Earthquake Magnitudes from Dynamic Strain

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., ML). 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 (A) 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 3.5≤Mw≤7.2, and hypocentral distances range from 6≤R≤500 km. The 1D representation of geometrical spreading and attenuation of A common to all strain data is logA0(R)=−0.00072R−1.45log(R). After correcting for instrument gain, site terms, and event terms, the magnitude scale, MDS=logA−logA0(R)−log(3×10−9), scales as ≈0.92Mw with a residual standard deviation of 0.19. This close association with Mw 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 M 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.

Results From a Decade of Optical Fiber Strainmeters at Piñon Flat Observatory

“…The sensitivity required for a pair of GNSS antenna to discern strain signals of 100 nε would be a few mm with antennas separated by a few tens of km, prohibiting localizing the strain signals within several km of the source. Earthquake early warning (e.g., Barbour et al, 2021) may also be enhanced by this technology because an OFS is both a good seismometer and capable of rapid detection of large coseismic offsets; note also the large dynamic range accessible with this technology, covering six orders BSM). Spurious peaks from well-known electronic issues in the PBO BSM spectra near 0.084 and 0.042 Hz have been suppressed (see Barbour & Agnew, 2011).…”

Fifteen Years of Continuous High-Resolution Borehole Strainmeter Measurements in Eastern Taiwan: An Overview and Perspectives

“…Strainmeters have the capability to record the whole spectrum of elastodynamic deformation (static and dynamic) [34] with little noise level, without saturation, and with no additional signal processing, and therefore show potential for EEW applications [82]. An earthquake magnitude scale based on local broadband dynamic strain waveforms has recently been developed by Barbour et al (2021) [85]. Its application to the 2019 M w 6.4 and 7.1 Ridgecrest earthquakes showed very promising results with magnitude estimates being in agreement to within about 0.3 magnitude units [85].…”

“…An earthquake magnitude scale based on local broadband dynamic strain waveforms has recently been developed by Barbour et al (2021) [85]. Its application to the 2019 M w 6.4 and 7.1 Ridgecrest earthquakes showed very promising results with magnitude estimates being in agreement to within about 0.3 magnitude units [85]. Therefore, the strainmeter networks may have a role to play in future EEW systems in Taiwan [86], provided a robust magnitude-scale calibration can be derived from past near-source large events (e.g., 2013 Ruisui, 2018 Hualien).…”

The apparent focal depth, emergence angle, and take-off angle of seismic wave measured by YRY-4-type borehole strainmeter as one kind of strain seismograph

“…Numerous studies have shown that the borehole strainmeter can be used for seismic wave observation (Byerly, 1926;Johnston et al, 1986;Borcherdt and Glassmoyer, 1989;Borcherdt et al, 2006;Johnston et al, 2006;Blum et al, 2010;Barbour and Agnew, 2012;Qiu et al, 2015;Barbour and Crowell, 2017;Canitano et al, 2017;Cao et al, 2018;Farghal et al, 2020;Barbour et al, 2021). This initially realized seismologists' expectations of strain seismographs (Benioff et al, 1961;Aki and Richards, 2002).…”