CVM-H User Guide

User Guide for the Southern California Earthquake Center

Community Velocity Model: SCEC CVM-H 11.1.0

Andreas Plesch, Carl Tape, John H. Shaw, Patrick Small, Geoff Ely

Harvard University, University of Southern California

January 21, 2011

This PDF file can be downloaded directly from: http://structure.harvard.edu/cvm-h/download/cvmh_manual.pdf

Overview

The SCEC CVM-H is a 3D model of the elastic structure of southern California. It contains volumetric representations of compressional wave velocity (Vp), shear wave velocity (Vs), and density (rho). It also contains three primary surfaces: the topological/bathymetric surface, the basement surface, and the Moho surface. The model is constructed from numerous datasets (Süss and Shaw, 2003) and has been used within parallel-computing based wavefield simulations of earthquakes within southern California (e.g., Komatitsch et al., 2004). See Section 6 for details.

Downloading CVM-H

1. Start at SCEC website: http://scec.usc.edu/scecpedia/CVM-H

2. Read the description of the model.

3. Navigate to the “Source Code” section and click the download link to download the latest version. NOTE: this file is large (500 MB), so the download make take awhile.

Requirements

The system requirements are as follows:

1. UNIX operating system (Linux, Solaris, MacOS)
2. GNU make
3. tar and for opening the compressed files
4. Optionally GTS (GNU Triangulated Surface Library) for cvmdist http://gts.sourceforge.net

Installation

• Download the latest version tarball and untar into a ./cvmh subdirectory with this command:

% tar zxvf cvmh_11.1.0_RC.tgz

The files you should see are these:

CMxVM_Model3D_CalMex_BATO.ts -- bathymetry/topography as tsurf, version 4
CVMH_CalMex_BATO.ts -- bathymetry/topography as tsurf, version 5
CMxVM_Model3D_CM_BASE_Folded.ts -- top of the basement as tsurf
CVMH_Moho.ts -- Moho surface
ts2gts.awk -- script to translate from .ts to .gts
ts2gts.sh -- run script for ts2gts.awk
Makefile -- for compilation
interpolate -- directory with routines for inverse distance weighted interpolation
gctpc -- projection library
src -- directory for source files
bin -- directory for RUN
doc -- directory containing documentation including user guide
test -- directory for unit/acceptance tests
viz -- directory for simple GMT visualization of horizontal slices from CVM
lib -- directory for VX C API library file

• The package is built by executing the following commands:

% cd ./cvmh
% make clean;make all

• Ensure that the s/w is correctly built by running the unit tests. All tests should pass.

% cd ./test
% ./unittest

Model Description

Geotechnical Layer

A near-surface geotechnical layer (GTL) exists, derived from a Vs30 map of southern California as described in (Ely 2010). The GTL covers the following region:

GTL Transition Depth: >=350m depth. See notes below.
Resolution: 250m
SW corner X: -31000.0 UTM easting
SW corner Y: 3410000.0 UTM northing
NE corner X: 849000.0 UTM easting
NE corner Y: 4274000.0 UTM northing

Vp, Vs, and density (rho) at the free surface (depth 0m) are derived from the Vs30 values with the following relations:

Vs = Vs30

Vp = 0.9409 + Vs30/1000 * (2.0947 - Vs30/1000 * (0.8206 - Vs30/1000 * (0.2683 - Vs30/1000 * 0.0251)))
Vp = Vp * 1000.0

rho = Vs30/1000 * (1.6612 - Vs30/1000 * (0.4721 - Vs30/1000 * (0.0671 - Vs30/1000 * (0.0043 - Vs30/1000 * 0.000106))))
if (rho < 1.0) {
  rho = 1.0;
}
rho = rho * 1000.0

Between depth 0m and the pre-defined transition depth (>=350m), Vp, Vs, and rho are interpolated between the above material properties and the Vp, Vs, and rho as reported by the CVM-H lr/bk model at the transition depth. The interpolation relation is described in (Ely 2010). The transition depth is nominally 350m but may be greater to accomodate points in which topo - mtop > 350m. At these points, the transition depth is set to topo - mtop so that data is guaranteed to be available.

