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GMEG - Geophysics Unit of Menlo Park, CA- (GUMP)

 

Geophysics Unit of Menlo Park, CA (GUMP)

U.S. Geological Survey - Western Region - Geology and Geophysics

Watt Main

 

CV

3D Geologic Model of the Hayward-Calaveras Fault Junction

haycal_google

The Google Earth image above shows the mapped surface traces of the Hayward and Calaveras Faults (red lines) in the vicinity of the M5.4 Alum Rock Earthquake (yellow star).

Based on geologic, geophysical, and seismicity data we suggest that the Hayward and Calaveras Faults merge at a depth of ~5 km, forming a single through-going structure. We are currently creating a 3D geologic model of the Hayward-Calaveras junction, which will be used to investigate fault behavior. Data from the model will be utilized in both finite element modeling of fault stress and in 3D numerical ground motion simulations of rupture scenarios along the Hayward and Calaveras Faults.

haycal_mapview haycal_xsection
Above left: Map view of the 3D model area showing the Hayward and Calaveras Fault traces in red and the complex zone of surface faulting along the southern Hayward Fault in green. Notice that the earthquakes at depth (red crosses) do not line up with the surface traces, suggesting that the southern Hayward and Central Calaveras Faults meet at depth. Above right: A cross-section of the 3D model near the Alum Rock Earthquake (pink square-aftershocks represented by purple squares) showing how we have modeled the complexity of the junction at the surface the simplicity at depth.
haycal_3dflts
The image above shows a 3D view of the Hayward-Calaveras Fault junction as we have modeled it. These two faults converge at approximately 5 km depth, just north of the recent M5.4 Alum Rock Earthquake hypocenter.
3dgeology

The image above shows a preliminary 3D geologic model of the Hayward-Calaveras junction. Notice how the Great Valley rocks are thrust over the younger sediments of the Evergreen Basin, illustrating the deformation taking place where these two faults converge.

MORE TO COME SOON!

For additional information see the following publications:

Watt, J.T., Graymer, R.W., Simpson, R.W., Ponce, D.A., Jachens, R.C., Phelps, G.A., and Wentworth, C.M., 2007, A Three-dimensional geologic model of the Hayward-Calaveras Fault junction: Eos Trans. AGU, v. 88, no. 52, Fall Meet. Suppl.

Graymer, R.W., Simpson, R.W., Jachens, R.C., Ponce, D.A., Phelps, G.A., Watt, J.T., and Wentworth, C.M., 2007, Segmentation of the Calaveras-Hayward Fault System based on 3-D geometry and geology at large-earthquake depth: Eos Trans. AGU, v. 88, no. 52, Fall Meet. Suppl.

Graymer, R.W., Langenheim, V.E., Simpson, R.W., Jachens, R.C., and Ponce, D.A., 2007, Relatively simple through-going fault planes at large-earthquake depth may be concealed by the surface complexity of strike-slip faults, in Cunningham, W.D., and Mann, Paul, eds., Tectonics of Strike-Slip Restraining and Releasing Bends: Geological Society of London Special Publication, v. 290, p. 189-201. doi: 10.1144/SO290.5 0305-8719/07.

Ponce, D.A., Hildenbrand, T.G., and Jachens, R.C., 2003, Gravity and magnetic expression of the San Leandro gabbro with implications for the geometry and evolution of the Hayward fault zone, northern California: Bulletin of the Seismological Society of America, v. 93, no. 1, 11 p. PDF (13.4 Mb).

Ponce, D.A., Simpson, R.W., Graymer, R.W., and Jachens, R.C., 2004, Gravity, magnetic, and high-precision relocated seismicity profiles suggest a connection between the Hayward and Calaveras Faults, northern California: Geochemistry Geophysics Geosystems, v. 5, no. 7, 39 p. PDF (5.1 Mb).

Links:

Active Traces of the Hayward Fault
ShakeMaps for the 1868 Hayward Earthquake
Double-Difference Relocated Earthquakes along the Hayward and Calaveras Faults
Geometry and Evolution of the Hayward Fault

 

 

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