Presenter: Hung, Ruei-Jiun
Date: 2016/10/06
Abstract
Although the cross correlation of ambient noise has been widely used to explore subsurface structure, several research has indicated the noise Green’s function seems to be sensitive to the distribution of noise source, especially for the problems of phase errors and asymmetric of amplitudes in time domain. These problems may be resolved by using coda waves. It has been shown that coda waves are result from local scattering effect which will provide more diffused wavefield. By taking this advantage, it’s possible to resolve the subsurface material configuration or monitor the temporal changes via coda without source bias. Here, I present several studies based on coda waves analysis. All of these papers refer cross correlation technique as their procedure to obtain the results. At the first part, I would introduce the moving window cross spectrum, and its application on seismic coda waves to monitor the temporal variation of seismic velocity before an eruption of a volcano. Then, I would move to the cross correlation function by using coda waves to discuss the possibility of removal phase errors. Finally, the correlation of coda of the correlation function (C3) function will be presented. This technique could enable us to obtain more symmetric Green’s function in both positive and negative time domain. To our TCDP borehole data, the ambient noise cross correlation functions show very asymmetric waveforms, as well as the faster phase travel time. This indicates the noise energy at TCDP well site is very inhomogeneous. Therefore, we may use coda to retreat more reliable results. These studies will enlighten me for future research for obtaining more reliable Green’s function, and thus, we could use these function to monitor the possible temporal variation of fault-zone seismic structure.
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