The Use of Plate Motion Vectors to Predict the Orientation of Highly Permeable Structures in Active Geothermal Fields Related to Subduction

Abstract

Subduction produces deformation of the upper tectonic plate in a manner that can be predicted from plate motion vectors to indicate whether subduction is perpendicular, weakly oblique or strongly oblique. Perpendicular subduction produces reverse faults parallel to the arc and arc-normal faults, which when the intersection is within a volcanic arc, may localise intrusives with geothermal systems hosted by intrusion margin permeability. Where subduction is slightly oblique, faults with an element of strike-slip motion that strike parallel to the direction of obliqueness can intersect the arc and have associated permeable structures in orientations that can be determined from the strike of the fault and its sense of movement. Where subduction is strongly oblique and subduction is steep, arc-parallel strikeslip faults can form. These frequently run along the volcanic arc and have associated permeable secondary structures whose orientations can be determined similarly. The latter is the optimum tectonic environment for the development of permeable geothermal fields and is found in Sumatra, east-central Philippines, Colombia, Ecuador and southern Chile.