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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 (RLAM) 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, RLAM 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.
