Subsurface profiling along Banni Plains and bounding faults, Kachchh, Western India using microtremors method. (15th September 2017)

• Record Type: Journal Article
• Authors: Sant, Dhananjay A.; Parvez, Imtiyaz A.; Rangarajan, Govindan; Patel, Satish J.; Bhatt, Madhuri N.; Sanoop Salam, T.A.
• Is Part Of: Journal of Asian earth sciences. Volume 146(2017)
• Page Start: 326
• Page End: 336
• Publication Date: 2017-09-15
• Subjects: Banni Plains, Kachchh Mainland Fault -- Microtremor -- Ambient noise -- Fundamental resonant frequency -- H/V spectral ratio -- Positive flower structure; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2017.06.002
• Languages: English
• ISSNs: 1367-9120

Abstract

Graphical abstract: Highlights: Microtremor studies prove to be a cost effective and rapid tool for approximation of depths for the subsurface interfaces, faults, and plutons. This study provides a mechanism to investigate faults and fault geometries correlating surface structural grains with subsurface structures. A cluster of four imbricate faults (F1, F2, F3, and F4 ) characterises. The Kachchh Mainland Fault Zone/Banni Foot Wall Syncline. These faults have disrupted both Q-T and M-B interfaces. The geometry of the fault cluster signifies a positive flower structure comparable to step-overs, restraining bends that display push-ups because of localized shortening, which occurs between two converging bends. Two episodes of deformations are explained in the Banni Footwall Syncline. The initial event led to the subsidence within the KMFZ bringing Mesozoic sequence juxtaposed to the Basement (F4 ). However, the later event developed a positive flower structure in the KMFZ (F1 to F4 ). Abstract: The present article is a maiden attempt to map shallow subsurface rheological interfaces laterally across the Banni Plains and to decode geometry of the antecedent faults associated with the Kachchh Mainland Fault using the microtremor method. We conducted microtremor data acquisition for thirty-one sites along N-S transect from Loriya in Mainland Kachchh to Bhirandiara towards Patcham Island. Results from H/V spectral ratio technique show presence of two distinct rheological interfaces characterised by the resonant frequency ( fr ) ranges 0.23–0.27 Hz and 0.8252–1.5931 Hz respectively. The above frequency ranges are correlated with the depths of the Mesozoic-Basement (M-B) interface and the Quaternary-Tertiary (Q-T) interface. Using either the velocity ( Vs ) of seismic waves at the M-B and Q-T interfaces (calculated as 1830 m/s and 411 m/s respectively) or the standard non-linear regression relationship derived for the Banni Plains ( h = 110.18 fr −1.97 ) we estimate the depth range for M-B interface to be 1442–1965 m and for Q-T interface to be 44–160 m. The subsurface profile across the Banni Plains educe cluster of four faults that develop an array of imbricate faults at the forefront of the Kachchh Mainland Fault within the Banni Footwall Syncline. The geometry of the faults suggests a 'positive flower structure' indicating step-overs and strain restraining bends displaying push-ups resulting from localized shortening between converging bends of Kachchh Mainland Fault and the South Wagad Fault. The Banni Footwall Syncline preserves evidence of two episodes of deformations. The initial deformation event led to subsidence within the Kachchh Mainland Fault Zone bringing Mesozoic sequence juxtaposed to the basement rocks, whereas the later event is dominated by an uplift developing a positive flower structure in the Kachchh Mainland Fault Zone. Finally, the present study provides a mechanism to investigate faults and fault geometries correlating surface structural grains with subsurface structures.