U.S. DEPARTMENT OF THE INTERIOR

                     U.S. GEOLOGICAL SURVEY


    Maps of peak horizontal and vertical accelerations recorded 
  for the Northridge, California,  earthquake of January 17, 1994 
         and general geology of the epicentral region 


                          Compiled by

   C.M. Wentworth, R.D. Borcherdt, R.K. Mark, and D.M. Boore 1


                  Open-File Report 94-197


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.


_________________________
1  Menlo Park, CA 94025



                     Description of the Maps

The magnitude 6.7 Northridge earthquake, which occurred northwest of central
Los Angeles, California, on January 17, 1994, was recorded on a large number
of strong-motion seismic stations maintained by the California Division of
Mines and Geology (Shakel and others, 1994), the University of Southern
California (Trifunac and others, 1994), and the U.S. Geological Survey
(Porcella and others, 1994).  

Two colored maps are presented at page size that display the peak horizontal
and peak vertical accelerations recorded in the Northridge 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.    

The maps were prepared digitally and the parts assembled in ARC/INFO, a
commercial geographic information system.  The geologic background was
prepared by editing a crude scan of the linework from the Geologic Map of
California (Jennings, 1977), the original scale of which is 1:750,000, and
simplifying the bedrock unit identities from that already very generalized
map.  The acceleration contours were prepared by gridding the station values
(grid spacing 0.02 degrees of latitude and longitude) with a minimum curvature
gridding routine (Webring, 1981, USGS Open-file Report 81-1224) and then
contouring the grids at a contour interval of 0.05 g.