Fault Creep Project Under a New Source of Strain
April 21, 2007 2:00 PM
The dangerous faults that twice terrorized the Bay Area now provide job opportunities for geology students.
Founded in 1979, the SF State Fault Creep Monitoring Project collects data on roughly 30 California fault locations. The San Andreas Fault, which was responsible for the Great Quake of 1906 and Loma Prieta, is among the faults monitored by the project.
Undergraduate and graduate SF State geology students are employed by the Geosciences Department to take measurements of fault creep, which, according the project, is the fault slip that occurs in the uppermost part of the earth’s crust between large stress-relieving earthquakes.
Professor of geology and oceanography Karen Grove, who was a former principal investigator with the Fault Creep Project, added to the definition.
“Fault creep is aseismic movement, meaning it is movement on the fault that isn’t associated with earthquakes,” she said. “So it’s just very slow movement.”
Every weekend students are deployed to a few of the various locations in groups of two. Once on site the students, using high precision equipment, take measurements of the fault creep. Nails, already implanted in the ground, serve as a frame of reference for the movement that occurs.
“We set up our instruments on the nails and measure the changes in the angles,” said Jessica Fadde, 35, an applied geosciences graduate student. “We determine whether something is moving left or right laterally.”
Monitoring the behavior of faults in the Bay Area is of particular importance because it is a region prone to seismic activity that often culminates in an earthquake.
“Fault creep occurs on a lot of faults in the Bay Area due to many of the rock sites not being able to stand friction,” said Jon Perkins, 23, a senior geology major who has been involved with the project since 2004. “The faults, in response to strain and plate tectonics, move at a more constant rate than a lot of other faults.”
Surface earthquakes are largely thought to be caused by excessive pressure build-up on a fault. Tremors occur when faults can no longer withstand the strain caused by friction.
Some faults move at a more accelerated rate than others. The Hayward Fault, which was responsible for the recent small-scale quakes that occurred in Lafayette, Berkeley and Hayward, moves at a particularly rapid rate.
Although fault creep is not the sole indicator of a potential earthquake, it can provide insight on the behavior of faults, especially after an earthquake has occurred.
“The biggest thing that was seen in this time of data was after the Loma Prieta earthquake,” said Grove. “A couple of the faults stopped creeping and others started creeping in the opposite direction.”
But a reduced budget, effective last month, may put a different kind of strain on the project. The creep project, which is largely financed by the National Earthquake Hazard Reduction Program (NHRP), experienced a 35 percent reduction of funds during the last grant proposal period.
“We’ve never been funded the requested amount,” said Grove. “But with the new funding cycle, the grant amount was somewhat reduced from previous years.”
While the NHRP could not be reached for comment, Fault Creep collaborators have their own take on the budget cut.
“My cynical reaction to why [the budget] was cut is that we haven’t had a big enough earthquake in a long time,” said Theresa Hoyt, a 21 year veteran of the project.
Grove provided further insight on the project’s financial situation.
“I heard they want us to do more with the data,” said Grove. “In other words they want to see more analysis of the data.”
The budget cut did not affect the $11.50 hourly wage the students receive for the labor they provide to the program, but some participants observed a decline in the number of times they will survey the fault sites in the future.
“We noticed when we got the schedule that only six sites are being read this month,” said Jonathon Polly, 35, an applied geosciences graduate student who has been involved with the project since 2004. “We usually survey a lot more.”
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