but also due to the concentrated in the Furukawa area of Osaki City and the ground motions, e.g., elevated bridges of the Tohoku Sanuma area of Tome City, which are both located in Shinkansen (Takahashi, 2011) and geotechnical structures inland areas of Miyagi Prefecture (Goto, 2011). The (Tohata et al., 2011). Strong ground motions during the seismic intensities observed at the seismic stations located earthquake were observed over almost the entire county of in these areas were in the range of 5.5–6.5. On the other Japan. At least 18 stations observed peak horizontal hand, no significant damage was reported in the Tsukidate area of Kurihara City, where a seismic intensity of over 6.5 nCorresponding author. was observed (Goto, 2011). This means that the damage E-mail address: goto@catfish.dpri.kyoto-u.ac.jp (H. Goto). grades are not consistent with the JMA intensities. Peer review under responsibility of The Japanese Geotechnical Society. In this paper, we review the source process and the ground motions during the earthquake, and then discuss the ground motion characteristics related to the damage in the Tsukidate and Furukawa areas.

0038-0806 & 2012 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. Open access under CC BY-NC-ND license. http://dx.doi.org/10.1016/j.sandf.2012.11.002 770 H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779

2. Characteristics of source process earthquake were not evaluated. The earthquake ruptured over several segments, which had been evaluated as The earthquake, officially named ‘‘The 2011 off the independent earthquakes. Pacific Coast of Tohoku Earthquake’’ by JMA, occurred Fig. 2 shows the distribution of seismic intensities on the at 14:46 (JST, GMTþ9) on 11 March 2011. The hypo- JMA scale. Intensities over 6.5 were recorded at K-NET center was located in the offshore region of the eastern MYG004, located in Kurihara City of Miyagi Prefecture, part of mainland Japan, and the depth was 24 km. The and at KiK-net TCGH16, located in Haga Town of moment magnitude ðMW) was 9.0 (Hirose et al., 2011), Tochigi Prefecture. Intensities over 6.0 were widely making it the largest earthquake observed in Japan since recorded in Miyagi, Fukushima, Ibaraki, and Tochigi 1900, and the fourth largest earthquake in the world since Prefectures (see Fig. 1)(Hoshiba et al., 2011). The 1900. Fig. 1 shows the distribution of aftershocks occur- observation of intensity over 6.5 occurred for only the ring within 24 h after the main shock, which almost covers second time since the 1995 Kobe earthquake in Japan; the the fault zone of the main shock. This implies that the other was the record in Kawaguchi during the Mid-Niigata dimensions of the fault zone were about 500 km in length Prefecture earthquake of 2004. The intensity distribution is along the coast line by about 200 km in width. Fig. 1 also not simply attenuated from the east coast, but also varies shows the centroid moment tensor (CMT) solutions strongly along the coast line. This implies that the source estimated by JMA (Hirose et al., 2011) and F-net orga- rupture process was not spatially uniform. nized by the National Research Institute for Earth Science Fig. 3 shows the envelopes of the borehole accelero- and Disaster Prevention (NIED). They indicate that the grams observed by KiK-net (NIED). In order to highlight mechanism was a reverse fault with a compressional axis in the high frequency components, the accelerograms are an almost east-to-west direction, which is estimated as filtered in the range of 0.5–10 Hz, and the envelopes are N 1031E by JMA and N1101E by NIED. The location of averaged with moving windows of 2.0 s. Stations were the seismic fault and the mechanism imply an inter-plate selected to be almost parallel to the strike direction of the earthquake on the plate boundary between the North seismic fault estimated by JMA (N1931E). First and American plate and the Pacific plates. second wave groups, with an interval of about 50 s, were The Headquarters for Earthquake Research Promotion mainly observed at the northern stations, e.g., wave groups had warned of the occurrence of an earthquake in offshore being observed at the earliest time at IWTH05. The wave Miyagi Prefecture with a probability of 99% and a scale of groups are not clear at the southern stations, but a third MJMA 7.5 within 30 years. The event was expected to be wave group was mainly observed at the southern stations, similar to the Miyagi-oki earthquake ðMW 7.6) of 1978. e.g., wave groups being observed at the earliest time at However, the events corresponding to the Tohoku TCGH13. This implies that the rupture process of the earthquake involved at least three significant events radiat- ing high-frequency energy. The first two pulses mainly

