The Effect of Thin High Velocity Layers on Seismic Refraction Data: An Example from Mahanadi Basin, India

Abstract

For the interpretation of seismic refraction profiles, an internal structure with continuously increasing layer velocity with depth may be an inappropriate model to fit the data. Moreover, velocity inversions, wherein high velocity layers (HVL) alternate with low velocity layers (LVL), are common features in the real earth. In models where the relative thickness of the LVL is large compared to the HVL, the refraction travel time shows a shift. The minimum thickness of the LVL required for such a shift depends on its layer velocity. These shifts can be modeled to determine the thicknesses of the HVL and LVL.An example of this phenomenon is visible in the alluvium-covered Cuttack depression of the on-shore Mahanadi basin, where travel-time shifts can be correlated with thin volcanic layers in the well data. Reinterpretations of the seismic refraction data, after considering the existence of volcanic layers and using forward modeling and a 2-D ray-tracing technique, show the extent of these layers within the depression.

Chipping of cratons and breakup along mobile belts of a supercontinent

“…Cretaceous volcanism obtained from the lithologies in the oil wells of Mahanadi MB ( Fig. 1(a)), also suggest plume-induced crust-mantle interaction (Tewari, 1998). A high velocity deep crust is inferred beneath the Bengal basin too (Kaila et al, 1992), which also exhibits a gravity high anomaly (∼20 mgal) sub-parallel to 90…”

85°E Ridge, India — constraints on its development and architecture

“…Studies made by Agarwal Rama (1976), Sarkar et al (1980), Paul et al (1990), Tewari (1998) and Subrahmanyam et al (1999) indicate a timing of 107 Ma for the volcanism in the Mahanadi basin at 19.5 o N, and 67 Ma for the volcanic rocks in the Afanasy-Nikitin seamount to the south across a distance of about 2200 km for the entire hot-spot track (Subrahmanyam et al, 1999). The hot spot track is not as linear as the Hawaiian-Emperor chain (Schubert et al, 2001), and contains volcanoes isolated from the main track as well, resembling more the Canary chain, which contains numerous solitary volcanoes located to the south of the main track (Nemèok et al, 2005).…”