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Re-Examination of the 1958 Huslia Earthquake Sequence and Regional Tectonics of the Northwestern Koyukuk Basin, Alaska in Light of Post-1974 Seismicity, Mapped Faults and Geophysical Data

Description: 

In 1958 a M_w 6.8 earthquake and several M_w>5.3 aftershocks occurred in the northwestern Koyukuk Basin near the village of Huslia (~ 400 km northwest of Denali). Tectonically, this region is located between the compressional forces due to the collision of the Pacific and Yakutat plates and extensional forces associated with the extrusion of western Alaska. Since 1969 several earthquake swarms with M_w 4-5 events have occurred ~50 km northwest of Huslia in the western Purcell Mountains, including a swarm in 2019-2022 with over 9500 events. Previous studies have suggested the 1958 mainshock occurred on a northeast striking, southeast dipping normal fault. This sense of rupture is inconsistent with the focal mechanisms and trends of post-1973 seismicity within the 1958 epicentral region that indicate strike-slip movement along northwest trending faults. A recently mapped east-west trending fault scarp located along the southern front of the Purcell Mountains is also inconsistent with northeast striking normal faulting. To better characterize the 1958 sequence and its relation to mapped faults and regional tectonics, we measure scarp profiles across the Purcell Mountains scarp, relocate historical seismicity, analyze first motions and waveforms of pre-1974 events, and model potential fields geophysical data. Our preliminary results suggest regional deformation is occurring along both east-west and northwest trending structures.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - III

Type: Oral

Date: 5/1/2024

Presentation Time: 02:15 PM (local time)

Presenting Author: Diane

Student Presenter: No

Invited Presentation: 

Authors