UC Santa Cruz

©2014. The Authors. Large dynamic strains carried by seismic waves are known to trigger seismicity far from their source region. It is unknown, however, whether surface waves trigger only small earthquakes, or whether they can also trigger large earthquakes. To partially address this question, we evaluate whether current data can distinguish between the magnitude distribution of triggered and untriggered small earthquakes. We use a mixing model approach in which total seismicity is decomposed into two classes: "triggered" events initiated or advanced by far-field dynamic strains and "untriggered" spontaneous events consisting of everything else. The b-value of a mixed data set, bMIX, is decomposed into a weighted sum of b-values of its constituent components, bT and bU. We utilize the previously observed relationship between triggering rate and dynamic strain amplitude to identify the fraction of triggered events in populations of earthquakes and then invert for bT. For Californian seismicity, data are consistent with a single-parameter Gutenberg-Richter hypothesis governing the magnitudes of both triggered and untriggered earthquakes.