Background Model

The CVM-H coverage region is extended by a 1D background model. The following table describes the depth-Vp relationship:

Table 1: Depth-Vp relation for SCEC 1D background model

Depth (km)	Vp (km/s)
0-1	5.0
5	5.5
6	6.3
10	6.3
15.5	6.4
16.5	6.7
22.0	6.75
31.0	6.8
33.0	7.8

Vs and rho are then derived from Vp with the following relations:

rho = 1865.0 + 0.1579 * Vp

Vs = Vp * sqrt( (0.5 - nu) / (1.0 - nu) )
where nu is from the relation:
if (rho < 2060.0) {
  nu = 0.40
} else if (rho > 2500.0) {
  nu = 0.25
} else {
  nu = 0.40 - ((rho - 2060.0) * 0.15 / 440.0)
}

Extracting Values from CVM-H

Two methods are provided for extracting material properties from CVM-H: command-line tools, and a C API. These are described in the following sections.

Extracting Values on the Command Line

Two utilities are provided for querying the community velocity model, vx and vx_lite. The vx utility is the original interface to Harvard's model. The vx_lite utility is an updated interface that supports additional functionality.

vx Utility

The vx code provides output consistent with directly querying the voxet in the Gocad software, and gives the position of the cell centers from which the data are provided. Also, elevation of the topographic, basement and Moho surfaces are provided, at the closest grid point to the input coordinates. Additional details are listed in Tables 1 and 2. For usage details, type vx -h. From the bin directory, try feeding the test points into the program. The test file, /bin/test_data/test.dat, contains eight input points:

-125 35 -7777
-118.56 32.55 -2450
360061 3750229 -1400
-118.52 34.12 -1400
-116.40 32.34 -1000
376592 3773379 -1770
376592 3773379 -17700
408669 3766189 -3000

Note that the input can be either (lon, lat, elevation) or (UTMx-11, UTMy-11, elevation). Execute vx with the command:

% ./vx < ./test_data/test.dat

The output has 8 rows and 18 columns (Table 1) and should look like this (here the columns are truncated):

  -125.000000      35.000000  -7777.00 -230844.88 3902223.73 -99999.00 -99999.00 -99999.00 -99999.00 -99999.00 -99999.00 nr -99999.00  -99999.00 -99999.00 -99999.00
  -118.560000      32.550000  -2450.00  353525.18 3602285.14 353625.00 3602375.00 -1114.91  -1150.00  -1327.54 -21571.67 lr 354000.00 3602000.00  -2400.00      2.00
360061.000000 3750229.000000  -1400.00  360061.00 3750229.00 360125.00 3750125.00   -56.93    -50.00  -1404.07 -24868.83 lr 360000.00 3750000.00  -1400.00      2.00
  -118.520000      34.120000  -1400.00  359819.67 3776309.78 359875.00 3776375.00   491.46    450.00     38.42 -28061.40 lr 360000.00 3776000.00  -1400.00      2.00
  -116.400000      32.340000  -1000.00  556464.74 3578092.46 556375.00 3578125.00   780.43    750.00    616.39 -31413.62 lr 556000.00 3578000.00  -1000.00      2.00
376592.000000 3773379.000000  -1770.00  376592.00 3773379.00 376625.00 3773375.00    99.38    100.00  -2374.53 -28165.35 hr 376552.25 3773500.00  -1800.00      3.00
376592.000000 3773379.000000 -17700.00  376592.00 3773379.00 376625.00 3773375.00    99.38    100.00  -2374.53 -28165.35 cm 380000.00 3770000.00 -18000.00      2.00
408669.000000 3766189.000000  -3000.00  408669.00 3766189.00 408625.00 3766125.00    93.89     50.00  -2820.45 -29799.86 hr 408552.25 3766250.00  -3000.00      2.00

The values for the eighth row are listed below, in transpose form, and with some annotations:

408669.000000
3766189.000000
-3000.00
408669.00
3766189.00
408625.00
3766125.00
93.89 --> elevation of topo/bath surface
50.00 --> elevation of top of model (below which there is data)
-2820.45 --> elevation of basement surface
-29799.86 --> elevation of Moho surface
hr
408552.25
3766250.00
-3000.00
2.00 --> value from tomography model
4997.06 --> Vp
2889.03 --> Vs
2534.30 --> density

Note that there is a discrepancy between the top of the model (50.00 m) and the topography (93.89 m). The “real” top of the model is defined by mtop, and there may be minor discrepancies between mtop and topo.

