Ambient tectonic tremor in the San Jacinto Fault

Alexandra A. Hutchison, & Abhijit Ghosh

Submitted August 15, 2017, SCEC Contribution #7704, 2017 SCEC Annual Meeting Poster #067

Multiple, discrete instances of ambient tectonic tremor were detected in the Anza Seismic Gap section of the San Jacinto Fault (SJF) during June 2011 using both high-density arrays and a variety of network stations. These events were detected, located and verified by using multiple independent techniques including a multi-beam backprojection (MBBP) technique [Ghosh et al., 2009; Ghosh et al., 2012], an envelope cross correlation (ECC) method [Wech and Creager, 2008], frequency analyses, and visual inspection. Both MBBP and ECC methods using completely independent sets of seismic stations provided very similar locations. Uncertainty analyses were performed for both techniques using two different velocity models [Scott et al., 1994; Allam & Ben-Zion, 2012]. They also resulted in similar locations for the tremor events. Tremor location uncertainty in map view (horizontal uncertainty) is between 6 and 10 km. ECC method does not have depth resolution. Using a simple 2-D estimate of the SJF, we apply beam-backprojection and determine a depth range of 13-24km for these events, which lie beyond the locked zone, estimated at ~12 km and possibly at the edge of the seismogenic zone determined to end at ~17km [Fialko, 2006; Wdowinski, 2009], consistent with depth ranges expected for tremor due to mechanical properties of the fault at such depths. In light of recent studies that can be interpreted to suggest creep at depth [Lindsey et al., 2014; Jiang and Fialko, 2016; Meng and Peng, 2016] and geodetic findings that the Anza Gap has produced slow slip events [Inbal et al., 2016], we interpret these instances of tremor to be indicative of slow-slip at the base of locked and seismogenic zone in the SJF. [Hutchison & Ghosh, 2017, In Press].

Key Words
tremor, slow earthquakes, san jacinto fault

Citation
Hutchison, A. A., & Ghosh, A. (2017, 08). Ambient tectonic tremor in the San Jacinto Fault. Poster Presentation at 2017 SCEC Annual Meeting.


Related Projects & Working Groups
Seismology