Correlation between Strain Rate and Seismicity and Its Implication for Earthquake Rupture Potential in California and Nevada

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

Submitted August 14, 2016, SCEC Contribution #6825, 2016 SCEC Annual Meeting Poster #307

Seismicity and strain-rate patterns indicate a region of increased hazard for large earthquakes across a broad region of high strain rates found mostly in California and western Nevada. These results are based on over three decades of GPS measurements and an earthquake catalog that spans the past century. From the geodetic data we develop strain-rate maps and correlate these with seismicity data. These correlations allow us to identify patterns of loading and unloading. Patterns of activity change with time, evolving through a (1) accumulation phase, (2) localization phase, and (3) rupture phase that have been observed in rock mechanics studies and dynamic simulations of fault development over many earthquake cycles. Following the approach of Helmstetter et al. (2007) and Shen et al. (2007), we classify strain rates as high or low and correlate these levels with changes in regional seismicity. We found that many of the moderate to large (M≥6.5) earthquakes are collocated with the regions of highest secular strain rates (e.g., the San Andreas fault system) whereas the smaller earthquakes are often spread out across regions of both high and low strain. For earthquakes with magnitude above M4.0 (completeness level since 1933), we identify clear spatial and temporal changes. For example, from 1933 to the mid 1990’s smaller magnitude seismicity occurred in both high and low strain rate regions (accumulation phase). From the mid 1990’s to 2013 this pattern changed and seismicity was more concentrated within the high strain rate areas (localization phase). The large-scale spatial and temporal changes in seismicity pattern may be consistent with future increased activity along faults in the active strain region and weaker activity in the surrounding areas. This pattern is similar to the precursory earthquake model defined as the Mogi doughnut (Mogi, 1969). This increased rate of earthquakes in high strain rate areas and decreased rate of earthquakes in low strain rate areas has many implications for future earthquakes in California and Nevada.

Key Words
Strain rate, Seismicity

Zeng, Y., Petersen, M. D., & Shen, Z. (2016, 08). Correlation between Strain Rate and Seismicity and Its Implication for Earthquake Rupture Potential in California and Nevada. Poster Presentation at 2016 SCEC Annual Meeting.

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