ZONING OF SEISMIC MOTION CHARACTERISTICS AT THE ENGINEERING BASE LAYER AROUND THE SOUTHEASTERN FOOT OF MT. FUJI REGION IN JAPAN

Transcription

1 ZONING OF SEISMIC MOTION CHARACTERISTICS AT THE ENGINEERING BASE LAYER AROUND THE SOUTHEASTERN FOOT OF MT. FUJI REGION IN JAPAN Yoshikazu SHINGAKI 1, Tetsushi KURITA 2, Tadashi ANNAKA 3 and Yoshiki MORI 4 ABSTRACT To understand the seismic motion characteristics at the engineering base layer in the sites without seismograph, we studied the spatial distribution of the characteristics based on the seismic observation records around the southeastern foot of Mt. Fuji region in Japan. The average ratios of 5% damped acceleration response spectra between the observed values and calculated values by an attenuation relation represent the index for the seismic motion characteristics in this study. We drew the spatial distribution maps of the average ratios by using the interpolation to understand the spatial distribution of seismic motion characteristics and classified the region by the proposed zoning methods, e.g. comparing the spatial distribution maps with topographical maps and geological maps. As a result of the zoning, the region was classified into five zones. INTRODUCTION Recently, the necessity to understand the seismic motion characteristics in various sites is increasing. The seismic motion characteristics in the seismographic stations can be evaluated on the basis of the seismic observation records. However, it is difficult to evaluate the seismic motion characteristics at any sites without seismograph. In order to solve the problem, some estimation methods can be applied to compensate a lack of observation data. Because strong motion seismograph networks are getting denser recently, the studies about the seismic motion characteristics based on the seismic observation records are proceeded. For example, Onishi et al. (1999) developed the attenuation relation based on JMA strong motion records and studied the relationship between the geomorphological land classification considering surface geology and the amplification ratio by the attenuation relation. Nozu et al. (2007) evaluated the site amplification factors for seismographic stations in Japan by using the spectral inversion technique and explained the characteristics of the factors with districts. The effect of the deep ground structures below the engineering base layer is considered in the factor. Kataoka et al. (2008) proposed the attenuation relationships for ground motion in rather-long period range using strong motion records observed in Japan. By using the spatial interpolation algorithm, they developed the maps of the site amplification characteristics obtained from the attenuation relationships. Senna and Midorikawa (2009) proposed the estimation method of the spectral amplification factor for each geomorphology based on H/V spectral ratio of the microtremor. As above, the seismic motion characteristics were estimated at the level of the ground surface or the seismic bedrock in many of the previous studies. The seismic observation records at the ground surface are strongly affected by the 1 M.E., Tokyo Electric Power Services Co., Ltd., Tokyo, 2 Dr., Tokyo Electric Power Services Co., Ltd., Tokyo 3 M.S., Tokyo Electric Power Services Co., Ltd., Tokyo 4 Tokyo Electric Power Company, Tokyo 1

