Delineation of Subtrappean Mesozoic Sediments in Deccan Syneclise, India, Using Travel-Time Inversion of Seismic Refraction and Wide-Angle Reflection Data

Abstract

2-D shallow velocity structure is derived by traveltime inversion of the first arrival seismic refraction and wide-angle reflection data along the E-W trending Narayanpur-Nandurbar and N-S Kothar-Sakri profiles, located in the Narmada-Tapti region of the Deccan syneclise. Deccan volcanic (Trap) rocks are exposed along the two profiles. Inversion of seismic data reveals two layered velocity structures above the basement along the two profiles. The first layer with a P-wave velocity of 5.15-5.25 km s -1 and thickness varying from 0.7-1.5 km represents the Deccan Trap formation along the Narayanpur-Nandurbar profile. The Trap layer velocity ranges from 4.5 to 5.20 km s -1 and the thickness varies from 0.95 to 1.5 km along the Kothar-Sakri profile. The second layer represents the low velocity Mesozoic sediments with a P-wave velocity of 3.5 km s -1 and thickness ranging from about 0.70 to 1.6 km and 0.55 to 1.1 km along the E-W and N-S profiles, respectively. Presence of a low-velocity zone (LVZ) below the volcanic rocks in the study area is inferred from the travel-time 'skip' and amplitude decay of the first arrival refraction data together with the prominent wide-angle reflection phase immediately after the first arrivals from the Deccan Trap formation. The basement with a P-wave velocity of 5.8-6.05 km s -1 lies at a depth ranging from 1.5 to 2.45 km along the profiles. The velocity models of the profiles are similar to each other at the intersection point. The results indicate the existence of a Mesozoic basin in the Narmada-Tapti region of the Deccan syneclise.

Extension of Godavari Gondwana sediments underneath Trap covered region of Satpura basin as evidenced from seismic studies in Deccan Syneclise, India

“…Like in our earlier studies (Murty et al, 2008(Murty et al, , 2010(Murty et al, , 2011 we have adopted velocity uncertainty of 0.1 km s À1 and boundary uncertainty of 0.1 km values used by Zelt and Smith (1992) Tables 1 and 2 for the two profiles respectively. The final velocity models are displayed in Fig.…”

Extension of flood basalt on the northwestern continental margin of India

“…Onshore data comprises P-wave velocities (Kaila et al 1981a(Kaila et al , b, 1987(Kaila et al , 1989a(Kaila et al , b, 1990; Kaila and Krishna 1992;Kumar et al 2000;Reddy 2005;Murty et al 2010) in Deccan flood basalt, which are derived from Deep Seismic Sounding (DSS) surveys carried out by National Geophysical Research Institute, Hyderabad, India. P-wave velocity derived from earthquake data (Krishna 2004) and from dispersion of short-period Love wave data (Tandon 1973), is utilized in this study.…”

Delineation of Trap and Subtrappean Mesozoic Sediments in Saurashtra Peninsula, India

“…In certain geological situations such as in regions with thin Trap lying over thick low-velocity sediments, distinct amplitude decay and time 'skip' in first-arrival refraction phases are observed. These signatures are indicative of the presence of low-velocity sediments below high-velocity Trap rocks [11][12][13][14][15][16][17] . Therefore, seismic refraction and wide-angle reflection datasets can be effectively used to build a wellconstrained subsurface velocity structure in Trap-covered regions.…”