Revisiting the Enigmatic Magnitude-7 Denali Fault Earthquake of July 7, 1912
The 2002 Mw 7.9 Denali fault earthquake ruptured 341 km within central Alaska. Its occurrence prompted a search for evidence of earlier earthquakes on the Denali fault, the most recent candidate being a Ms 7.2 earthquake on July 7, 1912. The enigma of the 1912 earthquake is twofold. First, the maximum reporting shaking intensity—documented by the Parker-Browne Denali mountaineering expedition—is ~250 km west of damaged trees documented by Carver et al. (2004), while empirical scaling suggests a rupture length of about 60-80 km for a magnitude 7.2 earthquake. We revisit the 1912 earthquake with two approaches: 1) probabilistic relocation of epicenter using globally recorded arrival times, and 2) compilation and reassessment of shaking intensity reports to estimate a macroseismic epicenter. Our preferred instrumental epicenter is west of the Parks Highway, in agreement with the maximum reported shaking by the Parker-Browne expedition. We also examine data choices that result in instrumental epicentral estimates that are toward the east and closer to the documented tree damage. We explore two possibilities for the 1912 earthquake, all of which assume the Denali fault as the host. The first scenario is that there was a single, exceptional earthquake having a long rupture and strong shaking, relative to its magnitude. The second scenario is that there were two earthquakes: a large one (M 7.2) in the west, near the Parks Highway, and a smaller one (M 6.5-7) in the east, near the Richardson Highway. The large event occurred on 1912-07-07 and produced the global arrival times and the strongest felt report near Denali, while the smaller event occurred minutes to months after the large event and was responsible for the tree damage reported by Carver. Further analysis of instrumental data, felt reports, and paleoseismic results may help discriminate among these scenarios.
Session: Cordilleran Strike-Slip Faults as Seismogenic and Seismological Features [Poster Session]
Type: Poster
Room: Exhibit Hall
Date: 5/2/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Carl Tape
Student Presenter: No
Additional Authors
Carl Tape Presenting Author Corresponding Author ctape@alaska.edu University of Alaska Fairbanks |
Anthony Lomax alomax@free.fr ALomax Scientific |
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Revisiting the Enigmatic Magnitude-7 Denali Fault Earthquake of July 7, 1912
Category
Cordilleran Strike-Slip Faults as Seismogenic and Seismological Features
Description