Deformation in the Lower Crust of the San Andreas Fault System in Northern California

• Published in: Science (American Association for the Advancement of Science) Vol. 278; no. 5338; pp. 650 - 653
• Main Authors: Henstock, Timothy J., Levander, Alan, Hole, John A.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for the Advancement of Science 24.10.1997; American Association for the Advancement of Science; The American Association for the Advancement of Science
• Subjects: Conceptual Tempo; Earth sciences; Earth, ocean, space; Earthquakes; Earthquakes, seismology; Exact sciences and technology; Faults (Geology); Geology; Internal geophysics; Mantle; Migration; Mohorovicic discontinuity; Plate tectonics; Reflectance; Seismology; Strike slip faults; Strikes; Tectonics. Structural geology. Plate tectonics; Travel; Travel time; Upper mantle; Upwelling water; San Andreas Fault; Northern California; Coast Ranges; California; United States; United States > US; strike-slip faults; Mohorovicic discontinuity; velocity structure; deformation; upper mantle; lower crust; seismic discontinuities; tectonics; North America; seismic waves
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.278.5338.650

A continuous seismic velocity and reflectivity cross-section of the San Andreas fault system in northern California shows offsets in the lower crust and the Mohorovicic Discontinuity near the San Andreas and Maacama strike-slip faults. These faults may cut through the crust to the upper mantle in a zone less than 10 kilometers wide. The northern California continental margin to the eastern edge of the Coast Ranges is underlain by a high-velocity lowermost crustal layer that may have been emplaced within 2 million years following the removal of the Gorda plate slab. The rapid emplacement and structure within this layer are difficult to reconcile with existing tectonic models.