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Recurrence Model for Puerto Rico Subduction Zone Interface and Muertos Thrust Belt Earthquakes

Description: 

In preparation for the 2025 update to the Puerto Rico and U.S. Virgin Islands portion of the USGS National Seismic Hazard Model, we compiled geologic, geodetic, geophysical, and seismologic observations to characterize earthquake recurrence along the Puerto Rico subduction zone (PRSZ) and the Muertos thrust belt. Limited historical seismicity suggests the PRSZ is active and capable of hosting Mw 8+ ruptures. Previously reported geologic observations document precolonial (pre-1492 C.E.) inundation of Anegada, consistent with either a subduction interface event or an outer rise event. Because geologic observations to constrain subduction interface rupture recurrence are scant, we estimate recurrence from geodetically determined coupling and convergence rates. Eight subduction interface fault sections are defined on the basis of structural and geometric discontinuities and coupling is generalized along uniform patches, ranging from 10 to 20%. Recurrence is inferred from moment accumulation rates with magnitudes derived from scaling relations. This approach yields preliminary recurrence intervals of 2900-5800 years for Mw 8.6-8.8 ruptures along the PRSZ for a set of prescribed interface events. A key question is whether highly oblique convergence along the PRSZ is partitioned into only trench-normal interface rupture, or if nearly trench-parallel rupture occurs on the dipping interface (e.g., Sagami Trough-style). Historical seismicity on the subduction interface is consistent with highly oblique rupture on the interface and we retain that possibility in the model. Based on seismicity, geodesy, and limited geophysical data, we model three sections along the Muertos thrust belt as 50% coupled with their down-dip extents near the southern coast of Puerto Rico. Using a methodology similar to the PRSZ yields earthquakes of Mw 7.8-8.5 with recurrence intervals of 770-9200 years on the Muertos thrust belt. Outstanding issues include constraining recurrence of outer rise events, testing the recurrence model against limited geologic and seismologic data, and incorporation of considerable epistemic uncertainty into the model.

Session: The 2023 USGS National Seismic Hazard Model and Beyond [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Richard

Student Presenter: No

Invited Presentation: 

Authors