Master's Theses

Date of Award

2016

Document Type

Thesis

Department

Earth and Atmospheric Sciences

First Advisor

Karin Block

Second Advisor

Steven Kidder

Third Advisor

Pengfei Zhang

Keywords

Submarine, landslides, seismic, reflection, slope, sediments

Abstract

Multiple submarine landslides have been previously documented on the north flank of the Santa Barbara Channel, and such failures are considered to be capable of generating local tsunamis hazards to the Santa Barbara region. 2D seismic-reflection datasets provide a general view of regional framework geology, including faulting and folding associated with north-south compression. However, better understanding of the relationships between faults, folds, stratigraphic architecture, and submarine landslides can be obtained with 3D seismic datasets. In this study we use an industry 3D seismic-reflection volume that encompasses the slope and shelfbreak surrounding the Gaviota submarine landslide (3.8 km2) to investigate structural and stratigraphic controls on slope failure in this region. The depth-migrated seismic volume shows a network of stacked thrust faults, backthrusts, and splays that result in both broad and local zones of compression, folding, and uplift along the slope and shelf. One localized zone of enhanced folding and uplift associated with small-scale thrust faults is located directly beneath the Gaviota landslide, while another zone is located directly below the westernmost extent of a seafloor fissure inferred to represent incipient failure. In addition, 3D seismic attribute analysis provides insight into the shallow sedimentary section of the failed and non-failed sedimentary packages. Calculation of RMS amplitude within a windowed region below the seafloor horizon delineates an apparent zone of gas-charged strata that onlaps onto older folded sediments. The up-dip limit of these gas-charged sediments appears to align with the location of seafloor fissures and the Gaviota landslide headwall. The slope gradient surrounding the Gaviota slide is only 4°, which is significantly lower than the internal friction angle for fine-grained marine sediments. It is therefore proposed that the combination of active 8 deformation and fluid charging acted to pre-condition and trigger the failure of the Gaviota landslide through a reduction in shear strength. These conditions are also present in intact sections of the slope adjacent to the Gaviota landslide, which should be considered prone to future landslides.

Available for download on Thursday, August 23, 2018

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