2 site response of surficial sedimentary layers. At the level of the seismic bedrock, the site effects of the sedimentary can be neglected, but it is difficult to obtain the seismic records and geotechnical information. On the other hand, many seismic records and geotechnical data such as PS loggings are collected recently at the level of the engineering base layer. Usually many input ground motions for seismic design are provided at the level of the engineering base layer. Thus, we estimated the seismic motion characteristics at the engineering base layer from the seismic observation records and discussed zoning of the spatial distribution of the characteristics to understand them in various sites. We selected the region around the southeastern foot of Mt. Fuji region in Japan for the zoning because topography, geology and the seismic motion characteristics are complicate in the region. Note that the effects of the S wave velocity structures between the engineering base layer and the seismic bedrock cannot be neglected. In the following discussion, we assume that the seismic motion characteristics at the engineering base layer are subject to the effect. We discussed the local site effects related to the characteristics without the velocity structures. ZONING METHOD The flow chart for the zoning is shown in Figure 1 and the details of each step in the flow chart are described below. (1) Collecting the seismic records (6) Drawing the spatial distribution maps of ARSR (2) Examining and selecting the seismic records (3) Examining geotechnical information and modeling geotechnical structures (7) Estimate the zoning in the following steps (4) Estimating the time histories of seismic motion at the engineering base layer (5) Calculating the average response spectral ratio (ARSR) at the engineering base layer (a) Classifying the region in each map of (6) into some zones only by the pattern of contour maps of ARSR (b) Arranging the zones of (a) by the site effects index values (c) Rearranging the zones of (b) by comparing with topography and geology maps (d) Looking see the resemblance of shapes of ARSR in each zone Figure 1. Flow chart for the zoning of seismic motion characteristics at the engineering base layer (1) In this study, we used the available seismic records of 30 seismographic stations around the southeastern foot of Mt. Fuji region in Japan from TEPCO-net, K-NET and KiK-net, respectively. K- NET and KiK-net are strong motion seismograph network and have been operated by National Research Institute for Earth Science and Disaster Prevention. The location of the seismographic stations is shown in Figure 2. We collected records up to January 28, YMNH14 42 YMN003 KNGH KMGH19 TEPCO-PE TEPCO-TE TEPCO-PD KNG014 KNGH20 TEPCO-PG KNG012 TEPCO-TB KNGH22 TEPCO-TA SZO010 TEPCO-PC TEPCO-TC KNG013 TEPCO-PH SZO011 SZO009 TEPCO-PB TEPCO-PA 35.5 TEPCO-PI SZO012 TEPCO-TD SZO001 Mt. Fuji SZO SZOH38 TEPCO-PF Seismographic station TEPCO KiK-net K-NET Figure 2. Location of 30 seismographic stations around the southeastern foot of Mt. Fuji region in Japan

3 Y. Shingaki, T. Kurita, T. Annaka and Y. Mori 3 (2) Band-pass filtering was applied to eliminate the signal noises from the seismic records or the records with the very low S/N ratio were removed. After the examinations, we selected the records to meet the following criteria: (a) JMA magnitude is equal to or greater than 5.0; (b) The closest distance from the fault plane or the hypocenter to the seismographic station is equal to or nearer than 200km; (c) The central depth of fault plane is equal to or shallower than 100km. We finally used the records derived from 105 earthquakes, by reflecting the additional examination in the step (5) in Figure 1. The hypocenter distribution of 105 earthquakes is shown in Figure 3 and the basic information of 105 earthquakes is shown in Table 1. 50km 100km 150km 200km 250km Figure 3. Hypocenter distribution after examining and selecting the seismic records (the total number of earthquakes : 105, solid circles : hypocenter, color : depth, center : TEPCO-PD site) Table 1. Basic information of the selected earthquakes Num epicenter location occurrence time depth north latitude east longitude km year mon day h min sec deg min deg min M J hypocentral region SAGAMINADA EASTERN YAMANASHI PREF EASTERN YAMANASHI PREF SOUTHERN IBARAKI PREF SOUTHERN BOSO PENINSULA SE OFF BOSO PENINSULA NORTHERN NAGANO PREF NORTHERN CHIBA PREF KUJUKURI COAST BOSO PEN KUJUKURI COAST BOSO PEN TOKYO PREF SOUTHERN BOSO PENINSULA EASTERN YAMANASHI PREF WESTERN SAITAMA PREF SW IBARAKI PREF HAKONE REGION NEAR MIYAKEJIMA ISLAND TOKYO BAY REGION SW IBARAKI PREF EASTERN YAMANASHI PREF NEAR CHOSHI CITY SE OFF BOSO PENINSULA SW IBARAKI PREF NE AICHI PREF SOUTHERN IBARAKI PREF S OF SURUGA BAY CENTRAL CHIBA PREF CENTRAL CHIBA PREF SOUTHERN IBARAKI PREF CENTRAL CHIBA PREF NEAR CHOSHI CITY FAR S OFF BOSO PENINSULA HAMANAKO LAKE REGION CENTRAL SHIZUOKA PREF CENTRAL SHIZUOKA PREF SW IBARAKI PREF SW IBARAKI PREF SW IBARAKI PREF SOUTHERN IBARAKI PREF NEAR CHOSHI CITY KUJUKURI COAST BOSO PEN CENTRAL CHIBA PREF NEAR CHOSHI CITY SE OFF BOSO PENINSULA SOUTHERN IBARAKI PREF MID NIIGATA PREF MID NIIGATA PREF MID NIIGATA PREF MID NIIGATA PREF FAR S OFF TOKAI DISTRICT SW IBARAKI PREF NEAR CHOSHI CITY NEAR CHOSHI CITY Num epicenter location occurrence time depth north latitude east longitude km year mon day h min sec deg min deg min M J hypocentral region NEAR CHOSHI CITY CENTRAL CHIBA PREF SW IBARAKI PREF SW IBARAKI PREF E OFF IBARAKI PREF SE OFF BOSO PENINSULA SE OFF BOSO PENINSULA KUJUKURI COAST BOSO PEN KUJUKURI COAST BOSO PEN SE OFF BOSO PENINSULA NORTHERN IBARAKI PREF SW IBARAKI PREF NORTHERN IBARAKI PREF NEAR CHOSHI CITY SOUTHERN SURUGA BAY REG SOUTHERN TOCHIGI PREF NORTHERN CHIBA PREF SE OFF BOSO PENINSULA FAR S OFF BOSO PENINSULA NORTHERN GIFU PREF NORTHERN GIFU PREF FAR E OFF MIYAGI PREF NEAR CHOSHI CITY MT. FUJI REGION NEAR CHOSHI CITY SOUTHERN IBARAKI PREF NEAR CHOSHI CITY NEAR CHOSHI CITY NORTHERN IBARAKI PREF E OFF BOSO PENINSULA SW IBARAKI PREF NORTHERN NAGANO PREF NEAR CHOSHI CITY NEAR CHOSHI CITY SW IBARAKI PREF SW IBARAKI PREF FAR S OFF BOSO PENINSULA NEAR CHOSHI CITY E OFF IBARAKI PREF SW IBARAKI PREF NEAR CHOSHI CITY NEAR CHOSHI CITY E OFF IBARAKI PREF CENTRAL NAGANO PREF SW IBARAKI PREF SOUTHERN SURUGA BAY REG NORTHERN IBARAKI PREF HIDA MOUNTAINS REGION NORTHERN IBARAKI PREF KUJUKURI COAST BOSO PEN SE GIFU PREF EASTERN YAMANASHI PREF (3) We examined the geotechnical information of the seismographic stations. In some vertical array stations in TEPCO-net, we identified the optimum 1-D geotechnical structures for weak seismic motions and for strong seismic motions by the inverse analysis targeting Fourier spectral ratio. As an example, the comparison between the average Fourier spectral ratios calculated from the seismic