Table 1: Columns of the output produced by vx. Queries which fall outside of the model area return -99999, the no-data value, for all fields.

Column Index	Variable	Description
1	X	Input X (longitude or UTM coordinate)
2	Y	input Y (latitude or UTM coordinate)
3	Z	input Z (elevation, meters above sea level, i.e., positive up)
4	utmX	UTM coordinate (zone 11), easting
5	utmY	UTM coordinate (zone 11), northing
6	elevX	X coordinate of center of the cell which provided data value for elevations
7	elevY	Y coordinate of center of the cell which provided data value for elevations
8	topo	topographic/bathymetric elevation in m
9	mtop	top of model in m, below this depth there are data
10	base	basement elevation in m (generally negative)
11	moho	Moho elevation in m (always negative)
12	hr/lr/cm	flag to indicate whether high- (hr), low-resolution (lr) or lower crust/mantle voxet was used; (nr) if no data available
13	cellX	X coordinate of center of cell which provided velocity data value
14	cellY	Y coordinate of center of cell which provided velocity data value
15	cellZ	Z coordinate of center of cell which provided velocity data value
16	tag	tag: provenance of data point (see Table 2)
17	vp	compressional wave velocity in m/s
18	vs	shear wave velocity in m/s
19	rho	density in kg/m3

vx_lite Utility

The vx_lite utility is a new SCEC-developed interface which supports a number of enhancements, including query by depth, extension of the coverage region with a SCEC 1D model, and replacement of the original GTL with a Vs30-derived GTL.

The command line format for vx_lite is as follows:

% vx_lite [-s] [-d] [-v] [< input_coords]

where the options:

-s

Instructs use of SCEC 1D background model

-d

Interpret z coordinate as depth from free surface

-v

Interpret z coordinate as elevation

input_coords

3D point specified as either (lon, lat, z (meters)) or (easting, northing, z (meters)), space delimited. Input coordinates can be specified interactively or redirected to stdin from a file.

Note: Options -d and -v are mutually exclusive. Specifying neither option instructs vx_lite to interpret the z coordinate as elevation offset from free surface.

The query data is printed to stdout, and this may be redirected to a file.

CVM-H defines a set of sample test points (given in ./bin/test_data/test.dat):

-125 35 -7777
-118.56 32.55 -2450
360061 3750229 -1400
-118.52 34.12 -1400
-116.40 32.34 -1000
376592 3773379 -1770
376592 3773379 -17700
408669 3766189 -3000

These may be submitted to vx_lite with this command:

% ./vx_lite -s -v < ./test_data/test.dat

The material properties at the sample points will be printed to stdout. You can expect to see the following output, annotated here with column headers. The three important fields are the last three, containing vp, vs, and rho.

     X               Y             Z       utmX        utmY      elevX       elevY      topo      mtop      base      moho  hr/lr/cm cellX     cellY     cellZ       tag        vp        vs       rho
  -125.000000       35.000000  -7777.00 -230844.88  3902223.73  -99999.00   -99999.00      0.00      0.00 -99999.00 -99999.00 bk  -99999.00   -99999.00 -99999.00     14.00   6300.00   3637.31   2859.77
  -118.560000       32.550000  -2450.00  353525.18  3602285.14  353625.00  3602375.00  -1114.91  -1150.00  -1327.54 -21571.67 lr  354000.00  3602000.00  -2400.00      2.00   5575.15   3132.10   2631.81
360061.000000  3750229.000000  -1400.00  360061.00  3750229.00  360125.00  3750125.00    -56.93    -50.00  -1404.07 -24868.83 lr  360000.00  3750000.00  -1400.00      2.00   4554.52   2313.56   2469.78
  -118.520000       34.120000  -1400.00  359819.67  3776309.78  359875.00  3776375.00    491.46    450.00     38.42 -28061.40 lr  360000.00  3776000.00  -1400.00      2.00   5066.61   2916.30   2545.10
  -116.400000       32.340000  -1000.00  556464.74  3578092.46  556375.00  3578125.00    780.43    750.00    616.39 -31413.62 lr  556000.00  3578000.00  -1000.00      2.00   5372.79   3024.30   2595.55
376592.000000  3773379.000000  -1770.00  376592.00  3773379.00  376625.00  3773375.00     99.38    100.00  -2374.53 -28165.35 hr  376552.25  3773500.00  -1800.00      3.00   4181.37   2432.22   2418.45
376592.000000  3773379.000000 -17700.00  376592.00  3773379.00  376625.00  3773375.00     99.38    100.00  -2374.53 -28165.35 cm  380000.00  3770000.00 -18000.00      2.00   6533.31   3776.40   2841.47
408669.000000  3766189.000000  -3000.00  408669.00  3766189.00  408625.00  3766125.00     93.89     50.00  -2820.45 -29799.86 hr  408552.25  3766250.00  -3000.00      2.00   4997.06   2889.03   2534.30