CMT solution (NIED)

40°

Iwate Prefecture 40°

Miyagi Prefecture JMA intensity 38° 7.0 Fukushima Prefecture 38° 6.5

Tochigi Prefecture 6.0 CMT solution (JMA)

Ibaraki Prefecture 5.5 36° depth [km] 02550 36° 5.0 100 km 100 km 4.5 138° 140° 142° 144° 138° 140° 142° 144° Fig. 1. Aftershock distribution within 24 h after the main shock, and CMT solutions estimated by JMA and F-net (NIED). Fig. 2. Distribution of seismic intensities on the JMA scale. H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779 771

0.5−10Hz envelope (smoothing in 2s window) 500 IWTH08

IWTH13 IWTH08 IWTH02 40° IWTH13 400 IWTH02

IWTH04 IWTH04 IWTH05 IWTH05 300 MYGH06 MYGH06

MYGH08 MYGH08 38° MYGH09 [km] MYGH09 200 FKSH17 FKSH18 FKSH17 FKSH09 FKSH18 FKSH11 FKSH09 IBRH12 FKSH11 TCGH13 100 TCGH16 IBRH12 IBRH11 TCGH13 IBRH19 TCGH16 36° IBRH11 0 IBRH19 100 km

0 50 100 150 200 140° 142° time [s]

Fig. 3. Envelopes of borehole accelerograms in EW component observed by KiK-net (NIED). Stations are selected to be almost parallel to the strike direction of the seismic fault. affected the ground motions observed in Iwate and Miyagi close to each other (Asano and Iwata, in press; Kurahashi Prefectures, while the third pulse affected the ground and Irikura, 2011). This means that a time lag of about 50 s motions observed in Ibaraki and Tochigi Prefectures. was required between the events. Goto et al. (in press) Several research groups have reported on the source suggests that reflection waves from the free surface affected process during the earthquake. GPS data and low- the generation of the latter event. frequency ground motions imply that a large slip region is located on the shallower side of the seismic fault (e.g. Miyazaki et al., 2011; Suzuki et al., 2011; Yoshida et al., 3. Characteristics of ground motions 2011). They estimated a maximum slip of about 35–50 m, which is almost in the same order as the geodetic data Ground motions during the earthquake were observed observed just above the hypocenter (Sato et al., 2011). On by several seismic networks organized by NIED, JMA, the other hand, ground motions corresponding to the Port and Airport Research Institute (PARI), Building frequency components higher than 0.1 Hz imply that Research Institute (BRI), National Institute for Land several strong motion generation areas (SMGAs) are and Infrastructure Management (NILIM), and other located on the deeper side of the seismic fault (e.g. Asano organizations. Figs. 4 and 5 show the distributions of peak and Iwata, in press; Kurahashi and Irikura, 2011). A high- ground accelerations (PGA) and peak ground velocities frequency radiation area is also estimated by the back- (PGV), respectively, in the horizontal components calcu- projection method to be located on the deeper portion of lated from the available records of the ground motion. the fault (e.g. Ishii, 2011; Wang and Mori, 2011; Zhang PGA values do not simply attenuate from the east coast; et al., 2011). This implies that the locations of the seismic they vary strongly along the coast line, similar to the wave radiation areas depend on the frequency band (Koper seismic intensity distribution. Large PGAs were mainly et al., 2011); high-frequency radiation is generated along observed in the regions of (1) Miyagi Prefecture and (2) the deeper side, while low-frequency radiation and a large Tochigi and Ibaraki Prefectures, which are close to the slip are generated on the shallower side. The full rupture locations of the SMGAs. Si et al. (2011) compared the process, considering both the high- and low-frequency observed PGA and PGV to the ground motion prediction radiations, is estimated by Ide et al. (2011). equation by Si and Midorikawa (1999), which was devel- The ground motions observed in Miyagi and Iwate oped using data from earthquakes with MW 5.8–8.3. They Prefectures consist of two major wave groups with an summarized that PGAs observed within 100 km of the interval of about 50 s (see Fig. 3). The origins are estimated seismic fault are consistent with the equation for MW 9.0, to be on the deeper side of the hypocenter, and to be located whereas PGVs within 300 km are weaker than that. 772 H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779

Table 1 Top eight records of PGA in horizontal components.

