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Plate Boundary Observatory Strainmeter Data for Determining Earthquake Characteristics

Researchers: Andrew Barbour, U.S. Geological Survey and Brendan Crowell, University of Washington.

Written by Linda Rowan
23 May 2017


Summary

An analysis of borehole strainmeter data from Plate Boundary Observatory sites in the western United States for 144 earthquakes from 2004 to 2014 reveals correlations between the peak strain from these events with distance from the hypocenter and the earthquake magnitude. Such correlations can be utilized to determine crustal structure and better understand fault dynamics. Strainmeter data may also enhance earthquake early warning systems.


Observations

The Plate Boundary Observatory (PBO), a component of the National Science Foundation’s EarthScope project is operated and maintained by UNAVCO. PBO consists of 1140 GPS/GNSS sites, 79 borehole geophysical stations and other observing instruments. Most of the sites are located in the western United States along the North American – Pacific plate boundary, including the San Andreas Fault System, the Cascadia Subduction Zone and the Aleutian Arc subduction region. The borehole strainmeters can detect elastodynamic deformation over a broad frequency range; at seismic frequencies their performance characteristics are comparable to traditional seismometers.

Here, the authors consider high-frequency strainmeter measurements for earthquakes with magnitudes ranging from 4.5 to 7.2; restricting their analyses to local and regional events with hypocentral distances less than or equal to 500 kilometers. The final data set consisted of 144 events recorded at 68 borehole strainmeters; a total of 1792 records of dynamic strain.


Results

The maximum strain over the course of a seismic wave is correlated to the hypocentral distance and the earthquake magnitude. This relationship is verified by considering the magnitude 9 Tohoku-Oki earthquake and the strain measured by triangulation of GPS and strong-motion measurements at sites in Japan’s GEONET. The correlations show that borehole strainmeters can be utilized to determine earthquake characteristics. Many of the strainmeters are located in critical areas, and may be helpful for supplementing earthquake early warning systems by improving predictions of shaking at a given location. For example, thirty three of the 78 instruments used in this analysis are located near the Cascadia Subduction Zone, where a magnitude 9 earthquake is possible and early warnings could help save people and infrastructure.


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References

Dynamic Strains for Earthquake Source Characterization, A. J. Barbour and B. Crowell, Seismol. Res. Lett., 88(2A), 2017.doi:10.1785/0220160155.

Keywords

borehole strainmeter, strain, elastodynamic deformation


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