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 - The Map)


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


                               1995

____________________________

*  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 (kobe_acc.ps) and ASCII
versions of this report (kobe_A.txt) and its companion report (Open-File
Report 95-259B: kobe_B.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
wrgis.wr.usgs.gov.  The Files and README are located in
pub/geologic/other/of95-259.

To obtain the files over Internet via World Wide Web: 
http://wrgis.wr.usgs.gov.  Click on the "Other" button.

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, but 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
approximation, 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 upper 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, CDGSJ92010.

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, 1994, and general geology of the
epicentral region: U.S. Geological Survey Open-File Report 94-197, 3 p.