A seismological study of landquakes using a real-time broad-band seismic network.

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 (SD), peak ground velocity, rise time (TR), area of velocity envelope function (AE) from the closest station and estimated the collapse area (AC) and run-out distance (DR) by mapping satellite images. Based on aforementioned seismic and geometrical parameters, we defined the potential of initial impact (PI), the frequency of rock impact signal (fI) and the mean quasi-front velocity (Vf) 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 (AE) and collapse area (AC) 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. [ABSTRACT FROM AUTHOR]