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Geologist uncovers earth’s secrets, says Southern California is overdue for a major earthquake

BOONE—An Appalachian State University geologist uses everything from backhoes to trowels to reach deeply for evidence of earthquakes that have occurred over time. The knowledge she and fellow scientists are gaining provides valuable data to help understand risks from earthquakes in the years ahead.

“One of the best reasons to study the history of earthquakes is to know what your odds are for earthquakes in the future,” said Kate Scharer, an assistant professor in Appalachian’s Department of Geology.


Appalachian State University geology majors document evidence of paleo-earthquakes exposed in a trench wall along the San Andreas Fault in California. (Photos courtesy of Kate Scharer)

Students help researchers examine earthquake history

Geologist Kate Scharer and students in her structural geology class documented past earthquake activity this fall near Frazier Park, Calif., along the southern segment of the San Andreas Fault. The site of their excavation is usually saturated with water, but because of California’s drought, the water table dropped enough to give access to the section.

“When they are on a site, students realize how much careful pencil-to-paper work is involved in science, but they can also see the big picture. It’s a really great learning experience,” she said.

Scharer fell in love with geology and the science of earthquakes while a student at the University of Washington. After working with an environmental consulting firm for several years, she returned to school, earning a Ph.D. from the University of Oregon. She has taught at Appalachian since 2005.


Appalachian State University geology professor Kate Scharer studies evidence of ancient earthquakes along a trenched section of the southern San Andreas Fault. Findings by her and her colleagues indicate the southern area of the fault is overdue for a major quake.quakepath.jpg

This annotated photo of a 13-foot wide section of backhoe exposure shows prehistoric faulting in red lines that offsets older layers, which are highlighted in other colors.Scharer studies the deformation from “fossil,” or ancient, earthquakes along the San Andreas Fault in California. Her research is funded by the U.S. Geological Survey (USGS) and the Southern California Earthquake Center (SCEC) and used to update earthquake probability maps. That information is used by engineers designing major infrastructure, such as bridges or water lines near or crossing a fault, and by insurance companies when setting rates for property and buildings in the region.

Scharer says Southern California is overdue for a major earthquake. “We are finding in the geological records that the average length between major earthquakes along the southern San Andreas Fault is about 100 and 120 years. Although longer gaps of 200 years have occurred, by all estimates we are beyond the average at this point. That has hazard mitigation and public policy planners alert,” she said.

Evidence of prehistoric, large-magnitude earthquakes can be found in the earth’s strata. Because this is not always visible along the earth’s surface, scientists use a backhoe to cut through the sediment to dig long trenches 20 feet deep or more.

“When a rupture happens, the ground surface gets torn and ripped up,” Scharer said. “Sediment, such as gravel or sand, later covers and preserves the rips. We look for areas where sediment has been deposited quickly.”

Scharer and colleagues from the University of Oregon and USGS have documented dozens of earthquakes that occurred along the southern San Andreas Fault since approximately 3,000 B.C.

But it’s the 1857 California earthquake near Los Angeles that more people are familiar with, thanks to research and a fairly rich historical record.

Geologists can estimate the magnitude of the 1857 quake by correlating historic accounts, newspapers, diaries and missionary reports to similar events in more recent history, Scharer explained. Researchers estimate the 1857 event was a magnitude 7.9 earthquake.

“Another large quake occurred along the southern section in 1812, but because there were fewer literate people there at the time, the historic record is limited,” Scharer said. Scientists look for patterns that occur between these large magnitude ruptures along the southern segment of the San Andreas Fault. “Forty-five years elapsed between those two earthquakes, and it’s been 150 years since the 1857 earthquake occurred. That span is what concerns geologists,” she said.

An updated seismic hazard map which estimates the probability of future ruptures and ground shaking will soon be released by USGS for the entire United States. See

“Hurricane Katrina has shown us that we expect people of power in government to recognize what science is telling them and turn it into policy related to hazard mitigation and public policy planning,” Scharer said. “If you know these large quakes occur on the order of every 100 or 120 years, then you need to be responsive to the possibility that there will probably be a major quake in our lifetime.”