PGA ðcm=s2) Station 40° 2765 K-NET MYG004 K−NET MYG004 1970 K-NET MYG012 K−NET MYG012 1913 PARI Onahama-G 1844 K-NET IBR003 PGA [cm/s/s] 1807 K-NET MYG013 1614 K-NET IBR013 1425 K-NET TCG009 38° 900 1425 K-NET FKS016

PARI Onahama−G 600 K−NET IBR003 2000 300 ° K-NET MYG004 N161°E 36 0 2

] (Max. 2765 cm/s ) 2 100 km 0 -2000

K-NET MYG012 N92°E 138° 140° 142° 144° (Max. 1970 cm/s2) Fig. 4. Distribution of peak ground accelerations (PGA) in horizontal PARI Onahama-G N127°E components. acceleration [cm/s (Max. 1913 cm/s2)

K-NET IBR003 N323°E

(Max. 1844 cm/s2)

40° 0 50 100 150 200 time [s]

Fig. 6. Accelerograms of top four PGA records of the maximum component. PGV [cm/s] 100 38° located in Miyagi Prefecture, while PARI Onahama-G and K-NET IBR003 are located in Fukushima and Ibaraki 75 Prefectures, respectively (see Fig. 4). As discussed in the previous section, waveforms of K-NET MYG004 and 50 MYG012 contain two wave groups because of the two SMGAs located downdip of the hypocenter. On the other 25 36° hand, waveforms of PARI Onahama-G and K-NET IBR003 contain one wave group. 100 km 0 The frequency contents of the ground motions are discussed via the pseudo-velocity response spectrum 138° 140° 142° 144° (pSv), which is defined by dividing the acceleration response spectrum (Sa) by angular natural frequency o Fig. 5. Distribution of peak ground velocities (PGV) in horizontal components. 1 T pSvðTÞ¼ SaðTÞ¼ SaðTÞð1Þ o 2p Table 1 lists the top eight records of PGA in horizontal components, and Fig. 6 shows the accelerograms of the top The pseudo-velocity response spectrum gives the same four PGA records: K-NET MYG004, K-NET MYG012, information as plotting the acceleration response spectrum PARI Onahama-G, and K-NET IBR003. The largest when the oblique line has a gradient of 1=2p, a so-called PGA, 2765 cm=s2, was observed at K-NET MYG004. tri-partite plot (e.g. Chen and Scawthorn, 2002). It is not It is almost three times larger than the gravitational theoretically equal to the velocity response spectrum (Sv), acceleration. Even the second largest PGA observed at whereas statistically it is very close, except for the long K-NET MYG012 is about twice larger than the gravita- natural periods (Hudson, 1962). The acceleration and tional acceleration. K-NET MYG004 and MYG012 are displacement response spectra are flat in the shorter and H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779 773 longer natural periods, respectively, while the pseudo velocity response spectrum gives a clear peak around the transition periods. We focus on the peak value and the corresponding period of pSv to discuss the frequency 40° contents. Fig. 7 shows the pseudo-velocity response spectra of the K-NET MYG004 and the MYG012 records. The lines corresponding to each record are EW and NS components. The damping coefficient is set to be 0.05. The response spectra are compared to the JR Takatori records taken 38° during the 1995 Kobe earthquake, which were observed in the damage belt, the area with a seismic intensity of 7 on peak period of pSv the old JMA scale. In the area, more than 30% of the (> 50cm/s) wooden houses were reported as having collapsed on the < 1.0s basis of field reconnaissance (e.g. Kawase, 1996; JMA, > 1.0s 1997). pSv values of K-NET MYG004 and MYG012 exceeded the JR Takatori records at periods shorter than 36° 0.5 s, whereas those in the range of 1.0–2.0 s were almost one-fourth of those of the JR Takatori records. This means 100 km that the frequency content of the records with the large PGAs is not similar to that of the JR Takatori records. 138° 140° 142° 144° Fig. 8 shows the distribution of the peak periods of the pSv Fig. 8. Distribution of peak periods of pSv over 50 cm/s categorized into exceeding 50 cm/s, which are categorized into periods of periods of either less than or greater than 1.0 s. either less than or greater than 1.0 s. Most of the records show peak periods of less than 1.0 s. This means that the high-frequency radiation less than 1.0 s was significant during the earthquake and caused the large PGAs. On the other hand, several peak periods of over 1.0 s were observed, although the PGAs were not very large. Fig. 9 shows the distribution of the peak values and 40° periods of pSv in its maximum component. The color of the symbols highlights the periods in 1.0–2.0 s in order to emphasize the records similar to the JR Takatori records. Large pSv values with periods in the range of 1.0–2.0 s are JMA Furukawa (423cm/s, 1.2s)

