The Applications of ambient noise Cross Correlation
Speaker: Kai-Xun Chen Adviser: Po-Fei Chen
Abstract Date: 2015/03/05
It has been proven that the cross-correlation of ambient noise can provide an estimate of the fundamental mode surface wave empirical Green’s function between two stations. The ambient noise cross correlation technique has been widely applied to a variety of subjects, including station timing calibration, subsurface velocity structure and temporal variation of seismic properties.
The robust daily cross-correlation function (CCF) gives the opportunity to examine the timing problem of seismograph. Waveform similarity between causal and acusal part of CCF or between correct CCF and incorrect CCF can provide the measurements of time shift amount. Zha [2013] developed a new method for obtaining reliable OBS orientations through polarization analysis of virtual Rayleigh waves retrieved from CCF. The data quantity and azimuthal coverage of ray paths for the ambient noise method increase with the number of sensors, making it potentially more accurate for large OBS arrays. Chen [2011] examined the spatiotemporal properties of short period secondary microseisms (SPSM) around the offshore Taiwan using CCFs. Both the spatial and temporal variations of the SPSM excitations exhibit characteristic features which are likely linked to the diverse offshore settings and monsoon migration in Taiwan. Yu [2012] detect temporal changes of elastic properties associated with the 2006 Mw 6.1 Taitung earthquake in southeast Taiwan. Time lapse changes in the retrieved coda arrivals of CCFs are estimated for monitoring spatiotemporal variations of seismic velocities around the ruptured fault zones. For 3-D S wave tomographic inversion (Lin [2013], Fang [2015]), the short-period surface waves may provide greater constraint for velocity structure on shallow crust. In contrast with traditional seismic tomography, noise tomography method doesn’t have the problem of non-uniform distribution of earthquakes and attenuation problems because it don’t need earthquake. Besides, this method also provides sufficient robust measurements of group/phase velocity to inversion high-resolution tomography.
Reference
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