Earthquake hazard rick in seismically unpredictable Kachchh paleo-rift intra-plate basin in western India

Though earthquake science developed immensely all over the world, there are gaps in levels of predications due to site variability, plate settings and rheology as well as fault rupture and behavior. Further, a known behavior of one fault zone cannot be directly carried out to the other similar tectonic environments except some broad characteristics and features. Hence the nature of each fault even in the same tectonic basin needs to be understood separately and the overall paleoseismic character of the area can be inferred. Kachchh intra-plate basin is located on the margin of Aravalli craton of Indian plate. The basin generated during Gondwana rifting, while rift dominated sediments deposited in normal tectonic environment. Owing to its inverse tectonics in post Indo-Eurasia collision history, the sedimentary cover over the granitic basement deformed at numbers of fault locations on the surface and sub-surface. Inverse wedges of basement blocks frequently generate earthquakes due to movement of Indian plate to the NE and anticlockwise. The basinal faults like Nagar Parkar Fault-NKF, Island Belt Fault- IBF, Kachchh Mainland Fault-KMF, South Wagad Fault-SWF and North Kathiyawar Fault-NKF behave differently in time and space; and are reflected by present day earthquake pattern, paleoseismology and neotectonic behavior along these faults. The earthquake studies undertaken by various workers in the past two decades suggest highly erratic nature of various faults. As the historical records of property damage and ground rupture and also paleoseismic studies of 1819 Allahbund earthquake disclose the fact that a 90 km long, 16 km wide and 2.5m high ridge formed during this earthquake. Detail study on this earthquake suggests that no fault related to this earthquake on the surface exists, but the cumulative uplifts of Allahbund ridge and landscape modification of western great Rann in last 2.5ka is revealed. An event between 1400 to 2200 years BP is presumed for this fault where practically no fault is found on the surface. Further, for 1956 Anjar earthquake no specific fault location is found and no recurrence period has been till date due to lack of paleoseismic records. However it is established that this earthquake reactivated the secondary Katrol Hill Fault. In the highly instrumental era, 2001 Bhuj earthquake generated large number of data related to ground rupture, earthquake geophysics and physical damage but similar event of such size on the same fault is highly skeptical and the fault plane is practically a blind thrust portrayed by aftershock patterns. Size of liquefaction and ground rupture with the epicentral distance, microzonation studies, earthquake geophysics and plate motion studies pre and post disaster carried out for this devastating earthquake in which nearly 20000 people lost their lives with property damage worth billions of dollars. However no specific faults that today nicely exposed on the surface have reliable historical records of earthquake nor good geological ones except the KHF has displaced the Quaternary sediments gives very vague picture of KHF behavior as not devastating earthquake is reported in the human history, hence no earthquake recurrence can be deduced from the present day study. In addition, no matters how much vulnerability is envisaged in any of the area in Kachchh basin for any fault that reactivates in the basin that makes the entire area highly unpredictable for earthquake hazard probability. Even though plenty of earthquake geological work carried out in Kachchh faults in last two decades it is indeed in immature stage and many more new aspects need to be explored in future to mitigate the earthquake hazard risk in the fast developing largest district in India.