Updating the Seismic Source Model for a New USGS Earthquake Hazard Map of Alaska

Date: 4/24/2019

Time: 10:45 AM

Room: Pike

We are focused on updating the seismic source model for Alaska as a primary input for the next revision of the USGS National Seismic Hazard Model. The last USGS probabilistic seismic hazard map for Alaska dates to 2007, and there are 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. Significant updates include: 1) Changes in megathrust earthquake recurrence rates along most of the length of the subduction zone inferred from recent paleoseismology. 2) Inclusion of large intraslab earthquakes, prompted by recent damaging M7.0 to M7.9 events. 3) Refined 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. 4) A slip rate of ~5 cm/yr on the Queen Charlotte-Fairweather fault system inferred from offshore mapping. Moreover, a search for and failure to identify active fault traces to the east implies that virtually all of the plate boundary motion occurs on this fault alone. 5) Refinement of interior Alaska tectonic models clarify the relationships between the Denali fault, Totschunda fault, and thrust faults on both the north and south sides of the Alaska Range. 6) Recognition that Holocene activity on the Castle Mountain fault is predominantly thrust faulting, not strike-slip. 7) New details of contractional structures in the Chugach-St. Elias orogen. 8) The potential for large earthquakes in the eastern Brooks Range associated with the westward extrusion of crust revealed by the 2018 M6.4 Kaktovik earthquake. Significant remaining unknowns include the rate and magnitude of large earthquakes in the western Aleutians, and probably lower magnitude events in the vast region spanning western and northwestern Alaska.

Presenting Author: Peter J. Haeussler

Authors