4 records and the theoretical transfer function of the optimum 1-D geotechnical structure of TEPCO-PI site is shown in Figure 4. In the other sites, the geotechnical structures were constructed from the PS logging. NS direction EW direction Figure 4. Comparison between the average Fourier spectral ratio calculated from the seismic records and the theoretical transfer function of the optimum 1-D geotechnical structure in TEPCO-PI site (4) Based on the 1-D wave propagation theory, we calculated the time histories of seismic motion at the engineering base layer from the horizontal seismic records at the ground surface. To apply the attenuation relation used in the step (5) in Figure 1, we selected the engineering base layer so that its S wave velocity is approximately equal to 300 ~ 600 m/s. If there is no appropriate layer, the layer whose S wave velocity is sufficiently larger than that of the upper layer was regarded as the engineering base layer. (5) We calculated the ratios of 5% damped acceleration response spectra between the observed values obtained in the previous step and calculated values by an attenuation relation. In this study, we used the attenuation relation proposed by Annaka and Nozawa (1988). The attenuation relation was derived from the seismic data at the engineering base layers, whose S wave velocity is 300 ~ 600 m/s, in the Kanto District of Japan. The input parameters of the attenuation relation are based on the following references (in order preference): (a) the fault models evaluated in the previous study; (b) the seismological and volcanological bulletin of Japan by Japan Meteorological Agency; (c) JMA Unified Hypocenter Catalogs published on Hi-net web site. We eliminated the ratios whose shapes are significantly different from the others, because they are strongly influenced by the seismic source property. As an example, the response spectral ratios and the hypocenter distribution after examining and selecting the seismic records collected from SZO010 are shown in Figure 5 and Figure 6, respectively. In Figure 5, the green lines denote the response spectral ratios of the shallow volcanic earthquakes occurred off Izu Peninsula and Izu Islands. The red line denotes the ratio of the earthquake occurred near Choshi City in April 11, 2005 (M J 6.1). Over the wide range of natural period, these ratios are smaller than the ratios of the other earthquakes denoted by blue lines in Figure 5. The response spectral ratios of the other seismographic stations exhibit the similar pattern. We used the geometric mean of the response spectral ratios calculated from the other earthquakes as the index for the seismic motion characteristics at the engineering base layer. We call it the average response spectral ratio (hereinafter, the ARSR ). The large ARSR denotes that the engineering base layer of the target site tends to shake. The ARSRs of 30 stations are shown in Figure 7. This figure shows that the seismic motion characteristics at the engineering base layer vary with local areas. The response spectral ratios of the shallow volcanic earthquakes occurred off Izu Peninsula and Izu Islands The response spectral ratios of the earthquake occurred near Choshi City in April 11, 2005 (M J 6.1) The response spectral ratios of the other earthquakes Figure 5. Response spectral ratios after examining and selecting the seismic records collected from SZO010 4

