Records of seismic waves produced by local ocean bottom seismographs OBS or coastal networks are noisy. The noises, such as high-amplitude microquakes, different anthropogenic noises related to engineering works, explosions, land and sea transport noises, microseisms, or the high-frequency ambient noise, complicate the detection of earthquakes and, in particular, microearthquakes in continuous records produced by local seismic networks. Here we present an algorithm for the automated detection of useful signals in seismic records contaminated by noises. Typical useful and noisy signals at offshore and coastal sites are described together with a brief analysis of the application of the well-known methods to detect useful signals. The proposed algorithm makes a use of the following observations: i an increase in the signal amplitude, ii consistency over different seismic stations, and iii the signal duration. The cumulative short-term-average and long-term-average envelope function is used to estimate the signal duration and to distinguish useful seismic signals from short high-amplitude noisy microquakes. The proposed algorithm was tested on the records produced by local network in the north Egypt coast zone during engineering seismological studies and revealed its effectiveness.
Microearthquakes, OBS network, automated detection, ambient noise, microquakes; explosions
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