Stepover or Relay Ramp in Normal Fault Zones

GEOTHERMAL ENERGY

Stepover or Relay Ramp in Normal Fault Zones:

Stepover or relay ramps are a type of displacement transfer structure between overlapping normal fault segments. Multiple intersections between the overlapping fault strands results in increased fracture density that enhances hydrothermal fluid flow.

Other definitions:Wikipedia Reegle

Controlling Structures

List of controlling structures typically associated with geothermal systems:

• Major Normal Fault
• Termination of a Major Normal Fault
• Stepover or Relay Ramp in Normal Fault Zones
• Apex or Salient of Normal Fault
• Fault Intersection

• Accommodation Zone
• Displacement Transfer Zone

• Pull-Apart in Strike-Slip Fault Zone
• Intrusion Margins and Associated Fractures
• Stratigraphic Boundaries
• Fissure Swarms
• Caldera Rim Margins
• Lithologically Controlled

Step-over or relay ramp between two overlapping normal fault segments with multiple minor faults providing hard linkage between two major faults. Illustration by James E. Faulds.

Faulds uses this term as a structural control found in the Basin and Range province of the US.

Stepover or relay ramps between overlapping fault strands are one of the most favorable structural settings for geothermal activity. As of 2011, ~32% of the more than 200 document geothermal fields in the Basin & Range were associated with step-overs or relay ramps in normal fault zones. Increased fracture density generated by intersections between multiple overlapping fault strands results in enhanced permeability that facilitates hydrothermal fluid flow. According to Faulds et al. (2011):

"Step-overs in normal fault systems are more prevalent within the extensional terrane that characterizes much of the Great Basin northeast of the Walker Lane.”

Examples

Want to add an example to this list? Select a Geothermal Resource Area to edit its "Controlling Structures" property using the "Edit with Form" option.

CSV

Geothermal Resource Area	Geothermal Region	Tectonic Setting	Host Rock Age	Host Rock Lithology	Mean Capacity	Mean Reservoir Temp
Desert Peak Geothermal Area	Northwest Basin and Range Geothermal Region	Extensional Tectonics	Mesozoic	greenstone	23 MW 23,000 kW 23,000,000 W 23,000,000,000 mW 0.023 GW 2.3e-5 TW	481.15 K 208 °C 406.4 °F 866.07 °R
Dixie Valley Geothermal Area	Central Nevada Seismic Zone Geothermal Region	Extensional Tectonics	Jurassic	Basalt	62 MW 62,000 kW 62,000,000 W 62,000,000,000 mW 0.062 GW 6.2e-5 TW	504.15 K 231 °C 447.8 °F 907.47 °R