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Monster quakes of centuries past reveal new details about faults

Predicting earthquakes might sound like a pretty forward-looking job. But some seismologists are digging up information about past earthquakes to better understand the hazards of today.

A research team from the University of Nevada and the University of Oregon reports in the Bulletin of the Seismological Society of America this week that it's been working on a new way to study California's southern San Andreas fault. By analyzing data from more than 50 quakes from eight different locations, they have been able to estimate the most common types of slips. The legendary1857 Fort Tejon earthquake (7.9 on the Richter scale), which was the largest in modern Southern California history, was hardly unique, say the researchers. Their analysis found that at least a handful of similar earthquakes have rocked the area since 900 C.E.

Meantime, an international team (from the Universidad Nacional Autónoma de México in Mexico City and Insitiuto Nazionale di Geofisica e Vulcanologia in Milan) has been gathering clues from a massive 1787 tsunami that washed fish as far as 3.7 miles (6 kilometers) inland. The researchers confirmed that the gigantic wave was triggered by an earthquake along the Mexican subduction zone and measured approximately 8.6 on the Richter scale – one of the biggest quakes in the area in the past 500 years. The study, also published this week in the Bulletin of the Seismological Society of America, notes that this same area of Mexico and Central America has experienced smaller tremors over the past century, but that doesn't mean another big one won't hit again.

Earlier this week, a 4.3 rumble was felt in California's Bay Area (with an epicenter outside of San Jose). For more on earthquakes, see our in-depth report.

Image of the San Andreas fault (the ridge that runs vertically through the photo) near the location of the 1857 Fort Tejon earthquake courtesy of Scott Haefner/USGS

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