Challenges in Assessing Earthquake Rates for Seismic Hazard in Hawaii

Session: Forthcoming Updates of the USGS NSHMs: Hawaii, Conterminous U.S. and Alaska [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The complicated volcanic and tectonic processes in Hawaii present challenges for estimating the probabilities of earthquakes using methods developed for standard probabilistic seismic hazard analysis (PSHA), which usually considers only tectonic earthquakes with stationary rate. These processes, which range from volcanic eruptive and intrusive activity near the summit calderas and rift zones to gravity-driven deformation on the flanks, vary over space and time. Likewise, the characteristics of the seismicity in Hawaii, which range from earthquake swarms to M≥7 ruptures, also vary over space and time. The standard PSHA practice of obtaining a Poissonian rate of independent earthquakes by declustering, using methods such as Reasenberg (JGR, 1985), is difficult in Hawaii because of this time-varying behavior. Therefore, it is difficult to determine a long-term rate and Gutenberg-Richter b-values that are appropriate to use for long-term (e.g., 50-year) seismic hazard assessments. This is a significant challenge being faced as the USGS updates its seismic hazard model for Hawaii.

A particular challenge lies in quantifying the hazard due to seismicity associated with the 2018 Kilauea eruption and the collapse of the summit caldera. During the eruption, caldera collapse events occurred almost daily from the end of May until the beginning of August, characterized by M~5 very long period earthquakes with diminished high-frequency shaking (Neal et al., Science, 2019). While such caldera collapses happen infrequently, they are still a source of hazard that should be included in a complete seismic hazard assessment. We present one way to assess the seismic hazard of the Kilauea caldera collapse by treating it as a special seismicity source, characterized by a rate of collapses and a distribution for the number of M≥5 events in a collapse. We explore a range of possible values for these parameters based on past caldera collapses in Kilauea as well as in other calderas.

Presenting Author: Andrea L. Llenos

Authors