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HYDRO-SEISMOLOGY: SEISMIC GROUNDWATER MONITORING

HYDRO-SEISMOLOGY: SEISMIC GROUNDWATER MONITORING

Groundwater covers about 30% of the global water supply, approximately 0.76% of the entire global water, including snow and ice-covered areas (School, 2019). All the living beings on Earth depend on water. Water is an essential naturally available commodity that is almost impossible to live without water. Have you ever imagined about living without water? We human beings can even live without food but cannot live without water for more than three days (Johnson, 2019).

So, how do we measure and monitor groundwater availability? Submersible pressure transmitter monitors and measures the groundwater levels. This transmitter suspends through a cable into the well, bore well or deep bore well. The underground line or Programmable Logic Controller (PLC) system by telemetric systems collects the groundwater availability data (Microsites Wika).

Ground Water Monitoring In Mountains

However, it is pretty challenging to monitor the groundwater in less accessible areas such as mountainous regions. The mountainous regions are frozen for some part of the year, which keeps the slopes stable like a flat surface. But when the ice starts to melt, it becomes life-threatening for people living in the valleys. Similarly, constant rainfall in mountainous regions can cause floods. Landslides are also highly prevalent in mountainous regions owing to the sloppy areas. Landslides are primarily caused due to earthquakes, volcanic eruptions, and heavy rainfall and mainly due to changes in the groundwater. We can predict the occurrence of these natural calamities in the mountains using groundwater monitoring. Hence, groundwater monitoring in mountainous regions is of practical importance.

Figure 1: Earthquake prediction using Seismic waves; Image Courtesy: (Waikato)

The subsoil present can store water in itself. This concept inspired Researchers from Germany and their colleagues from Nepal to monitor the groundwater using seismic waves. Their research is published on 18th May 2021, in AGU Advances (L. Illien, 2021). Seismic waves are caused due to the movement between the layers of the Earth. The seismic waves result from earthquakes, volcanic eruptions, and other naturally or artificially occurring calamities that disturb the surface of the Earth. The seismic waves are measured using a highly sensitive instrument called a seismometer. The seismometer can predict the occurrence of an earthquake using the data from seismic waves. The seismic waves propagate rapidly and let go of destructive forces if any subsurface ruptures. The waves propagate dissimilarly in the surface saturated with water compared to the unsaturated water surface. The earthquake prediction data can be extrapolated further based on the dissimilarity in the seismic waves propagation in the subsurface, which retains the water. The subsurface that retains the water is called the vadose zone.

Figure 2: The Propagation of seismic waves in the subsoil; Image Courtesy: (Brûlé, 2017)

The Researchers from Germany used two seismic stations, one at 1200 meters above sea level and the other at 2300 meters above sea level. They collected data on available groundwater over three monsoon seasons. They created a groundwater model that, compared to the seismic waves’ data, could provide accurate details about groundwater availability at that particular time.

The researchers divided the annual cycle based on the groundwater modelling and seismological, hydrological and meteorological observations into four stages. The first stage is the dry stage, in which the groundwater reservoir is depleted. In the second stage, the de-coupled stage, there is a little bit of subsurface moisture after the conversion of precipitation in the pre-monsoon stage but does not fill the reservoir. The third, coupled stage-in which the vadose zone is filled its capacity and the groundwater is recharged amid monsoon season. The fourth stage, the coupled stage, is when the monsoon precipitation stops, there is slowed groundwater recharge and the dry stage sets in again.

The transition from the de-coupled to the coupled stage can be easily found by monitoring the subsurface moisture. During the transition, the subsurface moisture stops to increase, the seismic velocity decreases. Natural hazards such as landslides and floods in the mountains are predicted based on this transition. Thus, the German Research Centre for Geosciences researched various influencing factors such as groundwater storage, land use, land cover and precipitation changes in Nepal that will help predict the future of freshwater resources in their research article. We can also anticipate the mountain landscapes and climatic changes by seizing these factors.

Works Cited

Brûlé, S. J. (2017). Flat lens effect on seismic waves propagation in the subsoil. Sci Rep 7 .

Johnson, J. (2019, May 14). Medical News Today. Retrieved from https://www.medicalnewstoday.com/articles/325174

Illien, C. A.-S. (2021). Subsurface Moisture Regulates Himalayan Groundwater Storage and Discharge. AGU Advances .

Microsites Wika. (n.d.). Retrieved from https://microsites.wika.com/newscontentgeneric_ms.WIKA?AxID=470#:~:text=Groundwater%20level%20measurement%20is%20mostly,bore%20well%20or%20monitoring%20well.

School, W. S. (2019, November). USGS. Retrieved from https://www.usgs.gov/special-topics/water-science-school/science/how-much-water-there-earth

Waikato, U. o. (n.d.). Sciencelearn. Retrieved from https://www.sciencelearn.org.nz/