Discovery of Offshore Very Low Frequency Earthquakes in the Cascadia

Kuntal Chaudhuri, & Abhijit Ghosh

Published August 16, 2021, SCEC Contribution #11533, 2021 SCEC Annual Meeting Poster #228

Cascadia subduction zone is one of the most complicated plate boundaries. Significant amount of stress in this subduction zone is released due to ETS in the form of tremors, low frequency earthquakes (LFE), and onshore very low frequency earthquakes (VLFE) (Brown et al., 2009; Doran & Laske, 2017; Ghosh et al., 2015; Hutchison, 2020; Hutchison & Ghosh, 2019; Kao et al., 2010; Plourde et al., 2015). This study detects multiple VLFEs along offshore Cascadia using ocean-bottom seismometers (OBS). They are the only seismic stress markers in this area with occasional earthquakes (Han et al., 2017; McGuire et al., 2018; Michel et al., 2019). Using centroid moment tensor inversion and matched filtered method, we detected, and located repeating sequences for 12 VLFEs. The VLFEs along the northern section near Vancouver Island have a focal mechanism that is consistent with the overall deformation in the area. However, the VLFEs offshore Washington and north Oregon seem to have major strike-slip component, which has been attributed to sediment consolidation, subduction bending, and transpressional regimes created by the complex plate tectonics going on in this area (reference). The discovery of such VLFEs opens a new avenue of investigating fault stress release offshore Cascadia subduction zone, which is poorly studied due to lack of detected regular fast earthquakes.

Key Words
Cascadia, VLFE, OBS, Centroid Moment Tensor,

Chaudhuri, K., & Ghosh, A. (2021, 08). Discovery of Offshore Very Low Frequency Earthquakes in the Cascadia . Poster Presentation at 2021 SCEC Annual Meeting.

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