Earthquake Insights From the Best Recorded Volcanic Caldera Collapse In History

Two outstanding problems in seismology are predicting the recurrence times of earthquakes and understanding the physical processes that immediately precede them. While geodetic measurements record elastic strain accumulation, most faults have recurrence intervals far longer than available measurements. Foreshocks provide the principal observations of processes prior to mainshocks, yet variability between sequences has limited generalizations of pre-failure behavior. In 2018 Kilauea volcano erupted over 1 km^3 of basalt, causing the volcano summit to collapse up to 500 meters. The eruption was recorded by near-field seismic, geodetic, and remote sensing platforms making it by far the best instrumented caldera forming eruption in history. Caldera formation was not continuous, but occurred in discrete, near daily collapse events generating a sequence of repeating M 5 earthquakes. We show that M 5 recurrence intervals are well predicted by stress histories inferred from near-field deformation measurements. We further document a critical phase, minutes before mainshocks, where foreshocks grew larger, and the seismic moment rate surged by a factor of ~ 5. As the average stress increased ruptures were more likely to overcome geometric barriers and grow larger, leading to characteristic mainshocks. We argue that stress heterogeneity influences both earthquake nucleation and growth, including on hazardous tectonic faults.

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