Regional Source Parameters, Seismic Energy, and Discrimination

Abstract

We have examined broadband waveforms from a large number of NTS explosions and earthquakes throughout the southwestern United States in order to characterize seismic sources. Explosions were found to be richer in coda energy than earthquakes. Most earthquakes show relatively little long-period (T>4 sec) coda energy and tend to be richer in long-period and shear-wave energy than explosions. We have developed several seismic discriminants based on these observations and our modeling experience. One promising discriminant is the ratio of short-period vertical component, P-wavetrain energy, to long-period surface wave energy, averaged over three components. Explosions tend to have a higher ratio than do earthquakes, essentially an extension of m_b:M_s. Magnitude threshold for this discriminant is about 3.5. Another useful discriminant is based on the total broadband energy to moment ratio where explosions are distinguished by their stronger energy levels relative to their long-period amplitudes. This approach requires Green's functions, a source estimator program, and processes all events as earthquakes. For this method to be effective requires the calibration of the region using relatively large earthquakes, M>5, but does not require calibrations of explosions.