Using the SCEC Version2 southern California
        reference seismic  velocity model
                 6/21/00
         revised 7/19/00
         revised 8/22/00
         revised 9/06/00

 On 9/06/00 a revised version of the model, version2.2, was
installed in response to feedback from model users. This version
differs from version2.1 in
  - curing problems in getting consistent velocities with respect
    to the order that points are given
  - fixing errors in the geotech database

 On 8/22/00 a revised version of the model, version2.1, was
installed in response to feedback from model users. This version
differs from version2 in
  - fixing glitches in some reference surfaces
  - implementation of a smoother tomography velocity interpolator
  - changing the default minimum density from 1000 to 1500 kg/m^3

 The model exists as a fortran code and associated files.
The code reads a file of points specified by latitude, longitude and
depth, and writes out Vp, Vs, and density at those points.

 The compressed tar file Version2.2.tar.Z contains all the files.
First uncompress (assuming a Unix machine):
  uncompress Version2.2.tar.Z
       or
  zcat Version2.2.tar.Z > Version2.2.tar
Next extract the files:
  tar xvf Version2.2.tar 
Then compile:
  f77 version2.2.f -o version2.2

 The file of points should be named "btestin" (this can be changed
in the subroutine "readpts"). Here is a sample file:

8
33.50000 -118.50000 30.0
33.50000 -118.50833 30.0
33.50000 -118.51667 30.0
33.50000 -118.52500 30.0
33.97200 -118.08800   3000.0
33.97200 -118.08800   3001.0
33.97200 -118.08800   3002.0 
33.97200 -118.08800   3003.0  

 The first line contains the number of points in the file
(8 in this example). The code has array dimensions allowing
up to 750,000 points. To handle more points, the arrays can
be redimensioned by changing the parameter "ibig" in the include
file "in.h", or by dividing the total point set into chunks
of less than 750,000.
 The remaining lines are the latitude, longitude (both in
decimal degrees, with the longitude negative, because this
is the western hemisphere), and depth (in meters. Note in the
version 1 model the depth was given in feet). These are read
with free format. It is a common error to forget the negative
longitudes.
 The model consists of rule and object parameterized basins
embedded in a tomography background. The objects are reference
surfaces outlined by polygons, so the code must figure out
which polygon an input point is within. You can speed up the code
by putting all of the points at the same latitude and longitude
sequentially in the input file (as in the last 4 points in the
sample). See note 2 below.
 The output will be a file name "btestout" (this name can be
changed in the subroutine "writepts"). Here is a sample (for
the last 4 points of the input sample):

33.97200 -118.08800   3000.00   3509.8   1817.4   2304.0
33.97200 -118.08800   3001.00   3510.8   1818.1   2304.2
33.97200 -118.08800   3002.00   3511.8   1818.9   2304.3
33.97200 -118.08800   3003.00   3512.8   1819.6   2304.5
 
 These echo the latitude, longitude and depth, and then give
Vp, Vs (both in m/s), and density (in kg/m^3).

 Notes and warnings:

 1. This is a research code, and bugs and glitches may be revealed
as it is subjected to new applications.
 2. Input points can be in any order, although the code will run
faster if the points are given with the same lat-longs sequentially.
If you want to recover the geotechnical borehole shear wave
you must give the lat-long to within 50 m of the borehole's lat-long.
 3. The code assigns a minimum density of 1500 kg/m^3 to points
with a Vp of 1586 m/s or less. This is done at line 779 of the
main program.
 4. The boundary between the Los Angeles area basins (see note 6) and
the background model is relatively smooth except along the south and
west edges (mostly in the ocean) of the basins model. This produces
an artificial abrupt transition from the seismically slow basin
sediments to the faster background model. This may produce unrealistic
artifacts in, for example, waveform modeling. Watch out.
 A crude Salton Trough model is included. It has similar unrealistic
abrupt boundaries.
 5. Points outside the area of the tomographic background (see note 6)
will be assigned velocities from a smooth Hadley-Kanamori 1D model.
 6. The Version 2 model is documented in:
Magistrale, H., S. Day, R. W. Clayton, and R. Graves, 2000. The SCEC
southern California reference 3D seismic velocity model Version 2,
in press, Bull. Seismol. Soc. Am.