Beyond the Teleseism: Introducing Regional Seismic and Geodetic Data into Routine USGS Finite-Fault Modeling

Abstract

Abstract The U.S. Geological Survey (USGS) National Earthquake Information Center (NEIC) routinely produces finite-fault models following significant earthquakes. These models are spatiotemporal estimates of coseismic slip critical to constraining downstream response products such as ShakeMap ground motion estimates, Prompt Assessment of Global Earthquake for Response loss estimates, and ground failure assessments. Because large earthquakes can involve slip over tens to hundreds of kilometers, point-source approximations are insufficient, and it is vital to rapidly assess the amount, timing, and location of slip along the fault. Initially, the USGS finite-fault products were computed in the first several hours after a significant earthquake, using teleseismic body wave and surface wave observations. With only teleseismic waveforms, it is generally possible to obtain a reliable model for earthquakes of magnitude 7 and larger. Here, we detail newly implemented updates to NEIC’s modeling capabilities, specifically to allow joint modeling of local-to-regional strong-motion accelerometer, Global Navigation Satellite System (GNSS), and Interferometric Synthetic Aperture Radar (InSAR) observations in addition to teleseismic waveforms. We present joint inversion results for the 2015 Mw 8.3 Illapel, Chile, earthquake, to confirm the method’s reliability. Next, we provide examples from recent earthquakes: the 29 July 2021 Mw 8.2 Chignik, Alaska, United States, the 14 August 2021 Mw 7.2 Nippes, Haiti, and the 8 July 2021 Mw 6.0 Antelope Valley, California, United States, earthquakes. These examples confirm that jointly leveraging a variety of geophysical datasets improves the reliability of the slip model and demonstrate that such a combination can be leveraged for rapid response. The inclusion of these new datasets allows for more consistent finite-fault modeling of earthquakes as small as magnitude 6. As accelerometer, GNSS, and InSAR observations worldwide become more accessible, these joint models will become more routine, providing improved resolution and spatiotemporal constraints on rapid finite-fault models, and thereby improving the estimates of downstream earthquake response products.