5 Y. Shingaki, T. Kurita, T. Annaka and Y. Mori 5 the earthquake occurred near Choshi City in April 11, km 100km 150km 200km the earthquakes occurred off Izu Peninsula and Izu Islands Figure 6. Hypocenter distribution after examining and selecting the seismic records collected from SZO010 (solid circles : hypocenter, color : depth, center : SZO010) 地震計の凡例 TEPCO KiK-net K-NET TEPCO KiK-net K-NET Figure 7. ARSRs of 30 stations around the southeastern foot of Mt. Fuji region in Japan (6) To understand the spatial distribution of seismic motion characteristics, we drew the spatial distribution maps of the ARSRs by using the interpolation algorithm with the representative values obtained in the previous step. The representative value is calculated as the geometric mean of ARSR within a particular period range. In this study, we focused on two period ranges shown in Figure 8, i.e. the short period range ( second) and the long period range (0.7-2 second). The two period ranges are defined to be able to grasp the spatial distribution of seismic motion characteristics easily for comparing with topographical maps and geological maps. The contour maps are shown in Figure 9.

6 The border values used in the contour maps are (0.501), (0.631), (0.794), 10 0 (1.000), (1.259), (1.585), (1.995) in ascending order, namely, from blue to red in contour color. short period range long period range Figure 8. ARSRs of 30 stations and two period ranges (the short period range and the long period range) (i) short period range ( second) (ii) long period range (0.7-2 second) Figure 9. Spatial distribution maps of ARSR We used land classification maps ( ) shown in Figure 10 to compare the spatial distribution of the ARSRs with the spatial distribution of topography. In the long period range, the spatial distribution of the ARSRs corresponds to that of topography sufficiently. For example, the ARSRs are small in the mountains and the volcanic mountains, i.e. (f) Mt. Tanzawa, (a) Mt. Ashitaka and (e) Mt. Hakone. For another example, the ARSRs are large in (c) Oyama Town, (h) Ashigara Plain and the surround areas. In the short period range, the spatial distribution of the ARSRs corresponds to that of topography roughly. For example, the ARSRs are small in (f) Mt. Tanzawa and the volcanic footslope between (a) Mt. Ashitaka and (e) Mt. Hakone. For another example, the ARSRs are large in the volcanic mountains, i.e. (a) Mt. Ashitaka and (e) Mt. Hakone. Thus the characteristics of ARSR by area can be described bellow: In the volcanic mountains i.e. (a) Mt. Ashitaka, (e) Mt. Hakone and the surround areas, ARSR is large in the short period range and small in the long period range. In (f) Mt. Tanzawa and the surround areas, ARSR is small in the entire range of natural period. However, it is difficult to explain that the ARSR in (c) Oyama Town and the surround areas is large in the entire range of natural period only by the spatial distribution of topography. Subsequently, we used Engineering geological map of Kanto District (1996) shown in Figure 11 to compare the spatial distribution of the ARSRs with the spatial distribution of geology. The spatial distribution of geology does not correspond to that of the ARSRs in comparison with that of topography. In particular, the magnitude of the ARSR varies by area within the same geological category in the long period range. For example, the ARSRs in the northeast of the areas categorized as volcanic ash and scoria fall deposits (bt2, bt1, at1) are large but the ARSRs in the southwest are small. However the large ARSR seen in (c) Oyama Town and the surround areas can be explained by the spatial distribution of geology along with topography. Namely, the ARSR in the areas categorized as volcanic ash and scoria fall deposits (bt2, bt1, at1) within the volcanic footslope in (c) Oyama Town and the surround areas is large in the entire range of natural period. 6

