Geo-Database Development in Kansai Area of Japan and Its Application in Assessing Liquefaction Potential

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1 Geo-Database Development in Kansai Area of Japan and Its Application in Assessing Liquefaction Potential Koji Yamamoto Geo-Research Institute, Japan Mamoru Mimura Disaster Prevention Research Institute Kyoto University, Japan ABSTRACT The Committee for Geo-Database Information in Kansai Area of Japan has developed the geotechnical database (Geo-Database) for this area. The database development has focused in urban areas because of their social and economical importance. More than 30,000 borehole data were collected and digitized. Basically, the information including soil classification, gradation, NSPT values, and groundwater levels has been entered in the Geo-database. However, compression parameters, coefficients of permeability, strengths, elastic rigidity, etc. are not included due to difficulties associated with their availability. So far, the geo-databases for Osaka, Kobe and Kyoto have been developed, but for the surrounding areas efforts are underway. This paper introduces the geo-database for Osaka, Kobe and Kyoto cities, and describes their application such as in assessing ground liquefaction potential of an particular area. By using the geo-database, cross-sections of an area can be easily drawn over the computer screen, and soil parameters such as soil classification, gradation, the thickness of each ground stratum, groundwater level, N SPT values, etc. can also be readily known. The use was also made of the developed geo-database for assessing liquefaction potentials of urban areas of Osaka, Kobe and Kyoto. The validation of the results obtained was confirmed by comparing them with the actual records during the 1995 Hyogoken-Nambu Earthquake. The liquefaction prediction has also been carried out for Kyoto Basin considering an earthquake to be caused by the failure of faults as well as a huge interplate earthquake that is expectedly going to hit this area within 40 years. KEYWORDS: Urban Geo-Database, Hazard map, Liquefaction, Kansai area 1. INTRODUCTION Osaka Bay is the heart of Kansai economy surrounded by Osaka, Kobe, Kyoto and Nara, which are some of the major urban business centers in Japan. Figure 1 shows the development of metropolises around Osaka Bay of an oval shape (60, 30 km in size). This beautiful creation was shaped by the couple of rising of the surrounding mountains and precipitation of the base ground in the center of the bay. The seabed deposits of the Osaka Bay have been formed due to the soil supply from the rivers. Naturally, the soil properties for each area are strongly influenced by the sedimentation environment and the subsequent tectonic movement. For example, the seabed deposits of the Osaka Bay have been formed due to the soil supply from the rivers. Although it is common that the clay deposits formed under this environment should be normally consolidated, the Pleistocene clays in Osaka Bay exhibit slight overconsolidation with OCR of 1.2 to 1.5 in average. This apparent overconsolidation is thought not to arise from the mechanical reason but to be subjected to the effect of diagenesis, such as aging effect and/or development of cementation among clay particles. In the sense, the Pleistocene clay KYOTO deposited in Osaka Bay is so-called quasi-overconsolidated clays without definite mechanical overconsolidation history as seen for the post-glacial clays in North America and Europe. The subsoil condition of Kobe is slightly different from that of Osaka whereas those two cities are very close KOBE each other. As Rokko Mountains consisting of OSAKA mainly granite are located just behind the plains in Kobe, sandy materials of granite origin have been supplied, which results in having rich and thicker sand gravel strata in Kobe. Some of the same marine clay strata can also be seen in Kyoto. However, those Pleistocene clays found in Kyoto exhibit remarkable overconsolidation 大阪湾 NARA behavior because those clays underwent the definite Figure 1 A relief map of Kansai urban area

