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Taffeta-Like Structural Fabric Produced by Internal Deformation of Miocene-Pliocene Sedimentary Rocks within the Transcurrent Hosgri Fault Zone

Greene, H. Gary; Nishenko, Stuart; and Hogan, Phillip
[email protected]

Time-slices from a 3D volume constructed from recently collected closely spaced (37.5 m line spacing) seismic-reflection profiles offshore of Point Sal using a 14 streamer PCable and low-energy (1.5 kJ) boomer show for the first time the shallow structural complexity of an active transcurrent fault zone. Ductile deformation of the Oligocene-Miocene Lospe Formation and the Miocene Monterey and Point Sal formations composed of sandstone, mudstone, shale, dolomite and chert produce many doubly plunging and truncated anticlines and synclines within the southern segment of the Hosgri Fault Zone, a right-lateral strike-slip zone of deformation. Normal and reverse conjugate faults are recognized in the 3D data set. The pattern of deformation is best described as “Taffeta-like” as it resembles the fabric taffeta. Multiple animated time slices have been used to show how the deformation changes with time and to produce the present-day near surface structural fabric. By using this slow deformation animation piercing points are being identified that can be used to determine rates of displacements along faults of the fault zone. This study is being undertaken to update the seismic hazards for the Pacific Gas and Electric Diablo Canyon Power Plant and represents the state-of-the-art technique for assessing offshore fault displacements, a proto-typical example. We will illustrate how small areas over active fault zones can be imaged using 3D seismic-reflection techniques to assist in the determining modern rates of fault motion.

 

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013