Wave Gradiometry for EarthScope Seismic and Strain Data

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Wave Gradiometry for EarthScope Seismic and Strain DataCharles A. Langston, Principal InvestigatorCenter for Earthquake Research and InformationUniversity of MemphisA new empirical method to analyze seismic waves, called wave gradiometry, is being used to study earthquake data recorded by the EarthScope Transportable Array and to calibrate Plate Boundary Observatory (PBO) borehole strain meters. Quantitative attributes of seismic waves from large, distant earthquakes such as their speed, azimuth of propagation, and amplitude changes are being determined by computing seismic array strains and rotations. Empirical maps of these quantities are then used to first identify anomalous regions of the crust and mantle and then to quantitatively determine large-scale seismic velocity structure of the North American continent. Seismic gradiometry techniques allow the determination of regional strain fields induced by the seismic waves to serve as a known reference strain to compare with observed strains from PBO strain meters. The reference and observed strains are being combined through matrix mathematics and time series analysis methods to produce precise calibration of individual borehole strain meters. Calibration of the PBO strain meters is an essential step in making the strain data useful for seismic and tectonic studies of active geological processes within the Plate Boundary Observatory.