Analysis of Near-Source Waves: Separation of Wave Types Using Strong Motion Array Recordings

摘要

Algorithms are developed for the separation and identification of seismic wave types in the near-source region. Two large earthquakes recorded by over twenty-five digital, three component accelerometers that make up SMART 1 (Strong Motion Array Taiwan 1), are used to demonstrate the methods. A sub-array of the SMART 1 array, consisting of the center station and the inner and middle rings, is used to analyze the ground acceleration wavefield. Two complimentary analyses of the cross-spectral matrix are applied to the three rotated components of ground acceleration. Frequency-wavenumber spectral analysis demonstrates that the mixture of wave types that propagated across a 2 km radius sub-array was different for the two earthquakes. In contrast, the polarization of the wavefields over the 2 km sub-array was similar for the two earthquakes. For both earthquakes, polarized (coherent), broadband P-wave energy and S-wave energy, significantly different than noise at the 95 percent confidence level, was observed. A crustal anomaly or 'heterogeneous scattering center' has been located 1 to 1.5 km southeast of the array center and is estimated to be at a depth between 1.5 and 2.0 km.