Estimation of shear wave velocity structure using joint inversion of surface-wave phase and group velocities derived from ambient noise recordings

Takumi Hayashida, Toshiaki Yokoi, & Mukunda Bhattarai

Submitted August 15, 2019, SCEC Contribution #9827, 2019 SCEC Annual Meeting Poster #057

The usual geophysical exploration method using ambient noise (microtremor) array is focusing on deriving phase velocity dispersion curves of longer wavelength (2-10 times of sensor-to-sensor distance) Rayleigh wave and estimating S-wave velocity structure model from the dispersion curve inversion (Aki, 1957; Okada, 2003). On the other hand, a number of recent studies have applied seismic interferometry to ambient noise data from regional to continental scale seismic networks in order to obtain group velocity characteristics of shorter wavelength (i.e. smaller than sensor-to-sensor distance) surface waves. The successful use of both approaches indicates that broad-range wavelength characteristics of surface wave could be obtained by applying the two different techniques to the same dataset. We investigated the possibility of joint inversion of surface-wave phase and group velocities toward better estimation of S-wave velocity structure for deep sedimentary layers. Our numerical experiments showed that the combined use of phase and group velocities from the same dataset has an advantage in constraining thickness and S-wave velocity of the whole layers without deploying smaller arrays. We applied this technique to ambient noise array data measured in the Kathmandu Valley, Nepal where thick sedimentary layers exist. In addition to phase velocity dispersion curve in the lower frequency range, distinct wave trains corresponding to surface waves were detected by seismic interferometry in the higher frequency range, making it possible to obtain dispersive characteristic of surface-wave velocities in wide frequency range from limited ambient noise data. The estimated S-wave velocity structure model using the joint inversion without smaller array corresponds well to those of existing results, indicating that our approach can be a reasonable tool to reduce time and effort for actual survey.

Key Words
ambient noise, phase velocity, group velocity, seismic interferometry, joint inversion

Citation
Hayashida, T., Yokoi, T., & Bhattarai, M. (2019, 08). Estimation of shear wave velocity structure using joint inversion of surface-wave phase and group velocities derived from ambient noise recordings. Poster Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
Seismology