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National Chiao Tung University Comprehensive Landtoring Lab (CoLLab) Web Page |
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National Chiao Tung University Comprehensive Landtoring Lab (CoLLab) Web Page |
With real-time broadband seismic recording from Broadband Array in Taiwan for Seismology (BATS) seismic network, we have developed a real-time landquake monitoring (RLM) system,which monitor landquake activities in the Taiwan Island. For acquiring continuous real-time data stream, slarchive, is maintained by Incorporated Research Institutions for Seismology (IRIS), is used. The RLM system performs a series of data-processing procedures, including converting data format from seed to SAC (Seismic Analysis Code), cutting the specific time window for waveform modeling, applying a bandpass filter and resampling the waveform data. First, RLM system applies a gird-based general source inversion technique to obtain the preliminary source location and force mechanism. A 2-D virtual sources in Taiwan Island is gridded with an interval of 0.2 degree in both latitude and longitude.The synthetics are obtainedusing Greens functions computed by the propagator matrix approach for 1-D average velocity model. The 1-D velocity model does not account for surface topography, which may up to 3 km inthe mountain areaof Taiwan. Thus, the depth of each grid points fixed on the 3km, which does not significantly influence inversion results. Each grid-point to station pair has nine elementary synthetic seismograms corresponding to six elementary moment tensorsand three orthogonal (north, east and vertical) forces. A synthetic seismograms database is stored in the hard disk.Based on resulting of GSI, the landquake source can be simply identified by observing the improvement in waveform fitness values. To improve the insufficient accuracy of GSI-determined location, we calculate the root-mean-square (RMS) amplitudes of the high-frequency (1-3 Hz) horizontal-component waveforms to create horizontal envelope functions. The grid point with highest fitness value is taken as centre to establish the finer grid with a +-0.2 range and 0.01 degree spacing. Then, we use a cross-correlation-based location method. s) that maximizes the coherency of the horizontal envelope functionsto determine the final source location. With good knowledge about the source location,we perform landquake force history inversion techniqueto investigate the dynamic process of source, especially for large-sized landslide event.
