Vs30 Info

Vs30

VS30 is defined as the average seismic shear-wave velocity from the surface to a depth of 30 meters. Vs30 has found wide-spread use as a parameter to characterize site response for simplified earthquake resistant design as implemented in building codes worldwide.

UCVM Vs30 Values

UCVM provides two sources of Vs30 information, and these two sources of Vs30 may not agree. (1) The UCVM Map-based Vs30 information is stored in a UCVM etree. This etree is defined for a region larger than the state of California, and it is created when the UCVM software release is prepared. A seperate etree is created to cover other regions such as the Utah region, where UCVM has registered velocity models. (2) UCVM can also calculate Model-based Vs30 values using the material properties from the seismic velocity models itself.

Map-Based Vs30

UCVM software framework contains a number of datasets that are used in certain UCVM function. These datasets include (1) a digital elevation model, (2) a bathymetry model, and (3) Vs30 data. These datasets are defined for the full UCVM coverage region. The elevation and bathymetry data are used to support query by elevation and query by depth functions in UCVM. The Vs30 data is used in the Ely/Jordan GTL calculation.

The DEM and bathmetry sources are listed in the primary UCVM reference paper. The Vs30 data is based on two sources. Within California, the UCVM map-based Vs30 data is based on a Wills CGS Vs30 map. The current version of the Vs30 data used is Wills 2017 map, a reference is available in the UCVM release notes, and will be added below. Earlier versions of UCVM used earlier versions of the Wills map.

Outside of California, notably nothern Mexico, the UCVM map-based Vs30 data is based on the DEM model (noted above) and a Wald topography relationship, that converts topograpy information into estimated Vs30 values. This Wald method is described in the Wald et al paper, but the basic idea is that regions with steep slopes have high Vs30s, and flat regions have lower Vs30 values.

As noted above, the UCVM Map-based Vs30 values are used to add the Ely/Jordan GTL to velocity models. But please note, the Vs30 values are not derived from the seismic velocity model themselves. The Map-based Vs30 data is defined externally.

1. Map-based Vs30 values Map-based Vs30 values are returned as part of material properties returned by a standard ucvm_query. The Vs30 values returned are

The basic query format is: ucvm_query [-m models] [-f config] < file.in

Where file.in contains "long lat depth" lines, with long and lat in decimal degrees and depth in meters, like these:

  -118.0 34.0 0
  -118.0 34.0 100
  -118.0 34.0 1000

The ucvm_query output format is:

  lon lat Z surf vs30 crustal cr_vp cr_vs cr_rho gtl gtl_vp gtl_vs gtl_rho cmb_algo cmb_vp cmb_vs

The UCVM map-based Vs30 value is returned in column 4.

Model-based Vs30

In some cases, users want to calculate Vs30 from seismic velocity models registered into UCVM. UCVM includes two C language programs that will sample the top 30 meters of a seismic velocity model, and calculate the Vs30 from the model. The two available routines include vs30_query.c and vs30_query_mpi.c. The serial and MPI versions of this program implements the same algorithm, but the MPI version runs a parallel job for cases in which vs30 is calculated for many points.

vs30_query.c

  Usage: vs30_query [-h] [-m models] [-f config] [-i inter]
    -h This help message
    -f Configuration file. Default is ./ucvm.conf
    -i Interval between query points along z-axis (m, default is 1)
    -m Comma delimited list of crustal/GTL models to query in order

Comparing Map-Based Vs30 and Model-Based Vs30 Values

Below, we use a selected number of southern Californ points to show results from these two queries.

cvms4 model

[ucvm@0884cbf3a2e2 target]$ ucvm_query -f /app/ucvm/conf/ucvm.conf -m cvms < querypts.txt
Using Geo Depth coordinates as default mode.
 -118.4810    34.3120    100.000    386.051    397.973       cvms   2185.167    989.497   2210.038       none      0.000      0.000      0.000      crust   2185.167    989.497   2210.038
 -118.5000    34.5000    100.000    573.044    527.718       cvms   2804.750    905.521   2307.870       none      0.000      0.000      0.000      crust   2804.750    905.521   2307.870
 -117.5000    33.5500    100.000    381.905    518.900       cvms   5132.648   2826.527   2675.445       none      0.000      0.000      0.000      crust   5132.648   2826.527   2675.445
 -117.5000    35.5000    100.000    721.905    394.017       cvms   5396.041   3331.242   2717.035       none      0.000      0.000      0.000      crust   5396.041   3331.242   2717.035
 -116.5000    34.4000    100.000    791.036    293.500       cvms   5411.267   3029.934   2719.439       none      0.000      0.000      0.000      crust   5411.267   3029.934   2719.439