Table 2: Columns of the output produced by vx_lite. Queries which fall outside of the model area return -99999, the no-data value, for all fields.

Column Index	Variable	Description
1	X	Input X (longitude or UTM coordinate)
2	Y	input Y (latitude or UTM coordinate)
3	Z	input Z (elevation, meters above sea level, i.e., positive up)
4	utmX	UTM coordinate (zone 11), easting
5	utmY	UTM coordinate (zone 11), northing
6	elevX	X coordinate of center of the cell which provided data value for elevations
7	elevY	Y coordinate of center of the cell which provided data value for elevations
8	topo	topographic/bathymetric elevation in m
9	mtop	top of model in m, below this depth there are data
10	base	basement elevation in m (generally negative)
11	moho	Moho elevation in m (always negative)
12	hr/lr/cm/gt/bk	flag to indicate whether high- (hr), low-resolution (lr) or lower crust/mantle voxet was used, (gt) for GTL, (bk) for 1D background; (nr) if no data available
13	cellX	X coordinate of center of cell which provided velocity/Vs30 data value
14	cellY	Y coordinate of center of cell which provided velocity/Vs30 data value
15	cellZ/Vs30	Z coordinate of center of cell which provided velocity data value; Vs30 value if value derived from GTL
16	tag	tag: provenance of data point (see Table 2)
17	vp	compressional wave velocity in m/s
18	vs	shear wave velocity in m/s
19	rho	density in kg/m3

Extracting Values in a C Program

SCEC has developed a C API to the Harvard model. The header containing the datatype and function definitions is located in ./src/vx_sub.h. By including this header in your source, and the libvxapi.a library at link time, your program can directly query CVM-H.

Extracting Distances to Surfaces in CVM-H

There is also an additional program, cvmdst, to compute the the distance to, and the location, of the closest points on the topographic/bathymetric, top of the basement, and Moho surfaces which are provided with CVM-H. The input file has the same format as the input file to vx, the query code to CVM-H.

To use this capability, you need GTS (GNU Triangulated Surface Library), available from http://gts.sourceforge.net. (Using a Linux-Ubuntu platform, it may be as simple as installing all “gts” packages from the Synaptic Package Manager.) With GTS installed, you can now compile. From the main cvmh directory, compile with this command:

% make cvmdst

This will create a cvmdst executable in the ./bin directory.

Try the program with the same test data as before:

% cd bin
% ./cvmdst < ./test_data/test.dat > ofile2.dat

The output file ofile2.dat has 17 columns described in Table 3. Note that the basement surface is not defined over the entire area of the model.

Table 3: Columns of the output produced by cvmdst

Column Index	Variable	Description
1	X	Input X (longitude or UTM coordinate)
2	Y	input Y (latitude or UTM coordinate)
3	Z	input Z (elevation, meters above sea level, i.e., positive up)
4	utmX	UTM coordinate (zone 11), easting
5	utmY	UTM coordinate (zone 11), northing
6	t_x	X coord of location of the closest point on the topographic/bathymetric surface
7	t_y	X coord of location of the closest point on the topographic/bathymetric surface
8	t_z	X coord of location of the closest point on the topographic/bathymetric surface
9	t_dst	distance to the closest point on the topographic/bathymetric surface
10	b_x	X coord of location of the closest point on the basement surface
11	b_y	Y coord of location of the closest point on the basement surface
12	b_z	Z coord of location of the closest point on the basement surface
13	b_dst	distance to the closest point on the basement surface
14	m_x	X coord of location of the closest point on the Moho surface
15	m_y	Y coord of location of the closest point on the Moho surface
16	m_z	Z coord of location of the closest point on the Moho surface
17	m_dst	distance to the closest point on the Moho surface

Extracting a Horizontal Slice from CVM-H

The following utility is provided:

vx_slice

Visualization utility for extracting a 2D horizontal slice of Vp, Vs, or Rho (density) from the model, suitable for plotting with a graphics package.

