We detected 12 landquakes in Taiwan with collapse areas between 0.27 and 2.48 km2 associatedwith rock collapse, rockslide and debris and/or rock avalanche during the passage of TyphoonMorakot in 2009. These events were recorded by seismic stations of the Broadband Arrayin Taiwan for Seismology. Their locations were determined by a cross-correlation techniquethat maximizes the coherency of horizontal envelope function among seismic stations with amean location error of 1.92 km. We applied time-frequency analysis to estimate the bandwidthof seismic energy generated by the landquakes. The predominant frequency ranges from 0.5to 5.0 Hz, with higher-frequency signals likely caused by block impact. We extracted signalduration (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) bymapping satellite images. Based on aforementioned seismic and geometrical parameters, wedefined the potential of initial impact (PI), the frequency of rock impact signal (fI) and themean quasi-front velocity (Vf) as indicators of landquake types, especially for events withdam formation (dam-formation-type events). We also derived an empirical linear relationshipbetween the envelope area (AE) and collapse area (AC) with a high correlation coefficient of0.83. Our automatic approach is very effective for rapid determination of landquake centroidlocation and collapse area, and for identifying dam-formation event using records from existingreal-time broad-band seismic networks, thus providing an important alternative for landquakehazard mitigation.
- Time-series analysis