[ucvm@0884cbf3a2e2 target]$ vs30_query -f /app/ucvm/conf/ucvm.conf -m cvms < vs30pts.txt
 -118.4810    34.3120    207.030
 -118.5000    34.5000    233.076
 -117.5000    33.5500   1437.217
 -117.5000    35.5000   1693.852
 -116.5000    34.4000   1540.644

cvm-h model

[ucvm@66975967506b target]$  ucvm_query -f /app/ucvm/conf/ucvm.conf -m cvmh < querypts.txt
Using Geo Depth coordinates as default mode.
 -118.4810    34.3120    100.000    386.051    397.973       cvmh   1946.508    505.610   1880.905       none      0.000      0.000      0.000      crust   1946.508    505.610   1880.905
 -118.5000    34.5000    100.000    573.044    527.718       cvmh   3994.835   2271.410   2392.620       none      0.000      0.000      0.000      crust   3994.835   2271.410   2392.620
 -117.5000    33.5500    100.000    381.905    518.900       cvmh   5087.308   2795.410   2548.363       none      0.000      0.000      0.000      crust   5087.308   2795.410   2548.363
 -117.5000    35.5000    100.000    721.905    394.017       cvmh   4855.963   2866.868   2513.006       none      0.000      0.000      0.000      crust   4855.963   2866.868   2513.006
 -116.5000    34.4000    100.000    791.036    293.500       cvmh   4730.289   2751.258   2494.663       none      0.000      0.000      0.000      crust   4730.289   2751.258   2494.663

[ucvm@66975967506b target]$ vs30_query -f /app/ucvm/conf/ucvm.conf -m cvmh < vs30pts.txt
 -118.4810    34.3120    165.039
 -118.5000    34.5000   1210.907
 -117.5000    33.5500   1424.097
 -117.5000    35.5000   1458.000
 -116.5000    34.4000   1407.656

Interpretation of Vs30 results

We interpret these results this way. For both seismic velocity models (cvms and cvmh), when we run the ucvm_query, ucvm_query returns the same vs30 values for a given lon/lat because these Vs30 values come from the UCVM Map-based Vs30 dataset. Also, although not shown, the Vs30 value returned by ucvm_query for a given lon/lat will be the same, regardless of the depth or elevation used in the query.

We see that the Vs30 for all the input points returned from the Map-based Vs30 dataset is less than 800m/s. These Vs30 values are based on the Wills map. However, the model based Vs30 values returned from CVM-S4 and CVM-H models are quite high for several points, in several cases they approach 1500m/s. This high model-based Vs30 values reflects the high near surface Vs values defined for background regions (non-basin regions) by these models.

References

• DEM and Bathmetry Reference - The DEM is synthesized from the U.S. Geological Survey (USGS) National Elevation Dataset (Gesch et al., 2002; Gesch, 2007) and the ETOPO1 Global Relief Model (Amante and Eakins, 2009).

1. Gesch, D., Oimoen, M., Greenlee, S., Nelson, C., Steuck, M., Tyler, D., 2002.The national elevation dataset. Photogrammetric Engineering and Remote Sensing 68, 5–11.
2. Gesch, D.B., 2007. The national elevation dataset, in: Maune, D. (Ed.), Digital Elevation Model Technologies and Applications: The DEM Users Manual, 2nd Edition. American Society for Photogrammetry and Remote Sensing, Bethesda, Maryland, pp. 99–118.
3. Amante, C., Eakins, B., 2009. ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis. noaa technical memorandum nesdis ngdc-24 ed. National Geophysical Data Center, NOAA. doi:10.7289/V5C8276M. [last accessed, November 2014].

• Ely Jordan GTL Reference

1. Ely, G.P., Jordan, T.H., Small, P., Maechling, P.J., 2010. A Vs30-derived near-surface seismic velocity model, in: Abstr. AGU Fall Meet., San Francisco, California, December 13–17.

• Thompson California Vs30 Model

1. Thompson, E.M. (2018), An Updated Vs30 Map for California with Geologic and Topographic Constraints (ver. 2.0, July 2022): U.S. Geological Survey data release, doi:10.5066/F7JQ108S.

• Wills Map Reference Earlier version of UCVM used, before UCVM v22.4 used the Wills Vs30 map. References for that model are given below:

1. Wills, C.J., Clahan, K.B., 2006. Developing a map of geologically defined site-condition categories for California. Bull. Seismol. Soc. Am. 96, 1483–1501. doi:10.1785/0120050179.
2. https://www.conservation.ca.gov/cgs/Documents/Program-SMIP/Reports/Petralogix 2017 - CSMIP Report.pdf

• Wald Topography Relation Reference

1. Wald, D.J., Allen, T.I., 2007. Topographic slope as a proxy for seismic site conditions and amplification. Bull. Seismol. Soc. Am. 97, 1379–1395. doi:10.1785/0120060267.