Full-wave tomography: Method and application to the south-east Tibetan plateau
The so-called 'finite-frequency' study in seismic tomography was introduced about a decade ago, and has become computationally affordable in recent years. In this thesis, I studied the finite frequency behavior of head waves, and validated the scatter-integral method using numerical simulations of wave propagation in 3D reference models. Moreover, I applied the scattering-integral method to the Tibetan plateau. Head waves provide important information for layered media, such as the Earth. Our numerical study show that head waves have sensitivities not only on the layer interface but also in the lower layer. More importantly, the maximum sensitivity in the lower layer is at a depth that depends on the wavelength and epicentral distance, below the layer interface. This result has been published in 2007 (see the title page of chapter one). For many years, compressional and shear velocities (Vp and Vs correspondingly) of the Earth were studied separately. In a synthetic test, we validate the scattering-integral method and show that S velocity controls not only propagation of S waves, but also affects P waves. In contrast, P velocity has little influence on S waves. This result has been published in 2008 (See the title page of chapter 2). We apply the so-called scatter integral method, one of the finite-frequency tomography implementations, to the Tibetan plateau. Generally, all three components of seismic records are used, depending on the quality of the data, and the records are filtered into three frequency bands, 10-30s, 20-60s and 40s-120s. P and S velocities are inverted together. We observe a velocity anomaly boundary around the Indus-Yalu suture, which suggests that the Indian crust probably extends to the suture. North east of the eastern syntaxis, we find a high velocity upper crust overlying a low velocity lower crust, which supports the lower crust flow model. Also, in an east-west vertical profile, we observe that the high velocity upper crust is segmented by low velocity anomalies. This structure may be related to the north-south trending rift system observed on the surface and erosion of the river system on the southeast Tibetan plateau.
"Full-wave tomography: Method and application to the south-east Tibetan plateau"
Dissertations and Master's Theses (Campus Access).