An Eastern Aleutian Trench Seismic Record
R. von Huene, J. Miller, M. Fisher, G. Smith, 1983. "An Eastern Aleutian Trench Seismic Record", 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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After the 1964 Alaska earthquake, seismic records were collected across the eastern Aleutian Trench to study subduction-zone tectonics because geologic and seismologic studies indicated a subduction-related cause. Single-channel seismic-reflection records collected during the 1960s penetrated strata in the trench and about 1,000 m (3,281 ft) of rocks under the slope; only rarely was the top of the igneous oceanic crust detected for more than several kilometers beneath the front of the subduction zone (von Huene, 1972). In the first published multichannel seismicreflection records across the eastern Aleutian Trench (Seely, 1977), the reflection from the oceanic crust can be traced about 40 km (25 mi) landward of the trench, and the deformed stratification above this crust was shown in sufficient detail that a general structural style could be outlined. Structural style was also apparent in a series of records collected subsequently (von Huene, 1979; von Huene et al, 1979), but none of these multichannel records are migrated. The record presented here, from the Aleutian subduction zone off southern Kodiak Island (Figure 1), is migrated. A comparison of the unmigrated and migrated sections shows the improved resolution of structural detail that results from the migration process. This record and those from previous publications show a remarkable diversity of structural style in the subduction zone near Kodiak Island. In the record displayed here, the foot of the landward slope of the trench has a relatively simple structure in comparison with that evident in adjacent records from a seismic network off southern Kodiak Island. This record exemplifies one structural style of the subduction zone off southern Kodiak Island and shows the local formation of thrust packets within an accretionary complex.
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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.