Southern Hayward Fault Earthquake Simulation

The following is a finite difference simulation of a Mw6.7 earthquake located on the southern Hayward Fault. The red lines show the locations of major Bay Area faults. The earthquake initiates at the southern end and ruptures toward the north.. The color shows the amplitude of waves in meters per second. Blues indicate negative amplitudes and the reds indicate positive amplitudes. The asymmetry of the wavefield is due to three-dimensional geologic structure, which has been incorporated in this simulation. Note that the largest amplitudes occur along the portion of the Hayward Fault where the earthquake rupture takes place and in the San Pablo Bay where sedimentary rocks in the model amplify the ground motions.  The movie shows 48 seconds of the wavefield. Even after 48 seconds the ground motions in the San Pablo Bay remain quite large. In comparison the length of time for the fault to rupture was  11 seconds. To view the movie again push the reload button.

The simulation may be used to produce a map of peak horizontal strong ground shaking. The following map shows the distribution of peak horizontal ground velocity in units of meters per second. The location of UC Berkeley is shown by the arrow. Several stations of the Berkeley Digital Seismic Network (BDSN) operated by the Berkeley Seismological Laboratory are shown as inverted triangles. Because of the northward direction of rupture there is tremendous focusing of waves which is evident by the very large near fault ground motions exceeding 1 meter per second along the northern part of fault. The ground motions decay rapidly north of the end of the fault, but on the Berkeley Campus the estimated ground motions are on the order of 0.60 meters per second. Accelerations of between 20 to 30% of the acceleration of gravity are predicted for this particular earthquake rupture scenario.

Seismograms simulated at the BDSN sites in Stawberry Canyon, at Haviland Hall and at the Richmond Field station. The Richmond Field Station site shows high frequency ground motions and the simulated acceleration is greater than what is simulated at the two campus sites, even though it is nearly 15 km further from the earthquake. This amplification is due to the relatively softer sedimentary materials beneath the site.