Abstract
Hydrates are near-surface phenomena that occur when temperatures and pressures are appropriate. Among such stable continental margins is the East Coast of the United States that, with its ubiquitous, leisurely, uniform deposition and relatively minor deformation, there can be associated hydrates. The geologic uniformity and long-term stability provide opportunities for stress homogenization with few perturbations, creating zones of weakness. With widely spaced sampling adequate to define a regional model, uncertainty can be reasonably calculated. Along unstable continental margins such as the northern Gulf of Mexico that contain such dynamic elements as salt and/or shale, as well as highly variable and massive deposition rates, there can be deformed stress fields that result from compression, lateral motions and variations thereof. Locally, any stress may be principal for an indeterminate time. With such variability, no detailed regional model can be developed. Risk analysis is possible only when a 3D model at sufficient resolution is available so that reasonable integrations can be performed and posed questions can be answered. To derive such a 3D model requires that all impacting processes, their intensities and periodicities, and spatial distributions be catalogued and understood. Thus, the “final” 3D model will be of variable resolution. To know at what resolution data need to be collected will be determined by the specific processes being mapped in a given locality. To apply an equitable risk analysis along unstable passive continental margins could be premature, given the uncertainty of all the operative processes. A conceptually valid 3D model of processes is not available, nor is an understanding of intensities and periodicities. Synergistic relationships can only be guessed. The principles of risk analysis are formulated; data and methodologies for use on unstable margins are not.