AN AUTOMATED RAYLEIGH-WAVE DETECTION ALGORITHM

The desire to operate denser networks in order to monitor seismic acti vity at lower thresholds leads to greater emphasis on automated data p rocessing. An algorithm for detecting and characterizing long-period R ayleigh-wave arrivals has been developed and tested. The routine conti nuously monitors all directions of approach to st station, in a manner similar to beamforming. The detector is based on cross-powers between the Hilbert-transformed vertical and rotated horizontal signals, so i t is sensitive to both the power and polarization properties of the th ree-component wave field. Elliptically polarized Rayleigh arrivals are enhanced, while linearly polarized Love waves and body phases are sup pressed. A test using one month of data from station ANMO demonstrated that this technique can, with high reliability, detect Rayleigh arriv als that are visible on the records. The measured arrival times and az imuths are accurate enough to permit automated association of the dete ctions to events in a bulletin.