7 Y. Shingaki, T. Kurita, T. Annaka and Y. Mori High-reliefed mountains 600m relief Middle-reliefed mountains 400m relief 600m Low-reliefed mountains 200m relief 400m Piedmont lowland 100m relief 200m Piedmont lowland relief 100m (f) (g) (c) (d) (b) (h) (e) (a) 7 Low-reliefed dissected hills High-reliefed volcanic mountains 600m relief Middle-reliefed volcanic mountains 400m relief 600m Low-reliefed volcanic mountains 200m relief 400m Piedmont or fan situated at the foot of a volcanoes (Kanagawa Pref) Piedmont or fan situated at the foot of a volcanoes Shizuoka Pref, 100m relief 200m Piedmont or fan situated at the foot of a volcanoes Shizuoka Pref, relief 100m Piedmont or fan situated at the foot of a volcanoes Yamanashi Pref, 100m relief 200m Piedmont or fan situated at the foot of a volcanoes Yamanashi Pref, relief 100m Volcanic hills Volcanic fans Lava plateau and Lava flows Gravelly uplands and terraces (middle terrace) Fans Delta lowlands Sandvars and Gravel bars Figure 10. Land classification map (edited the original map) (a) Mt. Ashitaka, (b) Gotemba City, (c) Oyama Town, (d) Mt. Ashigara, (e) Mt. Hakone, (f) Mt. Tanzawa, (g) Hadano Basin, (h) Ashigara Plain (f) (c) (b) (g) (d) (h) (a) (e) Sandstone, mudstone and conglomerate (Ashigara Group) Granites and diorites (Neogene Igneous rocks) Andesite, rhyolite and basalt lavas, tuff and tuff breccia (Lower Tanzawa Group and its equivalents) Debris avalanche (Late Pleistocene-Holocene volcanic rocks) Volcanic piedmont fan deposits (Late Pleistocene-Holocene volcanic rocks) Volcanic piedmont fan deposits (Early-Middle Pleistocene volcanic rocks) Basalt lavas (Late Pleistocene-Holocene volcanic rocks) Basalt lavas (Early-Middle Pleistocene volcanic rocks) Andesite lavas (Early-Middle Pleistocene volcanic rocks) Dacite and rhyolite lavas (Late Pleistocene-Holocene volcanic rocks) Basaltic ash and scoria fall deposits, breccias, etc. (Late Pleistocene-Holocene volcanic rocks) Basaltic ash and scoria fall deposits, breccias, etc. (Early-Middle Pleistocene volcanic rocks) Andesitic ash and scoria fall deposits, breccias, etc. (Early-Middle Pleistocene volcanic rocks) Figure 11. Engineering geological map of Kanto District (edited the original map) (a) Mt. Ashitaka, (b) Gotemba City, (c) Oyama Town, (d) Mt. Ashigara, (e) Mt. Hakone, (f) Mt. Tanzawa, (g) Hadano Basin, (h) Ashigara Plain Summarizing the above, except for the S wave velocity structures, the seismic motion characteristics at the engineering base layer are closely related to topography. However, in the some particular category of topography, the effect of both topography and geology on the seismic motion characteristics is significant.

