Modeling the Occurrence of M similar to 5 Caldera Collapse-Related Earthquakes in Kilauea Volcano, Hawai'i

During the 2018 Kilauea eruption and caldera collapse, M similar to 5 caldera collapse earthquakes occurred almost daily from mid-May until the beginning of August. While caldera collapses happen infrequently, the collapse-related seismicity damaged nearby structures, and so these events should be included in a complete seismic hazard assessment. Here, we present an approach to forecast the seismic hazard of the collapse earthquakes. We model their occurrence by combining a Poisson distribution for the number of collapses with a negative binomial for the number of earthquakes in a collapse, based on observations at Kilauea. This rate model is then combined with a ground motion model to assess the seismic hazard posed by caldera collapse events. The rate model is non-Poisson but a Poisson model is adequate for low exceedance probabilities (e.g., <10% in 50 years). This approach could be generalized to model the hazard from earthquakes triggered by other underlying processes. Plain Language Summary During the 2018 Kilauea eruption and collapse of the summit caldera, M similar to 5 caldera collapse earthquakes occurred almost daily for more than 2 months, damaging nearby structures. These types of events are relatively rare, but their potential to cause damaging shaking should be considered in a complete seismic hazard assessment. This study presents a new way to forecast the seismic hazard of these collapse earthquakes. We model their occurrence rate by combining probability distributions for the number of caldera collapses and the number of earthquakes per collapse, based on historical observations at Kilauea. We then combine the occurrence model with a ground motion model to forecast the ground shaking the caldera collapse events may cause in the next 50 years. This approach may be useful to forecast the hazard of earthquakes triggered by other kinds of processes.