Chemical changes in the soil hold clues
.jpg "Scientists monitor seismic activity at the NGRI lab")
AN EARTHQUAKE measuring 8.9 on the Richter scale recently shook Japan, causing a massive tsunami.
Changes in groundwater electrical conductivity and soil radon gas can help predict an earthquake in quake-prone regions, according to a team of geologists in India. Earlier studies by Japanese scientists have shown that prior to an earthquake, seismic stress causes opening and closing of rock microfractures leading to the release of radon gas. They also observed changes in water levels of wells which led the Indian team to embark on the study.
Researchers from National Geoph-ysical Research Institute (NGRI) in Hyderabad measured the total concentration of dissolved salts in water in drilled wells in Ukalu, a quake-prone region between the Koyna and the Warna region in Western Ghats of Maharashtra. They planted a radon probe, an instrument to measure the levels of radon gas, 60 cm below the soil. They measured gas concentration levels with air pressure starting from March 2009. A rise in gas levels was seen prior to two earthquakes measuring 4.7 and 5.1 in December 2009. For the quake measuring 5.1, the gro-undwater electrical conductivity, a measure of the salt present in water, reduced 40 hours before the quake and reached normal levels 20 hours after the quake at another well in the same region. An increased soil porosity and reduced air pressure was accompanied by mixing of freshwater from the top zone in wells.
The drop in groundwater electrical conductivity for a short period can be connected to dilation or increased gaps in the earth’s crust. Dilation increased the flow of less mineralised water from the soil’s upper zone into the well due to reduced air pressure. Radon gas increased due to dilation when new fractures were formed due to tectonic plate movements. The drop in gas levels at the time of the quake showed that fractures had closed. This meant that the radon gas responds to seismic stress and acts as a precursory signal. “These parameters may help check this natural calamity in the future,” said D V Reddy, lead researcher. Findings of the study have been published in the January 26 issue of Applied Geochemistry.
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
.png)
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.