8 (7) We classified the region in each map of Figure 9 into some zones only in terms of the color pattern. We set the index values for the geometric means of the ARSRs (hereinafter, the site effects index values ). The site effects index values are shown in Table 2. Then we classified the zones particularly by using the site effects index values. We rearranged the classified zones by comparing with topographical maps and geological maps. Then, we assumed that the representative topography and geology cover almost all of the area in each zone macroscopically. There are a few locally incompatible areas with the representative topography and geology in the rearranged zones. The seismographic stations in such areas were eliminated from the zone because they are inconsistent with the others in the zone. We finally looked see the resemblance of shapes of ARSR in each zone. When a seismographic station did not resemble the other stations in the same zone in shape of ARSR, we rearranged the zones or did not use the ARSR of the station. Table 2. Site effects index values based on the geometric means of ARSRs Site effects index values Short period range ( second) Long period range (0.7-2 second) hard to shake medium easy to shake hard to shake medium easy to shake RESULTS OF ZONING The results obtained by the above mentioned zoning are shown in Table 3 and Figure 12, respectively. There should be nine ( 3 3 ) zones from a combination of two index values in Table 2. The ARSRs classified into medium in long period range were not finally used as results of the above mentioned zoning. Where the zone classified into medium in the short period range and easy to shake in the long period range is called Zone B1 and the zone classified into hard to shake in the short period range and easy to shake in the long period range is called Zone B2. The shapes of ARSR are similar to each other in Zone B1 and Zone B2. Thus, we reclassified the two zones into the common category called Zone B in Table 3. As a result, the number of zones decreased to five. In this study, KNG014 (K-NET) was eliminated from Zone B because it is an incompatible with the representative topography in Zone B. 1:25,000 scale topographic map around KNG014 is shown in Figure 13. It can be seen from the figure that the topography around KNG014 denoted by an open square is the basin enclosed in mountains and hills. On the other hand, the topographies at the other seismographic stations in Zone B are categorized into volcanic mountains, volcanic footslopes or hills. Namely, there is a major difference in topography between KNG014 and the other seismographic stations in Zone B. Also, it is very different in the shape of ARSR from others. The ARSRs of KNG014 and the closest seismographic station, i.e. KNGH22 (KiK-net) located in Zone B, are shown in Figure 14. The geometric mean of the ARSRs of the seismographic stations in Zone B is also shown in the figure. It can be seen from the figure that the ARSR of KNG014 becomes larger in the short period. On the other hand, the ARSR of KNGH22 and the geometric mean of the ARSRs in Zone B become larger in the long period. Table 3. Classified zones by the site effects index values Zone Short period range Long period range Number ( second) (0.7-2 second) of stations A easy to shake easy to shake 2 B medium/hard to shake easy to shake 6 C easy to shake hard to shake 5 D medium hard to shake 2 E hard to shake hard to shake 4 8

9 Y. Shingaki, T. Kurita, T. Annaka and Y. Mori Mt. Fuji Elimination due to the local topography, Zone A Zone B Zone C Zone D Zone E Seismographic station TEPCO KiK-net K-NET Figure 12. Schematic view of zone (Zoning result based on the seismic motion characteristics at the engineering base layer) KNG014 (K-NET) KNGH22 (KiK-net) Figure 13. Topographic map around KNG014 (edited 1:25,000 scale topographic map by Geospatial Information Authority of Japan) Figure 14. ARSR of KNG014, ARSR of KNGH22 and the geometric mean of the ARSRs of the seismographic stations in Zone B

10 We regarded the shapes of the ARSRs as the most important index for the decisive zoning. We estimated the resemblances of the shapes quantitatively by calculating the correlation coefficient and the residual sum of squares (hereinafter, the RSS ) between the pair of seismographic stations in the five zones from the common logarithms of the ARSR in the entire application range of natural period for the attenuation relation ( second). The correlation coefficient is the index for similarity and RSS is the index for difference of modulus. Examples of the relationship between the correlation coefficient and the RSS are shown in Figure 15. The resemblance of the shapes between the pair is strong in the right upper part of the figure, namely, the positive correlation is strong and RSS is small. It can be seen from the figures that the positive correlation is stronger and RSS is smaller in the same zone except for Zone A. As for Zone A, the index values shown in Table 2 were emphasized. Zone A (TEPCO-PD) correlation coefficient Zone B (KNGH22) correlation coefficient RSS RSS Zone A Zone B Zone C Zone D Zone E Zone C (TEPCO-PA) correlation coefficient Zone A Zone B Zone C Zone D Zone E Zone D (TEPCO-PE) correlation coefficient RSS RSS Zone A Zone B Zone C Zone D Zone E 100 Zone A Zone B Zone C Zone D Zone E Zone E (YMNH14) correlation coefficient RSS Zone A Zone B Zone C Zone D Zone E Note ; The zone-name is followed by the representative seismographic station in the zone. Figure 15. Examples of the relationship between the correlation coefficient and the RSS 10

