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Very low frequency earthquakes in Cascadia migrate with tremor
Author(s) -
Ghosh Abhijit,
HuescaPérez Eduardo,
Brodsky Emily,
Ito Yoshihiro
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl063286
Subject(s) - episodic tremor and slip , seismology , geology , slip (aerodynamics) , moment tensor , subduction , seismic moment , slow earthquake , moment magnitude scale , shear (geology) , geodesy , physics , interplate earthquake , geometry , paleontology , tectonics , fault (geology) , oceanography , deformation (meteorology) , mathematics , scaling , thermodynamics
We find very low frequency earthquakes (VLFEs) in Cascadia under northern Washington during 2011 episodic tremor and slip event. VLFEs are rich in low‐frequency energy (20–50 s) and depleted in higher frequencies (higher than 1 Hz) compared to local earthquakes. Based on a grid search centroid moment tensor inversion, we find that VLFEs are located near the plate interface in the zone where tremor and slow slip are observed. In addition, they migrate along strike with tremor activity. Their moment tensor solutions show double‐couple sources with shallow thrust mechanisms, consistent with shear slip at the plate interface. Their magnitude ranges between Mw 3.3 and 3.7. Seismic moment released by a single VLFE is comparable to the total cumulative moment released by tremor activity during an entire episodic tremor and slip event. The VLFEs contribute more seismic moment to this episodic tremor and slip event than cumulative tremor activity and indicate a higher seismic efficiency of slow earthquakes in Cascadia than previously thought. Spatiotemporal correlation of VLFE and tremor activity suggests that they are the results of the same physical processes governing slow earthquakes.