Driving pressure index (DPI) estimated from orientations of dilational fractures

Dikes and mineral veins are formed by the injection of crustal fluids into fractures. Repeated influx of fluid with varying pressure results in the formation of those dilational fractures. Their orientations reflect the prevailing stress condition at the time of their formation. The orientations can be used to infer the stress regime and the maximum fluid pressure during fracturing. In this paper, we explain the driving pressure index (DPI) defined by Faye et al. (2018). The DPI represents the driving pressure ratios of the overpressured geofluids that formed a swarm of dilational fractures, and is a conservative and approximate estimate of the highest driving fluid pressure ratio observed amongst multiple high-pressure fluid influx events. Several applications of the DPI in the interpretation of crustal fluid activity are also introduced.