Sierra El Mayor Earthquake of April 4, 2010, Baja California

Surface fault rupture and other ground failure investigations are underway by a collaborative team comprised of representatives from the U.S. Geological Survey, California Geological Survey, Southern California Earthquake Center, and other organizations. The Earthquake Engineering Research Institute also deployed a group of its members to the region soon after the event struck. Major geologic findings reported thus far is the south of the border occurrence of extensive surface rupture with oblique slip offset (east down, right lateral) in places exceeding 2 meters along a 28 km portion of the Borrego fault. North of the border, coseismic strike slip not exceeding 1-2 cm (as reported thus far) is being mapped along a series of faults within a 10 km-wide northwest trending zone that extends about 15 km into California.

Considerable ground failure in the form of surface fault rupture and liquefaction has been documented along various roads and canal levees south of the border. No reports of liquefaction or earthquake-induced landslides have yet been reported north of the border. Clearinghouse updates will be posted periodically as information from the field investigations continue to arrive.

	Figure 1. SCEC field team members Tom Rockwell (L) and John Fletcher (R) stand on opposite sides of surface rupture along the Borrego fault (photo by SCEC team; view to north)		Figure 2. Hillside surface rupture along the Borrego fault, Baja California (photo from SCEC team; westerly view)
	Figure 3. Maximum observed rupture (2.5 +- 0.75 m oblique offset) along Borrego fault (overflight photo from SCEC team, view westerly).		Figrue 4. Borrego fault rupture across utility road near Hwy 2 (overflight photo by SCEC team; view to SW).

	Figure 5. Annotated epicenter and aftershock map, Sierra El Mayor Earthquake, Baja California (image base from Google, 2009)

Note: Since posting of Figure 5, the epicenter has been relocated 11 miles to the northwest.