History of CVM-H Releases

Please reference at least Süss and Shaw (2003) if you use this model. The latest model, CVM-H 11.1.0, contains several components that may warrant referencing, depending on the objectives of a particular study. For example, the background crustal tomography model is from Tape et al. (2009), the upper mantle model is from Prindle and Tanimoto (2006), and the Moho surface is obtained primarily from Yan and Clayton (2007). Additional references for basins within the high-resolution model are within these papers: Komatitsch et al. (2004), Lovely et al. (2006), Munster (2007). References for the Vs-30 derived GTL are (TBD).

Table 4 documents the references for each release (up to Plesch et al. (2009)), as well as references for new components associated with each release. The CVM-H model has also been presented at these SCEC meetings: Stidham et al. (2001a), Suess and Shaw (2002), Shaw et al. (2004).

Table 4: History of CVM-H releases

Version	Data	Reference	New Mantle	New Moho	New Crust	New Basins	New GTL
CVM-H 1.0	2003	Süss et al. (2003)	-	-	-	SS2003	-
CVM-H 2.0	Sept 2005	Suess and Shaw (2005)	1D		H2000	K2004, L2006
CVM-H 4.0	Sept 2006	Suess and Shaw (2006)
CVM-H 5.0	Sept 2007	Plesch et al. (2007)	PT2006		L2007	M2007	M2000, M2002
CVM-H 5.5	Sept 2008	Plesch et al. (2008)					BJ1997
CVM-H 6.0	Sept 2009	Plesch et al. (2009)		YC2007	T2009
CVM-H 6.2	Jan 2010	Plesch et al. (2009)
CVM-H 6.3	Sept 2010	Plesch et al. (2009)

References

• BJ1997 (Boore and Joyner , 1997)
• H2000 (Hauksson, 2000), L2007 (Lin et al., 2007)
• L2006 (Lovely et al., 2006)
• K2004 (Komatitsch et al., 2004)
• M2000 (Magistrale et al.,2000)
• M2002 (Magistrale, 2002)
• M2007 (Munster , 2007)
• PT2006 (Prindle and Tanimoto,2006)
• SS2003 (Süss and Shaw, 2003)
• T2009 (Tape et al., 2009, 2010)
• YC2007 (Yan and Clayton, 2007)
• 1D (Kanamori and Hadley, 1975; Dreger and Helmberger , 1991; Wald et al.,1995)

Acknowledgements and Contact Info

Support for the development and maintenance of the CVM-H model has been provided by the Southern California Earthquake Center (SCEC), the National Earthquakes Hazard Reduction Program (NEHRP), and the National Science Foundation (NSF). SCEC is funded by NSF Cooperative Agreement EAR-0106924 and USGS Cooperative Agreement 02HQAG0008.

Contributions to this manual were made by: Andreas Plesch, Carl Tape, John Shaw, Patrick Small, Geoff Ely, and Thomas Jordan.

Please email software@scec.org for help on downloading and using CVM-H, and for any suggestions for the delivery of the code or for this manual.

Please reference at least Süss and Shaw (2003) if you use this model; other references should be considered, depending on the purpose (see History of CVM-H releases section).

