Recent felt earthquakes (Mw 5.0–5.9) in Mizoram of north‐east India region: Seismotectonics and precursor appraisal

Abstract

Eight medium magnitude (Mw 5.0-5.9) severely felt earthquakes, mostly at a shallower depth (<35 km), occurred in a short period of 7 months only, April-October, 2020, in Mizoram State, north-east region (NER) of India, and it created much panic in the state. The increasing population growth as well as rapid urbanization in Aizawl, the capital city of Mizoram, may be under severe threat for an impending large earthquake in the region. The NER, India, is jawed between two arcs, the Himalayan Arc collision zone to the north and the Indo-Burma (Myanmar) Arc subduction zone to the east, and witnessed two great earthquakes (Mw ≥ 8.0, 1897 and 1950) and a total of 25 large earthquakes (Mw ≥ 7.0) in the past since 1869. The 2020 sudden burst of seismic activity in Mizoram, along with a strong (Mw 6.7) earthquake in Manipur in 2016 and a medium magnitude (Mw 5.7) earthquake in 2017 in Tripura, adjacent to the Mizoram State, are critically examined to understand the ongoing seismotectonics and the precursor implications, if any. The 2016 Manipur earthquake is interpreted to be an intra-plate earthquake triggered by the transverse Kopili Fault by strike-slip motion. The 2017 Tripura earthquake is also interpreted to be typically an intra-plate strike-slip event in the eastern margin of the Bengal Basin. The seismic activity in Mizoram, on the other hand, is found to have occurred in the accretionary Indo-Burma Wedge, between the Churachandpur Mao Fault and Eastern Boundary Thrust. The centroid moment tensor solutions of the events suggest the dextral-slip motion of the wedge along the Indo-Burma Arc.A preliminary analysis of the Mizoram seismicity recognizes a precursor anomaly, a temporal variation of much higher seismic activity, for an impending large earthquake in the study area.

Recent large and strong earthquakes in the eastern Himalayas: An appraisal on seismotectonic model

“…The 28 April 2021 foredeep earthquake Mw 6.1 occurred at the northern end of the Kopili Fault in the Assam valley (Figure 3), and it caused severe shaking, damage to the weak structures, ground liquefaction, fractures, and so on resulting in maximum intensity VII within a radius of 50 km (Dey et al, 2022). The GCMT solution with a centroid depth at 39 km shows strike‐slip faulting, and the NW trending northeast dipping nodal plane is conformable with the Kopili Fault (Figure 3; Hazarika & Kayal, 2022) inferred this event to the Kopili Fault, that occurred by right‐lateral strike‐slip movement.…”

“…The recent seismicity recorded by the local network shows intense bimodal seismic activity along the Kopili Fault; the earthquakes are intense in the upper crust at a shallower depth (0–20 km) as well as in the lower crust and crust–mantle boundary at a deeper depth (30–50 km), the middle crust remaining less active (Kayal et al, 2012). The 2016 earthquake Mw 6.7 in Imphal (Manipur) is inferred to have occurred by strike‐slip faulting at the southernmost end of the Kopili Fault at a deeper depth (40 km) where it intersects the thrust system in the Indo‐Burma Arc (Hazarika & Kayal, 2022; Figure 3).…”

The 2020 earthquake sequence and seismic hazard scenario of Mizoram state in northeast India

“…Vorobieva et al (2021) very recently, using the Block-and-Fault Dynamics model, showed that the India-Burma megathrust is locked and can generate an M8+ event in the area. Similarly, Hazarika and Kayal, (2022), postulated that the IBW is accommodating a part of the plate movement by strike-slip motion along the plate boundary causing shallower earthquakes in Mizoram and suggested that this could be a precursor for an impending large earthquake in the magnitude range M w ~7.0 in the IBW, which is not unusual in the subduction zone as observed in the past (Gupta and Singh, 1989). Vorobieva et al (2021) further inferred that aseismic slip in the CMF significantly reduces the seismic hazard of great interplate earthquakes in the region and CMF almost does not contribute to regional shortening.…”

“…The remaining motion might be accommodated between India and Sunda plates (Hazarika and Kayal, 2022). Mallick et al (2019) argued that the India and Burma plates are fully coupled up to a depth of ~30 km and the active convergence across the IBR is going on at a rate of ~12-24 mm/year.…”

Spatial variations of crustal thickness and Poisson's ratio in the northeastern region of India based on receiver function analysis

“…The complicated tectonics of the region produced two great earthquakes, the 1897 Shillong Plateau earthquake (Mw 8.4) and the 1950 Assam earthquake (Mw 8.6) (Ambraseys & Douglas, 2004; Ben‐Menahem, Aboodi, & Schild, 1974; Tillotson, 1951). Besides these great earthquakes, the region witnessed a total of 25 large earthquakes (Mw ≥ 7.0) in the past, since 1869 (Hazarika & Kayal, 2022; Kayal, 2008; Nandy, 2001). The great and large earthquakes are mostly due to the collision tectonics in the north and subduction tectonics in the east (Copley & McKenzie, 2007; Gahalaut et al, 2013; Gahalaut & Kundu, 2016; Kayal, 2008; Kumar, Mitra, & Suresh, 2015; Satyabala, 2003).…”