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.
- 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.
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.
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
