Late Quaternary activity of the San Diego Trough fault zone offshore Northwest Baja California

Mark R. Legg

Published August 16, 2021, SCEC Contribution #11581, 2021 SCEC Annual Meeting Poster #017

The San Diego Trough fault zone stretches more than 340 km offshore southern and Baja California, from Dume submarine canyon in the north to Bahía Soledad in the south. The San Diego Trough section offshore southern California has a relatively straight S30°E trend along the axis of the San Diego Trough half-graben. This fault continues into Mexican waters for 60-75 km offshore northern Baja California. Seismic reflection profiles show the vertical fault intersection with the shallow northeast-dipping Thirtymile Bank detachment fault where minor vertical separation and a southwest-dipping conjugate fault offset the detachment surface. Relocated hypocenters show that the vertical fault defines the western limit of micro-seismicity through the entire seismogenic crust beneath the San Diego Trough. South of the international border, the 100+ km Thirtymile-Boundary-Navy Bank escarpments form the western boundary of the San Diego Trough and terminate in the Descanso Plain. This broad, sediment-filled basin extends south about 75 km toward Punta Santo Tomás and Maximinos Knolls. Turbidite fill of the San Diego Trough and Descanso Plain is derived from well-defined submarine fans along the base of the Coronado-Descanso escarpment. Seafloor morphology shows 1-5 km dextral offsets and deflections of upper fan valleys along the San Diego Trough fault. In high-resolution seismic reflection profiles, basin turbidite sequences provide clear images of shallow fault character and late Quaternary deformation. One profile crossing a flat seafloor shows varying thicknesses and vertical separation of prominent sequences offset by the vertical fault. A few kilometers to the south, another profile across a small seafloor bump (2.5 km x 3 km) shows up to 700-m of vertical structural relief at a small restraining bend along the fault. These and other features along the southern San Diego Trough fault zone demonstrate Holocene activity and inferred 1-2 m/ky slip rates consistent with seafloor observations in the San Pedro Basin more than 125 km to the northwest (Ryan et al. 2012).

Key Words
San Diego Trough, fault offset, slip, Baja California

Citation
Legg, M. R. (2021, 08). Late Quaternary activity of the San Diego Trough fault zone offshore Northwest Baja California . Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
SCEC Community Models (CXM)