The accumulation of interseismic strain along the Hayward fault

Project Summary The Hayward fault is a major strand of the San Andreas fault system accommodating nearly 25% of the deformation across the plate boundary. The fault exhibits a diversity of slip behaviors including large coseismic rupture, frequent micro-seismicity, and aseismic creep. Surface creep is observed along the entire length of the fault in the range of 3-9 mm/yr and the rates appear to be consistent over the past several decades. The geologic slip rate on the fault is estimated at ~9 mm/yr. The difference between the geologic and contemporary creep rates suggests that a slip deficit exists and that the accumulated strain will presumably be released in a future earthquake.

The most significant earthquake to occur on the Hayward fault in historic times is a M6.8 event in 1868. The event nucleated on the southern portion of the fault and ruptured as far north as Berkeley. No earthquake greater than M4.5 has been observed on the Hayward fault since seismic instrumentation was installed in the early twentieth century. However, paleoseismic data suggest that several large earthquakes have produced surface rupture on both the northern and southern portions of the Hayward fault. The lack of significant seismic moment release on the northern segment of the fault within recorded history has raised concern that this segment may be due for a large earthquake. The Working Group on California Earthquake Probabilities [1999] identified the Hayward fault as a significant potential threat to the loss life and property in California. The hazard associated with such an event is significant because the Hayward fault passes beneath several urban communities in the San Francisco Bay Area.

We use Interferometric Synthetic Aperture Radar (InSAR) and the Global Positioning System (GPS) to monitor interseismic surface deformation along the Hayward Fault. Our objective is to address the seismic hazard associated with the fault by modeling the aseismic slip-rate distribution at depth. Inversions reveal that the fault is characterized by both locked and creeping patches.

Tools InSAR, GPS, surface creep observations, microseismicity, forward and inverse elastic boundary-element modeling

Geographic Location San Francisco Bay Area

Project Duration Ongoing

Group Members Involved David Schmidt, Roland Bürgmann, Robert Nadeau, Matt d'Alessio

More Information < Science Paper on the northern Hayward Fault >