2 history of mechanical overconsolidation due to the effect of upheaval and erosion. Compared to the subsoil condition in Osaka, the strata of Kyoto are much more complicated because Kyoto is a basin that has been formed associated with serious tectonic movement. Geotechnical database plays a significant role to investigate the regional subsoil conditions prior to detailed investigation. Geo-Database Information Committee in Kansai has developed the geotechnical database in Kansai area.[1], [2], [3] For the development of the database, urban area has been focused because of its social, economical importance. More than 30,000 borehole data was collected and digitized. In the present paper, the Geo-databases for Kansai urban area, such as Osaka, Kobe and Kyoto are introduced. Cross-sectional view of the required underground can be easily drawn on PC together with various soil properties such as classification, gradation, the thickness of each layer, ground water level, N SPT values and so on. The regional geotechnical characteristics can easily be grasped by the distribution of those soil properties. Sedimentation environment and the tectonic movement are very important to realize the present shape of the ground. The Geo-database can provide sufficient and helpful information. As for the geotechnical disasters due to earthquake, liquefaction is one of the best known and symbolic. Then, the application of the Geo-database to assessment of liquefaction potential for urban areas is explained. The simplified procedure based on the N SPT values is used to evaluate the liquefaction potential for Kobe area and the calculated results are validated by comparing with the actual records of liquefaction occurrence due to the 1995 Hyogoken-Nambu Earthquake. The method is extended to apply to predict the liquefaction potential of Kyoto Basin. Geotechnical hazard maps both for Kobe and Kyoto are shown in terms of the distribution of the critical acceleration for the occurrence of liquefaction. Based on those performances, the usefulness of the Geo-database and its applicability to geotechnical engineering and disaster mitigation engineering are discussed. 2. INVESTIGATION OF SUBSOIL CONDITION BASED ON THE GEO-DATABASE 2.1 Kobe and the adjacent area [2] A representative cross-sectional view of subsurface ground for Kobe and the adjacent area is shown in Figure 2 drawn by the Geo-database. The selected area is from the west of Kobe to Kanzaki River, the border between Osaka and Hyogo Prefecture. As the Rokko Mountains are located just behind the plains with a distance of 1.5 to 2.5 km, alluvial fans and deltaic plains have been formed in the narrow W 20 0 Nagata-Wadamisaki Chuo Higashinada Mukogawa Myohoji R. Nagata gravels Ikuta R. Ishiya R. Suminoe R. Ogi sands Ashiya R. Miya R. Shuku R. Muko R. Kanzaki R. E Ma13 Ma12 Elevation (OPm) -50 Ma12 Ma Kobe Nishinomiya Ashiya Amagasaki E W (m) Figure 2 Cross-sectional view of subsurface ground in Kobe and the adjacent area

3 Figure 3 Distribution of the thickness of upper sand layer area between mountains and coastal line in this area. On the basis of the geological characteristics, the area can be divided into 4 regions (Nagata - Wada, Chuo, Higashinada and Mukogawa from west to east).[2], [4] In Nagata -Wada region, coarse gravel beds are distributed at shallowest part underlain by the Holocene clay (Ma 13) along the coast. These gravel beds are thought to be Holocene origin and formed by tidal current. On the back of this sand bank by Nagata gravels, back marsh is extended with peat and organic materials. The kind of soft soils existing in back marsh possibly causes amplifying the seismic waves due to earthquake. In fact, high concentration of building damage was investigated during the 1995 Hyogoken-Nambu Earthquake in accord with the distribution of the back marsh. Holocene non-marine sand and gravel are developed in Chuo region. The typical marine clay layers such as Ma13 or Pleistocene clay (Ma 12) can only be found near shore and offshore because the talus materials carried from mountainous area by the rivers prevented those marine clays from extending into inland. The distribution of sand dune deposits called Ogi sands is characteristic in Higashinada region. This sand dune is underlain by the Holocene clay (Ma13) and thought to be also Holocene origin. The strata in Mukogawa region is the most similar to those in subsurface at Osaka Bay. Pleistocene clay layer (Ma 12) is thick and continuous overlain by the firm gravel layer that is normally used as a bearing stratum for buildings in Osaka. Holocene clay layer (Ma 13) is also continuous, but the thickness of both marine clay layers decreases towards west. It is because the effect of Rokko Mountains supplying much sandy and gravelly materials becomes significant as approaching Kobe area. Regional characteristics of subsoil can be definitely understood by showing the distribution of geotechnical information. Figure 3 shows the thickness of upper sandy deposits that were extracted from the borehole data in the Geo-database. A due consideration for the occurrence of liquefaction is required for those sandy deposits with N SPT value of less than 40. Relatively rich sandy strata exist both in Mukogawa and Higashinada regions with a thickness of 10m. The latter one is natural Ogi sands stated before. The western part of the area, such as Chuo and Nagata-Wada regions, has thinner sandy layers because the gravel become predominant in those regions due to sufficient supply of granite from Rokko Mountains. Soil types and their N SPT values in the depth of 5 to 10 meters are illustrated in Figure 4. It is interesting that Ogi sands are relatively firm with the N SPT value of about 20 to 25 while sandy deposits in Mukogawa region are weaker. There is a definite tendency that the weaker sand deposits exist near the coast and N SPT values on the mountainside are relatively high. The distribution of underground water levels in Kobe and the adjacent area is shown in Figure 5. Generally, the underground water levels are high in this area, particularly high water level is remarkable in Mukogawa region with a range of 1.0 to 2.0m from the ground surface.

