Spatiotemporal Evolution Pattern of Seismicity across California-Nevada and Its Implication for Future Large Earthquakes

Yuehua Zeng, Mark D. Petersen, & Zheng-Kang Shen

Submitted August 6, 2019, SCEC Contribution #9345, 2019 SCEC Annual Meeting Talk on Tue 1030

Rock mechanics studies and dynamic earthquake simulations show patterns of seismicity evolving with time through (1) accumulation phase, (2) localization phase, and (3) rupture phase. We observe a similar pattern of changes in seismicity during the past century across California and Nevada. To quantify these changes, we correlate GPS strain rates with seismicity. We find small and large earthquakes display different modes of behavior with time. While large earthquakes (M>6.5) were located within regions of highest strain rates, mostly along the San Andreas and other major California faults, small earthquakes (M≥4) showed strong spatiotemporal variation. For example, from 1933 to the late 1980s, earthquakes (M≥4) were more diffused and broadly distributed in both high and low strain rate regions (accumulation phase), particularly across the northern Walker Lane and further into a broad central and western Nevada region because of the stress shadows from the 1906 San Francisco earthquake. There were also significant increases in seismic activity along the central California creeping section to reduce the slip deficit from the 1906 and 1857 earthquakes that ruptured the northern and southern San Andreas segments of the section, respectively. From the late 1980s to present, seismicity has become more concentrated within the current high strain rate areas along the major fault strands (localization phase). During the same time period, the rate of large events (M>6.5) also increased significantly in the high strain rate areas, including the recent M7.1 Ridgecrest earthquake occurred in the East California Shear Zone. The strong correlation between current strain rate and the later period of seismicity suggests that the strain rate has evolved with time. We conclude that as the stress field has evolved out of the stress shadow of the last major earthquake, and seismicity and strain refocused on the major fault systems, California may have entered into a localization phase of its earthquake cycle which suggests increased seismic activity for large earthquakes.

Key Words
Seismicity, Strain rate, Spatiotemporal Evolution

Citation
Zeng, Y., Petersen, M. D., & Shen, Z. (2019, 08). Spatiotemporal Evolution Pattern of Seismicity across California-Nevada and Its Implication for Future Large Earthquakes. Oral Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)