U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Preliminary Map of Peak Horizontal Ground Acceleration 

for the Hanshin-Awaji Earthquake of January 17, 1995, Japan

(Part A of 2-TheMap)

digitally compiled by 

C.M. Wentworth, R.D. Borcherdt, and R.K. Mark

from

preliminary information kindly provided by 

the primary agencies and investigators in Japan

Open-File Report 95-259A

This report is preliminary and has not been reviewed for conformity with U.S. Geological 

Survey editorial standards or with the North American Stratigraphic Code. Any use cf 

trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

1995

1 Menlo Park, CA 94025
Introduction

The Hanshin-Awaji earthquake of January 17, 1995, near Kobe, Japan, offers a valuable dataset for a 

strong nearby event in a region that contains extensive soft-soil deposits.

A small-scale map has been prepared that shows strong motion stations and recorded accelerations 

together with general contours of those accelerations over a background of the regional geology. A 

similar map is available for the Northridge earthquake (Wentworth, Borcherdt, Mark, and Boore, 

1994; and World Wide Web at http://wrgis.wr.usgs.gov). Note that the Hanshin-Awaji ground motion 

data are preliminary, the contours are very general and represent a sparse dataset, and the background 

geology is derived from a generalized map of Japan prepared at the country scale of 1:1,000,000.

The peak acceleration map was prepared digitally and the parts assembled in ARC/INFO, a commercial geographic information system. It is included here as a colored page-sized illustration (fig. 1) and 

is also available in digital form as a poster-sized (30x21 inch) postscript image. Broader description 

and discussion of the data are provided in the companion report (Borcherdt and Wentworth, 1995).

How To Obtain the Digital Image and Reports

A 12 MB postscript file of the poster-sized map image (kobepga.ps, 30 by 21 inch), a 10 MB pagesized version (kobepgapg.ps), and ASCII versions of this report (kobeA.txt) and its companion report 

(Open-File Report 95-259B: kobeB.txt) can be obtained over Internet by anonymous ftp or World 

Wide Web or by sending the database coordinator a tape on which the files will be copied and 

returned.

To obtain the files over Internet by ftp, connect via anonymous ftp to quake.usgs.gov. The files are 

located in the subdirectory pub/www/QUAKES/shake/kobe.

To obtain the files via World Wide Web (WWW), connect to the Web site: 

http://quake.wr.usgs.gov/QUAKES/shake/kobe/kobeshake.html.

V

To obtain the files on magnetic tape in UNIX tar format: send an 8 mm Exabyte tape or 150-MB 

1/4-inch cartridge tape and request to Database Coordinator c/o BWRG, U.S. Geological Survey, 345 

Middlefield Road MS-975, Menlo Park, CA 94025.

Description of the Map

The map displays the peak horizontal accelerations (in gals) recorded in the epicentral region over a 

generalized geologic background. Acceleration values are shown near the stations at which they were 

recorded and contours of those values are superimposed on the maps. Fore- and aftershocks over a 

two-day period indicate the approximate location of the source and circles at a distance interval of 25 

km around the mainshock epicenter indicate both map scale and position of features relative to the 

mainshock. A 1-degree grid of latitude and longitude is superimposed on the geology. 

The prominent dumbbell-shaped high in the acceleration contours is centered over the Bay-margin 

fringe of Holocene sediment in the Kobe City area adjacent to the northeastern end of the source fault.
It's relatively narrow shape and rapid falloff northeastward along strike are real, based on the distribution of control around it's northeastern end. The dumbbell peaks rise to 600-700 gals, b'it two 

stations in the intervening gap reach above 800 gals (other nearby stations with lower values force the 

saddle in the contours).

The geologic units are those of the generalized Geologic Map of Japan, which distinguishes rock and 

sediment formed during different intervals of geologic time (time stratigraphic units). Although the 

materials can be inferred to increase in stiffness or hardness with increasing age, as a first aoproximation, the textures in the Holocene and Pleistocene sediments that are important for evaluating local 

amplification are not well distinguished. For this presentation, the full distinctions in the upp~.r Cenozoic time-stratigraphic units on the source map are retained, but the older bedrock units are 

combined. Note that the recent land fill that has been placed along the margins of Osaka Bay and at 

Kansai International Airport (location of the 160 gal station in Osaka Bay) is not included.

Data and Sources

A brief description of the data and sources is provided here. See the companion report (Borcherdt and 

Wentworth, 1995) for more detail.

