ANN ARBOR—University of Michigan experts are available to discuss July 4’s magnitude-6.4 earthquake in California. The U.S. Geological Survey said the earthquake occurred in a remote area 121 miles north-northeast of Los Angeles and 89 miles east of Bakersfield.

Nathan Niemi

Nathan Niemi is a professor of geological sciences in the Department of Earth and Environmental Sciences. His research focuses on the tectonic processes that lead to mountain building.

“Large earthquakes in this region are known from the paleoseismic record, but are infrequent,” Niemi said. “Faults in this region typically host earthquakes every thousand or more years. The last major earthquake in this general region was the Lone Pine earthquake of 1872, which had a magnitude of about 7.5. Further to the south, a series of large earthquakes ruptured within the Mojave Desert in 1992 and 1999.”

Today’s earthquake appears to be on the southern end of the Little Lakes fault zone in California, according to Niemi. The location of the fault, the current predicted magnitude (6.4), and the depth of the earthquake (about 10 km) suggest that a surface rupture is unlikely. The motion of the earthquake is strike-slip, with the two sides sliding past, rather than over or under one another, he said.

The Little Lakes fault zone is a complex tectonic zone where north-south oriented faults associated with the Basin and Range, to the north, intersect and interact with the east-west trending Garlock fault, a major fault that bounds the Mojave Desert, and which connects to the west with the San Andreas fault.

“Although this part of California is generally lightly populated, this earthquake appears to have occurred near one of the largest cities in the region, Ridgecrest, which is associated with Edwards Air Force Base and the China Lake Naval Weapons Center,” Niemi said. “The proximity of the earthquake to Ridgecrest, approximately 14 miles, suggests that damage in Ridgecrest is likely.”

Contact: 805-587-2237, [email protected]

Ben Van Der Pluijm

Ben van der Pluijm is an earthquake geologist and a professor in the Department of Earth and Environmental Sciences.

The July 4 California earthquake did not occur on the San Andreas Fault but in another seismically active part of the state at the southern end of Owens Valley/Southern Sierra Nevada fault zone, just north of the Garlock Fault.
A magnitude-6.4 earthquake is equivalent to the explosion of 60,000 tons TNT or four atomic bombs, van der Pluijm said.

“Does this earthquake change the potential for the Big One? No, but continuing Pacific-North American plate movement mandates that a large quake along the San Andreas Fault must occur in the near future. The July 4 earthquake does nothing to reduce that threat.”

Contact: 734-678-1397, [email protected]