The Mizoram state of India lies in close proximity to the active Indo-Burma subduction zone and had experienced several moderate to large earthquakes, including the M7 event in 1938. Since 2015, only two events with 5<M<6 have occurred in the area, however, a sudden enhancement of earthquake activity (M3.0–M5.7) was observed from June to August 2020 in the eastern part of the Mizoram state, including the four events of M ≥ 5.0. We analysed the waveform data of 21 events recorded by the local and regional BBS to estimate the source parameters. The focal depth of these events varies from 13 to 45 km, while other parameters such as corner frequency, source radius, stress drop, and scalar seismic moment of the events are found in the range of 0.45–3.36 Hz, 0.77–5.58 km, 1.3–193 bars, and 3.98107E+13 to 6.30957E+17 Nm, respectively. The seismicity pattern shows two distinct clusters along the well-demarcated faults in the region, and most of them are generated by strike-slip movements. The Churachandpur-Mao Fault (CMF) is found to be the most active tectonic element in the study area. Hence, an M8 event has been simulated on the same fault using the stochastic simulation technique. The technique was validated by simulating the three M+5 events on the same source zone and comparing the simulated PGA, frequency, and response spectrum with the observed data. The simulation reveals that a PGA ∼480 gals is expected near the fault zone. The easternmost districts of Mizoram, such as Champai, Serchhip, Lunglei, Saiha, and Aizawl, may experience severe PGA (250–450 gals). The response spectral acceleration corresponding to single-storey, double-storey, 3–4 storey, and 5–6 storey buildings has also been estimated in the present study and it is found to vary in the range of 1,400–200 gals. The result of the present study will be useful in various engineering applications and help reduce the loss of lives and damage to infrastructure due to future large events in the region.
We present crustal thickness and Poisson's ratio determinations from receiver function analyzes at 32 sites on the Archaean and Proterozoic terrains of South India. The crustal thickness in the late Archaean (2.5 Ga) Eastern Dharwar Craton varies from 34–39 km. Similar crustal thickness is observed beneath the Deccan Volcanic Province and the Cuddapah basin. The most unexpected result is the anomalous present‐day crustal thickness of 42–51 km beneath the mid‐Archaean (3.4–3.0 Ga) segment of the Western Dharwar Craton. Since the amphibolite‐grade metamorphic mineral assemblages (5–7 Kbar paleopressures) in this part of Western Dharwar Craton equilibrated at the depths of 15–20 km, our observations suggest the existence of an exceptionally thick (57–70 km) crust 3.0 Ga ago. Beneath the exhumed granulite terrain in southernmost India, the crustal thickness varies between 42–60 km. The Poisson's ratio ranges between 0.24–0.28 beneath the Precambrian terrains, indicating the presence of intermediate rock type in the lower crust. These observations of thickened crust suggest significant crustal shortening in South India during the Archaean.
This chapter provides an overview of the earthquake precursory research scenario in India. The progression path of these activities is traced for two contrasting tectonic blocks, the Himalayan interplate region, where working models for earthquake occurrences are reasonably well established, and the Koyna–Warna zone, located in the stable shield region and known as a classic case of reservoir-triggered seismicity. The seismic swarm quiescence and nucleation trend have been used successfully to issue medium- and short-term forecasts, respectively, although they remain a case of singular success restricted to a single study area. The existence of short-term precursors to earthquakes in geophysical, geochemical and hydrological parameters is also abundantly documented, which broadly conforms to the hypothesized physical mechanism. In consideration of singular success stories, selective appearances and changing diagnostic signatures, no precursor or class of precursors can be considered deterministic for real-time short-term prediction, but they also cannot be rejected as chance detection. In the continued endeavour to improve the understanding of physical processes and prediction capabilities, two new initiatives include the establishment of Multi-Parameter Geophysical Observatories, making simultaneous measurements of multiple parameters, to enable their validation with each other and arrive at a synthetic probability for use in forecasting, and a major mission to drill a deep borehole and set up an observatory in Koyna to study the earthquake process in in situ conditions. The discussion ends with a brief account of the earthquake early warning program and the arrival time of destructive surface waves to urban cities prior to the earthquake's arrival.
'%3e%3ccircle r='20' fill='%23008'/%3e%3ccircle r='17.5' fill='%23fff'/%3e%3ccircle r='3.5' fill='%23008'/%3e%3cg id='d'%3e%3cg id='c'%3e%3cg id='b'%3e%3cg id='a' fill='%23008'%3e%3ccircle r='.875' transform='rotate(7.5 -8.75 133.5)'/%3e%3cpath d='M0 17.5.6 7 0 2l-.6 5L0 17.5z'/%3e%3c/g%3e%3cuse xlink:href='%23a' transform='rotate(15)'/%3e%3c/g%3e%3cuse xlink:href='%23b' transform='rotate(30)'/%3e%3c/g%3e%3cuse xlink:href='%23c' transform='rotate(60)'/%3e%3c/g%3e%3cuse xlink:href='%23d' transform='rotate(120)'/%3e%3cuse xlink:href='%23d' transform='rotate(-120)'/%3e%3c/g%3e%3c/svg%3e)