Observations and Inversion of Rayleigh Wave Ellipticity in the Deccan Volcanic Province

Abstract

Traditionally, surface wave imaging is carried out by inverting phase and group velocity dispersion measurements. This method exhibits weak sensitivity to the shallow surface when using passive seismic methods due to the lack of high frequency data. Rayleigh wave ellipticity (H/V ratio), is the ratio of amplitudes in the horizontal and vertical components. H/V ratio shows an increased localized sensitivity to the near surface, even at relatively longer periods (over a few seconds), making it ideal for studying the shallow crustal structure. It also allows for the retrieval of earth structure beneath each station without the need of a description of the structure between source and receiver. This feature is particularly relevant in areas with low or uneven data coverage. In this thesis, we compute robust measurements of H/V ratio using ambient noise and earthquake data. To obtain these measurements, we compared and compiled methods and quality control criteria from different studies on computing H/V ratio from ambient noise and earthquake data for the best results. These measurements are inverted along with Group velocity and Receiver Functions in a Trans-dimensional Bayesian framework to obtain shear-wave velocity models in the Deccan Volcanic Province. Our inversion framework is able to map sedimentary layers at shallow depths and also significant interfaces and structures at depth, showing good correlation with previous studies. We also notice high and low velocity anomalies of interest in the inverted profile. We also find the existence of an NE-SW oriented azimuthal anisotropy in the shallow crust, detected by H/V ratio.