11 Y. Shingaki, T. Kurita, T. Annaka and Y. Mori 11 As the results obtained by the above mentioned zoning, the ARSRs and the geometric means in each zone are shown in Figure 16. The site effects of each zone can be explained by the geometric mean of ARSRs. The characteristics of each zone are described bellow: In Zone A, the ARSR is large in the entire range of natural period. The volcanic footslope with the geological deposits of scoria constitutes the major area of Zone A. In Zone B, the ARSR is not large in the short period range and large in the long period range. The volcanic mountain, the volcanic footslope and the hill are the representative topographies in Zone B. In Zone C, the ARSR is large in the short period range and small in the long period range. Most of Zone C is covered by the volcanic mountain and the volcanic footslope. In Zone D, the ARSR is small in the long period range. The mountain footslope and the terrace occupy most of Zone D. In Zone E, the ARSR is small in the entire range of natural period. The mountain is dominant in Zone E. The ARSRs of the seismographic station The geometric mean of ARSRs in each zone Figure 16. The individuals and geometric mean of ARSRs in each zone (Zoning result based on the seismic motion characteristics at the engineering base layer) CONCLUSIONS In this study, we statistically analyzed the spatial distribution of seismic motion characteristics at the engineering base layer around the southeastern foot of Mt. Fuji region in Japan by using the ARSRs calculated from the seismic observation records. Based on the result, the target region was classified into five zones by the proposed zoning method of the spatial distribution of seismic motion characteristics. The principal results are summarized bellow: The seismic motion characteristics at the engineering base layer vary with local areas. The spatial distribution of the seismic motion characteristics at the engineering base layer corresponds to that of topography sufficiently in the following four zone: (1) The volcanic mountains, the volcanic footslops and the hills around Gotemba City, the foot of Mt. Hakone and the west of Ashigara Plain tend to shake in the long period; (2) Mt. Ashitaka (volcanic mountain) and the surround volcanic footslope tend to shake in the short period and hard to shake in the long

12 period; (3) The terrace in Hadano Basin and the surround mountain footslopes tend hard to shake in the long period; (4) Mt. Tanzawa area tends very hard to shake. The spatial distribution of the seismic motion characteristics at the engineering base layer corresponds to that of geology in addition to topography sufficiently in the following zone: The volcanic footslope with the geological deposits of scoria in Oyama Town and the neighboring area tend to shake. ACKNOWLEDGMENT We used strong motion data and geotechnical information of K-NET and KiK-net provided by National Research Institute for Earth Science and Disaster Prevention, 1:25,000 scale topographic maps by Geospatial Information Authority of Japan, the seismological and volcanological bulletin of Japan by Japan Meteorological Agency and JMA Unified Hypocenter Catalogs published on Hi-net web site. We are grateful to the organizations. REFERENCES Annaka T and Nozawa Y (1988) A probabilistic model for seismic hazard estimation in the Kanto district, Proceedings of Ninth World Conference on Earthquake Engineering, Vol.II, Engineering geological map of Kanto District (1996), Editorial Committee of engineering geological map of Kanto District Kataoka S, Matsumoto S, Kusakabe T and Toyama N (2008) Attenuation relationships and amplification map for ground motion in rather-long period range, Journal of JSCE, Division A, Vol.64, No.4, (in Japanese with English abstract) Land classification maps ( ) Land classification map (Shizuoka Pref.), Land classification map (Kanagawa Pref.), Land classification map (Yamanashi Pref.), Japan Map Center Nozu A, Nagao T and Yamada M (2007) Site amplification factors for strong-motion sites in Japan based on spectral inversion technique and their use for strong-motion evaluation, Journal of JAEE, 7(2), (in Japanese with English abstract) Onishi J, Yamazaki F and Wakamatsu K (1999) Relationship between geomorphological land classification and amplification ratio based on JMA strong motion records, Journal of Structural Mechanics and Earthquake Engineering, JSCE, No.626, I-48, (in Japanese with English abstract) Senna S and Midorikawa S (2009) Estimation of spectral amplification of ground motion based on geomorphological land classification, Journal of JAEE, 9(4), (in Japanese with English abstract) 12