K-NET MYG004 38° K-NET MYG012 1995 JR Takatori K−NET TCG006 (359cm/s, 1.3s) 1000 pSv (h = 0.05) 300cm/s 150cm/s sec. 36° 0.1 1 10

100 km 100

pSv (h = 0.05) [cm/s] 138° 140° 142° 144°

Fig. 9. Distribution of peak pSv and periods. Color of the marks highlights the periods in 1.0–2.0 s.

10 0.1 0.5 1 2 5 concentrated in the northern part of Miyagi Prefecture. We period [s] focus on the typical records with the large pSv values and the period range of 1.0–2.0 s, JMA Furukawa and K-NET Fig. 7. Pseudo-velocity response spectra (h¼0.05) of K-NET MYG004 and MYG012, compared to JR Takatori records during 1995 Kobe TCG006, as indicated in Fig. 9. PGAs of JMA Furukawa 2 2 earthquake. The two lines plotted together for each event correspond to and K-NET TCG006 are 568 cm=s and 421 cm=s , EW and NS components. respectively, which are almost half of the gravitational 774 H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779 ] JMA Furukawa 2 K-NET CHB008 EW K-NET TCG006 500 2 1995 JR Takatori (Max 157 cm/s )

1000 K-NET CHB024 EW 0 (Max 203 cm/s2) acceleration [cm/s 0 50 100 150 200 time [s]

Fig. 11. Accelerograms in Tokyo Bay area. 100 pSv (h = 0.05) [cm/s] in Furukawa area. We performed damage reconnaissance not only for residential structures, but also for Japanese shrines and temples in both areas. Focus was placed on the elements common to the shrines and gravestones at 10 temples, because these are almost uniformly distributed 0.1 0.5 1 2 5 in all of Japan. In the case of the shrines, several elements period [s] are addressed; such as , a gate made of wood and/or stones, suibansha, a basin containing water for Fig. 10. Pseudo-velocity response spectra (h¼0.05) of JMA Furukawa and K-NET TCG006, compared to JR Takatori records during 1995 ritual purification of mouth and hands before entering the Kobe earthquake. The two lines plotted together for each event corre- shrine grounds, , statues of lions or lion dogs that spond to EW and NS components. guard the shrine, , the Main Hall or hall where the kami (god) is enshrined, and sando, the approach to the acceleration. Fig. 10 shows the pSv of the JMA Furukawa shrine or honden, lined with trees or lanterns (Young et al., and the K-NET TCG006 records compared to the JR 2004). The difference in damage patterns emphasizes the Takatori records. Both peak periods are almost similar to relative difference in damage grades between the areas, the peak period of the JR Takatori records. The peak although the quantitative research has been limited in the value of JMA Furukawa is almost similar to that of the JR damage grade of the honden at the Japanese shrine Takatori records, whereas that of K-NET TCG006 is a (Yamada et al., 2008), and for the damage ratio of the little less. gravestones (e.g. Ishiyama, 1982; Midorikawa and In the following section, we discuss the differences in Fujimoto, 1996; Kaneko and Hayashi, 2000). Therefore, structural damage around the seismic stations of K-NET we compare the actual damages to the honden and to the MYG004 and JMA Furukawa, which are typical of the gravestones with the estimation curves developed quanti- stations for which the largest PGA and the significant tatively in previous studies, and introduce patterns of the characteristics of pSv, respectively, were observed. other damages developed qualitatively. Long-duration ground motion is also a typical charac- teristic of this earthquake, because the generation of the seismic waves continued about 160 s (Suzuki et al., 2011) 4.1. Tsukidate area due to the rupture propagation of such a large-scale seismic fault. This caused liquefaction damage, especially The Tsukidate area is located in Kurihara City, Miyagi in the Tokyo Bay area (Tohata et al., 2011). Fig. 11 shows Prefecture, which is about 60 km north of Sendai City. accelerograms at K-NET CHB008 and CHB024 located in There is one seismic station, K-NET MYG004, which the Tokyo Bay area. An acceleration of over 50 cm=s2 observed the largest PGA of 2765 cm=s2 and a seismic continued for about 50 s at CHB008. CHB024 shows a intensity of 6.6 on the JMA scale. drastic change in amplitude, a reduction in high-frequency Damage reconnaissance around the seismic station was components, and spike-like phases after about 100 s, which performed on 2 April 2011. Fig. 12 shows the location of all correspond to the characteristics of the records on the K-NET MYG004 