The northern Los Angeles basin is influenced by two structural styles: the west-trending
compressional Transverse Ranges to the north, and the strike-slip Peninsular
Ranges to the south. The interaction of these two structural styles has resulted in a
complex fold/fault belt at the northern margin of the Los Angeles basin, which deforms a
variable sequence of late Miocene through Quaternary marine strata.
Subsurface mapping of Quaternary marine gravels by electric-log correlation
documents the latest phase of deformation in the northern Los Angeles basin. The
Quaternary marine gravels are folded at the Wilshire arch, the Hollywood basin, the
central trough, the Newport-Inglewood fault, and the Santa Monica fault. The west-plunging
Wilshire arch, which follows Wilshire Boulevard east of the Newport-
Inglewood fault, is a broad fold identified and named in this study. Deformation of the
Wilshire arch, which is underlain and caused by the potentially-seismogenic Wilshire
fault, began around 0.8 - 1.0 Ma. A fault-bend fold model, based on the shape of the
Wilshire arch, indicates a dip-slip rate of 1.5 - 1.9 mm/yr for the Wilshire fault, whereas
a three-dimensional elastic dislocation model indicates a right-reverse slip rate of 2.6 - 3.2
mm/year for the Wilshire fault.
The finer-grained marine Pliocene strata include the late Pliocene to early
Pleistocene Pico member, and the early Pliocene Repetto member, of the Fernando
Formation. Thickness and lithology variations in the Pico and Repetto strata, which were
influenced by syndepositional structures, indicate that the entire Pliocene and the latest
Miocene were characterized by compression. The primary structure present throughout
the Pliocene is a south-dipping monocline, which was underlain and caused by a deep
reverse fault, dipping ~55 - 60° to the north, referred to here as the Monocline fault.
Relative subsidence of the central trough resulted in deposition of up to 7000 ft (2135 m)
of Pico strata, and up to 5000 ft (1525 m) of Repetto strata, compared to zero deposition
on the monoclinal high. In the western part of the study area, the south-dipping
monocline is interrupted by the secondary East Beverly Hills fold, which may be a rabbit-ear
fold that accommodates excess volume by bedding-parallel slip. The East Beverly
Hills fold was active in the latest Miocene through Pliocene, and was most active during
early Pliocene Repetto deposition. In the eastern part of the study area, the monocline is
interrupted by the Las Cienegas fold, which formed in the hangingwall of the Las
Cienegas fault. The Las Cienegas fault was a normal fault in the late Miocene, and was
reactivated in the Pliocene as a steep reverse fault. Folding and uplift on the Las
Cienegas anticline occurred throughout the Pliocene, with the greatest amount occurring
during lower and lower-middle Pico deposition. / Graduation date: 1994
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/35964 |
| Date | 08 March 1994 |
| Creators | Hummon, Cheryl |
| Contributors | Yeats, Robert S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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