The Plate Boundary and the Faults of Southern California

Some of the stress and slip generated by the plate boundary also seems to be shunted off the main plate boundary and onto the Eastern California Shear Zone (ECSZ), shown in yellowish-orange on the map of fault traces at right. This broad area of right-lateral shearing motion branches off from the San Andreas fault zone near Indio, just south of the epicenter of the 1992 Landers earthquake (magnitude 7.3). The ECSZ continues in a north-northwest direction through the Mojave, past Barstow, and on into Owens Valley, crossing the Garlock fault as it goes. Seismicity continues along this trend well into Nevada.

Also contributing to fault activity in this area is the Basin and Range tectonic province to the east of this zone. This region of extensional faulting, shown in light blue, is most pronounced to the north of where the ECSZ crosses the Garlock fault. Unlike the features mentioned above, it may have no direct connection with the Big Bend of the San Andreas fault, though it does most likely originate from the interaction of the North American Plate with the Pacific Plate.

The activity below will help you test your knowledge and understanding of the processes at work within these different regions of southern California.

"Find that fault slip!"

Are you familiar enough with the tectonics of southern California to find a fault with a particular sense of slip? Try these real world maps and see -- you may surprise yourself!