By
OurAmazingPlanet
updated 2/10/2011 1:36:04 PM ET 2011-02-10T18:36:04

The valley of Coachella in Southern California is known for concerts held there every year, but new research has shed light on a more dangerous kind of rocking that has occurred there over the past millennium: quakes on a mysterious part of the San Andreas fault.

The southernmost 60 miles of the San Andreas fault is the only stretch of the fault that has not ruptured in recorded history. This makes it hard to gauge when the next earthquake might strike there or how damaging it might be. This uncertainty is especially troubling considering a major quake there could severely damage Los Angeles, roughly 140 miles to the west.

To learn mor

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e about the southern part of the 800-mile-long fault, scientists focused on an area of the city of Coachella that was untouched by orchards or by canals, golf courses or other developments, making evidence of past earthquakes relatively easy to see.

Related story: Scientists detail impact of 'Big One'

The researchers investigated three trenches about 25 feet deep and up to roughly 1,300 feet  long. These exposed how the earth along the fault was layered, helping the scientists look at how the ground might have shifted because of past quakes.

Their analysis uncovered at least five and up to seven major earthquakes at this part of the San Andreas during the past 1,100 years, with one occurring about every 180 years. The most recent quake occurred there around 1690. Because this stretch of the fault has had more than 300 years to accumulate stress, the researchers said it is likely to produce a major quake in the next few decades.

"I would tell people living in Southern California that a major San Andreas fault earthquake will very likely happen during their lifetimes and that they need to be as prepared as possible," researcher Belle Philibosian, a geologist at the California Institute of Technology, told OurAmazingPlanet.

Of course, scientists can't say exactly when this or any other fault might rupture, but Philibosian emphasized the need for preparedness.

"The exact timing of large earthquakes appears to be inherently unpredictable — at least, all scientific efforts have so far failed — so the way to deal with earthquakes is through building codes and emergency planning," she added. "People should, if possible, have their houses assessed for earthquake risk and have them retrofitted if need be. It's also very important to have a cache of emergency supplies."

For researchers, the next step is to see how much the fault slipped during each of these past earthquakes, to figure out the quakes' size and extent, Philibosian said.

Philibosian and her colleagues Thomas Fumal and Ray Weldon detailed their findings in the February issue of the Bulletin of the Seismological Society of America.

© 2012 OurAmazingPlanet. All rights reserved. More from OurAmazingPlanet.

Interactive: What causes earthquakes?

Explainer: A dozen killer earthquakes

  • USGS

    Thousands of earthquakes happen every day around the world. Most are hardly felt, if at all. But sometimes pieces of Earth's crust suddenly slip past each other in a massive release of pent-up stress. The jolted Earth rumbles, buildings collapse, streets buckle, and thousands of people die. These movements are nature's most violent act and take a grim toll on human life and infrastructure.

    The deadliest earthquake in recorded history rattled the Shensi province of China on Jan. 23, 1556, and killed an estimated 830,000 people. The death toll was particularly high among peasants who lived in artificial caves that were dug into soft rock and collapsed during the quake. This picture shows a pagoda whose peaked top was lost in the shaking. Earthquake damage is also visible on the corners. Click on the "Next" label to learn about 11 more deadly quakes.

    — John Roach, msnbc.com contributor

  • 1906: The Great Quake

    USGS

    The California earthquake of April 18, 1906, ranks as the most deadly in U.S. history: About 3,000 people perished. The Great Quake, as the event is known, was estimated at magnitude 7.9 and ruptured along 296 miles of the northernmost section of the San Andreas fault. Broken gas lines, fractured chimneys and toppled chemical trucks sparked a series of fires that torched large sections of San Francisco, as seen in this image taken from Golden Gate Park.

  • 1964: Good Friday?

    USGS

    The most powerful earthquake in North American history shook the state of Alaska on March 27, 1964, the Friday before Easter. The magnitude-9.2 temblor triggered a tsunami that was responsible for 113 of the 128 deaths associated with the earthquake, according to the U.S. Geological Survey. The giant waves struck along the West Coast down to California, and rolled across the Pacific to Hawaii. This image shows the coastal town of Seward, Alaska, in the wake of the tsunami.