and the damage along the reconnais- liquefied ground (e.g., Holzer et al., 1989; Iai et al., 1995). sance trails. The trails cover the downtown of Tsukidate. We observed a few fallen pieces of block walls, peeled off 4. Damages due to ground motions in Tsukidate and exterior faces of stores, cracks on the columns of residential Furukawa areas houses, broken windows, and the caving in roads, which are marked as squares in Fig. 12. There were no collapsed We focus on the detailed damage due to the ground or severely damaged houses along the reconnaissance trails. motions in two typical areas of Miyagi Prefecture, Tsuki- One shrine, Tsukidate Shrine, and one temple, date and Furukawa. The largest PGA site, K-NET Sorinji Temple, are located in the area. At Tsukidate MYG004, is located in the Tsukidate area, and the Hachiman Shrine , only one komainu fell down, and the remarkable site in terms of pSv, JMA Furukawa, is located damage of the honden was categorized into D1 in the H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779 775 damage rank by Okada and Takai (1999) (Fig. 13). At the downtown. There are four seismic stations, K-NET Sorinji Temple, the gravestones were classified into three MYG006, JMA Furukawa, Furukawa Gas, and NILIM categories: (a) collapse of the main gravestone, (b) move- Furukawa. However, the records for the main shock at ment of the gravestone or the other damage, and (c) no Furukawa Gas were unfortunately missed (Goto et al, damages. The number of gravestones corresponding to 2012). K-NET MYG006, JMA Furukawa and NILIM each category was (a) 36, (b) 111, and (c) 457. Ratios of the Furukawa observed PGAs of 583 cm=s2, 568 cm=s2, and collapsed and damaged gravestones are 0.06 and 0.24, 483 cm=s2, and seismic intensities of 6.1, 6.2, and 6.1, respectively. Collapsed gravestones around the observed respectively. station in the JR Takatori records from the Kobe earth- Damage reconnaissance in the area around the seismic quake were reported in the ratio of 0.70 by Midorikawa stations of K-NET MYG006 and JMA Furukawa was and Fujimoto (1996), which is higher than the ratio for the performed on 4 days, namely 14, 15, 29, and 31 March Tsukidate area. 2011. Fig. 14 shows the location of the seismic stations and the significant damage along the reconnaissance trails. Furukawa Gas is located about 1 km west of the area, 4.2. Furukawa area and NILIM Furukawa is located about 2 km east of the area. Uplifted manholes and uneven walkways due to The Furukawa area is located in Osaki City, Miyagi liquefaction were observed in the western area of JR Prefecture, which is in between the Tsukidate area and Furukawa Station. Severe residential damage was Sendai City. Furukawa Station of the JR Tohoku Shin- observed in the area nearby the liquefaction area. We kansen and JR Riku-u-tosen is located at the center of classified the residential damage into four categories, namely (1) totally collapsed houses, (2) severely damaged houses, (3) raw land, and (4) other. The total number of houses in categories (1)–(3) was 37. Three shrines and three temples are located in the area. Figs. 15–17 show the details of the shrine damage to the shrines. The marked squares indicate collapsed stone monuments, while the arrows show the collapse directions. Several stone monuments, i.e., stone lanterns and komainu, collapsed at the shrines. Wooden honden at the Konpira Tsukidate and Shrines, and the suibansha of the Nishi- hachiman shrine nomiya Shrine were severely damaged. The damage to the honden at Konpira, Kanaya, and Nishinomiya Shrines was categorized into D3, D1, and D3 in the damage rank by Sorinji temple Okada and Takai (1999), respectively. We classified the Osaki city hall damage levels of the gravestones at the Zuisenji Temple into the same categories as the Sorinji Temple, and the evidence of ground motion reconnaissance trail number of graves corresponding to each category was (a) K-NET MYG004 200m 193, (b) 64, and (c) 93 in the half-yard of the gravestone garden. The ratios of the collapsed and damaged grave- stones are 0.55 and 0.73, respectively, which are higher than for Sorinji Temple. Although gravestones at Ichijyoji Fig. 12. Location of seismic station, K-NET MYG004, and the signifi- Temple were also severely damaged, the number of cant damages observed in Tsukidate area. damaged gravestones at Seiganji Temple was very few.

