Investigation of earthquake effects on groundwater level and discharge of water wells following the 2013 Mw 6.3 Kaki earthquake occurred in Bushehr province (Iran)

When an earthquake occurs, a part of the released energy is propagated in the form of elastic waves at a speed that depends on the nature of the propagation environment. The radiated energy from earthquake focus in all directions is called radiation pattern and depends on the fault mechanism. The environment response to longitudinal waves appears as compression and expansion of the environment. This can affect on water levels in aquifers, wells and springs before, during and after the event. The changes of the groundwater levels caused by an earthquake are important with respect to other induced parameters; they may generate crustal deformations, affect on water supplies and production of oil wells, initiate liquefaction, control the distribution of aftershocks, trigger earthquakes and mud volcano eruptions. In this study, the effect of April 2013 Kaki earthquake (Mw6.3) on water levels in wells located in a range of 50 km radius around the earthquake epicenter was compared in successive months in the preceding years, during and after the event. Regarding the earthquake focal mechanism and using the estimated tensile and compressive zones in the study area, the correlation of these areas with changes in water levels and discharge of wells and springs was examined. The results of evaluations indicate that the water levels in wells rose and the discharge of the wells and springs located within the radiation range of the pressure waves increased after the earthquake. The wells located in the direction of compressive radiation showed a level of elevation. In contrast, wells located along the shear strain either experienced a drop in water level or had no significant changes. The results show that there is compatibility between the pattern of seismic waves and the changes in the water levels in wells and springs. Because of the difference in characteristics of geological formations, the response of the wells located in the same seismic pattern may not be the same. On the other hand, since the earthquake occurred in the low rainfall time, changes in water levels cannot be caused by rainfall. Field data shows other recorded effects such as the recovery of the springs of Kale and Seyyed Ali which indicates the increase in discharge of water in the region. The liquefaction created in the area is a reason for the passage of a compressive wave that has led to increase of water levels in the wells. The amount of decrease or increase in water level depends on the magnitude and distance to hypocenter of the earthquake and geological characteristics of the well. The water level in the well located in Shonbe village (28.34°N, 51.76°E) increased 1.6 m after the earthquake.