Ross Heyburn and David Bowers
Earthquake depth estimation using the F trace and associated probability
Bulletin of the Seismological Society of America (February 2008), 98(1):18-35

Abstract:
Determining the depths of seismic disturbances is of great importance when monitoring compliance with the Comprehensive Nuclear Test Ban Treaty (CTBT), in plate-tectonic studies and in seismic hazard assessments. We have developed a semiautomated method that uses the output from the F-detector (a processing technique that detects correlated signals crossing a seismometer array) as a tool for identifying candidate depth phases, and hence estimating hypocenter depth. The F trace can be interpreted approximately in terms of probability; this can be used to help interpret signals and identify candidate depth phases. Here a method of calculating F-probability traces that optimally highlight candidate depth phases is presented. The values of the probability trace at the predicted times for pP and sP for a given depth are then weighted and summed over several high-quality medium-aperture array stations. A clear maximum in the trace sum function with depth is interpreted as the probable hypocenter depth. Results for earthquakes from the Lop Nor and Hindu-Kush regions indicate that this method of depth estimation is effective for many earthquakes with magnitude greater than about m _b 4.0 and depths greater than around 10 km. The method is best suited as a tool to be used by analysts to estimate the depths of individual seismic disturbances of special interest, or groups of earthquakes in regions where there is a good azimuthal distribution of medium-aperture array stations.