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Tectonic Characterization of the THUMS-Huntington Beach Fault, Southern California


The THUMS-Huntington Beach fault branches from the Palos Verdes fault zone and south of that point forms the southwestern border of the Wilmington and Huntington Beach anticlines. The fault extends southeastward from the Huntington Beach anticline and merges with the Newport-Inglewood fault zone. Wilmington and Huntington Beach oil fields are located to the east of the THUMS-Huntington Beach fault, with timing and trapping mechanisms closely related to the evolution of the California Continental Borderland. Although the THUMS-Huntington Beach Fault is a part of Inner Continental Borderland, tectonic relationships among the fault zones and anticlines within the Borderland have not been clearly established. Previously, the THUMS-Huntington Beach fault has been interpreted as a discontinuous feature. Correlation of newly acquired 2-D (specifically collected for this research) and existing industry 2-D and 3-D seismic and well data made it possible to identify that this is a continuous (21.5 miles) right-slip fault zone with three segments and two steps. The first and third segments of the fault zone strike W-N60°W with an average dip of 70° to the northeast; the second segment strikes N40°W with an average dip of 80° to the northeast. Parts of the fault segments with restraining geometry are associated with the Wilmington and Huntington Beach anticlines. These anticlines are inverted basins formed as structural lows and then uplifted as a result of THUMS-Huntington Beach fault activity in late Miocene-early Pliocene time. The fault was initiated as a transtensional strike-slip fault before early Pliocene time and subsequently transformed into the transpressional strike-slip system, with a change of dip from southwest to northeast. This dip change resulted in a juxtaposition of disparate features on opposite sides of the THUMS-Huntington Beach fault, which gave a false impression of vertical slip. The fault geometry may be closely related to the Palos Verdes and Newport-Inglewood fault zones due to a possible transfer of slip to or from both fault systems. This study revealed that the THUMS-Huntington Beach Fault, with the associated anticlines, should be thought of as an active and evolving system in which fault kinetics, including slip, is not constant over the length of the system.