Earthquake Depth Estimation Using the F Trace and Associated Probability

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.