  • 1970: Mountains moved

    USGS

    The magnitude-7.9 earthquake that struck just off the west coast of Peru on May 31, 1970, reduced the coastal towns of Casma and Chimbote to rubble and killed at least 3,000 people. Even greater disaster struck the towns of Yungay and Ranranhirca. The shaking sent an avalanche of mud, rock and ice down the slopes of the Cordillera Blanca and buried the cities under tens of feet of debris. An estimated 70,000 lives were lost. Here, a statue of Christ is all that remains in Yungay.

  • 1976: Chinese region flattened

    USGS

    The deadliest earthquake in modern times flattened the industrial city of Tangshan, China, in the early morning of July 28, 1976. The Chinese government put the death toll at 255,000, though many geologists believe it was much higher — up to 655,000. Nearly 800,000 more were injured. Tremors and damage from the magnitude-7.5 quake extended as far as Beijing, about 90 miles from the epicenter. Here, a few tents and temporary shelters are visible amid the debris.

  • 1985: Mexico shaken

    USGS

    On Sept. 19, 1985, a magnitude-8.2 earthquake off Mexico's Pacific coast wreaked the greatest havoc in Mexico City, about 220 miles from the epicenter. There, hundreds of buildings were toppled, and thousands of people died. Government officials put the death toll at about 9,000, though other sources say it may have been as high as 35,000. A triggered tsunami sent waves rising almost 10 feet crashing into the coastal towns of Lazaro Cardenas, Zihuatanejo and Manzanillo. Here, a 21-story steel-constructed building in Mexico City lies in ruins.

  • 1995: Tremors hit Japan

    Roger Hutchison via NGDC/NOAA

    More than 6,400 people died in the aftermath of a magnitude-6.8 earthquake that hit Japan on Jan. 17, 1995. Most of those deaths occurred in Kobe, the city closest to the epicenter. Many buildings suffered partial collapse, such as the one shown in this picture. Total damage was estimated at more than $100 billion.

  • 2003: Iranian city crumbles

    Majid  /  Getty Images

    On Dec. 26, 2003, a magnitude-6.6 earthquake crumpled the adobe city of Bam, Iran, killing an estimated 30,000 people. About 60 percent of the city's buildings were destroyed and nearly all the rest were damaged. The event ranks as the deadliest in Iran's history. Here, one of the victims is carried to the grave.

  • 2004: The Asian tsunami

    Dita Alangkara  /  AP file

    On Dec. 26, 2004, a magnitude-9.1 earthquake ruptured the ocean floor off the west coast of Sumatra, Indonesia, and triggered a series of destructive tsunamis that killed at least 225,000 people in 11 countries. Millions more were stripped of their homes. Scientists estimate the energy released in the event was more than 1,500 times the power of the atomic bomb dropped on Hiroshima in 1945. Here, villagers walk through a devastated area of Pangdandaran on the Indonesian island of Java.

  • 2005: Landslides in Kashmir

    David Guttenfelder  /  AP file

    At least 86,000 people were killed when a magnitude-7.6 earthquake hit the Kashmir region of northern Pakistan on Oct. 8, 2005. Millions more were left homeless at the outset of the harsh Himalayan winter. Landslides swept away villages and blocked roads for relief and rescue workers, worsening the human toll. At least 1,350 people were killed in neighboring India, and the shaking was also felt in Afghanistan. Here, rescue workers dig through the rubble looking for survivors at a school in Balakot, Pakistan.

  • 2008: Catastrophe in China

    Image: Searching rubble
    Xinhua via AFP - Getty Images

    An estimated 70,000 people died and millions were left homeless when a magnitude-7.9 earthquake hit a region north of Sichuan's provincial capital, Chengdu, on May 12, 2008. Tremors were felt as far away as Beijing and Shanghai. One of the most tragic episodes was the collapse of a high school in Juyuan. This picture shows searchers digging through the school's rubble.

  • 2010: Huge setback for Haiti

    Image: Rescue in Haiti
    Radio Tele Ginen via AP

    Extreme poverty and extremely poor construction standards contributed to the devastation and death in Haiti when a magnitude-7.0 quake hit Port-au-Prince and its surroundings on Jan. 12, 2010. The death toll amounted to more than 230,000, and aid officials say it will take years for Haiti to recover fully ... if it ever can. This picture shows rescuers carrying one of the injured away from the rubble.

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