References

1. Boore, D. M., and W. B. Joyner (1997), Site amplifications for generic rock sites, Bull. Seis. Soc. Am., 87 (2), 327–341.
2. Brocher, T. M. (2005), Empirical relations between elastic wavespeeds and density in the Earth’s crust, Bull. Seis. Soc. Am., 95 (6), 2081–2092.
3. Dreger, D. S., and D. V. Helmberger (1991), Source parameters of the Sierra Madre earthquake from regional and local body waves, Geophys. Res. Lett., 18 (11), 2015–2018.
4. Ely, G., T. H. Jordan, P. Small, P. J. Maechling (2010), A Vs30-derived Near-surface Seismic Velocity Model Abstract S51A-1907, presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec. http://earth.usc.edu/~gely/pub/Ely2010-AGU-Vs30-GTL.pdf
5. Hauksson, E. (2000), Crustal structure and seismicity distribution adjacent to the Pacific and North America plate boundary in southern California, J. Geophys. Res., 105 (B6), 13,875–13,903.
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14. McCulloh, T. H. (1960), Gravity variations and the geology of the Los Angeles basin of California, Tech. rep., U.S. Geol. Survey, Washington, D.C., Professional Paper 400-B.
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16. Plesch, A., P. Suess, J. Munster, J. H. Shaw, E. Hauksson, T. Tanimoto, and members of the USR Working Group (2007), A new velocity model for southern California: CVM-H 5.0, in 2007 Southern California Earthquake Center Annual Meeting, Proceedings and Abstracts, vol. 17, p. 159.
17. Plesch, A., J. H. Shaw, E. Hauksson, and T. Tanimoto (2008), SCEC Community Velocity Model (CVM-H 5.5), in 2008 Southern California Earthquake Center Annual Meeting, Proceedings and Abstracts, vol. 18, p. 142.
18. Plesch, A., C. Tape, J. H. Shaw, and members of the USR working group (2009), CVM-H 6.0: Inversion integration, the San Joaquin Valley and other advances in the community velocity model, in 2009 Southern California Earthquake Center Annual Meeting, Proceedings and Abstracts, vol. 19, pp. 260–261. Prindle, K., and T. Tanimoto (2006), Teleseismic surface wave study for S-wave velocity structure under an array: Southern California, Geophys. J. Int., 166, 601–621.
19. Shaw, J. H., A. Plesch, M. P. Süss, and the SCEC USE Focus Area Group (2004), Progress toward a Unified Structural Representation, in 2004 Southern California Earthquake Center Annual Meeting, Proceedings and Abstracts, vol. 14, pp. 61–62.
20. Stidham, C., M. P. Suess, J. Shaw, D. Komatitsch, and J. Tromp (2001a), 3D velocity and density model of the LA basin and spectral element method earthquake simulations, in 2001 Southern California Earthquake Center Annual Meeting, Proceedings and Abstracts, vol. 11, p. 113.
21. Stidham, C., M. P. Süss, and J. H. Shaw (2001b), 3D density and velocity model of the Los Angeles basin, in Geol. Soc. Am. 2001 Annual Meeting Abstracts, vol. 33, Geol. Soc. Am., Denver, Colo., USA.
22. Suess, M. P., J. H. Shaw, P. Lovely, J. Mueller, and A. Plesch (2005), The new SCEC Community Velocity Model (CVM-H 2.0), in 2005 Southern California Earthquake Center Annual Meeting, Proceedings and Abstracts, vol. 15, p. 189.
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Miscellaneous Technical Notes

This section contains notes on previous versions of the CVM-H model. Note that the information here does not necessarily apply to the current model.

Log file from 6/2007 onward:

• 09/2010 AP: ???
• 01/2010 AP: ???
• 10/2009 AP: minor update of Moho surface in CM, corresponding update to changed cells, truncated border by one cell in LR, fixed VP/VS in interpolation area
• 09/2009 AP: replaced LR and HR data files with Tape et al. (2009) m16 model as background, replaced Moho data with update, changed tagging
• 06/2009 AP: returned GTL cells in Salton trough to original CVM-H values, higher coordinate output precision
• 03/2009 AP: changed density scaling to Nafe–Drake (Brocher , 2005)
• 09/2008 AP: fixed VS in buffer zone, used model VP/VS, not interpolated VS, in core zone to be consistent with VP there
• 08/2008 AP: enlarged area to fit TeraShake box, added model VS in all voxets, no tt file creation
• 01/2008 AP: replaced striped artifacts offshore San Diego with depth-basin depth-seafloor calibrated model data
• 11/2007 AP: clarified geodetic datum with P. Suess
• 10/2007 AP: added VS voxet for lower crust/mantle, switched to Brocher (2005) VS in LR/HR, truncated min. VP at 121 m/s, made HR consistent with LR for nodata points.
• 9/2007 AP: updated lower crustal/mantle voxet to include Socal background VP
• 9/2007 AP: added lower crustal/mantle voxet, elevation voxets; updated background tomographic model
• 6/2007 AP: modified to be consistent with direct query of voxet in gocad, provide cell center

