## 1 Introduction  
Many studies have investigated groundwater responses to earthquakes because groundwater levels (GWLs) are highly sensitive to stress changes in geological media [1; 2; 3; 4; 5; 6]. Changes in GWLs during earthquakes can be attributed to several mechanisms, as follows: (1) the compression of alluvial deposits [7], (2) the undrained expansion and consolidation of saturated sedimentary rocks [8; 9; 10], (3) a reduction in fluid pressure due to gas outflow from pores [11], (4) changes in rock mass permeability caused by the removal of clogging and the relaxation of fractures induced by fluid movement during seismic activity [12; 13], (5) stress changes in upper allwimum, such as liquefaction [14], and (6) the inflow of surface water due to the altered permeability of the rock mass.  
The sensitivity of GWLs to stress changes has made them a valuable tool for earthquake research [1; 2; 3; 4; 5]. For example, in the 2000 Iceland strike-slip fault earthquake, the GWLs increased in areas experiencing stress increases and decreased in regions of stress relaxation [15]. Interestingly, post-earthquake stress redistribution exhibited opposite trends compared to the co-seismic period. Similarly, in the Wenchuan earthquake in China, areas of an increased volumetric strain experienced GWL decreases due to a reduced pore water pressure, while regions of a decreased volumetric strain showed an increased pore pressure and corresponding GWL rises [16]. A comparable pattern was observed during the 2012 Emilia earthquake in Italy, where co-seismic displacement induced an increased volumetric strain in shallow areas, leading to a decreased pore pressure and GWLs, while deeper regions exhibited a decreased volumetric strain, an increased pore pressure, and rising GWLs [17].  
The objective of this study is to investigate the relationship between the stress redistribution induced by the Gyeong-Ju earthquake (GJEQ) (local magnitude ML 5.8, moment magnitude Mw 5.4), which occurred at 11:32 (UTC) on 12 September 2016, and its impact on groundwater level changes in the southeastern region of the Korean Peninsula.  
The GJEQ caused noticeable changes in the GWLs across the southeastern region of the Korean Peninsula. These changes have drawn considerable attention, particularly due to their impact on the GWLs at the Wolsong LILW disposal site, located approximately 20 km from the earthquake hypocenter. Such observations highlight the broader significance of understanding earthquake-induced GWL changes, as these changes can alter groundwater flow paths and have implications for hydrogeological dynamics, including radionuclide transport.  
Seismic events can trigger complex processes, including aquifer deformation, pore pressure redistribution, and dynamic stress changes, which significantly influence groundwater systems. These mechanisms are transient and spatially variable, necessitating tools beyond direct observation for effective analysis. This study does not focus specifically on the Wolsong site. Instead, we focus on understanding the mechanisms driving earthquake-induced hydrogeological changes. To address these challenges, the study aims to develop a numerical workflow to simulate an earthquake event and its effects on pore pressure evolution and GWL changes. By using numerical modeling as a first-order approximation, this study seeks to enhance the understanding of the processes by which seismic events influence groundwater systems.