The Scientists have found the first geological evidence of an earthquake at Himebasti Village on the border of Assam and Arunachal Pradesh, documented by historians as Sadiya earthquake in history, which is recorded to have caused massive destruction in the region and almost destroyed the town in 1697 CE.
This finding could contribute to a seismic hazard map of the eastern Himalaya, which can facilitate construction and planning in the region.
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 they contribute to the seismic budget of the region, which is home to millions of inhabitants.
Scientists from Wadia Institute of Himalayan Geology (WIHG), a research institute under the Department of Science and Technology (DST), Govt. of India, carried out a mega trench excavation at Himebasti village, Arunachal Pradesh, India.
They found the first geological surface rupture signatures in the form of exposed deposits associated with rivers and streams deformed by a thrust fault along a Northeast dipping fault zone.
In order to constrain the causative faulting event at this site, the team dated twenty-one radiocarbon samples from the trench exposure.
The seismic hazard map of India is a critical input data for planning and implementation of retrofitting/reconstruction programs for existing houses located in seismic vulnerable zones.
The information provided in this map helps State governments, urban local bodies, and highways departments to plan infrastructure and develop housing schemes keeping in mind the earthquake risks. This information should be considered as minimum standards which need to be modified considering specific conditions of each region.
The current, as well as future earthquake hazards, can be visualized using this Map. Seismic Hazard Maps are used by national and international organizations for various studies related to Earthquake Risk assessment, disaster risk management, infrastructure, etc.
India has been divided into four seismic zones (II, III, IV, and V) based on scientific inputs relating to seismicity, earthquakes occurred in the past and tectonic setup of the region.
Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.
The Richter scale is used to rate the magnitude of an earthquake - the amount of energy it released. This is calculated using information gathered by a seismograph. The Richter scale is logarithmic, meaning that whole-number jumps indicate a tenfold increase. In this case, the increase is in wave amplitude.
The Mercalli intensity scale (or more precisely the Modified Mercalli intensity scale) is a scale to measure the intensity of earthquakes. Unlike with the Richter scale, the Mercalli scale does not take into account energy of an earthquake directly.