Earthquake magnitudes from dynamic strain

Bulletin of the Seismological Society of America
By: , and 

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Abstract

Dynamic strains have never played a role in determining local earthquake magnitudes, which are routinely set by displacement waveforms from seismic instrumentation (e.g., MLML). We present a magnitude scale for local earthquakes based on broadband dynamic strain waveforms. This scale is derived from the peak root‐mean‐squared strains (AA) in 4589 records of dynamic strain associated with 365 crustal earthquakes and 77 borehole strainmeters along the Pacific‐North American plate boundary on the west coast of the United States and Canada. In this data set, catalog moment magnitudes range from 3.5Mw7.23.5≤Mw≤7.2, and hypocentral distances range from 6R500  km6≤R≤500  km. The 1D representation of geometrical spreading and attenuation of AA common to all strain data is logA0(R)=0.00072R1.45log(R)logA0(R)=−0.00072R−1.45log(R). After correcting for instrument gain, site terms, and event terms, the magnitude scale, MDS=logAlogA0(R)log(3×109)MDS=logA−logA0(R)−log(3×10−9), scales as 0.92Mw≈0.92Mw with a residual standard deviation of 0.19. This close association with MwMw holds for events east of the −124° meridian; west of this boundary, however, a constant correction of 0.41 is needed to adjust for additional along‐path attenuation effects. As a check on the accuracy of this magnitude scale, we apply it to dynamic strain records from three strainmeters located in the near field of the 2019 MM 6.4 and 7.1 Ridgecrest earthquakes. Results from these six records are in agreement to within 0.5 magnitude units, and five out of six records are in agreement to within 0.34 units.

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Publication type Article
Publication Subtype Journal Article
Title Earthquake magnitudes from dynamic strain
Series title Bulletin of the Seismological Society of America
DOI 10.1785/0120200360
Edition Online First
Year Published 2021
Language English
Publisher Seismological Society of America
Contributing office(s) Earthquake Science Center
Country Canada, United States
State California, Oregon, Washington
Other Geospatial British Columbia
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