4 Figure 4 Distribution of N SPT values for upper sand layer Figure 5 Distribution of under ground water level 2.2 Kyoto basin[3] A representative cross-sectional view of subsurface ground for Kyoto Basin is shown in Figure 6 drawn by the Geo-database. The selected line crosses the center of Kyoto Basin from north to south. On the basis of the geological characteristics, the area can be divided into 4 regions. The elevation of the ground at the north end (north of Kyoto City) of this line exceeds 100m and continuously declines

5 to the south. The ground surface becomes almost flat at the Keihan Railway in region C. The difference in elevation is almost 90m between the north of Kyoto City and the Keihan Railway in a distance of about 17km. Compared to region A, the surface of region C and D is flat with an elevation O.P. +10m to +20m. As is easily known, the subsoil of Kyoto Basin consists mainly of gravels in the northern part (region A and B) while soft fine soils such as silt and sand can be seen at the shallow part in the southern part (region C and D). Pleistocene marine clay (Ma 9) appears at the elevation of 40m to 50m. This clay was found from the deep borings, KD-1 and KD-2 and confirmed as marine clay by pollen analysis. Figure 6 Cross-sectional view of subsurface ground in Kyoto Basin The distribution of the thickness of sand and gravel of which N SPT values are less than 15 is shown in Figure 7. Here, the thickness means the summation of each thickness of all sand or gravel layers underlain by the Pleistocene firm strata extracted from the Geo-database. These layers are thought to be Holocene origin. Gravel is predominant in the northern part of the Basin, particularly thick gravel deposits of alluvial fans are found along Kamo River. The deposits along Katsura River are also gravelly. In contrast, sand is predominant in the southeast part of the Basin because Kizu River has carried a lot of sand from granite from the upstream. At the conjunction of three rivers, thick and weak sandy deposits have been formed. Attention against liquefaction should be paid to this area not only because of this weak and thick sandy deposits but because high water level is certainly expected. Another fact to be pointed out is that spot of sandy deposits can be seen in the northeast part of the Basin among gravels. This sand is called Shirakawa sand that comes from granite existing in the upstream of Shirakawa River flowing here. It is very interesting that liquefaction induced sandboils due to historical earthquakes have been found around Shirakawa River as well as the conjunction of three rivers.[5] This kind of information is also a good reference for liquefaction assessment. Figure 8 shows the distribution of underground water level in Kyoto Basin. Although some points exhibit relatively low water level such as more than 5m below the ground surface, Kyoto Basin has generally very high underground water level. 3. ASSESSMENT OF LIQUEFACTION POTENTIAL Liquefaction has been highlighted since serious disaster induced by liquefaction occurred at Niigata Earthquake and Alaska Earthquake in A number of procedures for assessing liquefaction have been proposed and updated on the basis of the records of liquefaction by earthquakes taking place one

