2021 U.S. National Seismic Hazard Model for Hawaii

Abstract:

The 2021 USGS National Seismic Hazard Model for the state of Hawaii updates the Klein et al. 2001 model by incorporating new data and modeling techniques that improve the underlying shaking forecasts from volcanic and tectonic earthquakes. The improved seismic source model accounts for two additional decades of recorded earthquakes, a new Quaternary fault database, a new rate model for seismogenic caldera collapses — motivated by Kilauea's 2018 sequence, incorporation of GPS data in strain rate models, and an updated fault model that accounts for large flank earthquakes rupturing at depths of ~10 km along shallowly dipping decollements. An earthquake catalog is compiled to assess earthquake rates for both shallow and deep earthquakes, declustered using two different methods to remove spatial and temporal bias, and gridded smoothing using adaptive smoothing methods with alternative nearest-neighbor numbers - eliminating the need for the ramp-type source applied in 2001. As in the 2001 model, we account for earthquake rates that are significantly higher when calculated using the pre-1959 portion of the catalog compared to earthquakes since 1959. The hazard model also includes new local ground motion models that were developed using the 2006 M6.7 Kiholo Bay and the 2018 M7.2 Kalapana earthquakes and global shaking models that are consistent with Hawaii data. We are evaluating how changes in the input seismic sources and ground motion models compare with the 2001model. Ground motions are highest in the southern portion of the island of Hawaii due to large forecasted flank earthquakes similar to M≥7 events in 1868, 1975, and 2018. Shaking decays to the northwest where earthquakes are associated with flexure of the plate beneath older volcanos. Ground motion hazard uncertainties are large, exceeding a factor of two at Honolulu. The new models indicate increased risk across the island chain due to the higher hazard and population exposure.