Fault kinematic analysls shows that the geothermal system in Tongonan is greatly structurally
controlled by the segment of the Phllippine Fault traversing Leyte Island. This fault provides much of the fracture-related permeability within the geothermal reservoir and as a consequence, faults are being utilized as primary targets during drilling.

Preliminary fault set analysis shows that the Tongonan geothermal l`leld ls controlled by a complex fault system wherein quantifiable compressional and extensional local stress regimes coexist. This technique permits the effective identification of extensional (usually open) and compressional (usually tight or closed) fault structures in the various sectors of the Tongonan geothermal field. In general, observations show that permeable areas are usually located in regions where normal faults (extensional) prevail, and not in areas controlled by strike-slips (compressional). This application is particularly helpful ln the selection of drilling targets or in other related developmental activities such as hydrological modeling and tracer testing.