Establishing primary surface rupture evidence and magnitude of the 1697 CE Sadiya earthquake at the Eastern Himalayan Frontal thrust, India

Abstract

Historical archives refer to often recurring earthquakes along the Eastern Himalaya for which geological evidence is lacking, raising the question of whether these events ruptured the surface or remained blind, and how do they contribute to the seismic budget of the region, which is home to millions of inhabitants. We report a first mega trench excavation at Himebasti village, Arunachal Pradesh, India, and analyze it with modern geological techniques. The study includes twenty-one radiocarbon dates to limit the timing of displacement after 1445 CE, suggesting that the area was devastated in the 1697 CE event, known as Sadiya Earthquake, with a dip-slip displacement of 15.3 ± 4.6 m. Intensity prediction equations and scaling laws for earthquake rupture size allow us to constraints a magnitude of Mw 7.7–8.1 and a minimum rupture length of ~ 100 km for the 1697 CE earthquake.

On mitigation of earthquake and landslide hazards in the eastern Himalayan region

“…The eastern region has experienced a few historical earthquakes, and some recent paleoseismological studies have highlighted interesting results. For example, the study carried out by Rao et al (2017), based on trenches at Pasighat, Arunachal region has provided chronological constraint on the paleoearthquake surface rupture and suggested that the 1950 (Mw 8.7) Assam earthquake did break the eastern Himalayan front and produced a co-seismic slip of 5.5 ± 0.7 m. Another recent study from Pasighat (Coudurier-Curveur et al 2020) inferred uplift and abandonment of terraces of elevations between 2.6 ± 0.1 m to 7.3 ± 0.1 m and 11.5 ± 0.1 m. Similarly, another episode of surface rupture was reported from the trench studies (across a scarp in Himebasti Village) on the eastern bank of the Subansiri River along the MFT (Pandey et al 2021). The causative earthquake was believed to have occurred in the age ranging between 1655 and 1826 CE and it is further argued that the most recent rupture at Himebasti occurred after 1450-1650 A.D.…”

Evidence of the 1950 Great Assam Earthquake Surface Break Along the Mishmi Thrust at Namche Barwa Himalayan Syntaxis

“…Inset 1 shows epicenter of last millennial earthquakes in the Himalaya and the Indo-Eurasian plate convergence (Bettinelli et al, 2006;Stevens & Avouac, 2015 A trench at Pasighat reported 1950 surface faulting beneath a ∼3.1 m high fault scarp on the HFT with a co-seismic slip of 5.5 ± 0.7 m (Priyanka et al, 2017). Approximately 130 km west of Pasighat site at Himebasti village, surface faulting by the historical 1697 Sadiya earthquake was documented (Pandey et al, 2021). Further west at Harmutty, the surface faulting with a smaller offset of 2 m was correlated with the 1950 event only because of the closeness of the trench to the 1950 epicentral region (Kumar et al, 2010).…”

“… (a) Regional seismo‐tectonic map of the eastern Himalaya showing the study area at a‐Kamlang Nagar (green solid square), rupture zones of major historical earthquakes (after Bilham, 2019; light green polygons), thrust faults—Himalayan Frontal Thrust (HFT), Mishmi Thrust (MT) and Naga Thrust (NT) denoted by red line with dentition, location of archeological Bhismaknagar Fort (Kri, 2010; light green ellipse), co‐seismic landslides (Rao, 1953), Indian Meteorological Department earthquake data from 1969 to 2017 and ISC‐EHB earthquake catalog from 1905 to 2017, epicentral location (red star) and fault plane solutions of 1950 earthquake (Ben‐Menahem et al., 1974; Chen & Molnar, 1977), previous paleoseismological trench locations (yellow solid squares) at b‐Pasighat (Priyanka et al., 2017), c‐Marbang (Jayangondaperumal et al., 2011), d‐Himebasti (Pandey et al., 2021), e‐Harmutty and f‐Nameri (Kumar et al., 2010), g‐Sarpang Chu (Le Roux‐Mallouf et al., 2016), 1950 isoseismals (Rao, 1953; black dashed lines), LL is the locking line at 3.5 km elevation contour (Avouac, 2003; Mishra et al., 2016). Inset 1 shows epicenter of last millennial earthquakes in the Himalaya and the Indo‐Eurasian plate convergence (Bettinelli et al., 2006; Stevens & Avouac, 2015; black arrows).…”

An embryonic fold and thrust belt south of the Himalayan morphological front: Examples from the Central Nepal and Darjeeling piedmonts

“…)Mishra et al (2016); (34) Kumar et al (2010); (35) LeRoux-Mallouf et al (2020); (36) Dashgupta et al (2013);(37)LeRoux-Mallouf et al (2016); (38)Gupta et al (2017); (39)Pandey et al (2021); (40)Jayangondaperumal et al (2011); (41) Priyanka et al (…”