Earthquake Magnitudes and Ground Motions Derived from Borehole Strainmeter Data

Session: Earthquake Early Warning: Current Status and Latest Innovations [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Using data from borehole strainmeters deployed along the plate boundaries of the West Coast of the United States, we derive relationships between dynamic strains, earthquake magnitudes and associated ground motions. We derive a relationship between earthquake moment magnitudes and raw uncalibrated peak dynamic strains and test this relationship on the largest two events in the Ridgecrest Sequence of July 2019, the M6.4 foreshock and M7.1 mainshock. Our estimates from the closest two stations, within 50 km hypocentral distance, are within 0.2 units of the final magnitude of the earthquakes, and we compare them to the performance of the ShakeAlert early warning system of the U.S. West Coast. We also derive a relationship between maximum shear strain from strainmeters and peak ground velocity (PGV) measured by surface seismometers, an indicator of felt shaking and damage often used in earthquake science and engineering. From the strain records of nine earthquakes in California, including the Ridgecrest Sequence 2019 foreshock and mainshock, we calculate PGV values and compare them to those obtained from seismometers. We find strain-based PGV values to mostly lie within the range of seismic PGV values for the same source-to-station distance. The robust nature of these correlations can be used as a component of earthquake early warning systems to improve earthquake magnitude estimates and therefore the accuracy of alerting.

Presenting Author: Noha S. Farghal

Authors