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Updating the Crustal Seismic Sources for the 2023 National Seismic Hazard Model for Alaska

Description: 

We present the crustal and intraslab seismic sources for Alaska, based on geologic observations, as a primary input for the 2023 revision of the USGS National Seismic Hazard Model (NSHM). Since the 2007 USGS probabilistic seismic hazard map for Alaska there have been significant improvements to our understanding of active faults across the state. We build on the 2013 Alaska Quaternary fault and fold database (Koehler, 2013) by updating it with recent findings, and new observations from recent high-resolution statewide DEMs. We then simplify that database into a model of 83 fault sections for which we provide basic geometric and rupture parameters including sense-of-offset and slip rate. Significant updates from prior maps include: 1) A slip rate of ~53 mm/yr on the Queen Charlotte fault system inferred from offshore mapping which accommodates all of the plate boundary motion (based on a lack of recognized active structures to the east). 2) Determination of long-term slip rates on megathrust seafloor splay faults in the southern Prince William Sound region and near Kodiak Island derived from seismic reflection and thermochronology studies. 3) Significantly improved details of contractional structures in the Chugach-St. Elias orogen. 4) Recognition that Holocene activity on the Castle Mountain fault is predominantly thrust faulting, not strike-slip. 5) Refinement of interior Alaska tectonic models that clarify the relationships between the Denali fault, Totschunda fault, and thrust faults on both the north and south sides of the Alaska Range. 6) We eliminate two faults in previous compilations: the Chatham Strait fault, and the Togiak-Tikchik sections of the Denali fault. The main unreconciled differences between our model and geodetic data are the lack of geologic evidence for active faulting in western Alaska, southwest of the Denali fault system, and the lack of geologic evidence for faulting to the east of the communities in southeastern Alaska, in the vicinity of the Coast Shear Zone. The revised NSHM could be tested by lacustrine paleoseismic records of strong shaking, such as at Eklutna and Skilak Lakes.

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

Type: Poster

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Peter J. Haeussler

Student Presenter: No

Invited Presentation: 

Authors