Vol. 5, No. 8 August 1995 INSIDE • South-Central Section Meeting, p. 160 GSA TODAY • New Members, p. 161 A Publication of the Geological Society of America • New Fellows, Student Associates, p. 163 The 1995 Hanshin-Awaji (Kobe), Japan, Earthquake Thomas L. Holzer, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 34° 135° 10' 45' 135° 15' 135° 20' R o k k o M o u n t a i n s Nikawa-Yurino Holocene Alluvium and Reclaimed Ground Active Faults (Late Quaternary Activity) Figure 1. Neotectonic CRYSTALLINE ROCK OUTCROP FILTRATION Dashed where inferred ALLUVIAL DEPOSITS PLANT Pliocene - Pleistocene Sediment gravel, sand, clay Faults (Early Quaternary or map of Osaka Bay region ANCIENT SHORELINE, 6000 yr B.P. Miocene Sediment and Volcanics Tertiary Activity) LITTORAL & LAGOONAL DEPOSITS (generalized from River sand & clay Pre-Tertiary Intrusives, Sediment, and Major Tectonic Line in Metamorphic Rock Pre-Tertiary Basement Sangawa et al., 1983; SHORELINE circa 1885 RECLAIMED GROUND 34° 45' Tsukuda et al., 1982; and -10 BASE OF MARINE CLAY 0 25 50 km Elevation, m Asiya Mukogawa Tsukuda et al., 1985). JMA INTENSITY 7 134°-30' 135° 135°-30' 2 ? ? ? Nishinomiya 2 Hanshin Expressway Daikai Kobe 5 Harbor TRAIN 25' 10 m ° STATION 43 35° 35° Expressway 20 m 135 34° 40' Hanshin Rokko Island Expressway Port 30 m 43 5 Island Figure 2. Generalized OSAKA geologic map of Kobe Osaka Bay 0 5 km KOBE (from Huzita and Kasama, N EPICENTER 1983) and Japanese 34° 40' I N L A N D S E A 34°-30' 34°-30' Meteorological Agency ° 135° 15' 135° 20 135° 25 O S A K A B A Y (JMA) intensity 7 area. 135 10' AWAJI ISLAND 44 134°-30' 135° 135°-30' 42 ABSTRACT unprepared; society is more likely to prepare when earth scientists map The January 17, 1995, earth- M=34 5 6 7 8 and quantify earthquake hazards. quake that devastated Kobe, Japan, 1961–94 Earthquakes 40 caused about $100 billion in prop- INTRODUCTION erty losses, making it the most Eurasian Plate expensive earthquake ever to strike The January 17, 1995, Hanshin- Earthquake an urban area. The earthquake killed Awaji, Japan, earthquake, which Depth (km) 38 5378 people, damaged or destroyed severely damaged Kobe, a modern city 0 about 152,000 buildings, and inciner- with many engineered structures, is 100 ated the equivalent of 70 U.S. city the most expensive earthquake ever Median Tectonic 200 blocks. The earthquake confirms the to occur. Previous earthquakes such as Line 36 credibility of predictions of major the 1976 Tangshan, China, earthquake, Tokyo 300 400 property losses when urban areas which killed 650,000 people, have Kobe in the United States are subjected to forcefully demonstrated the potential 500 local moderate earthquakes. It also for great loss of life when buildings 34 1944 provides an unusual opportunity are not earthquake resistant. The 1995 Pacific to study the effects of near-source Hanshin-Awaji earthquake confirms Plate 1946 gh ground shaking on both the build- the credibility of predictions of major rou 32 i T ings and infrastructure of a modern property losses when urban areas in ka an Philippine city and to deduce implications for the United States are subjected to near- N 200 km the United States. Damage to build- source ground shaking. This confirma- Plate ings, which accounted for about tion should motivate additional efforts 60% of the total property loss, was to mitigate the earthquake hazard in 130 135 140 145 greatest in buildings constructed urban areas in the United States that Figure 3. Japan, showing seismicity from 1961 to 1994, location of the 1995 Hanshin-Awaji under older building codes. The con- are underlain by active faults; these earthquake, and projected rupture areas of largest historical earthquakes to shake Kobe, which centration of damage in older build- areas include Los Angeles, Salt Lake were subduction-zone earthquakes in 1944 and 1946. (Figure prepared by Grant A. Marshall, ings highlights the need to address City, San Francisco–Oakland, San Diego, U.S. Geological Survey.) the seismic hazard from buildings and Seattle-Tacoma. This earthquake that do not conform to current code. also provides a special opportunity to The infrastructure of Kobe, including learn about the potential of near-source expressways, railways, port facilities, ground shaking and liquefaction to hazard. Salt Lake City sits atop the Awaji Island in Osaka Bay (Fig. 1). The and water, gas, electrical power, and damage modern engineered structures Wasatch fault system, which has been earthquake ruptured bilaterally along a sewer systems, also sustained major and urban infrastructure. documented by earth scientists to be 35–50-km-long northeasterly trending damage. The massive damage to Kobe presents interesting direct capable of generating moderate earth- zone; the northeastern part of the rup- infrastructure highlights the need parallels with cities in the United quakes. As in Kobe, the fault has had ture zone passed beneath Kobe. The to consider the seismic hazard to