Slip and Dilation Tendency Analysis of the Patua Geothermal Area

Critically stressed fault segments have a relatively high likelihood of acting as fluid flow conduits (Sibson, 1994). As such, the tendency of a fault segment to slip or to dilate provides an indication of which faults or fault segments within a geothermal system are critically stressed and therefore likely to transmit geothermal fluids.

Slip and dilation were calculated using 3DStress (Southwest Research Institute).
Slip and dilation tendency are both unitless ratios of the resolved stresses applied to the fault plane by ambient stress conditions. Values range from a maximum of 1, a fault plane ideally oriented to slip or dilate under ambient stress conditions to zero, a fault plane with no potential to slip or dilate. Slip and dilation tendency values were calculated for each fault in the focus study areas at, McGinness Hills, Neal Hot Springs, Patua, Salt Wells, San Emidio, and Tuscarora on fault traces.

Stress Magnitudes and directions
Stress field variation within each focus area was approximated based on regional published data and the world stress database as well as local stress information.

Slip and dilation tendency analysis for the Patua geothermal system was calculated based on faults mapped in the Hazen Quadrangle (Faulds et al., 2011). Patua lies near the margin between the Basin and Range province, which is characterized by west-northwest directed extension and the Walker Lane province, characterized by west-northwest directed dextral shear. As such, the Patua area likely has been affected by tectonic stress associated with either or both of stress regimes over geologic time. In order to characterize this stress variation we calculated slip tendency at Patua for both normal faulting and strike slip faulting stress regimes. Dilation tendency results for a strike-slip faulting stress regime and for a normal faulting stress regime are virtually identical, so we present one result for dilation tendency applicable to both strike-slip and normal faulting stress conditions along with slip tendency for both a normal faulting and a strike-slip faulting stress regime. Under these stress conditions, north-northeast striking steeply dipping fault segments have the highest dilation tendency. Under the strike-slip faulting stress regime, north-northwest and east-northeast striking, steeply dipping fault have the highest slip tendency, while under normal faulting conditions north northeast striking, 60 degrees dipping faults have the highest slip tendency.