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Geologic and Seismotectonic Data for the 2026 American Samoa and Mariana Islands National Seismic Hazard Model Update

Description: 

A primary responsibility of the National Seismic Hazard Model (NSHM) Project of the U.S. Geological Survey is to model the ground shaking hazard from potentially damaging earthquakes for U.S. territories. The previous and initial assessments for American Samoa, Guam, and the Commonwealth of the Northern Mariana Islands were completed in 2012, and significant updates are currently being planned for a release in 2026. The research and development process is consistent with past NSHM workflows and includes compiling new earthquake catalogs for the regions, reviewing possible new fault sources, and revising previously included fault sources, all in order to develop earthquake rupture forecasts (ERF) for the NSHMs. To support the 2026 update, we examined available geological and geophysical data on the islands and the surrounding ocean floor, and we developed a geodatabase that summarizes the fault section inputs. New inputs for the ERF component of the model include updated and additional crustal fault sections. The areas of interest have been adjusted from the 2012 update, but they still cover significant regions of Micronesia (Guam and the Northern Mariana Islands) and Polynesia (American Samoa). The previous extent of the Micronesia subregion is largely retained, including the major features of Mariana subduction zone. The area of interest for American Samoa in the update will be smaller than the assessment from 2012: the Tonga subduction zone is included with an area of backarc spreading, but only the northernmost section, whereas the previous work included Fiji and islands of New Zealand. The area also extends far enough north to capture seismicity related to the Samoan hotspot track. Development of the geological and geophysical inputs for the 2026 NSHM represents a catalyzing step in the workflow that informs the ERF and other components of the source and ground motion models for the probabilistic seismic hazard assessment.

Session: Advancing Seismic Hazard Models [Poster]

Type: Poster

Date: 4/17/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Rich

Student Presenter: No

Invited Presentation: 

Poster Number: 56

Authors