## 2 Materials and Methods
### Brief Geological Background  
Figure 2a highlights the general location of the significant subsidence under study on the Israeli map, marked with a yellow star. Figure 2b, integrating satellite imagery and a geological map, provides a more detailed view of Road 431 and our study area. Road 431, between Modi'in in the east and Ramla in the west, traverses a terrain underlain predominantly by alluvial clays.  
The area of interest is characterized by a geological framework dominated by sedimentary formations. The bedrock consists of carbonates from the Bina Formation of the Judea Group, predominantly limestone and dolomite (Figure 2b, green polygons with \"Kub\"  
Figure 1: A workflow chart.  
Figure 2: **(a)** The general location of the significant subsidence event studied is marked with a yellow star on the Israeli map (Google Earth). **(b)** Detailed view of Road 431 and the study area, spanning between Modi’in in the east and Ramla in the west. The map integrates satellite imagery and a geological map, highlighting sedimentary formations such as the Bina Formation (green polygons with “Kub” geo-code), the Menuha Formation (brown polygons coded as “Kub”, representing predominantly limestone and dolomite), and Quaternary deposits (in white and gray). Alluvial clays predominantly underlie the terrain. Modified from [29].  
geo-code), overlaid by the Menuha Formation of the Mount Scopus Group, predominantly chalk (brown polygons with \"Kum\" geo-code in Figure 2b), overlaid by a sequence of Quaternary and Eocene sedimentary rocks including chalk, marl, and alluvium deposits (no particular color area in Figure 2b). The region's surface geology primarily features Quaternary sediments like clay and silty-clayey sands. These materials are prevalent in historically urbanized areas and are significant due to their susceptibility to compaction and erosion, exacerbating subsidence risks. Since 2022, this section of Road 431 has experienced several subsidence events, prompting extensive investigations to understand the underlying causes. These incidents have necessitated drilling studies and repeated assessments to characterize subsurface conditions and identify the mechanisms of ground sinking. Figure 3 presents an updated orthophoto captured at night during our initial site visit (December 2023) following a significant subsidence event, marked by the yellow star and magnified within the yellow circle. The orthophoto includes a grid of manual GPS elevation measurements from three prior periods, delineating areas affected by earlier road repairs. In early 2022, subsidence was initially localized to a small blue polygon and, later, in 2022, expanded to an area marked by a red polygon, necessitating progressive road repairs. By the middle of 2023, the affected area had stabilized and resurfaced, as evidenced by the \"fresh\" black patch marked with a black dashed line in the orthophoto. These findings underscore the dynamic nature of subsurface conditions and the ongoing challenges in mitigating ground movement in this region.  
Figure 4 illustrates the interpretation of subsurface layers in the study area, derived from historical drilling logs. The location of the last major subsidence event in 2022, marked with a red polygon in Figure 3, is also represented in Figure 4 for reference. The red layer corresponds to clay soil, while the orange layer represents the underlying chalk and marl bedrock. Green vertical lines indicate drilling logs (K-2, K-5, etc.) and the horizontal green lines represent SPT (Standard Penetration Test) values, where shorter lines correspond to softer soil with lower compaction resistance. The dark blue triangle also denotes the possible position of the water anchorage area (local water table), which has been suspected to contribute to the observed surface subsidence.  
Figure 3: Updated night-time orthophoto of the study area following the major subsidence event.