N

Fig. 13. Damage to Tsukidate Hachiman Shrine. Symbol of gate is the location of torii, squares are komainu, symbol of house is honden, and shaded area is sando. 776 H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779

collapsed residence K-NET MYG006 severe damaged residence raw land Seiganji temple sand boiling uplifted manhole Ichijyoji temple reconnaissance trail 200m

Kanaya fudoson shrine Konpira shrine JMA Furukawa Zuisenji temple

Nishinomiya shrine

JR Furukawa St.

Fig. 14. Location of seismic stations, K-NET MYG006 and JMA Furukawa, and the significant damages in Furukawa area.

N N

Fig. 15. Damage to Konpira Shrine. Symbol of gate is the location of Fig. 17. Damage to Nishinomiya Shrine. Symbol of gate is the location of torii, squares are komainu and stone monuments, symbols of house are torii, vertical markers are wooden lanterns, symbol of house is honden, honden and suibansha, and shaded area is sando. and shaded area is sando.

N of the typical gravestones as a damage curve, based on the actual damages during the historical earthquakes (e.g., Midorikawa and Fujimoto, 1996; Kaneko and Hayashi, 2000). The damage curve proposed by Kaneko and Hayashi (2000) is as follows:

R ¼ F½ðln PGVln 76Þ=0:4; ð2Þ

where R is the damage ratio and F denotes the cumulative distribution function of the normal distribution. The unit Fig. 16. Damage to Kanaya Shrine. Symbol of gate is the location of for the PGV is cm/s. The observed PGVs at K-NET torii, squares are komainu and stone monuments, symbol of house is MYG004 and JMA Furukawa are 106 cm/s and 84 cm/s, honden, and shaded area is sando. respectively, and they estimate the damage ratios as 0.80 and 0.60 using Eq. (2), respectively. The value is consistent The aspect ratios for 10 samples randomly selected from with the one for Zuisenji Temple, whereas it is larger than the gravestones at Zuisenji Temple averaged 0.44, defined the actual damage ratio for Sorinji Temple. by the ratio of width to height of the stone. It is similar to Yamada et al. (2008) proposed the damage curve for the the form of typical Japanese gravestones, averaging 0.40 of honden calibrated by the damages during the 2007 Niiga- the aspect ratio. Several researchers proposed a relation taken Chuetsu-oki earthquake. It is defined by a ratio of between the ground motion indices and the damage ratio higher than D3 in the damage rank within a 2 km radius of H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779 777 the observation site JMA Furukawa in the Furukawa area. The waveforms contain two wave groups with an interval of about 50 s. R ¼ F½ðln PGVln 100Þ=0:31: ð3Þ The peak velocities are about 100 cm/s, 90 cm/s, and 80 cm/s, The observed PGVs at K-NET MYG004 and JMA respectively. PGAs and PGVs of K-NET MYG004 are larger Furukawa lead to estimations of damage ratios of 0.57 than the records for the Furukawa area, whereas the indices and 0.28, respectively. In the Tsukidate area, only one seem to contradict the damage patterns in both areas. This sample, D1, is available. In the Furukawa area, three implies that PGAs and PGVs were not indicative of the samples, D3, D1, and D3, indicate the ratio of 0.67, which damage grade around the seismic