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Improving static slip characterization of near-shore earthquakes with amphibious datasets: A Cascadia example

Jessie K. Saunders, & Jennifer S. Haase

Published August 15, 2017, SCEC Contribution #7741, 2017 SCEC Annual Meeting Poster #261

The rupture location of a Mw~8 megathrust earthquake can dramatically change the near-source tsunami impact, where a shallow earthquake can produce a disproportionally large tsunami for its magnitude. Because the locking pattern of the shallow Cascadia megathrust is unconstrained due to the lack of widespread seafloor geodetic observations, near-source tsunami early warning systems need to be able to identify shallow, near-trench earthquakes. Onshore GPS displacements provide low frequency ground motions and coseismic offsets for characterizing tsunamigenic earthquakes, however the one-sided distribution of data may not be able to uniquely determine the rupture region. We examine how augmenting the current real-time GPS network in Cascadia with different offshore station configurations improves static slip inversion solutions for Mw~8 earthquakes at different rupture depths. Two offshore coseismic data types are tested in this study: vertical-only, which would be available using existing technology for bottom pressure sensors, and all-component, which could be achieved by combining pressure sensors with real-time GPS-Acoustic observations. We find that both types of offshore data better constrain the rupture region for a shallow earthquake compared to onshore data alone when offshore stations are located above the rupture. However, inversions using vertical-only offshore data tend to underestimate the amount of slip for a shallow rupture, which we show underestimates the tsunami impact. Including offshore horizontal coseismic data into the inversions improves the slip solutions for a given offshore station configuration, especially in terms of maximum slip. This suggests that while real-time GPS-Acoustic sensors may have a long development timeline, they will have more impact for static inversion-based tsunami early warning systems than bottom pressure sensors.

Saunders, J. K., & Haase, J. S. (2017, 08). Improving static slip characterization of near-shore earthquakes with amphibious datasets: A Cascadia example. Poster Presentation at 2017 SCEC Annual Meeting.

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