life- States. For example, the geology of only modest historical seismicity, and focal mechanism shows strike-slip lines; catastrophic failure of one of Oakland, California, which sits atop the public perception of and level of motion on a nearly vertical fault. Sur- these systems may undermine the the highly active Hayward fault, is preparation for the earthquake hazard face faulting was observed only above functionality of a city. The lessons similar to that of Kobe. Both cities are are not as high as in more seismically the southwest end of the rupture zone, from Kobe for the earth sciences built on young alluvial deposits and active areas. where a 9-km-long segment of the are similar to those from the 1994 ground reclaimed from adjacent Nojima fault broke the land on the Northridge and 1989 Loma Prieta, drowned estuaries. Both estuaries The Earthquake northwest side of Awaji Island. Surface California, earthquakes. Areas subject have thick accumulations of soft silt faulting was primarily strike slip, with The Hanshin-Awaji earthquake to either near-source ground shaking and clay. Thus, the earthquake in Kobe a maximum horizontal displacement (M = 6.9) occurred at 5:46 a.m. local or special site effects are at particular is a good analog for what may happen W of 1.7 m; locally, vertical offsets time on January 17, 1995. The epicen- risk from earthquakes. Earthquakes in Oakland. Salt Lake City presents a ter was located off the northeast tip of become disasters when society is parallel in public perception of the Kobe continued on p. 154 Kobe continued from p. 153 GEOLOGIC SETTING Geologic mapping in Japan has re- IN THIS ISSUE vealed many onshore or nearshore Japan is an island arc that has reached 1.0 m. Seismic profiles in faults that show evidence of Quater- formed on the east boundary of the Osaka Bay revealed scarps off the nary activity (Research Group for The 1995 Hanshin-Awaji Eurasian tectonic plate (Fig. 3). The northeast end of Awaji Island with an Active Faults in Japan, 1991). The (Kobe), Japan, Earthquake . 153 geologic history of Japan is dominated aggregate length of 7 km. The offshore Hanshin-Awaji earthquake of January by subduction of the Philippine and Slide Set Available on Kobe faults are offset about 5 km to the 17, 1995, occurred on one of these Pacific plates beneath the Eurasian Earthquake Damage .............. 154 southeast of the Nojima fault. mapped faults. Kobe is about 250 km plate. In southwestern Japan, subduc- About People ...................... 154 Damage was concentrated in a northwest of the Nankai Trough and tion occurs along the Nankai Trough. narrow elongate zone (Fig. 2). The about 50 km north of the Median Tec- In Memoriam ...................... 154 Although most of the seismic energy earthquake killed 5378 people, injured tonic Line (Fig. 3), a major geologic associated with plate convergence is Travel Grant Program .............. 154 33,189 people, damaged 152,297 boundary that divides southwestern released along the downgoing slab, buildings, and incinerated an area Japan into a northern “Inner Zone” GSA on the Web ................... 154 Japan also faces a significant onshore of 671,253 m2, the equivalent of 70 and southern “Outer Zone.” Basement earthquake hazard. About eight moder- Washington Report ................ 157 U.S. city blocks (Asahi Evening News, rocks of the Inner Zone consist chiefly ate or larger earthquakes occur per cen- 1995). Total property losses were about 1995 Dibblee Medal ............... 157 tury onshore (Wesnousky et al., 1982). $100 billion. Kobe continued on p. 155 GSAF Update ...................... 158 1996 South-Central Section Meeting ................... 160 New GSA Members ................ 161 Slide Set Available on Kobe Earthquake Damage New GSA Fellows, Students ........ 163 Here is an excellent tool for educational use: a set of 35 mm illustrate the Holocene history of Kobe. The set is supplied Calendar .......................... 164 color slides compiled by author Thomas L. Holzer, USGS, with a printed text describing the views. expanding on this article. These 30 slides, taken by several GSA Section Meetings ............. 166 investigators, document geologic conditions and damage Order slide set SLI001, Kobe Earthquake Damage, from the GSA Annual Meetings .............. 166 resulting from the January 17, 1995, M 6.9 Hanshin-Awaji Geological Society of America, P.O. Box 9140, Boulder, CO earthquake that devastated Kobe, Japan. Views illustrate 80301-9140, phone 800-472-1988 or (303) 447-2020. 1995 Penrose Conferences ......... 166 damage to buildings, transportation facilities, and lifelines. Orders may be faxed to GSA at 303-447-1133; please include Classifieds ......................... 167 The set includes pictures of liquefaction and ground settling complete credit card information. List price $47, postpaid by in areas of reclaimed ground, including the Port of Kobe, the surface mail; GSA members may claim their discount.