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Group B, Poster #016, Seismology

Analysis of aftershock migration following the 2022 Ferndale sequence

Max Liu, Saeed Y. Mohanna, Lingsen Meng, & Roland Bürgmann
Poster Image: 

Poster Presentation

2023 SCEC Annual Meeting, Poster #016, SCEC Contribution #13242 VIEW PDF
The 2022 M6.4 Ferndale earthquake ruptured a geometrically complex region near the Mendocino Triple Junction. The Northern California Seismic Network’s (NCSN) double difference catalog shows that the seismicity follows an orientation that does not align with onshore surface traces of mapped faults. We applied the EdgePhase multi-station phase picking algorithm (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GC010453) to one month of continuous data following the mainshock, intending to investigate fault geometry and seismicity migration during the aftershock sequence. We use software (REAL, Hypoinverse, HypoDD, GrowClust) within the LOC-FLOW algorithm to perform the phase assoc...iation and event relocation. In our updated catalog, we detect 2.3 times more events than the local catalog, with a 57% match to the events found by NCSN. Analysis of the spatiotemporal evolution of seismicity along the strike and dip directions of the USGS finite fault inversion result reveals that pore fluid diffusion (which follows a √t relation) may have played a role in aftershock production in this sequence. We will explore other possible migration mechanisms, such as rate-and-state friction, and analyze geodetic data to look for indications of afterslip. Comparing the 3-D locations of the events with the location of the Gorda plate geometry in addition to the orientations of focal mechanism nodal planes with offshore faults, we find that the mainshock likely occurred within the Gorda plate with aftershocks migrating down-dip in the subducting slab.