Automatic Detection And Discrimination Of Volcanic Tremors And Tectonic Earthquakes: An Application To Ambrym Volcano, Vanuatu

摘要

An algorithm of automatic detection and discrimination of volcanic tremors, defined as events containing only P-type wave, and tectonic earthquakes, containing both P- and S-waves, is applied on data recorded on a 3-component STS-2 broad-band seismometer, installed from July to November 2000 at Ambrym volcano, Vanuatu. The algorithm consists in detecting P-waves and, if any, S-waves according to a modified version (Zhizhin, M., Rouland, D., Bonnin, J., Gvishiani, A., Burtsev, A., 2006. Rapid estimation of earthquake source parameters from pattern analysis of waveforms recorded at a single 3-component station. Bull. Seism. Soc. Am, 96, 6,2329-2347) of the Component Energy Comparison Method (CECM) proposed by Nagano et al. (Nagano, K., Niitsuma, H., Chubachi, N., 1989. Automatic algorithm for triaxial hodogram source location in downhole acoustic emission measurement. Geophysics, 54, 4, 508-513). The duration and maximum amplitude are automatically measured for each volcanic tremor and for each tectonic earthquake with corresponding duration-and amplitude-magnitudes. During the four-and-half months of observation, 1959 local and regional tectonic earthquakes with epicentral distances (estimated from S-P interval time) ranging from a few kilometres to about 800 km, and 14942 volcanic tremors with duration ranging from 10 to 2000 s, have been detected. The Gutenberg and Richter laws of tectonic earthquakes and volcanic tremors are examined according to their duration-and amplitude-magnitudes, and completeness of the corresponding catalogues is studied. The observations on the coherence of some long duration volcanic tremors, which display four different intermittencies (77+/-17 min, 165+/-10 min, 565+/-50 min, 1065+/-50 min), are interpreted as different types of degassing.