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The Himalaya is a mountain range of 2400 km between 75°E and 98°E, extending from Kashmir to Arunachal Pradesh in the north-east and divided longitudinally and transversely into different parts viz Punjab Himalaya, Kumaon Himalaya, Nepal Himalaya and Assam Himalaya. Transversely, the Himalaya is further divided as the Greater Himalaya, Middle Himalaya and Lesser Himalaya. It is originated due to the convergence of Indian and Eurasian plates some 50 ma, where compressional forces existing between two plates (Gansser 1964)
Geological investigations suggest that the Himalaya was built-up by the sliver of the Indian continent that was over-thrusted to the south (Gansser, 1964; Le Fort, 1975).
From the beginning of convergence in Late Cretaceous time, followed by the collision in the Middle Eocene (50 Ma) along the Indus-Tsangpo suture zone, the successive zones of deformation have progressively advanced or jumped southward, resulting in faulting and folding along the prominent structural features of the Himalayan orogenic belt (Gansser, 1964; Seeber and Armbruster, 1981; Lyon-Caen and Molnar, 1983). These major tectonic features (Indus-Tsangpo Suture Zone - ITSZ; Main Central Thrust - MCT; Main Boundary Fault - MBF; and Himalayan Frontal Fault - HFF) have played a pivotal role in the structural and topographic architecture of the Himalaya.
The MCT and MBT are considered to be the sites of Cenozoic shortening along the entire length of the Himalaya (Gansser, 1964; Valdiya, 1984b), however, the present tectonically active boundary between the Indian and Eurasian plates is marked by the HFF (Nakata, 1972, 1975, 1989), where active anticlines and synclines are the surface manifestations of displacement on a buried decollement fault (Yeats et al., 1992, 1997).
The focus of the present dissertation work is on Garhwal Himalaya which had suffered number of major and moderate earthquake since 1803 still have an active seismic hazard potential.
The latest two earthquakes of Uttarakashi and Chamoli earthquake of 1991 and 1999 having magnitude 6.4 Ms. and 6.8Ms respectively indicates the active nature of the Garhwal. Himalaya. The occurrence of theses earthquake and migration of seismic activity along the Garhwal Himalaya was an important aspect which needs to understand that how different thrust or faults are behaving with time and space. Considering this aspect in mind the present work has been focused on seismic migration behavior of seismicity in Garhwal Himalaya and efforts have been made to see if it is possible to identify active seismic zone which can be capable of generating earthquake in near future.
The Garhwal region, North-west Himalaya was again shook by a large magnitude earthquake on 1st September, 1803 as documented in historical records mentioning the damage from Panjab in the west to Kolkata in the east and extended to the south to few cities located in Indo-Gangetic plains Rajendran and Rajendran (2005). According to Raper (1810); Hodgson (1822); Bard-Smith (1843), there was an damage to building and temples in the region killing 300 peoples reported severe damage in Uttarkashi region during 1803. Some of the historical documents indicated its locations near Mathura in Indo-Gangetic plain based on the damage pattern and extensive liquefaction (Piddington, 1804; Oldham, 1883; Bard and Smith (1843).
The location of the 1803 earthquake (M 8.1) is very uncertain. According to Oldham (1883), there was extensive damage in the Garhwal Himalaya, in the Kumaon Himalaya and in the Nahan region of Himachal (west of Garhwal), at the Qutab Minar, New Delhi, and further south near Mathura where extensive fissures in the field and liquefaction was reported. Little information was been given by Oldham (1883) on the damage to the east and west of the Kumaon region from this earthquake, but sufficient details were mentioned by Ambraseys and Jackson (2003) from the accounts of a British officer diary who visited several affected places after the earthquake.
These officers have also mentioned major damage from Joshimath to Karanprayag in the Garhwal Himalaya and to the south up to Mathura and even Jabalpur in the west and up to Calcutta in the east. Ambraseys and Jackson (2003); Rajendran, (2005) also suggested its epicentre in Garhwal whereas; IMD has suggested the location of A. D. 1803 earthquake in the Central Himalayan region. According to Rajendran and Rajendran (2005) comparatively, the same region has very less damage from 1991 Uttarkashi earthquake (mb 6.8), hence it was inferred by them that 1st September 1803 earthquake was bigger than 1991 earthquake.
Based on liquefaction reports (Piddington, 180, Oldham, 1883) it is believed that 1803 earthquake might have intensity more than VII (MSK-64) in Mathura (liquefaction can normally only occur at intensity larger than VI). This raises the question that whether it was the same earthquake which had caused damage both in Garhwal and Mathura or if there were two different earthquakes, one near Garhwal and another one near Mathura ? or it was a single event. If it is a single event which had caused extensive damage in Himalayan region as well as southern part near Mathura, thus reflects either site amplification or occurrence of an earthquake along a transverse features. A
ccording to presence of Delhi-Haridwar ridge along the same line, it can be possible that 1803 earthquake might have caused along the transverse feature which allow the damage to be cause in Garhwal, Kumaon, Huimachal and southern part near Mathura. It is inferred that this earthquake might have occurred along a transverse feature which displaced the major longitudinal features and thus caused extensive damage in comparison to the 1505 event. We have in our evaluation concluded that it was indeed an M 8.1 earthquake as shown in Table-1. The review of 1505 and 1803 earthquake have revealed that both earthquake have occurred in Garhwal region within a gap of almost 300 years and both event have been characterised as great earthquake as per historical records.
Garhwal Region in Himalayas. (2021, Dec 17). Retrieved from https://studymoose.com/garhwal-region-in-himalayas-essay
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