Vs30 Info
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 provides two sources of Vs30 information, and these two sources of Vs30 may not agree. The UCVM Map-based Vs30 information is stored in UCVM etree. This etree is created when the UCVM software release is prepared. The Model-based Vs30 values are calculated using the material properties from the seismic velocity models itself.
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 defines 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 version of the Vs30 data used is Wills 2017 map. Earlier version of UCVM used earlier version of the Wills map.
Out side of California, notably nothern Mexico, the UCVM map-based Vs30 data is based on the DEM model (noted above) and a Wald topography relationship, the converts topograpy information into estimated Vs30 values. The method is described in the Wald et al paper, but the basic idea is 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.
- 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.
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 avialable routines include vs30_query.c and vs30_query_mpi.c. The MPI version of this program implements the same algorithm, but it runs a parallel job for cases in which vs30 is calculated for many points.
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
Using a selected number of southern Californ points to show results from these two queries.
[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
[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
We interpret these results this way. In both cases, when we run the ucvm_query, we get the same vs30 values because these values come from the UCVM Map-based Vs30 dataset. Also, although not show, the Vs30 value for a given lon/lat regardless of the depth or elevation.
In the CVM-S4 model, we see see that the Vs30 given from the Map-based Vs30 dataset is maximum less than 800m/s. This is based on the Wills map. However, the model based Vs30 values for CVM-S4 are quite high, which reflects the high near surface Vs values in CVM-S4 in background regions.
