Garnet is widely used as a gemstone from the bronze age. But this beautiful gemstone can be used to reveal the historical mega-earthquake in the earth history. The mega-earthquake footprint is recorded by the garnet mineral itself in the structure of the garnet mineral. Garnet is widely used to determine the temperature and pressure a rock has been exposed during the metamorphism process. Through this regular cycle of the garnet, scientist revealed some more interesting from this remarkable mineral.
How can garnet reveal the past Maga Earthquake?
Usually, the catastrophic earthquake occurs in the subduction zone and produce devastating tsunami like 2004, Mw 9.2 Sumatra-Andaman and 2011 Mw 9.0 Tohoku-Oki, Megathrust earthquake. In these subduction setting, the rock undergoes metamorphism at high pressure and low temperature. When the seismic waves pass through the overpressure is released as the seismic waves vibrate the medium and release the overpressure in the rock. After a Mega earthquake, overpressure again begins to develop as it is the garnets usual mechanism for the growth and it continues to grow in the rocks. These cycle of overpressure and dissipation can be recorded in garnet for the individual earthquake events. Sources; (Sci. Adv. http://doi.org/cmrt; 2018).
This is mechanism is similar to the tree-rings as a store of a history of climate and environmental changes. The geochemical zonation in garnet lock the record of earthquake-induced cycles of rising and falling pressure. Scientist found four substantial pressures pulses each of 100-350 Mpa within a geologically brief age of 300000 years.
Future and past record of a Mega earthquake by Garnet geochemical zonation;
The paleoseismic record based on the research of the sedimentary record can only reveal the 2.5 million years old historical earthquake. The chemical zoning in garnet can dating back at least 145 million years and may, therefore, allow the paleoseismic record extended much further back in time. These gemstones may help to reconstruct the ancient Mega earthquake and magnitude also.