Comparison of Three Mw ~7 Pre-Digital Era Intraplate Alaska Earthquakes to the November 30, 2018 Anchorage Event

Date: 4/26/2019

Time: 11:15 AM

Room: Pike

The occurrence of the November 30, 2018 Anchorage earthquake (~ 50 km from Anchorage) allows us to compare the waveforms and effects of this well recorded intraplate earthquake to three pre-digital era intraplate events of similar magnitudes that occurred on April 27, 1933 (Mw~6.9), November 3, 1943 (Mw~7) and October 3, 1954 (Mw~6.8) within 100 km of Anchorage. The 1933 earthquake (~75 km from Anchorage) occurred within Upper Cook Inlet at a depth of 9±4 km, likely along one of the numerous offshore faults mapped within the Cook Inlet basin. The 1943 earthquake (~100 km from Anchorage) occurred at a depth of 27±4 km. Its relationship to the regional tectonics is not well understood. The 1954 earthquake (~100 km from Anchorage, depth 60±10 km) occurred within the subducting Pacific plate. Initial comparisons of intensity data for the 1933 and 2018 events suggest a lower intensity of shaking in 1933 for communities located northeast of the 1933 epicenter, although intensities in Anchorage (VI to VII) were comparable. Intensities reported in Anchorage in 1943 were considerably lower (IV) than in 2018, however the 1954 event caused intensities of VIII from Anchorage to the southern Kenai Peninsula. Waveform comparisons indicate that neither the 1933 or 1943 events had focal mechanisms similar to the 2018 event. The 1954 event has similar waveforms to the 2018 event at some stations, suggesting there may be larger component of normal faulting involved in 1954 that previously estimated.

Presenting Author: Diane I. Doser

Authors