A seismological study of landquakes using a real-time broad-band seismic network
Journal
Geophysical Journal International
Journal Volume
194
Journal Issue
2
Pages
885-898
Date Issued
2013
Author(s)
Abstract
We detected 12 landquakes in Taiwan with collapse areas between 0.27 and 2.48 km2 associated with rock collapse, rockslide and debris and/or rock avalanche during the passage of Typhoon Morakot in 2009. These events were recorded by seismic stations of the Broadband Array in Taiwan for Seismology. Their locations were determined by a cross-correlation technique that maximizes the coherency of horizontal envelope function among seismic stations with a mean location error of 1.92 km. We applied time-frequency analysis to estimate the bandwidth of seismic energy generated by the landquakes. The predominant frequency ranges from 0.5 to 5.0 Hz, with higher-frequency signals likely caused by block impact. We extracted signal duration (<it>S</it><inf>D</inf>), peak ground velocity, rise time (<it>T</it><inf>R</inf>), area of velocity envelope function (<it>A</it><inf>E</inf>) from the closest station and estimated the collapse area (<it>A</it><inf>C</inf>) and run-out distance (<it>D</it><inf>R</inf>) by mapping satellite images. Based on aforementioned seismic and geometrical parameters, we defined the potential of initial impact (<it>P</it><inf>I</inf>), the frequency of rock impact signal (<it>f</it><inf>I</inf>) and the mean quasi-front velocity (<it>V</it><inf>f</inf>) as indicators of landquake types, especially for events with dam formation (dam-formation-type events). We also derived an empirical linear relationship between the envelope area (<it>A</it><inf>E</inf>) and collapse area (<it>A</it><inf>C</inf>) with a high correlation coefficient of 0.83. Our automatic approach is very effective for rapid determination of landquake centroid location and collapse area, and for identifying dam-formation event using records from existing real-time broad-band seismic networks, thus providing an important alternative for landquake hazard mitigation.
Type
journal article