2021 and 2022 North Coast California Earthquake Sequences Light Up Gorda Plate Faults Beneath the North American Plate
The Mendocino Triple Junction (MTJ), north of 40N and west of 122W, is one of California’s tectonically most active and complex regions. Two earthquake sequences in the MTJ region, beginning on 2021-12-20 (2021) and 2022-12-20 (2022), respectively, highlight the faults in the Gorda plate as it subducts beneath the North American plate. Upgrades to the instrumentation in the region in recent years allow a detailed exploration of the seismicity and finite faulting associated with these earthquakes, in order to better define the faults within the subducting Gorda plate, as well as their modes of rupture. The December 2021 sequence began with a doublet, separated by ~11 s in time and 30 km in space. Detailed analysis indicates that the first event was offshore (2021-OFF) on the Mendocino fault (MF) between the Pacific and Gorda plates. The second event was onshore (2021-ON) at a depth of 24 km within the subducting Gorda plate and was most likely triggered by the S-waves of 2021-OFF. Simultaneous finite source modeling of the two events indicates that they have about the same magnitude, M~6.1, despite the waveforms of 2021-OFF appearing smaller in recordings because it was more distant from all recording stations which are onshore. The source analysis shows that 2021-OFF ruptured eastward along the MF, and 2021-ON ruptured to the NE. The 2022 sequence began with a mainshock (2022-MS, M6.4) just off Cape Mendocino to the NW of 2021-ON, also on a fault within the Gorda plate. Its largest aftershock (2022-AS, M5.4) took place 11 days later about 40 km to the ESE of the main fault rupture. Finite source analysis of 2022-MS indicates that it ruptured NE, toward the towns in the area and caused damage exacerbated by 2022-AS.
Session: Illuminating Complex, Multiplet Earthquake Sequences at Kahramanmaras (Turkiye), Herat (Afghanistan), and Beyond - II
Type: Oral
Room: Kahtnu 1
Date: 5/2/2024
Presentation Time: 11:30 AM (local time)
Presenting Author: Margaret Hellweg
Student Presenter: No
Additional Authors
Margaret Hellweg Presenting Author Corresponding Author hellweg@berkeley.edu University of California, Berkeley |
Douglas Dreger ddreger@berkeley.edu University of California, Berkeley |
Anthony Lomax alomax@free.fr ALomax Scientific |
Robert McPherson robert.mcpherson@humboldt.edu California State Polytechnic University, Humboldt |
Lori Dengler lad1@humboldt.edu California State Polytechnic University, Humboldt |
|
|
|
|
2021 and 2022 North Coast California Earthquake Sequences Light Up Gorda Plate Faults Beneath the North American Plate
Session
Illuminating Complex, Multiplet Earthquake Sequences at Kahramanmaras (Turkiye), Herat (Afghanistan), and Beyond
Description