Constraining the velocity structure near the tremorogenic portion of the San Andreas Fault near Parkfield, CA using Ambient Noise Tomography

Rachel C. Lippoldt, Robert W. Porritt, & Charles G. Sammis

Published August 15, 2016, SCEC Contribution #6999, 2016 SCEC Annual Meeting Poster #253

The central section of the San Andreas Fault (SAF) displays a range of seismic phenomena including tectonic tremor, low frequency earthquakes (LFE), repeating micro-earthquakes (REQ), and aseismic creep. We investigate the seismic velocity structure associated with this section of the SAF using surface wave tomography from ambient seismic noise. A high-resolution model of shear velocities in the crust and upper mantle is derived from data recorded between 2003 and 2015 by the USArray, the Parkfield Hi-Resolution Seismic Network (HRSN), and other regional networks. Fault perpendicular sections show that the SAF is revealed by lateral contrasts in relative velocities to depths to 50 km. At depths between about 15 and 30 km, the deep extension of the SAF appears to be localized to within about 50 km. This localization is consistent with the hypothesis that LFEs are shear-slip events on a deep extension of the SAF. Fault parallel sections show that LFE and REQ locations occur within low velocity structures, suggesting that the presence of fluids, weaker minerals, or hydrous phase minerals may play an important role in the generation of slow slip phenomena. Such correlations between seismic waves speeds and seismicity can provide insight and constraints on the physical mechanics that produce LFEs and REQs.

Citation
Lippoldt, R. C., Porritt, R. W., & Sammis, C. G. (2016, 08). Constraining the velocity structure near the tremorogenic portion of the San Andreas Fault near Parkfield, CA using Ambient Noise Tomography . Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology