Subsidence, a universal process that occurs in response to the voids created by extracting solids or liquids from beneath the Earth's surface, is controlled by many factors including mining methods, depth of extraction, thickness of deposit, and topography, as well as the in situ properties of the rock mass above the deposit. The impacts of subsidence are potentially severe in terms of damage to surface utility lines and structures, changes in surface-water and groundwater conditions, and effects on vegetation and animals. Although subsidence cannot be eliminated, it can be reduced or controlled in areas where deformation of the ground surface would produce dangerous or costly effects. Subsidence prediction is highly developed in Europe where there are comparatively uniform mining conditions and a long history of field measurements. Much of this mining has been carried out beneath crowded urban and industrial areas where accurate predictions have facilitated use of the surface and reduced undesirable impacts. Concerted efforts to understand subsidence processes in the United States are recent. Empirical methods of subsidence analysis and prediction based on local conditions seem better suited to the current state of knowledge of the varied geologic and topographic conditions in domestic coal mining regions than do theoretical/mathematical approaches. In order to develop broadly applicable subsidence prediction methods and models for the United States, more information is needed on magnitude and timing of ground movements and geologic properties.

Information from several sources indicates that the eastern Maine coast is subsiding. Recent releveling surveys indicate a current rate of subsidence in eastern Maine as much as 9 mm per year relative to Bangor. The anomalously rapid rise in sea level accompanying the subsidence has led to shoreline erosion, landsliding, and submergence of archaeological sites and historical manmade structures. In situ stress measurements, well-bore breakouts, and earthquake focal mechanisms show that the maximum principal stress is horizontal, strikes N 80° E, and is correctly oriented to produce thrusting on north-south faults, right-lateral motion with minor thrusting on northeast and east-northeast faults, and major thrusting with left-lateral motion on northwest-striking faults. Maximum seismicity in Maine occurs in the subsiding zone which also includes the maximum (positive) gravity anomaly in the State. Epicenters are diffusety aligned with the Oak Bay fault which strikes N 20° W. Deflection of isobase lines drawn on ice-marginal deltas forms a trough whose axis strikes approximately parallel to the Oak Bay fault. An acceptable contemporary crustal deformation model should incorporate zones of contrasting rock density and intensity of fracturing, localized seismicity, east-west tectonic compression, and weak compression or extension in the north-south direction.