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Assessing declustering methods in Hawaii for probabilistic seismic hazard assessment

Andrea L. Llenos, Andrew J. Michael, Morgan P. Moschetti, Charles S. Mueller, Mark D. Petersen, & Allison M. Shumway

Published August 13, 2019, SCEC Contribution #9523, 2019 SCEC Annual Meeting Poster #037

Probabilistic seismic hazard assessments often use background earthquake rate estimates determined from a spatially smoothed declustered earthquake catalog. Declustering aims to remove aftershocks from catalogs, leaving behind a rate of independent earthquakes that can be modeled as a stationary Poisson process. However, declustering can be a challenge in regions with complicated volcanic and tectonic processes such as Hawaii. Seismicity in Hawaii ranges from earthquake swarms to M≥7 ruptures with driving processes that range from volcanic eruptive and intrusive activity near the summit calderas and rift zones to gravity-driven deformation on the flanks, and these processes vary over space and time. Therefore, declustering fails to obtain a stationary rate of independent earthquakes over the long periods of time typically used to estimate background earthquake rates for long-term (e.g., 50 year) seismic hazard models.

The USGS is currently updating its seismic hazard model for Hawaii. Here we examine the declustering methods that have been considered in developing the earthquake rate model for the updated seismic hazard map. We explore the effects that different declustering methods, including Reasenberg (JGR, 1985), the nearest-neighbor method of Zaliapin et al. (PRL, 2008), and an ETAS-based stochastic declustering method (Llenos and Michael, 2019), have on the estimated earthquake rate as well as the Gutenberg-Richter b-value in space and time. These estimates can vary widely depending on what declustering method is used, and so the final hazard model will have some sensitivity to the choices that are made in declustering, as well as how the long-term seismicity rate in Hawaii is ultimately defined.

Llenos, A. L., Michael, A. J., Moschetti, M. P., Mueller, C. S., Petersen, M. D., & Shumway, A. M. (2019, 08). Assessing declustering methods in Hawaii for probabilistic seismic hazard assessment. Poster Presentation at 2019 SCEC Annual Meeting.

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Earthquake Forecasting and Predictability (EFP)