6 after another. Laboratory tests such as undrained cyclic triaxial tests on reconstituted sand specimen have played significant roles for those studies on liquefaction. It is true that the experimental approach is important to know the mechanism of liquefaction, but the results from laboratory tests often have not provided a reasonable solution for the actual liquefaction disaster because liquefaction in the field is definitely the boundary value problem far from the laboratory conditions. Figure 7 Distribution of total thickness of upper sand layers In the practical sense, the regional distribution of hazardous area against liquefaction due to earthquake can provide very important and useful information for disaster mitigation. For this purpose, geo-database can function efficiently. In this chapter, simplified procedure assessing liquefaction potential is introduced and applied to evaluate the regional liquefaction potential based on the Geo-database. The calculated performance is validated by comparing with the actual records of liquefaction occurrence in Kobe area during 1995 Hyogoken-Nambu Earthquake. Then the predicted performance is also shown for Kyoto Basin. 3.1 Simplified procedure The simplified procedure assessing liquefaction potential used in the present paper is a so-called F L method specified in the Specifications for highway bridges by Japan Road Association.[6] This

7 method has commonly used in Japan for designing the foundations. First, the safety factor against liquefaction, F L is defined as follows: Figure 8 Distribution of under ground water level FL = R/L (1) Here, R denotes a liquefaction resistance and calculated by R = c w R L. The parameter, c w is a correction factor depending on the type of earthquake. R L is a cyclic stress ratio defining liquefaction in the laboratory. This parameter is usually derived from N SPT values from standard penetration test (SPT) because it is not so common to carry out the undrained triaxial cyclic test on good quality sand samples. SPT is a simple and economical method to know the resistance of the foundation ground in the field, and commonly carried out for subsoil investigation. Naturally the Geo-database has the data of N SPT profiles for almost all borehole logs. Therefore, it is advantageous to introduce the present procedure for liquefaction assessment based on the N SPT values. R L can be calculated by the following equations:

8 N a 1.7 LLLLLLLLLLLL(N a < 14) R L = (2) N a ( N a 14) LL(N a 14) Here, N a is a corrected N SPT value in terms of the effect of fine components and expressed as follows: N = c N + c (for sand) (3) a N a [ log10 (D50 2) ] N1 = (for gravel) (4) Here, N 1 is a corrected N SPT value in terms of confining stress. As is easily known, N a can be calculated with mean particle size, D 50 (in mm) and N 1 whereas more effect of fine components should be taken into account for sand with the correction coefficients c 1 and c 2. The coefficients c 1 and c 2 are assumed as follows: c 1 c 2 1LLLLLL(0% FC 10%) = ( FC + 40) / 50L(10% FC 60%) FC / 20 1LLLLL(60% FC) 0LLL(0% FC 10%) = (FC 10) /18L(10% FC) (5) (6) Here FC denotes fine components less than 74µm of diameter included in sand. As stated here, the liquefaction resistance, R L can be derived from N SPT values. The parameter, L denotes shear stress ratio mobilized in the ground during an earthquake and is expressed in the following form: σ v L = rd c z k hg ' (7) σ v Here, σ v and σ v are total and effective overburden stresses in kgf/cm 2, c z is a regional correction factor (c z = 1.0 for Osaka, F L w(z) Kobe and Kyoto) that is determined on the basis of the probability of earthquake occurrence, k hg is a horizontal seismic coefficient at the ground surface. The parameter, r d is a reduction factor of the shear stress ratio during an earthquake in the vertical direction to consider the non-rigid response of the ground and expressed as follows: r d = z (8) Here, z denotes a depth from the ground surface. A soil layer with F L value larger than 1.0 is considered to be non-liquefiable while liquefaction potentially takes place in the case of F L It is true that F L denotes the safety factor at a certain depth but the integrated safety factor, P L (Figure 9) is considered to represent the liquefaction of mass foundation, which directly induces serious geotechnical disaster. In the sense, P L has been selected as the index for assessing liquefaction potential of regional ground in this paper. The integrated safety factor, P L against liquefaction is defined as follows: [7] Depth (m) Figure 9 Derivation of Liquefaction Potential, P L P L 20 = F w(z)dz (9) 0 L

