Widespread Very Low Frequency Earthquakes (VLFEs) Activity Offshore Cascadia

A significant amount of stress in the Cascadia subduction zone (CSZ) is released by different forms slow earthquakes including tremors, low-frequency earthquakes, and very (VLFEs)—all occurring onshore at deeper part transition zone. Their activity offshore, however, remains elusive. We discover widespread occurrence discrete VLFEs offshore using ocean-bottom seismometers. Barring occasional regular fast are only seismic indicators offshore. Using centroid moment tensor inversion matched filtering, we detect sequences 12 distinct families VLFEs. The northern CSZ have focal mechanisms consistent with area's deformation. Interestingly, southern show strike-slip faulting, attributed to faults, sediment consolidation, bending, transpressional regimes created complex plate tectonics. It challenges a canonical view seismogenic characterized frictionally homogeneous fault segment producing earthquakes.