Geometry and development of relay ramps in normal fault systems

Journal Article · Tue Feb 01 04:00:00 EST 1994 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:6965697

Peacock, D C.P. ^[1]; Sanderson, D J ^[2]

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1. Univ. of Southampton (United Kingdom) Univ. of Plymouth, Devon (United Kingdom)
2. Univ. of Southampton (United Kingdom)

Normal fault zones play a major role in the development of basins and in the migration and trapping of hydrocarbons. The mapping of normal fault systems using seismic data requires careful correlation of faults on adjacent sections, a procedure that often leads to the interpretation of faults as having long, continuous, sinuous traces. Recent work involving detailed mapping of fault traces, first by using land exposures but more recently using three-dimensional seismics, has demonstrated that faults are usually made up of many overstepping segments, linked by areas of complex deformation, termed transfer zones or relay ramps. Relay ramps occur between normal fault segments that overstep in map view. The geometry and evolution of exposure-scale relay ramps are described from the Somerset coast, England, and are compared with larger scale ramps from elsewhere. Relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments; these groups are interpreted as being evolutionary stages. In stage 1, the segments do not interact. Stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp. In stage 3, connecting fractures start to break the relay ramp. Stage 4 is when the relay ramp is destroyed to produce a single fault that has an along-strike bend. These evolutionary stages can develop through time, but they can also be seen spatially. A branch line between normal faults or an along-strike bend may represent a stage 4 relay, with progressively earlier stages occurring updip or downdip. Characteristic variability in displacement-distance profiles for fault segments and linked faults accompanies the interaction and linkage processes. Displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps. Relay ramps often contribute to a minimum in total fault displacement at a linkage point. 47 refs., 16 figs.

• OSTI ID: 6965697
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Vol. 78:2; ISSN 0149-1423; ISSN AABUD2
• Country of Publication: United States
• Language: English

Related Subjects

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03 NATURAL GAS
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DEVELOPED COUNTRIES
EUROPE
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGIC TRAPS
HYDROCARBONS
HYPOTHESIS
MAPPING
MIGRATION
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ORGANIC COMPOUNDS
SEDIMENTARY BASINS
SEISMIC WAVES
THREE-DIMENSIONAL CALCULATIONS
UNITED KINGDOM
WESTERN EUROPE