Structural imbrication with multiple detachments in the Subandean of Bolivia and active tectonics of the Wilmington and Palos Verdes faults, Los Angeles, California

Abstract

This thesis investigates patterns of structural imbrication with multiple detachment horizons in the Subandean of Bolivia and active tectonics of the Wilmington and Palos Verdes faults, Los Angeles, California. Our findings have significant implications for energy resource exploration, earthquake hazards, landscape evolution, and interpretations of fold-thrust belts worldwide. Chapter 1 investigates patterns of structural imbrication in the Subandean multi-detachment fold-thrust belt of Bolivia. We develop a new structural model for the region by integrating field observations, well data, and seismic reflection data. These data are interpreted to develop kinematic models, balanced cross sections, and map and 3-D representations of key structural elements. We document the dominant structural styles of the fold-thrust belt and demonstrate how these are related to structural imbrication involving multiple detachments. These insights suggest that certain features of the Subandean fold-thrust belt are diagnostic of a multiple detachment imbricate system and can be applied to interpret similar fold-thrust belts worldwide. Chapters 2 and 3 concern active tectonics in southern California. In Chapter 2, we define the Wilmington blind-thrust as a tectonically active fault. This overturns the long-held view that the fault became dormant in the Late Pliocene, barring its inclusion in state- of-the-art regional earthquake hazard assessments. Our analysis of 2- and 3-D seismic reflection surveys, petroleum and water wells, and recent mapping of ground-water aquifers in the region suggest the fault is capable of generating moderate-magnitude earthquakes (M 6.3–6.4), whereas potential linkages with other nearby faults (e.g., Huntington Beach, Torrance, and Compton) pose the threat of larger multisegment events (M > 7). In Chapter 3, we present a model for the origin of the Palos Verdes restraining bend and its implications for 3-D geometry of the fault and earthquake hazards in Los Angeles, California. We develop kinematic models that show folding of the Palos Verdes Fault Zone (PVFZ) by the Wilmington blind-thrust formed the restraining bend. North of the Peninsula, where debate persists over the extent, geometry, and activity of the PVFZ, we interpret seismic reflection data and present new mapping of the Santa Monica segment of the PVFZ, including multiple active splays (e.g., Redondo Canyon Fault Zone) that occur within a broad damage zone at the northern termination of the fault system. Together, these insights contribute to a new comprehensive model for the geologic evolution and 3-D geometry of the PVFZ and suggest the fault system is capable of larger earthquakes than previously estimated (M 6.9-7.8) with short recurrence intervals ( kyr.).