Patterns of syntectonic sedimentation in actively growing fault-related folds and its application to earthquake hazard assessment in southern California and reservoir characterization in deepwater depositional systems

Abstract

This thesis investigates the use of growth stratigraphy in deepwater environments to determine fault kinematics and reservoir distribution in the Niger Delta and assess earthquake hazards associated with blind-thrust faults in the Santa Barbara Channel, California. Chapter 1 analyzes the distribution of deepwater depositional systems related to contractional fault-related folds in the Niger Delta using high-quality 3D seismic reflection datasets. Deepwater channel systems, the primary reservoir rocks in the Niger Delta, record the growth history of anticlines and associated thrust faults in the toe-thrust belt. The patterns of the channels generally record the initiation of structural growth with their deflection around the nose of plunging anticlines. When folds grow with fixed lateral limits, progressively younger channels stack vertically above the fold. In contrast, when structures grow through lateral propagation progressively younger channel systems stack father away from the center of the fold. Results indicate that structures in close proximity can grow by different mechanisms or even a combination of mechanisms over different stages in their development. The patterns of the channel systems give important insight into reservoir distribution which have important implications for resources characterization. Chapter 2 investigates the 3D geometry and slip history of the Mid-Channel fault, and active blind thrust that accommodates significant shortening within the Santa Barbara Channel of southern California. We define a new method for relating structural relief to fault slip and use a series of nine precisely dated Pleistocene horizons ranging in age from 120 ka – 1.05 Ma to define the recent slip rate on the Mid-Channel thrust. Results indicate that the structure became active between 790 and 710 ka in the eastern part of the Channel and subsequently propagated west along strike. We calculated a slip rate on the Mid-Channel fault is 2.1 ± 0.2 mm/yr, suggesting that it may accommodate about one third of the observed geodetic contraction across the basin. Chapter 3 explores the linkage of the offshore Pitas Point fault and the onshore Ventura fault in the Santa Barbara Channel and Ventura Basin in southern California. The Ventura-Pitas Point fault system is one of the largest earthquake sources in southern California with several different forms of evidence suggesting that the system rupture in M>7.5 events. We create a series of balanced cross sections and show that the Pitas Point has the same distinct subsurface ramp flat ramp geometry as the Ventura fault, supporting their linkage as part of a the Ventura Pitas Point fault system and ability to source large (M 7.5 to 8) earthquakes. This study also explores the linkage of the Ventura – Pitas Point system to other large faults in the region. We also show that while the onshore Ventura fault consumes all slip at its tip-line associated with the Ventura Avenue anticline, offshore the slip on the fault system is partitioned between the shallow ramp of the Pitas Point fault and a detachment in its footwall that extends into the central part of the Santa Barbara Channel. This observation reconciles observations that slip and shortening on the Pitas Point fault is less than that of the Ventura fault. The improved 3D fault geometries further support the prospect for large, multi-segment ruptures and have important implications for patterns of interseismic strain accumulation and the tsunami and ground shaking hazards associated with the fault system.