Aftershock detection thresholds as a function of time: Results from the ANZA seismic network following the 31 October 2001 M-L 5.1 ANZA, California, earthquake

作者：Kilb Debi^*; Martynov Vladislav G; Vernon Frank L

来源：Bulletin of the Seismological Society of America, 2007, 97(3): 780-792.

DOI：10.1785/0120060116

We examine aftershock detectability thresholds for events in the initial part of the 31 October 2001, M-L 5.1 sequence in southern California. This sequence occurred directly below the broadband ANZA seismic network, which recorded continuous waveform data at 13 azimuthally well-distributed stations within the study region (seven had epicentral distances < 20 km). Of the 608 aftershocks (0 < ML < similar to 2.8) in the initial 2 hr of this sequence, the first five aftershocks recorded were only identifiable at stations within 30 km after applying a high-pass filter. Using a cluster (radius <= 1.1 km) of 200 representative aftershocks, we track the maximum seismogram amplitude versus earthquake magnitude. This relationship helps us quantify the visibility of aftershocks within the mainshock coda and assess our detection capabilities. We estimate that detectable aftershocks within the mainshock coda include (1) those over magnitude similar to 3 that are within 15 km of the network centroid that occur 12 sec or more into the sequence, and (2) those over magnitude similar to 2 that are within 30 km of the centroid of the network that occur 60 see or more into the sequence. We find a lack of large aftershocks in this sequence. The largest aftershock (M-L similar to 2.8) is substantially smaller than the mainshock (M-L 5.1). We suggest this relatively large-magnitude differential is dictated by a combination of factors that includes complexity of the San Jacinto fault system and the lack of large earthquakes in the region in the past similar to 20 years.

• 出版日期2007-6