There has been a major focus on earthquake hazards since a magnitude-9.0 temblor and ensuing tsunami in the Indian Ocean rocked Indonesia and many other surrounding countries Dec. 26.

But even before this happened, Penn State researchers were focusing on earthquake problems on a domestic level.

California is home to many fault lines, such as the San Andreas and Hayward faults, but not all of them can be seen on the surface.

"Blind-thrust faults have become a significant hazard in the past two years," Kevin Furlong, professor of geoscience, said.

Blind-thrust faults are faults that do not extend to the earth's surface, and there are no major shakes before the main earthquake hits, he said.

This is where the problem lies; the faults are difficult to find until an earthquake ruptures the fault.

However, Furlong and Eric Kirby, assistant professor of geoscience, have been studying the potential for a blind-thrust fault beneath Marin County, Calif., in the Mount Tamalpais region, which is just north of San Francisco.

They are focusing on this area because there are no signs of a fault on the surface, and geologists are unsure why Mount Tamalpais formed at this location.

"People said it must be related to the other faults," Furlong said, which is why they believe there is some type of fault connecting the two major faults that run parallel in that region -- the Hayward fault to the east and the San Andreas fault to the west.

Also, there is some discrepancy in the amount of slip in the two main faults.

Kirby said the portion of the San Andreas fault north of the Golden Gate Bridge is moving faster than the southern part, and the northern part of the Hayward fault is moving too slowly to account for that much of a difference in shift.

As in all scientific studies, there is a possibility of error, Furlong said, but "we trust we are right on most of the numbers."

Kirby said there needs to be something to help account for the extra shift; otherwise, a hole would open at the point where the faults no longer were in contact.

"Something has to be driving the mountain up," he said.

Geologic mapping, the typical method used to study faults, would not work in the region because of the type of rock found in the crust, so indirect ways of measuring uplift had to be found, he added.

Global positioning satellites are used to take measurements every few years, along with the study of erosion in the river systems on the mountain,

to determine how much uplift has occurred in the region, the researchers said.

Courtney Johnson (graduate-geoscience), another member of the team, said, "We are trying to create a link between erosion and uplift."

Johnson has been working on models for fault systems in the Mount Tamalpais region that would account for the excess slip in the faults.

About 10 years ago, Furlong began looking at the region as an area that could possibly have a blind-thrust fault after finishing work in the Santa Cruz Mountains along the southern San Andreas fault.

Furlong said Mount Tamalpais had similar geologic features to what the early stages of the formation of the Santa Cruz Mountains would have looked like.

Blind-thrust faults don't break the surface because they move more slowly than the larger faults that can easily be seen, such as the San Andreas. However, blind-thrust faults can still cause major damage, as was the case with a 1994 quake in Northridge, Calif., Kirby said.

That earthquake, which had a magnitude of 6.7, caused $15 billion in damages, according to a U.S. Geological Survey estimate.

"Even though [a blind-thrust fault] is slow, it could still host a mid-magnitude quake," Kirby said.

This could cause major damage to Marin County and could possibly extend to San Francisco, Furlong said.