Mapping Between Frequency-Domain and Depth-Domain Velocity Perturbations in Coda Wave Interferometry

Session: Advances in Seismic Interferometry: Theory, Computation and Applications [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Climatic, tectonic and anthropogenic forces alter the shallow seismic wavespeeds. To monitor and map these perturbations in space and time, seismologists explore phase delays in late coda waves of repeating earthquakes and/or ambient noise correlation functions. Most recent monitoring techniques use the wavelet transform to explore time-frequency dependence of these phase lags (e.g., Mao et al., 2019) and they show significant improvements of the resolution of velocity perturbation (dv/v) measurements in frequency domain. With the assumption of coda waves being dominated with surface waves, previous studies have assumed the sensitivity of these frequency-specific dv/v measurements (referred to as a dv/v spectrum) with depth. However, there remains to be performed the analysis of coda wave interferometry to local depth-varying dv/v, without the assumption of wave types in the coda. We develop a new method, the Wavelet Transform Stretching (WTS), to measure the dv/v spectrum and numerically explore the mapping from frequency- to depth- domain following three steps: (1) analysis of the effects of structural stochastic heterogeneity (scattering elastic medium) on the dv/v spectrum; (2) analysis of the effects of dv/v amplitude and the thickness and depth of the perturbed layer on the dv/v spectrum ; (3) mapping between dv/v spectrum and dv/v depth profile via a supervised learning method. Overall, our numerical analysis demonstrates that the measured dv/v spectrum provides a useful observational metric to monitor the spatiotemporal evolution of local dv/v. We will also discuss the results from real case examples using data from both urban and volcanic settings.

Presenting Author: Congcong Yuan

Authors