Initial deformation in a subduction thrust system: polygonal normal faulting in the incoming sedimentary sequence of the Nankai subduction zone, southwestern Japan
A. S. Heffernan, J. C. Moore, N. L. Bangs, G. F. Moore, T. H. Shipley, 2004. "Initial deformation in a subduction thrust system: polygonal normal faulting in the incoming sedimentary sequence of the Nankai subduction zone, southwestern Japan", 3D Seismic Technology: Application to the Exploration of Sedimentary Basins, Richard J. Davies, Joseph A. Cartwright, Simon A. Stewart, Mark Lappin, John R. Underhill
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3D seismic data from the Nankai margin provide detailed imagery documenting the onset of deformation at an active sediment-dominated accretionary prism, including a previously unmapped network of normal faults. The Nankai margin off southwest Japan is characterized by active subduction, seismogenesis, and a large accretionary prism with fold-and-thrust belt structure. Imbricate thrusting is the dominant structural style of the outer 20 km of the prism. This structural domain develops at the prism toe, where an incipient imbricate thrust displays significant along-strike variability in dip, offset, and development of hangingwall anticlines.
Compressional deformation is preceded by normal faulting that initiates seaward of the trench axis. Seismic data in this area reveal a complex, intersecting pattern of normal faults within the incoming hemipelagic sediments. Underlying the faulted section is a high-amplitude reflector interpreted as representing oceanic basement. This reflector contains elongate horsts and grabens oriented perpendicular to the margin interpreted as relict spreading centre fabric.
Analysis of the orientation of normal faults within the Shikoku basin sequence shows a correlation between fault geometry and basement structure. This faulting is notably similar to layer-bound compaction faults, documented in the North Sea and elsewhere, attributed to both hydrofracturing and volumetric contraction of fine-grained sediments. Mapped normal faults may thus be the result of a combination of differential compaction of sediments above irregular, dipping oceanic basement and compactional dewatering seaward of the toe of the accretionary prism.
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3D Seismic Technology: Application to the Exploration of Sedimentary Basins
A ‘new age’ of subsurface geological mapping that is just as far ranging in scope as the frontier source geological mapping campaigns of the past two centuries in emerging. It is the direct result of the advent of 2D, and subsequently 3D, seismic data paralleled by advances in seismic acquisition and processing over the past three decades. Subsurface mapping is fuelled by the economic drive to explore and recover hydrocarbons but inevitably it will lead to major conceptual advances in Earth sciences, across a broader range of disciplines than those made during the 2D seismic revolution of the 1970s. Now that 3D seismic data coverage has increased and the technology is widely available we are poised to mine the full intellectual and economic benefits. This book illustrates how 3D seismic technology is being used to understand depositional systems and stratigraphy, structural and igneous geology, in developing and producing from hydrocarbon reservoirs and also what recent technological advances have been made. This technological journey is a fast-moving one where the remaining scientific potential still far exceeds the scope of the advances made thus far. This book explores the breadth of the opportunities that lie ahead as well as the inevitable accompanying challeges.