# A Classification Tree for Modeling Ground Fractures from Subsidence
## 1 Introduction  
In areas with rapid urbanization and demographic growth, the prolonged exploitation of groundwater is causing the land to sink with consequent dangerous impacts [1; 2; 3]. One of the responses of soil sinking is the collapse of the superficial layers, which affects fragile buildings and buried facilities that fail in blocs or by kilometers, resulting in huge economic losses and detriments to the quality of life of citizens. Superficial ground fracturing is one of the soil phenomena that Mexico City must face with extreme urgency and humanism, since it occurs in large portions of the deprived regions of the metropolis (Figure 1). Understanding what provokes a soil fracture is vital for the Mexican metropolis. Soil rupture, with opening and/or vertical displacement, is a geomechanical process that could be associated with the pumping of groundwater from unconsolidated sedimentary aquifer systems, and normally develops in arid or semiarid basins. The generation and propagation of ruptures requires the development of failure conditions, that is, traction and/or shear stress not supported by shallow alluvial sediments. There are numerous analyses of stress fields that model the occurrence of ruptures, with locations in Mexico [4; 5; 6; 7; 8; 9], China [10; 11; 12; 13], and the United States [14; 15; 16; 17; 18; 19; 20; 21; 22; 23] being among the most cited investigations. In CDMX, cracks associated with pumping have been studied from local and regional, timeless and evolutionary, and forensic and predictive perspectives [24; 25; 26; 27; 28; 29; 30; 31; 32], which have represented great contributions to the state-of-the-art research and the documentation of events. However, the discussion is still open in regard to defining the risk levels in specific properties (vulnerability and threats to the management of the effects) and recommending (preventing) certain structural solutions or accepting urban projects in localities that are affected by this phenomenon. Tlahuac, a deprived mayoralty in southeastern Mexico City, is the subject of this research. In this study, area, cracks, fissures, and strong steps due to consolidation of soft layers on abrupt basement slopes, and differential subsidence in heterogeneous contacts, have been recognized [33]. The southern region of Mexico City has high levels of heterogeneity, and its typical stratigraphy is composed of superficial fillings (garbage and/or tuff strata) of poor or null capacity to resist load on extremely soft clays that were deposited on the steep slope of the perimeter of the basin (basement). These arrangements of materials manifest in complex behaviors whose prediction is a challenging open task. Identification of the processes is particularly difficult because the manifestations (cracks) are transfigured by interactions with inefficient foundations, inoperative communication routes, damaged buried infrastructure (leaks in water pipes), and the chaotic dynamics of the layers of debris (used to form a level when the urbanization of the area began) deforming under the stresses provoked by pumping wells. When the best-known models that use groundwater flow equations and a complex geomechanical characterization are used to evaluate vertical deformations (associated with groundwater extraction) in the Tlahuac scenarios, the predictions fail because they entail difficulties and uncertainties, most of which are related to the parameterization of the environment. The transformation of specific information (often scarce) in a 3D space, with near and far borders, is a fragile point when predictions are faced with field observations. The disconnect between interpretations and reality has its most negative effect when ruptures occur without being able to alert government actors, developers, and the public themselves about the risk in their environment.