Estimation of Uncertainties of Full Moment Tensors
Technical Report,17 Jun 2015,17 Jun 2017
University of Alaska Fairbanks Fairbanks United States
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A seismic moment tensor is a 3 x 3 symmetric matrix that provides a compact representation of a seismic source. We develop an algorithm to estimate moment tensors and their uncertainties from observed seismic data. For a given event, the algorithm performs a grid search over the six-dimensional space of moment tensors by generating synthetic waveforms for each moment tensor and then evaluating a misfit function between the observed and synthetic waveforms. The moment tensor M0 for the event is then the moment tensor with minimum misfit. To describe the uncertainty associated with M0, we first convert the misfit function to a probability function. The uncertainty, or rather the confidence, is then given by the confidence curve PV, where PV is the probability that the true moment tensor for the event lies within the neighborhood of M that has fractional volume V. The area under the confidence curve provides a single, abbreviated confidence parameter for M0. We apply the method to data from events in different regions and tectonic settings 63 small Mw 2.5events at Uturuncu volcano in Bolivia, 21 moderate Mw 4 earthquakes in the southern Alaska subduction zone, and 12 earthquakes and17 nuclear explosions at the Nevada Test Site. Characterization of moment tensor uncertainties puts us in better position to discriminate among moment tensor source types and to assign physical processes to the events.
- Seismic Detection and Detectors
- Operations Research