Additional notes:

• This program originated as a code designed for SCEC-IT to demonstrate the capability of a final interface for the HUSCV-model as described by Süss and Shaw (2003). The code is now available to the community as a simple tool to extract data from the HUSCV-model. In this new version also the High Resolution velocity volume is supported by the code. The Harvard University Southern California Velocity Model (HUSCV 1.0) describes the seismic P-wave velocity structure in the Los Angeles basin and surrounding areas. The model is defined by gridded volumes with higher and lower resolutions, as well as two surfaces used to define the volume of sediments (the top pre-Cretaceous basement and topography/bathymetry). A water-layer with a VP velocity of 1480 m/s is included. No VS is defined for water, and density is 1000 kg/m3.

• The model was designed in a UTM Zone-11 projection with the following coordinates, for the lower resolution model and lower crustal/mantle model:

Origin(SW) : 131000 3431000 (120d51’43.301’’W 30d57’23.387’’N)
NE-Corner : 828000 4058000 (113d19’58.583’’W 36d36’46.622’’N)

With grid resolutions of:

1000m x 1000m x 100m (low res.)
670 x 400 x 200 grid cells
and
10000m x 10000m x 1000m (mantle)
71 x 64 x 186 grid cells

For the high resolution model:

Origin(NW) : 371053.25 3774000 (-119.322991 / 33.013591)
NE-Corner : 417052.25 3774000 (-117.257011 / 33.034954)
SW-Corner : 371053.25 3725250 (-119.371155 / 34.770882)

With a grid resolution of:

250m x 250m x 100m
185 x 196 x 100 grid cells

• The velocity volumes are stored in the GoCAD voxet format.

• The program accepts geographic coordinates and UTM zone 11 (NAD27) coordinates. Coordinate transformation is performed by GCTPC2.0, a free projection library by the USGS. Sources for the library are included.

• Vs is calculated from VP using the “mudline” relation and “Brocher’s regression line” (Brocher , 2005):

Vs = (Vp − 1360)/1.16 .
For Vp < 1500 m/s, Vs is fixed at 121 m/s which corresponds to Vp = 1500 m/s.

CVM-H 5.1 and earlier versions used this relation:

Vp/Vs varies linearly from 1.732 in the deepest part of the basin (Poisson’s ratio of 0.25 at a depth of 8.5 km) to 2.0 in the shallow sediments near the surface (Poisson’s ratio of 0.3 at the surface).

The overall effect of the switch to Brocher (2005) relations are higher Vs.

• CVM-H contains a geotechnical layer (GTL) that describes the velocity structure in the shallow subsurface, where low shear wave speeds, in particular, can have a significant impact on strong ground motions. The GTL velocity values (both VP and VS) and density are derived from the Vs30 map and algorithm described in Ely (2010)

• Extrapolation.
  • vx60b and later: The models are extrapolated from their data limits to the model boundaries.
  • Up to vx60: Overall the models (tomography and basins) are embedded into the SoCal 1D velocity model provided by Dreger and Helmberger (1991). Beneath the lowest layer of the 1D model at 35 km depth, the background Vp and Vs is simply kept constant at the velocity of the lowest layer, e.g., 7800 m/s for Vp and 4500 m/s for Vs. The boundaries between areas defined by tomography and the 1D model are smoothed.

• Mantle data were provided by Toshiro Tanimoto (personal communication) and are derived from waveform matching of teleseismic surface waves (Prindle and Tanimoto, 2006).

• We adopt the Nafe–Drake scaling relationship to compute density from Vp (Ludwig et al., 1970; Brocher , 2005):

rho = 1.6612*Vp − 0.4721*(Vp)^2 + 0.0671*(Vp)^3 − 0.0043*(Vp)^4 + 0.000106*(Vp)^5,

where rho is in g/cm3 and VP is in km/s.

In CVM-H verions 5.6 and prior we used well-log calibrated density scaling defined by (McCulloh, 1960; Stidham et al., 2001b)

rho = Vp/3 + 1280,

where rho is in kg/m3; we also impose a water-level minimum of 2000 kg/m3.

• No specific shear quality factor is predicted by the model. A Qu of 90 has been used in the sediments by Komatitsch et al. (2004).