9 Here, w is a weighting function in terms of depth. Values of F L are determined to be zero for F L 1.0 whereas 1- F L for F L < Kobe and the adjacent area 8,000 borehole data of Kobe and the adjacent area from the Geo-database were used to model the subsoil condition. Among those data, target strata for liquefaction analysis were selected based on the following conditions: (1) Saturated deposits to the depth of 20 meters from the ground surface (2) Ground water level exists within 10 meters from the ground surface (3) Fine contents less than 35% or plastic index less than 15 (4) D 50 <10mm and D 10 <1mm All information listed above was easily extracted from the Geo-database as shown by Figures 2, 3, 4 and 5. The adopted soil parameters are shown in Table 1. As it was difficult and unrealistic to determine those values for each borehole, the average values were set for each type of soils on the basis of the Geo-database. It is very important to know the exact values of applied forces by an earthquake, but even in the case of Kobe the records were monitored only at several discrete points, which results in the difficulties to set the regional distribution of the applied forces for overall target area. In the present study, the maximum acceleration of the ground surface was backcalculated from the distribution of ground surface velocities evaluated on the basis of the degree of destruction and damage of houses due to the 1995 Hyogoken-Nambu Earthquake.[8] The input distribution of acceleration is shown in Figure 10. Table 1 Soil Parameters for liquefaction assessment for Kobe Area γ t (in tf/m 3 ) γ t (in tf/m 3 ) D 50 (mm) Fine contents Soil Type (below water level) (above water level) FC (%) Filling Material Clay Silt Sandy Silt Silty Sand Sand Gravel Hedoro Humic Soil The calculated distribution of P L values is shown in Figure 11 for overall target area. Let us pay attention to the fact that the backcalculated acceleration was applied as an input although the procedure used here requires the fixed one depending upon the type of earthquake and the geotechnical characteristics of the target area. The reason consists in that the analysis for Kobe and the adjacent area should be the benchmark for validating the present procedure by comparing the actual occurrence of liquefaction. For this purpose, it is indispensable to use the realistic input for acceleration, not the assumed fixed one. In Figure 11, values of P L are small in the inland area close to mountains because the Holocene soft deposits become thin, gravels predominant and values of N SPT also become larger that can be easily understood in Figures 2, 3, 4. On the contrary, the deposits near the coastal line are considered to be liquefiable with large values of P L. The result is also compatible to the geotechnical conditions in terms of the thickness of the deposits, less g ravels and low N SPT values there. Figure 12 shows the distribution records of liquefaction occurrence in terms of existence of sandboils at Kobe and the adjacent area during the 1995 Hyogoken-Nambu Earthquake. Those data are thought to be the solutions for the calculated results shown in Figure 11. The calculated distribution of P L values is well compatible to the actual occurrence of liquefaction. The seriously damaged area due to liquefaction is concentrated along the coastal line and inside the reclaimed islands. The values of P L for those areas exceed 25 from Figure 11 and the border separating liquefied and non-liquefied can be placed at around the value of P L equal to 15. Comparison of the calculated liquefaction potential and the actual records during the 1995 Hyogoken-Nambu Earthquake has provided the result that the estimated P L value with the present procedure reaches 15, liquefaction and its induced geotechnical disaster takes place. Then, the critical acceleration that is defined as the acceleration by which the estimated P L value becomes 15 is

