P. D‘Onfro, P. Glagola, 1983. "Wrench Fault, Southeast Asia", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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Seismic sections A-A' and B-B' cut across a left lateral wrench fault. The profiles are located by gray bars in Figure 1 which is a map of faults cutting seismic reflector R3. The wrench fault parallels an older Late Cretaceous arc-trench system. In middle Miocene strike-slip movements occurred on old fault planes in the basement melange (below R5 on the seismic sections) and initiated formation of a wrench fault system in the overlying sedimentary cover. Fault movements continued intermittently to the present.
In Figure 1, the heavy black line marks the trace of the major wrench fault D. The thin lines are subsidiary cults genetically related to D. The most prominent subsidiary faults are the Riedel shears, R. Riedel shears are oriented 10 to 20° counterclockwise from the main fault D and have the same sense of strike-slip offset as D. Field studies and laboratory experiments indicate that Riedel shears form 10 to 20° clockwise from D and also have the same displacement sense. P shears connect en echelon Riedel shears to form diamond-shaped horst and graben blocks that are characteristic of mature wrench fault zones. A horst block of this type is shaded gray in Figure 1. Extension faults, E, are oriented approximately 45° counterclockwise from the major wrench fault and have normal dip-slip separations.
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Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.