Active faulting in apparently stable peninsular India: Rift inversion and a Holocene‐age great earthquake on the Tapti Fault

Abstract

We present observations of active faulting within peninsular India, far from the surrounding plate boundaries. Offset alluvial fan surfaces indicate one or more magnitude 7.6–8.4 thrust‐faulting earthquakes on the Tapti Fault (Maharashtra, western India) during the Holocene. The high ratio of fault displacement to length on the alluvial fan offsets implies high stress‐drop faulting, as has been observed elsewhere in the peninsula. The along‐strike extent of the fan offsets is similar to the thickness of the seismogenic layer, suggesting a roughly equidimensional fault rupture. The subsiding footwall of the fault is likely to have been responsible for altering the continental‐scale drainage pattern in central India and creating the large west flowing catchment of the Tapti river. A preexisting sedimentary basin in the uplifting hanging wall implies that the Tapti Fault was active as a normal fault during the Mesozoic and has been reactivated as a thrust, highlighting the role of preexisting structures in determining the rheology and deformation of the lithosphere. The slip sense of faults and earthquakes in India suggests that deformation south of the Ganges foreland basin is driven by the compressive force transmitted between India and the Tibetan Plateau. The along‐strike continuation of faulting to the east of the Holocene ruptures we have studied represents a significant seismic hazard in central India.

Chapter 2 Active tectonics of Myanmar and the Andaman Sea

“…These characteristics allow the occurrence of unusually large intraplate events (M w 8+). Similar rupture characteristics have been observed in northwestern India in the 2001 Bhuj earthquake and inferred from prehistoric surface ruptures on the Tapti Fault (Copley et al 2011(Copley et al , 2014. The fact that the entire crust appears to be seismogenic in these regions is commonly attributed to unusual lower-crustal compositions, perhaps due to the absence of small amounts of hydrogen ions dissolved in the crystal lattice of nominally anhydrous minerals, which can greatly increase the strength of rocks (e.g.…”

Effect of Seismogenic Depth and Background Stress on Physical Limits of Earthquake Rupture Across Fault Step Overs

“…This effect has been proposed to explain a rupture depth of 25 km in the 2016 M w 7.8 Kaikoura earthquake inferred from geodetic data (Hamling et al, ). For the same thermal reason, we expect intraplate earthquakes to have a thicker seismogenic layer (Copley et al, ) and hence a larger H c than interplate earthquakes.…”

“…In addition to a thicker seismogenic layer (Copley et al, ), intraplate earthquakes have average stress drop significantly larger than interplate earthquakes (Allmann & Shearer, ; Scholz et al, ). Moreover, Kato () suggests that, in contrast to interplate faults, the loading of intraplate faults is dominated by regional plate stressing rather than by aseismic slip in deeper extensions of the fault; hence, the loading of the seismogenic zone tends to be more spatially uniform than on interplate faults.…”

Crustal Structure and Evolution of the Eastern Himalayan Plate Boundary System, Northeast India

“…The Dawki Fault is the major active fault in the region, with an offset of 13-15 km (this study) and a horizontal convergence rate of 3-7 mm/yr (Vernant et al, 2014). From scaling laws (Kanamori & Anderson, 1975) and examples 10.1002/2017JB014714 of previous intraplate earthquakes within the Indian Peninsula (Copley et al, 2014), such a fault is capable of producing ∼20 m slip, resulting in an M w ∼8 magnitude earthquake. The fault scarp is observed at least for a length of ∼200 km along the southern margin of the Shillong Plateau and given the seismogenic thickness of the Bengal Basin crust of ∼20 km and an offset of ∼15 km, the active fault dimension is estimated to be ∼200 km by ∼35 km.…”