Mumbai: Paleoseismic investigations can help trace and understand the history of earthquakes and help prepare for the future, a study by scientists from the Indian Institute of Geomagnetism has indicated. The scientist identified seismogenic liquefaction features like multiple sand dykes and sand sills in an active fault in the northeastern region (NER), called the Kopili fault (KF) zone which is known to have experienced large earthquakes in 1869 and 1943.
To mitigate future occurrences of earthquakes in the Kopili fault (KF) zone which is known to have experienced large earthquakes in 1869 and 1943, scientists identified seismogenic liquefaction features at three trench sites in the floodplain deposits of Kolong River, near KF. The liquefaction features include multiple sand dykes and sand sills and are a direct response to the liquefaction of saturated sediment induced during past seismic activity.
Seven samples from marker horizons have been processed to constrain the chronology of liquefaction features using an optically stimulated luminescence (OSL) dating technique.
The OSL age constraints indicate two earthquake-induced liquefaction in the vicinity of the KF during the past around 480 years. These details in turn will help interpret the long-term rupture history of faults and intraplate seismicity. The study published in Natural Hazards demonstrates that paleoseismic investigations can provide useful information on past earthquakes through the recognition of liquefaction features in the absence of surface rupture.
The occurrence of great earthquakes in the past, for which no historical or instrumental records are available, can be identified in the form of geological, geomorphological, fluvial signatures and radiocarbon dating, to arrive at the most crucial aspect of the recurrence period of major earthquakes in the region.
Liquefaction or transformation of granular material from a solid to a liquefied state due to increased pore water pressure is crucial secondary evidence of earthquakes. It occurs mostly in soft sedimentary sequences, especially interbedded sand and silt or clay. The structures resulting from liquefaction include sand dykes, sand blows, sand veins, pseudo-nodules, convolute bedding, load structure, and so on. This is important for designing bridges and big buildings to withstand future large earthquakes.
– global bihari bureau
