Using time-reversal to locate non-volcanic tremor and to fulfill the monitoring objectives of the nuclear-test ban treaty

Abstract

In this paper are presented the latest results of our group effort to apply Time Reversal (TR) to different seismology problems. The first problem considered is source location of non-volcanic tremor (NVT). NVT episodes involve quasi-continuous emissions of seismic energy making the identification of distinct events and phase arrival times very difficult. We locate 2 NVT episodes that were recorded near Hemet: one triggered by the 2002 Denali earthquake and one by the 2009 Mexicali earthquake. Locations indicate sources slightly off the known scarp of tectonic faults. In both cases, determination of the source mechanism is impossible. The second problem is determination of the depth of seismic events. There is currently no robust method to estimate the depth of small events (below Mw5.0), when depth determination is crucial in discriminating small earthquakes from man-made blast, since the blast will have to be within about 2 km of the surface where few earthquakes occur. We propose to use stacked autocorrelation (AC) signal to extract depth phases (i.e. phases reflected off the surface). AC is a variant form of TR. We show promising results from sparse IRIS stations in China for three nuclear blasts and a deep earthquake. © 2010 Acoustical Society of America.