Groundwater Hydraulics in Increased Spring Discharge following Earthquakes: Some Applications and Considerations

Abstract

Earthquakes often entail alterations in the groundwater flow regime, in the phreatic level, surges and losses of springs, and the discharge in brooks. A variety of theoretical approaches attempt to elucidate the post-earthquake effects on spring discharge. This study adopts a conceptual approach, primarily presenting diverse methods to estimate water released by earthquakes involving calculations of discharge surpluses in springs. This study delves into refined techniques rooted in groundwater hydraulics, displaying applications of analytical and simulation methodologies to quantify earthquake-induced groundwater discharge in springs. This research investigates springs as natural indicators and applies mathematical precipitation–runoff models, particularly the CREC model, to simulate hydrographs in post-earthquake scenarios. We apply analytical procedures or mathematical simulation techniques employed in groundwater hydraulics for natural aquifer recharge calculations. Firstly, we briefly describe the methods based on the analysis of depletion curves of hydrographs in spring discharge. Additionally, specific mathematical rainfall–runoff models used to simulate hydrographs of karstic springs, along with derived analytical approximations, are adapted for this scenario. These hydraulic calculations involve the depletion coefficient and hydrodynamic volumes of aquifers, parameters that reveal certain aspects of the relation between groundwater and earthquakes. Three main features are: (a) Acknowledging faults as the primary geological structures in transmitting pore pressures due to earthquakes. Thus, for large and deep faults, which connect the ground surface with the Earth’s crust bottom—where earthquakes trigger—the depletion coefficient, α, usually reaches high values (α = 0.1 days−1). Therefore, these faults become more sensitive to pore pressure than other lithologies. (b) Elucidating the mechanisms of permeability enhancement caused by earthquakes. (c) Highlighting the substantial volumes in motion within the Earth’s interior, which, for instance, could constitute a significant source for the origin of mineral deposits. Mathematical calculations enable the determination of the volume of mobilized water that can be discharged by gravity in each earthquake. This, along with its recurrence, justifies the substantial mineralization volumes.