Dynamic Triggering Seen Clearly: Utilizing Continuous Waveforms and High-Resolution Catalogs to Measure the Importance and Mechanisms of Dynamic Triggering

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Every time an earthquake occurs, seismic waves emanate from it and shake the ground. Thirty years ago it was discovered that these waves can trigger other earthquakes 100’s or even 1000’s of kilometers away from the first. This phenomenon is known as dynamic triggering and it is one of the few situations where a known, measurable, natural stress can be identified as the immediate cause of an earthquake. Dynamic triggering appears to be a common and expected consequence of large earthquakes, but it remains unclear what fraction of the world’s earthquakes are caused by dynamic triggering. Is dynamic triggering an important factor in determining when and where earthquakes happen or is it a mere curiosity? The primary goal of this project is to address this question using the large datasets now available due to recent advances in computation and instrumentation. The broader impacts of this proposal include collaboration with scientists at Kyoto University in Japan, support for a graduate student and a quantification of the hazard increase expected after earthquakes in the study. The capacity to study dynamic triggering has been limited by both the ability to accurately capture the triggering stresses and the ability to record the resultant earthquakes. Significant progress has been made in both areas recently. Measuring the triggering stresses can be improved by using the full waveforms of dense networks. Recent progress in catalog generation by template matching has resulted in catalogs that have increased by an order of magnitude and, in turn, increased the detectability of rate changes. Together, these data can provide a quantitative assessment of the importance of dynamic triggering. The same data can also be used for a secondary goal of assessing the predictions of proposed mechanisms of dynamic triggering. This project will (1) measuring triggering using waveforms and a modern catalog over a wide range of frequency and orientations, (2) measuring the time-dependence of the earthquake rate change, (3) measuring rate changes as a function of cumulative energy and evaluating non-earthquake sources of seismic waves and (4) interpreting triggered seismicity rates within the context of geodetic and hydrological measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.