stations. is larger than the estimation. Fig. 19 shows the pseudo response velocity spectra The quantitative values imply that the damage is not (h¼0.05) of K-NET MYG004, MYG006, and JMA Fur- exactly consistent with the observed PGVs. In addition, the ukawa. Periods at the peak values for K-NET MYG006 and damage patterns for the structures and the shrines suggest JMA Furukawa are in the range of 1.0–1.5 s, whereas those ground motions in the Tsukidate area. At least, the for K-NET MYG004 are less than 0.5 s. As shown in Figs. 7 patterns imply that the ground motion characteristics and 10, the spectrum shapes of JMA Furukawa are more should not be discussed only based on PGAs and PGVs. similar to those of the JR Takatori records than K-NET MYG004. The ground motions observed at the damaged sites during the Kobe earthquake and also in Furukawa area 5. Discussion contain similar frequency components. Sakai (2009) suggests that the components in the period ranging from 1.0 to 1.5 s Fig. 18 shows the velocity waveforms observed at K-NET affect the structural damages, and this is consistent with the MYG004 in the Tsukidate area, and K-NET MYG006 and observations in the Furukawa area. In Furukawa, the damage grades around the seismic stations were slightly different; K-NET MYG006 is not K-NET MYG004 EW located in the severely damaged region, while JMA 300 Furukawa is (see Fig. 14). The ratios of the horizontal (Max. 49.2 cm/s) component of the ground motions observed at JMA Furukawa to the horizontal component of the ground 200 motions observed at K-NET MYG006 during the same event, namely H/H spectrum ratios, are calculated. Fig. 20 K-NET MYG006 EW shows the H/H spectrum ratios during the main shock and 100 velocity [cm/s] the other significant earthquakes: (1) a M 7.0 intra-slab (Max. 91.9 cm/s) W earthquake that occurred in the Pacific plate on 26 May JMA Furukawa EW 2003, (2) a M 7.1 inter-plate earthquake that occurred on 0 W the plate boundary between the Pacific and North American (Max. 76.7 cm/s)

0 30 60 90 120 150 180 K-NET MYG004 time [s] K-NET MYG006 JMA Furukawa

1000 K-NET MYG004 NS 300 (Max. 104.8 cm/s)

200

K-NET MYG006 NS 100 100 pSv (h = 0.05) [cm/s] velocity [cm/s] (Max. 58.5 cm/s) JMA Furukawa NS 0 (Max. 81.1 cm/s) 10 0.1 0.5 1 2 5 0 30 60 90 120 150 180 period [s] time [s] Fig. 19. Pseudo-velocity response spectra (h¼0.05) of K-NET MYG004, Fig. 18. Velocity waveforms of K-NET MYG004, MYG006, and JMA MYG006, and JMA Furukawa. The two lines plotted together for each Furukawa. event correspond to EW and NS components. 778 H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779

periods than 1.0 s. On the other hand, several peak periods JMA Furukawa / MYG006 over 1.0 s were observed, although the PGAs were not large. The pseudo-velocity response spectrum of the JMA Furukawa records was similar to that of the JR Takatori 2.0 records with the peak period of 1.3 s. We have emphasized that the spectrum shapes recorded in the damaged areas during this earthquake and the Kobe earthquake are similar, and that the results are consistent to those in the 1.0 summary by Sakai (2009). We have also pointed out that the ground motions in 1.0–1.5 s at JMA Furukawa were

