Geologic Block Model
Bob Jachens, Russ Graymer, Carl Wentworth, Bob Simpson (USGS Menlo Park)
Introduction
The detailed and extended 3-D geologic maps of Central California, centered on the San Francisco Bay region, were made using the Dynamic Graphics EarthVision(TM) software. This program builds 3-D models starting with a hierarchy of fault surfaces that divide the volume of interest into Fault Blocks. These fault blocks are further subdivided by Zone Surfaces that most commonly represent contacts between rock units within a fault block.
The detailed model is surrounded by the extended model. In the extended model details away from the San Andreas Fault are grossly generalized in places.
The application of immediate interest is the construction of a 3-D velocity model for the San Francisco Bay region that could be used to explore the propagation of seismic waves generated by the 1989 Loma Prieta earthquake and the 1906 San Francisco earthquake. To this end, the various rock units in the model were assigned physical properties including seismic velocities based on rock type and depth. See the velocity model page for more information.
Domain
The detailed and regional velocity models are rectangular volumes in a Transverse Mercator (TM) projection with the following parameters:
- Scale factor for central meridian: 0.99960000
- Longitude of central meridian: -123.00000
- Latitude of origin: 35.00000
- False easting: 0.00000
- False northing: 0.00000
- Azimuths of sides: 53.638, 323.638
Bounding boxes of the models
KML file with bounding boxes.
Coordinates are WGS84 longitude/latitude. Models extend from sea level or top of ground surface down to 45 km below sea level. The model includes the material properties of water for the Pacific Ocean.
| Detailed | Extended | |||
|---|---|---|---|---|
| Approx. Dimensions | 290km | 140km | 650km | 330km |
| SE corner (lon,lat) | -120.644051 | 37.050062 | -118.944514 | 36.702176 |
| SW corner (lon,lat) | -121.922036 | 36.320331 | -121.930857 | 35.009018 |
| NW corner (lon,lat) | -123.858493 | 38.424179 | -126.353173 | 39.680558 |
| NE corner (lon,lat) | -122.562365 | 39.174505 | -123.273199 | 41.484869 |
Bounding boxes of detailed and extended velocity model regions. Gray lines denote major roads and white lines delineate major faults.
Bounding boxes of detailed and extended velocity model regions. Green lines show county boundaries and white lines delineate major faults.
Figures
Documentation
- Detailed Model
- Extended (Regional) Model
