Adaptive Waveform Correlation Detectors for Arrays: Algorithms for Autonomous Calibration

• Main Authors: Ringdal, F, Harris, D B, Dodge, D, Gibbons, S J
• Language: unknown
• Published: 2021
• Subjects: 58 GEOSCIENCES; AFTERSHOCKS; ALGORITHMS; CALIBRATION; DESIGN; DETECTION; EARTHQUAKES; EXPLOSIONS; FINE STRUCTURE; IMPLEMENTATION; MONITORING; PROLIFERATION; REFRACTION; SEISMICITY; WAVE FORMS; WAVELENGTHS; Svalbard
• Online Access: http://www.osti.gov/servlets/purl/966533; https://www.osti.gov/biblio/966533

Waveform correlation detectors compare a signal template with successive windows of a continuous data stream and report a detection when the correlation coefficient, or some comparable detection statistic, exceeds a specified threshold. Since correlation detectors exploit the fine structure of the full waveform, they are exquisitely sensitive when compared to power (STA/LTA) detectors. The drawback of correlation detectors is that they require complete knowledge of the signal to be detected, which limits such methods to instances of seismicity in which a very similar signal has already been observed by every station used. Such instances include earthquake swarms, aftershock sequences, repeating industrial seismicity, and many other forms of controlled explosions. The reduction in the detection threshold is even greater when the techniques are applied to arrays since stacking can be performed on the individual channel correlation traces to achieve significant array gain. In previous years we have characterized the decrease in detection threshold afforded by correlation detection across an array or network when observations of a previous event provide an adequate template for signals from subsequent events located near the calibration event. Last year we examined two related issues: (1) the size of the source region calibration footprint afforded by a master event, and (2) the use of temporally incoherent detectors designed to detect the gross envelope structure of the signal to extend the footprint. In Case 1, results from the PETROBAR-1 marine refraction profile indicated that array correlation gain was usable at inter-source separations out to one or two wavelengths. In Case 2, we found that incoherent detectors developed from a magnitude 6 event near Svalbard were successful at detecting aftershocks where correlation detectors derived from individual aftershocks were not. Incoherent detectors might provide 'seed' events for correlation detectors that then could extend detection to lower magnitudes. This year ...