Frequently Asked Questions

General

How can I get involved?

Contact Mary Lou Zoback (USGS Menlo Park).

Velocity Model

Where can I get the velocity model?

See the download section of the Velocity Model page.

What do DepthFreeSurf, FaultBlock, and Zone mean in the velocity model data?

These values allow one to calculate the material properties using the rules developed by Tom Brocher. DepthFreeSurf refers to the depth relative to topography or bathymetry (bottom of water column). FaultBlock and Zone refer to the fault block id and zone id in the geologic block model.

How do the different types of queries (MAXRES, FIXEDRES, AVGRES) work?

Beginning in version 0.2.0 (the current version is 0.2.2), the query routine has 3 different modes of operation, however, in each case it always does 1 point at a time. The difference is in what values are returned in the queries.

The MAXRES query will always return the values associated with the maximum resolution (smallest length scale) available in the Etree database for that particular point.

The FIXEDRES query will limit the resolution to be no greater (length scale will be no smaller than) a given value. The query routine uses an averaged value if the Etree database contains values at length scales smaller than the set resolution. For example, if you are using a finite-difference grid with a resolution of 200m, then setting the query type to FIXEDRES will the query routine will ignore data at resolutions of 25m, 50m, and 100m and will return the 200m average of these higher resolutions. This prevents aliasing (you won't get back values that apply to a 25m thick layer and apply then to an 200m thick layer).

The AVGRES query (name should probably be WAVERES) is similar to the FIXEDRES query, but instead of a fixed length scale, the query routine will start at the maximum resolution and compare the wavelength of the shear wave at a given period to the specified period and will work up to larger length scales until it finds a scale at which the wavelength of the shear wave is greater than the discretization size. This eliminates the need for a minimum Vs in the model in models that can adapt the grid size to the wavelength; you give it the minimum period and it will tell you the material properties at the scale of a shear wavelength.