Joe Clark, professor emeritus of the Geoscience Department, presented a talk at the Pacific Sections of the American Association of Petroleum Geologists and the Society for Sedimentary Petrology joint conference in Monterey California, April 2013.
Joe’s talk, entitled “Neotectonics of the Greater Monterey Area, California,” discussed work that has been ongoing for years by Joe and colleagues mapping the geology of the Monterey area.
Clark, Joseph C. and Lewis I. Rosenberg
The greater Monterey area is situated within the complexly deformed Salinian block between the active San Andreas fault to the northeast and the active offshore San Gregorio fault to the southwest.
Field mapping and subsurface analyses reveal that faults of the offshore Monterey Bay zone continue onshore as the Seaside, Ord Terrace, and Chupines faults that extend southeastward to the Laguna Seca area. Late Pleistocene terrace deposits and Holocene colluvium are locally offset by thrust faults near Monterey and by through-going, near-vertical faults in Carmel and in Carmel Valley. Radiocarbon dating indicates movement along the Tularcitos fault within the past 7,780 years, along the Sylvan thrust within the past 4,890 years, and probable movement along the Hatton Canyon fault within the past 2,080 years.
The Garrapata fault to the south trends on land N 55° W, where it vertically offsets the lowest marine terrace by 1.7 m. Inland this fault locally juxtaposes along a near-vertical shear zone granitic rock with four colluvial units, the two youngest of which yield radiocarbon dates of 1,200+60 and 9,750+60 ybp, suggesting recurrence intervals on the order of thousands of years.
Although earthquake focal mechanisms are poorly constrained, they suggest right-lateral strike slip on northwest trending vertical faults. Field mapping, drill hole data, and focal mechanisms suggest that the shorter, discontinuous thrust faults splay off of the longer, through-going strike-slip faults.
Department of Geoscience