Connecting long and short-range earthquake triggering with strain

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

Earthquake triggering provides a fundamental clue into earthquake nucleation. If an observational relationship could be established between seismicity rate changes and the triggering strain of an earthquake, then we would have a basic constraint on the nucleation process. Here we use a novel statistical approach and an abundance of modern data to measure the number of earthquakes triggered for both nearby and distant earthquakes. The preliminary results indicate that the intensity of triggering scales continuously as a function of dynamic strain as measured by seismic wave amplitude. The trend is consistent regardless of distance. However, some regions, like California, are more prone to triggering than others, like Japan. The lack of discernible crossover in triggering behavior at small distances implies that dynamic triggering is sufficient to explain local aftershocks. This result points the way to a new methodology for earthquake forecasting based on the amplitude of the observed seismic waves. This proposal presents a plan of study to test, analyze and apply these preliminary results. Specifically, we will: 1) Evaluate the robustness of the relationship between triggering rate and strain by: a) Varying the choices of parameters in the measurement scheme. b) Improving the proxies for dynamic and static strain by using observed seismograms corrected to depth and measured focal mechanisms. 2) Constrain the physics of earthquake triggering by: a) Determining whether immediate triggering or delayed triggering is a stronger signal using filtered waveforms and the distribution of the normalized inter-event times. b) Comparing the tendency to trigger across different tectonic regimes in New Zealand and globally. c) Comparing the results to standard models of earthquake triggering. 3) Apply the results to hazard mitigation by: a) Combining the interpolated ground velocity from an earthquake with the triggered rate function to predict triggered seismicity in the next hour.