RECOVERY OF THE AFTERSHOCK SEQUENCE OF THE NORTH ATLANTIC EARTHQUAKE USING WAVEFORM CROSS-CORRELATION

A short sequence of aftershocks of the mb=4.2 earthquake associated with volcanic and tectonic processes in the North Atlantic was used to evaluate the efficiency of the waveform cross-correlation method (WCC) in detecting weak signals and events at teleseismic distances. The results of the WCC application are compared with those obtained at the International Data Center (IDC) and presented in the Standard Event Bulletin (SEB). The WCC method allows spatially close repeating-signal detection threshold to be several times lower when compared to energy detectors. It has already been applied at the IDC to aftershock sequences of large and moderate earthquakes with relatively high signal-to-noise ratios for event-associated signals. 50 to 70 percent of events, defined as true by the IDC, were found in addition to those listed in the SEB. All hypotheses, automatically generated for the earthquake under consideration by the WCC, were processed by an experienced IDC analyst, which made it possible to generate events according to strict IDC quality criteria. 38 seismic events listed in the SEB were supplemented with 26 aftershocks trough the WCC method, with an iterative procedure applied to search for all possible sources using the newly found aftershocks for the repeated application of the WCC. High efficiency in detection of low-magnitude events in the North Atlantic at teleseismic distances from the recording stations applies also to seismicity studies in other regions, including subarctic and arctic.