Modeling Fault Creep on the Hayward Fault and Implications of Seismicity for Defining Patterns of Fault Creep

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Conference Proceeding

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The Hayward fault is considered to be one of the primary hazards in the San Francisco Bay region. Although it is documented to undergo significant creep, with some creeping patches accommodating 50% or more of the long-term fault displacement, the fault also experiences moderate to large earthquakes (most recent M ~6.8 in 1868). Under the assumption that the seismic hazard associated with a fault is related to the distribution and amount of slip deficit accumulated during interseismic periods. Therefore mapping creep patterns on a fault plane is an important component in the assessment of the seismic hazard. Combining observations of surface creep rate and the distribution of micro-seismicity, with modeling results derived from a visco-elastic finiteelement model driven by far field plate motions, we have analyzed the slip deficit that can be accumulated on the Hayward Fault. Our results show that the interaction of the fault with the surrounding lithosphere leads to a smooth transition of the creep rate from locked to fully creeping areas and implies significant slip deficit accumulation not only in fully locked zones but also in adjacent low friction areas. In order to link seismic potential to the rate at which moment accumulates on the fault plane, we need to understand the patterns and distribution of creep over time. As might be expected, the microseismicity observed on the fault produces only a negligible percentage of the seismic moment dissipated on the Hayward fault, whereas aseismic creep releases about 25% of the moment accumulating on the fault. The distribution of creep on the fault can change throughout the earthquake cycle, in particular after major seismic events. Although at present the post-seismic transients have mostly decayed, the pattern of accumulated moment is significantly different when these transients are included.

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Citation / Publisher Attribution

Modeling Fault Creep on the Hayward Fault and Implications of Seismicity for Defining Patterns of Fault Creep, in D. A. Ponce, R. Bürgmann, R. W. Graymer, J. J. Lienkaemper, D. E. Moore & D. P. Schwartz (Eds.), Proceedings of the Hayward Fault Workshop, Eastern San Francisco Bay Area, California, USGS, p. 13