10 calculated as a threshold for the occurrence of liquefaction. The distribution of the critical accelerations is shown in Figure 13. It is evaluated that the larger the values of critical acceleration become, the more the deposits can resist against liquefaction. From this figure, it is found that the relatively liquefiable deposits exist in the reclaimed islands, lowland along the coastal line and the Muko River. In the sense of the hazard map in terms of liquefaction occurrence during earthquake, the distribution of the critical acceleration (Figure 13) can be a good reference for geotechnical disaster prediction and the politics of disaster mitigation. Finally, the present procedure is found to function well for description and assessing the occurrence of liquefaction. Figure 10 Input acceleration at the ground surface backcalculated based on the ground velocity derived from damage of houses in the 1995 Hyogoken-Nambu Earthquake [8] Figure 11 Calculated liquefaction potential in terms of PL values in Kobe and the adjacent Area

11 Figure 12 Record of liquefaction occurrence in Kobe and the adjacent area during the 1995 Hyogoken-Nambu Earthquake Figure 13 Distribution of the critical acceleration that induces liquefaction in Kobe and the adjacent area 3.3 Kyoto basin The simplified procedure assessing liquefaction potential was validated by comparing the actual records of liquefaction in Kobe and the adjacent area during the 1995 Hyogoken-Nambu Earthquake. Kyoto City is located in the Kyoto Basin surrounded by the mountains and faults. The next interplate huge earthquake, called Nankai Earthquake is said to certainly take place within 40 years. In the sense, Kyoto is also a potential area to be hit by earthquake. In order to predict occurrence of geotechnical disasters, particularly liquefaction in Kyoto Basin, the simplified procedure based on the Geo-database is applied to Kyoto Basin. 8,000 borehole data from the Geo-database was used to model the subsoil condition. The major premise is almost the same as the case of Kobe and the adjacent area explained in 3.2. The soil parameters are different and determined based on the Geo-database as shown in Table 2. As far as the input earthquake force is concerned, the suggested intensity is adopted because we do

12 not have any information on the precise distribution of accelerations. The critical value of P L for the occurrence of liquefaction is set to be 15 on the basis of the performance obtained in the case of Kobe and the adjacent area. Table 2 Soil Parameters for Liquefaction Assessment for Kyoto Basin γ t (in tf/m 3 ) γ t (in tf/m 3 ) D 50 (mm) Fine contents Soil Type (below water level) (above water level) FC (%) Filling Material Clay Silt Sandy Silt Silty Sand Sand Gravel Humic Soil Figure 14 Calculated distribution of the critical acceleration for interplate earthquake in Kyoto Basin (Type-1 Earthquake) Figure 14 shows the distribution of calculated values of the critical acceleration by which the value of P L reaches 15 for Kyoto Basin. In the case, the input earthquake acceleration is assumed one from the interplate huge earthquake (Type-1). From the predicted performance, the central part of Kyoto requires more than 400 gal of acceleration for the occurrence of liquefaction. Only in the southern part

13 where the three rivers join together, 200 to 300 gal appears at intervals. However, compared to the case of Kobe and the adjacent area, the deposits of Kyoto Basin are tougher against liquefaction. According to the official report by the Kyoto municipal bureau, the predicted maximum acceleration due to the coming interplate earthquake is at most 150 gal. From the present results, serious liquefaction and its induced geotechnical disaster will not be expected for Kyoto Basin by the huge interplate earthquake. Figure 15 Calculated Distribution of the Critical Acceleration for Near Field Earthquake in Kyoto Basin (Type-2 Earthquake) The distribution of the critical acceleration (P L =15) is shown in Figure 15 against the scenario near field earthquake due to the failure of faults (Type-2). It is qualitatively similar that the central part of Kyoto is very tough against liquefaction with the required values of acceleration is 800 gal. On the contrary, 300 to 700 gal of the critical acceleration can be seen in the southern part. Particularly, low values of the critical acceleration are distributed along the rivers because a large amount of sand has been carried by those rivers and sedimented. Furthermore, floodplain has also been developed around the main flow of those rivers. Huge acceleration is certainly expected to be generated in the case of near field earthquake due to failure of faults. During the 1995 Hyogoken-Nambu Earthquake, more than 400 gal of acceleration was monitored in the natural deposits of Kobe and the adjacent cities.[9] In the sense, we should be prepared to undergo the acceleration of around 500 to 600 gal. From these results, serious liquefaction and its induced geotechnical disasters possibly take place in the southern part of Kyoto Basin, particularly attention should be paid to the areas along the rivers.

