Registering CS173 into UCVM

This page details the steps involved in delivering a velocity mesh to John Shaw and Andreas Plesch, so that the Harvard group's Central California basins can be integrated into a velocity model, which can be fed back into UCVM and used for CyberShake.

Velocity mesh region

The region we will extract is 560 km x 1218 km x 50.4 km (as measured in the WGS84 coordinate system), with 55 degree rotation counter-clockwise. The mesh will have 175m grid point spacing. The corner points are approximately

W: (37.30489, -127.62831)
N: (41.59023, -124.28641)
E: (35.17113, -112.97233)
S: (31.19740, -116.67400)

Mesh extraction process

To deliver the mesh, we will follow the following procedure:

1. CyberShake processing tools will be used to construct a mesh, with the location of each point defined as km offsets from the center of the mesh at the surface.
   1. The mesh will evenly discretize the region in x,y,z, but due to the rotation, this is not North,South. The resolution will be 175km as measured in the UTM coordinate system.
   2. A number of CyberShake codes, originally from RWG, are involved in this step. These codes use his great circle projection. These codes figure out the outer bounds of the mesh given the location of a site and fault surfaces. They use great circle will be a problem, and return a lat/lon of the mesh center.
   3. The codes used are in version control here: [1].
   4. Then we use the Proj 4 library to convert this center point to UTM Zone 11, which is the southern California UTM zone. While some of the mesh region extends north into UTM zone 10, we will use Zone 11 since the majority of our region of interest is in that zone. We'll do the remaining next steps in UTM.
2. The location of each mesh point will be redefined as a UTM easting and northing, by translating the center of the mesh from lat/lon to UTM coordinates in Zone 11 and then applying the offsets.
   1. The UTM mesh points will be written to a file, in fast x,y,z format, starting with all the mesh points are the surface, first changing x values, then y values, then moving down one the Z axis, and listing the next layer of points.
   2. This file in internal, and will not be part of the data sent to the USR group.
3. The Proj4 package will be used to convert the UTM coordinates at each point into a latitude and longitude value, to 5 decimal places.
   1. The proj4 coordinate system to coordinate system (cs2cs) conversion string used will be:
4. This list of points will be used to query UCVM and create a velocity mesh. Additionally, we will query the USGS topo model in UCVM to obtain the surface elevation at each point.
5. Smoothing will be applied to the velocity mesh for all points within 10 km of an interface, by averaging the neighbors for 10km in the N, S, E, and W directions.
6. Scott will deliver three meshes (one each with Vp, Vs, and rho) in fast y, x, z binary format with 4-byte floats, a list of the elevation of each surface point, a list of the coordinates of each surface point in lat/lon and UTM zone 11, and MD5 sums for all products.

Model Coverage Regions

The mesh is depicted in white; the region covered by CCA-06 is in blue, by CVM-S4.26 in red, and by USGS Bay Area in green.

Related Entries

• [USR]
• [CVM-S]
• [CVM-H]
• [UCVM]