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[SCG40-39] Large and small earthquakes can have similar seismic wave onsets of the San Andreas fault in Northern California
Keywords:Seismology, Earthquake Source Physics
Whether earthquakes of different sizes start in the same way and whether the growth process of the rupture of a large earthquake is predictable are fundamental questions in earthquake source physics, with practical implications for earthquake early warning (EEW) systems and probabilistic forecasting. Recent studies have shed light that the onsets of seismic waves from small and large earthquakes have similar characteristics in the Tohoku–Hokkaido subduction zone, Japan. In addition to Japan, California is also a natural earthquake laboratory with abundant seismicity and a nearly century-old high-quality seismic network. The majority of earthquakes in California occur inland and the spatial coverage of stations is dense and good, which helps to analyze the initial waveforms of large and small strike-slip earthquakes.
We conducted a systematic comparison of high-sensitivity seismic waveforms between 81 large (M >= 4.0) and small (M <= 3.0) earthquake pairs, including approximately 24,000 events over 20 years. We found 39 pairs with extremely similar seismic wave onsets and 1075 pairs with very similar onsets, suggesting that the hypocenters of two events were within 100 meters. Extremely high similarity is observed for pairs of earthquakes separated by a long period of over 20 years. Furthermore, examining the week and day before and after a large earthquake, we found that more than 80% of the small earthquakes occurred before the large earthquake. This frequent occurrence of very similar seismic wave onsets between different-sized earthquakes suggests that repeated cascading rupture processes in a widespread hierarchical structure not only along the subduction plate interface but also within the inland strike-slip fault zone, and that observationally negligible differences in the initial conditions and dynamics of an earthquake can alter its final magnitude.
We conducted a systematic comparison of high-sensitivity seismic waveforms between 81 large (M >= 4.0) and small (M <= 3.0) earthquake pairs, including approximately 24,000 events over 20 years. We found 39 pairs with extremely similar seismic wave onsets and 1075 pairs with very similar onsets, suggesting that the hypocenters of two events were within 100 meters. Extremely high similarity is observed for pairs of earthquakes separated by a long period of over 20 years. Furthermore, examining the week and day before and after a large earthquake, we found that more than 80% of the small earthquakes occurred before the large earthquake. This frequent occurrence of very similar seismic wave onsets between different-sized earthquakes suggests that repeated cascading rupture processes in a widespread hierarchical structure not only along the subduction plate interface but also within the inland strike-slip fault zone, and that observationally negligible differences in the initial conditions and dynamics of an earthquake can alter its final magnitude.