14 4. CONCLUSIONS Urban Geo-database has been developed in Kansai, Japan on the basis of data from about 30,000 borehole logs. The databases of Osaka, Kobe and Kyoto have already been achieved and can be used on PC. Any cross-sectional view of grounds can be drawn at will together with various information on soil properties, such as soil classification, grading, underground water level, N SPT value, consolidation parameters etc. The existence of faults can also be detected from the cross-sectional view of grounds. Distribution of soil properties indicates the regional characteristics of grounds and some of them can be used to determine parameters for various analyses. Practical application in terms of assessing the regional liquefaction potential of urban area has been carried out on the basis of the Geo-database. The necessary parameters for calculation have been determined from data of the Geo-database considering the local characteristics of soils. The simplified procedure has been adopted considering that borehole data normally contain only primary soil properties, such as soil classification, grading, N SPT values etc. The predicted liquefaction potential in terms of P L values were validated by comparing with the actual records of liquefaction occurrence during the 1995 Hyogo-ken Nambu Earthquake. The calculated distribution of liquefied blocks agreed well to the actual records of liquefied area in Kobe and the adjacent area. The Geo-database has played a significant role to obtain this reasonable description of liquefaction potential. Based on this validation, the liquefaction potential of Kyoto Basin was also assessed with the present scheme. In the case of Kyoto Basin, although the southern part where we have thick and weak Holocene deposits was found to possibly liquefy due to near field earthquake. In the sense of disaster mitigation, a due consideration is necessary for the possible earthquake induced geotechnical disasters and the countermeasures against them. For this purpose, the present Geo-database is versatile and should be widely utilized. ACKNOWLEDGEMENTS The authors would like to express their sincere gratitude to Geo-Database Information Committee in Kansai for their cooperation in providing important and useful geotechnical data. Thanks are also extended to Mr. Teruyuki Hamada of Geo-Research Institute for his assistance during the preparation of the figures for this paper. REFERENCES [1] Kansai Jiban (Ground of Kansai Area). Kansai Branch of JSSMFE, 212p., [2] Shin Kansai Jiban (Ground of Kansai Area Especially Kobe to Hanshin). Geo-Database Information Committee of Kansai, 270pp., 1998 [3] Shin Kansai Jiban (Ground of Kansai Area Especially Kyoto Basin). Geo-Database Information Committee of Kansai,196pp., [4] K. Takemura, M. Mitamura, N. Kitada and R. Saito, Subsurface Geology in the Kobe Earthquake Region, Central Japan, Active Fault Research for the New Millenium, Proceedings of the Hokudan International Symposium and School on Active Faulting, pp , [5] A. Sangawa, Jishin (Earthquake), Daikosha Co., (in Japanese) [6] Japan Road Association, Earthquake Resistant Design, Specifications for highway bridges, [7] T. Iwasaki, F. Tatsuoka, K. Tokita and S. Yasuda, Estimation of Degree of Soil Liquefaction During Earthquake, TSUCHI-TO-KISO, Vol. 28, No. 4, pp.23-29, 1980 (in Japanese). [8] Y. Hayashi, J. Miyakoshi and K. Tamura, Study on the Distribution of Peak Ground Velocity Based on Building Damage During the 1995 Hyogo-ken Nanbu Earthquake, J. Struct. Constr. Eng., AIJ, No. 502, pp.61-68, 1997 (in Japanese). [9] Japanese Geotechnical Society, Report on the Geotechnical Disasters During the 1995 Great Hanshin-Awaji Earthquake (in Japanese), 1995.