High-Resolution Imaging of Slow Earthquake Source Processes Resulting From the Cholame Dense Array Experiment

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

Despite over a decade of intense research, the processes governing Low Frequency Earthquakes (LFE), Non-Volcanic Tremor (NVT), and associated Slow-Slip Events (SSEs) remain enigmatic. Cholame, a densely instrumented segment of the San Andreas fault with one of the best LFE catalogs in the world, is a natural laboratory for studying slow-slip related processes. Cholame’s LFEs occur in 10-100 second-long bursts separated by several hours or more, are largely non-coeval with long-duration NVT, and exhibit migration speeds of tens of km/hour evidenced by successive activation of LFE families along-strike. The latter implies that LFEs may be driven by an underlying slow-slip event. However, due to the limited sensitivity of geodetic monitoring systems, and because LFEs are sparsely distributed along strike, the relation between SSE and LFE activity in Cholame is not well understood. To study LFEs and NVTs we deployed three dense (25-30 sensors, ~500 m aperture) arrays of 3C 5Hz Nodal seismometers < 20 km away from the fault. The arrays captured an unusually large 5-day-long period of significantly increased LFE activity that included families from Cholame to Parkfield. Here we present preliminary results from array- and network-based cross-correlation analysis of these data. Array analysis will be used to image propagation of tremor/LFE producing activity along the fault, and analyze spatiotemporal amplitude and coherency variations. The cross-correlation results will provide a more comprehensive LFE catalog, thus enhancing our resolution of repeating LFE sequences in space and time. These two complementary approaches will allow us to better understand what fraction of coherent energy emanating from the fault (which we interpret as fault slip) is made up of discrete LFEs helping to better constrain the physical processes giving rise to slow-slip related phenomena and the architecture of deep fault zones.

Presenting Author: Amanda M. Thomas

Authors