Analysis of coseismic water-level changes in the wells in the Koyna-Warna region, western India

We test the hypothesis that coseismic water-level changes in wells are proportional to coseismic volumetric strain by analyzing available data from the Koyna-Warna region of western India. A total of 18 cases of water-level changes have been reported at ten wells corresponding to six earthquakes of M> or =4.3 that occurred in the region from 1997 to 2005. Out of these, clear unambiguous steplike coseismic water-level changes have been observed in ten cases at five confined wells. We used basic poroelastic theory to simulate volumetric strain and corresponding water-level changes and find that all cases show consistency in sign between reported coseismic water-level changes and simulated volumetric strain. All confined wells with high strain sensitivity that are located near earthquake epicenters show good agreement in magnitude between simulated and reported volumetric strain, thereby supporting this hypothesis.