Precise relative stress drops

Bruce E. Shaw, William L. Ellsworth, Nana Yoshimitsu, Yihe Huang, & Gregory C. Beroza

Submitted August 10, 2016, SCEC Contribution #6613, 2016 SCEC Annual Meeting Poster #193

Earthquake stress drops are generally observed to be independent of seismic moment but vary by three orders of magnitude or more for any moment value. If correct, this predicts far greater variability in high-frequency ground motions than is observed. Because stress drop depends on the cube of the corner frequency, the question has been raised if stress drop variability is a source effect or measurement error. To address this problem, we present a new method that gives precise relative stress drop values for pairs and populations of earthquakes. Based on spectral ratios for nearby events, this approach uses the low- and high-frequency asymptotic values of spectral ratios and avoids the need to estimate corner frequencies. By avoiding the spectral shape near the corner frequency and attendant source complexity, the method produces precise stress drop ratios for pairs of events. The method is only weakly dependent on the assumed high-frequency asymptotic behavior of the spectrum. Closure rules for connected sets of ratios enable quantitative measures of method uncertainties and extension of the measurements from pairs to populations of earthquakes. Validation results comparing stress drop ratios with more traditional corner frequency based methods will be presented. Further results showing underlying intrinsic variability in stress drops, a question relevant to ground motion hazard estimates, will be presented.

Key Words
stress drops, hazard, uncertainties

Shaw, B. E., Ellsworth, W. L., Yoshimitsu, N., Huang, Y., & Beroza, G. C. (2016, 08). Precise relative stress drops. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups