Dear Anju,Seismic waves have ...

Dear Anju,

Seismic waves have two main types of effects on groundwater levels: oscillations , and "permanent" offsets . Muddy or turbid water at long distances from the epicenter are most likely an aftereffect of oscillations.Surface-water responses to earthquakes include changes in chemistry, seiches (wave oscillations) in lakes and other open water bodies, increases in stream, spring, and seep discharge, some instances of springs going dry or the appearance of new springs, and a very few examples of decreases in stream discharge.

Water levels in wells respond to the seismic-wave induced expansion and contraction of the aquifer tapped by the well, in turn causing step or oscillatory fluid-pressure changes.Stream flow may continue to increase for a few days and then gradually decline toward the pre-earthquake baseline condition for several months. Water flowing in a stream can come from overland flow or from ground water discharging into the streambed (base flow). An abrupt increase in stream flow without precipitation or upstream reservoir release indicates increased contributions from the ground-water system.

Japan has some of the best documented occurrences of precursory hydrogeological changes, preceding both the 1978 M6.8 Izu-Oshima earthquake and the more recent, disastrous 1995 M7.2 Kobe earthquake Before either or both of these events, water-level changes occurred in many wells, and there appeared to have been precursory changes in ground-water temperature, radon, chloride, and sulfate concentrations, as well as dissolved gas ratios in mineral springs The preseismic changes in chloride and sulfate content of the Kobe event were reconstructed by analyzing dated, bottled ground water that is distributed in the domestic market. The well-documented and similar hydrogeologic precursors at Izu-Oshima and Kobe have motivated the Japanese government to continue water-level monitoring at more than 30 wells in seismically active areas.

Please find attached herewith some case study.

With regards,

Prem Baboo