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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 28 (1944)

Issue: 12. (December)

First Page: 1780

Last Page: 1781

Title: Some Features of Santa Susana Thrust, Vicinity of Aliso Canyon Field, Los Angeles County, California: ABSTRACT

Author(s): John C. Hazzard

Article Type: Meeting abstract


This paper discusses a 6 mile segment of the Santa Susana thrust, a feature in which the northern block is thrust southward for 18 miles along the southern side of the Santa Susana Mountains. In part the surface trace of the thrust is relatively straight but in canyons such as Mormon and Brown's Canyons it is extremely lobate, due to deep dissection of its relatively flat part. Likewise in Aliso Canyon the fault is exposed in a small fenster. Features of the overthrust sheet include large scale folding and fault imbrication as well as several transcurrent or tear faults along which there has been both vertical and horizontal displacement.

Studies based on outcrops of the thrust plane and subsurface data indicate that in transverse cross-section the structure has the form of a crude inverted "L." The short segment varies from gently north-dipping to slightly south-dipping. There the thrust plane is smoothly irregular with culminations or structural highs developed in Aliso, Mormon, and Brown's canyons. The long segment of the "L" is steeply north dipping and well data show that this segment maintains its near-vertical character to at least 6,900 feet subsea. A hypothetical northward flattening at an undetermined depth is suggested.

An extensive shear zone, developed below the main plane of movement, is considered a portion of the static block. This zone includes material from all of the stratigraphic units recognized below the thrust. A minimum estimate of 8,000 feet is made for the north to south displacement; the vertical displacement appears to be close to the same amount.

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Evidence suggests that during its development, the thrust reached the surface as a steep fault; with additional movement, the fault followed roughly the erosion surface and its flatter segment was developed. The latest period of movement was probably Pleistocene, for terrace deposits considered to be of that age are overridden by the thrust. Many problems connected with the fault await solution, chief among them being the explanation of the major differences between the stratigraphic sections within the overthrust and static blocks.

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Copyright 1997 American Association of Petroleum Geologists