Strong Motion Data

The strong motion data were derived from preliminary information provided to R.D, Borcherdt by the 

various agencies and principal investigators and colleagues in Japan, together with the "Prompt Report 

on Strong Motion Accelerograms No. 46" (Science and Technology Agency of Japan, 1995). The 

mainshock location is from the above noted Prompt Report. Seismicity for the two-day period including the main shock is that reported via ftp by the Earthquake Research Institute, University of 

Tokyo, Observation Networks of Disaster Prevention Research Institute, Kyoto University, and Faculty of Science, Kochi University.

Acceleration Contours

The acceleration contours were prepared by gridding the station values at a spacing of 0.5 km using a 

minimum curvature gridding routine (Webring, 1981) and then contouring the grid at a contour interval of 50 gals. The contours provide a guide to the general variation of acceleration throughout the 

region. The data are sparse, however, the contours represent a generalized surface that does not pass 

through all the station values, and the contours continue into or across areas of little or no control, 

including Osaka Bay.

Geology

The geologic background was prepared from a digital version of the Geologic Map of Japan (Geological Survey of Japan, 1992). This is a very generalized map of the country at a scale of 1:1,000,000. 

In its representation in the poster-sized image, the Kobe region of the geologic map is enlarged about 

twofold (to a scale of 1:425,000), a process that adds no detail but simply makes room for the other 

data that are included.
Map Projection

The digital geology on the CD-ROM is stored in a coordinate system of decimal degrees of longitude 

and latitude. This was converted for graphical presentation into an Oblique Mercator projection with 

the following parameters, chosen to center the map on the Kobe region:

.9999 - scale factor at projection's center

34 48 07 - latitude of projection's center

129 30 04 - longitude of 1st pt on central line

29 40 16 - latitude of 1st pt on central line

147 45 11 - longitude of 2nd pt on central line

45 06 43 - latitude of 2nd pt on central line

References Cited

Borcherdt,R.D., and Wentworth, C.M., 1995, Preliminary map of peak horizontal ground acceleration 

for the Hanshin-Awaji earthquake of January 17, 1995, Japan (part B of 2, description of mapped 

data sets): U.S. Geological Survey Open-File Report 95-259B)

Geological Survey of Japan, 1992, Geological Map of Japan, Third Edition, CD-ROM Version: Geological Survey of Japan, CD-ROM series of Earth Science Databases, CDGSJ920K).

Science and Technology Agency of Japan, 1995, Prompt report on strong-motion accelerograms No. 

46: The National Research Institute for Earth Science and Disaster Prevention, Science and Technology Agency of Japan, 42 p.

Webring, Michael, 1981, A gridding program based on Minimum curvature: U.S. Geological Survey 

Open-file Report 81-1224, 41 and cd to p.

Wentworth, C.M., Borcherdt, R.D, Mark, R.K., and Boore, D.M., 1994, Maps of peak horizontal and 

vertical accelerations recorded for the Northridge, California earthquake of January 17, 19?4, and 

general geology of the epicentral region: U.S. Geological Survey Open-File Report 94-197, 3 p.
PRELIMINARY MAP OF PEAK HORIZONTAL GROUND ACCELERATION 

for the HAN6HIN-AWAJI EARTHQUAKE OF JANUARY 17, 1995, JAPAN

Bated en preliminary data provided by the primary ageneiee and inveetigatorc in Japan 

Digital compilation by C.M. Wentworth, R.D. Boreherdt, and R.K. Mark

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OPEN FILE NOTICE

OF-95-259A. Preliminary map of peak horizontal ground acceleration for the 

Hanshin-Awaji earthquake of January 17, 1995, Japan (Part I of 2 - The map) By 

C. M. Wentworth, R.D. Borcherdt, and R.K. Mark. 1995. 5 p.

This report describes a digital image in ARC/INFO postscript format of a map 

available in page size (10 MB) and poster size (30 by 21 inch, 12 ME).

Requirements: Access to Internet or a supported tape drive is required to 

download the files.

To obtain the digital files:

Over Internet via anonymous ftp to: quake.usgs.gov. Files are located ir. the 

subdirectory pub/www/QUAKES/shake/kobe.

Via World Wide Web: http://quake.wr.usgs.gov/QUAKES/shake/kobe/kobeshake.html

On magnetic tape in UNIX tar format: send 8mm Exabyte tape or 150-MB 1,/4-inch 

cartridge tape and request to Database Coordinator c/o 3WRG U.S. Geological 

Survey 345 Middlefield Road MS-975 Menlo Park, CA 94025