H/H spectrum ratio emphasized because of the soil nonlinearity. 0.5 Acknowledgments

main shock We thank the anonymous reviewer as well as the editor, other events Professor Akira Murakami, for their thorough comments. 0.2 0.5 1 2 5 We also thank many organizations for their contributions period [s] to the strong ground motion observations, namely Fig. 20. H/H spectrum ratios between JMA Furukawa and K-NET K-NET, KiK-net organized by NIED, JMA,PARI, BRI, MYG006 during the main shock and the other significant events on 26 NILIM, ERI of the University of Tokyo, and AIST. May 2003, 16 August 2005, and 14 June 2008. Damage investigations were conducted in collaboration with Associate Professor Yasuko Kuwata, Associate Pro- plates on 16 August 2005, and (3) a MW 7.0 intra-crust fessor Akihiro Takahashi, Associate Professor Yoshikazu earthquake that occurred on 14 June 2008. The spectrum Takahashi, and the geotechnical team of the JSCE Great ratio is calculated after filtering with a moving window of Tohoku Earthquake damage reconnaissance members. We length 0.2 s in width. The periods at the peaks of the H/H appreciate the information from and the discussions with spectrum ratios are about 0.5 s for the other events, whereas many researchers, and also the kind cooperation of the those for the main shock are larger than 0.5 s, especially people of Furukawa and Tsukidate. about 1.0 s in the NS component. PGAs at K-NET 2 MYG006 were 268 cm=s during the 2003 earthquake, References 151 cm=s2 during the 2005 earthquake, and 315 cm=s2 during the 2008 earthquake, respectively, which are about Asano, K., Iwata, T. Source model for strong ground motion generation a half the PGA during the main shock, 583 cm=s2.The in 0.1–10 Hz during the 2011 Tohoku earthquake. Earth Planets longer peak periods during the main shock imply the Space, in press. nonlinear behaviors of the shallow soils. The peak period Chen, W.F., Scawthorn, C., 2002. Earthquake Engineering Handbook, CRC Press, vol. 4, pp. 13–19. of the H/H spectrum ratios is almost close to the peak Goto, H., Morikawa, H., Kuwata, Y., 2012. Estimation of ground motion period of pSv at K-NET MYG006 and JMA Furukawa. at Furukawa gas during 2011 off the Pacific coast of Tohoku This means that ground motions in 1.0–1.5 s around JMA earthquake. Journal of Structural Mechanics and Earthquake Engi- Furukawa were emphasized because of the soil nonlinearity neering A1, JSCE 68 (4) I_111–118 (in Japanese with English compared to those at K-NET MYG006. abstract). Goto, H., Yamamoto, Y., Kita, S. Dynamic rupture simulation of the 2011 off the Pacific coast of Tohoku earthquake: multi-event genera- 6. Conclusion tion within dozens of seconds. Earth Planets Space, in press. Hirose, F., Miyaoka, K., Hayashimoto, N., Yamazaki, T., Nakamura, The 2011 off the Pacific Coast of Tohoku Earthquake M., 2011. Outline of the 2011 off the Pacific coast of Tohoku earthquake (Mw9.0)-seismicity: foreshocks, mainshock, aftershocks, caused severe damage not only because of the great and induced activity. Earth Planets Space 63, 513–518. tsunami, but also because of the ground motions. The Holzer, T.L., Youd, T.L., Hanks, T.C., 1989. Dynamics of liquefaction observed ground motions imply at least three significant during the 1987 Superstition Hills, California, Earthquake. Science events generating high-frequency radiation, which are 244, 56–59. consistent with the location of the SMGAs. They gave Hoshiba, M., Iwakiri, K., Hayashimoto, N., Shimoyama, T., Hirano, K., Yamada, Y., Ishigaki, Y., Kikuta, H., 2011. Outline of the 2011 off rise to two wave groups in the waveforms at the northern the Pacific coast of Tohoku earthquake ðMW 9.0)—earthquake stations, and a third wave group at the southern stations. early warning and observed seismic intensity. Earth Planets Space PGAs observed during the earthquake were extraordi- 63, 541–545. narily large. The largest PGA observed at K-NET Hudson, D.E., 1962. Some problems in the application of spectrum MYG004 was about three times larger than the gravita- techniques to strong-motion earthquake analysis. Bulletin of the Seismological Society of America 52, 417–430. tional acceleration. The pseudo-velocity response spectra of Iai, S., Morita, T., Kameoka, T., Matsunaga, Y., Abiko, K., 1995. the records are different from those of JR Takatori because Response of a dense sand deposit during 1993 Kushiro-Oki earth- the ground motions with large PGA give shorter peak quake. Soils and Foundations 35, 115–131. H. Goto, H. Morikawa / Soils and Foundations 52 (2012) 769–779 779

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