Apache Wrench Fault Zone of West Texas: ABSTRACT

AAPG Bulletin ◽  
1996 ◽  
Vol 80 ◽  
Author(s):  
G. Pat Bolden
Keyword(s):  
Fault Zone ◽  
West Texas ◽  
Wrench Fault

Geologic hazards of an embankment dam constructed across a major, active plate boundary fault

2000 ◽  
Vol 6 (4) ◽  
pp. 353-382
Author(s):  
Azm S. Al-Homoud
Keyword(s):  
Fault Zone ◽  
Plate Boundary ◽  
Large Earthquake ◽  
Normal Faults ◽  
Jordan Valley ◽  
Embankment Dam ◽  
Ground Acceleration ◽  
Dam Foundation ◽  
The Core ◽  
Wrench Fault

Abstract The geological structures associated with the site of the 55 million m 3 Karameh embankment dam constructed in the Jordan Valley and the tectonic effects on dam foundation and reservoir margins were reviewed. The dam crosses the strike-slip fault of the Jordan Valley Rift Zone. Trace evidence of the fault indicates a displacement of 8 to 15 m over a rupture length of some 130 km, which probably took place several centuries ago. Earthquakes with Richter magnitudes as great as 7.8 have occurred along the Jordan Valley Fault. Deterministic studies by Tapponnier (1992) indicated that the dam design should incorporate the possibility of a 7.8 event, a maximum horizontal rupture displacement on the fault of 10 m and a design peak ground acceleration (PGA) of 0.74 g at the site of the dam. These values are consistent with those which would be used in the USA for a similar case. However, the dam was actually designed by a consultant and constructed for a PGA of about a quarter of this value, based on seismic hazard analysis following guidelines of the International Committee on Large Dams (ICOLD) (1989). Moreover, the dam was designed for displacements of 6 m horizontal and 2 m vertically. Liquefiable sand layers were found in the dam foundation. A PGA of 0.50 g will trigger liquefaction of the sand layers in the dam foundation which would be expected to result in a crest settlement of 4.4 m. Slope stability analysis indicated deep failure planes in the foundation zone. The excavation of loose materials from under the dam foundation has not precluded the possibility of liquefaction occurring under the expected earthquake. Field mapping of geological features during the dam foundation excavation and construction revealed that: a) the most likely location of the Jordan Valley fault is in the area where the Wadi Mallaha stream crosses the dam axis, b) zones of en echelon type open fissures have been defined in the laminates sub-parallel to the Jordan Valley Fault Zone, c) at the Wadi Mallaha stream bed a parallel zone of faulting and warping of the Lisan Formation was identified, and d) the alignment is clearly confirmed by the exposure immediately upstream of the core at Ch 1375. The main wrench fault zone crosses the embankment footprint (upstream to downstream approximately) and reaches the surface around Ch 1375. The critical safety elements of the embankment are the core, the downstream fine filter, the chimney drain and the drainage blanket. To resist large earthquake events safely, the following safety measures should be implemented: 1. A freeboard of 7.0 m instead of the 5.0 m constructed. 2. The foundation of the dam should be stabilized against liquefaction. 3. The embankment internal zoning should be designed to accommodate damage resulting from earthquake events with a magnitude of 7.8. 4. The foundation needs relief measures downstream to lower the pore pressure. This paper describes the measures taken during construction as overall defense against future fault movements through a wide plastic core, an extensive upstream blanket, a 5.0-m thick downstream chimney filter and drain zones, a 5-m freeboard and an upstream crack stopper zone which may be critical for normal faults with a lateral extension component. The geological determination of the main wrench fault alignment resulted in the addition of an extra 2-m width to each of the already wide chimney filter and drain zones. In order to reduce potential seepage, local cut-off trenches or slush grouting were used for treatment of any open fissures at the upstream edge of the external blanket and the right bank ridge. The scale and scope of this dam and inherent engineering geological hazards are unprecedented. The design is considered deficient. This paper documents serious safety issues with the dam. The constructed dam presents serious safety risks and represents a case history of a disaster waiting to happen.

scholarly journals Three Types of Flower Structures in a Divergent-Wrench Fault Zone

2017 ◽  
Vol 122 (12) ◽  
pp. 10,478-10,497 ◽  
Author(s):  
Lei Huang ◽  
Chi-yang Liu
Keyword(s):  
Fault Zone ◽  
Wrench Fault ◽  
Flower Structures

Deep-burial dissolution and brecciation in dolostone reservoirs: Striking similarities between the Devonian Keg River Formation of western Canada and the Ordovician Ellenburger group of west Texas

2014 ◽  
Vol 2 (4) ◽  
pp. T221-T241 ◽  
Author(s):  
Jeffrey J. Dravis ◽  
Iain D. Muir
Keyword(s):  
Reservoir Quality ◽  
Pressure Solution ◽  
Secondary Porosity ◽  
Midland Basin ◽  
West Texas ◽  
Reservoir Development ◽  
Basement Faults ◽  
Eastern Shelf ◽  
Diagenetic Fluids ◽  
Wrench Fault

Deeper burial dissolution of dolomitized fabrics created most of the reservoir quality in several Devonian Keg River oil pools on the Comet Platform in northwestern Alberta, Canada. This process also created reservoir quality in two Ordovician Ellenburger dolostone oil pools on the Eastern Shelf of the Midland Basin in west Texas, and provided an alternative explanation for reservoir development unrelated to the subaerial karstification model. Several observations confirmed deeper burial dissolution of Keg River dolostones. First, dolomites replaced, or cemented, grains previously sutured by pressure solution. Their subsequent dissolution postdated this pressure solution, confirming burial dissolution. Second, late-forming saddle dolomites dissolved. Third, secondary porosity developed along, or cross cut, stylolites, often in zebra dolostone fabrics, or formed along fracture planes that cut stylolites. These burial fractures often intersected secondary pores, implying a causal relationship. Fourth, dolostone breccia clasts contained stylolites rotated at different angles to each other and the horizon, confirming deeper burial brecciation. In the Keg River Formation on Comet Platform, proximity to conjugate reactivated basement faults that developed off of a master wrench fault, the Hay River Shear Zone, controlled deeper burial dissolution and pool entrapment. Hydrothermal fluids, either calcium rich or acidic in composition, were moved along these faults and promoted extensive dissolution of completely dolomitized fabrics. Ellenburger dolostone reservoirs at Suggs and Withers Fields on the Eastern Shelf of Texas also resulted from deeper burial dissolution of completely dolomitized facies. The Keg River dissolution fabrics were replicated in Ellenburger samples, with the exception of zebra dolostones. Ellenburger reservoir development was closely aligned to faults and fractures associated with a master wrench fault, the Ft. Chadbourne Fault. These faults were inferred to have moved hot (possibly hydrothermal?), deeper burial diagenetic fluids that were calcium-rich, or periodically acidic, promoting dolomite dissolution and secondary porosity development.

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