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Digging deep: scientists drill into the planet to catch earthquakes in action.

In a quest to spy on earthquakes, researchers working on the National Science Foundation's EarthScope project have spent two years boring a hole far below Earth's surface. The hole--measuring 21.6 centimeters (8.5 inches) wide--extends nearly 4 kilometers (2.5 miles) deep. In August, these scientists reached their goal: They tapped into an unstable area of Earth's outer layer, or crust. There, rocks frequently break apart, resulting in ground-shaking quakes.

Until now, scientists have tried to learn as much as they can about earthquakes by studying the effects at Earth's surface. In this groundbreaking project, they hope to find out how and why quakes occur by directly monitoring them at the focus, or the point deep beneath Earth's surface where rocks first break apart.

SHAKY GROUND

For the drilling project, scientists homed in on the San Andreas Fault system (see map, left), one of the world's most active faults. This crack, which winds 1,288 km (800 mi) through California into Mexico, marks the boundary between two slowly moving rock plates. Along this fault, the Pacific Plate scrapes northward past the slab of rock that makes up North America. When these two plates suddenly break apart and slide past each other, energy is released. That jolt sends shock waves rippling across Earth's surface--an earthquake.

In the last 100 years, several major San Andreas earthquakes have rattled California. In 1994, a powerful quake caused $20 billion of damage and killed 58 people in the Los Angeles area.

CONSTANT MOTION

Instead of drilling into an area of the fault where violent--but infrequent--quakes occur, researchers set up a drilling site on a remote ranch in Parkfield, California. This site is known for small tremors that occur daily. "We wanted to drill into a piece of fault that was moving every day, so we'd be able to track what the fault was doing," says Stephen Hickman, a geophysicist with the U.S. Geological Survey who is involved in the project.

Earthquakes near the drilling site usually measure less than 2.0 on the Richter" scale, a scientific rating system for an earthquake's strength. Too weak to feel on Earth's surface, these mini-quakes may hold clues as to how and why more powerful quakes occur.

INSIDE SCOOP

This summer, scientists began using the borehole to pull up samples of rock from within the fault (see diagram, left). Geologists will examine the samples to see what types of rocks line the fault and look for clues as to how they change shape, or deform, under the high pressures and temperatures that occur deep underground.

The researchers also began lowering an array of sensors into the hole. For example, seismometers positioned in the borehole will record the vibrations during an earthquake. Other sensors will measure the temperature and deformation of rocks along the fault and send the data to recorders at the surface. By constantly monitoring these conditions, the scientists hope to spot patterns in the way the rocks behave before breaking apart in a quake.

If they do find patterns, scientists might be able to predict when a quake will strike. Currently, there's no way to forecast the tremors. The scientists got a jarring reminder of this last fall, when a magnitude 6.0 quake rumbled through the site. "This was more excitement than the drill crew was counting on," says Hickman.

DID YOU KNOW?

* The plates along the San Andreas Fault are moving past each other at a rate of approximately 5 centimeters (2 inches) per year, causing the southern California city of Los Angeles to move northward.

* The famous 1906 San Francisco earthquake lasted under one minute. But it cracked open nearly 430 kilometers (267 miles) of the San Andreas Fault and permanently shifted the ground 6 meters (20 feet) in some areas. Scientists estimate that the quake may have registered between 7.7 and 8.3 on today's Richter scale.

CRITICAL THINKING:

* Why might earthquakes of similar strengths cause more deaths and destruction in one area than another? What are some factors that contribute to this difference in damage levels?

CROSS-CURRICULAR CONNECTIONS:

ART: Do research to create a poster that instructs people on what safety measures they should take in the event of an earthquake.

RESOURCES

* "Drilling San Andreas," by Brad Lemley, Discover, March 2005.

* Learn more about the history of seismographs and how scientists measure earthquakes at: www.thetech.org/exhibits_events/online/quakes/seismo/

* This site has a lot of teen-friendly activities and information about earthquakes: http://earthquake.usgs.gov/4kids/

CHECK FOR UNDERSTANDING

DIRECTIONS: On a separate sheet of paper, use details from the article to help you write the following:

1. It's speech day at school. Write a speech to explain to your fellow students why California is so vulnerable to earthquakes.

2. You're a scientist working on the EarthScope project. News reporters have gathered around the hole you helped bore in Parkfield, California. Give a press conference to explain how you plan to use the hole to learn about earthquakes.

ANSWERS

Answers may vary, but they should include the following points:

1. The San Andreas Fault system is one of the world's most active faults. This crack, which winds 1,288 km (800 mi) through California into Mexico, marks the boundary between two slowly moving rock plates. Along this fault, the Pacific Plate scrapes northward past the slab of rock that makes up North America. When these two plates suddenly break apart and slide past each other, energy is released. That jolt sends shock waves rippling across Earth's surface. In the last 100 years, several major San Andreas earthquakes have rattled California. In 1994, a powerful quake caused $20 billion in damage and killed 58 people in the Los Angeles area.

2. Scientists hope to learn how and why quakes occur by monitoring them at the focus, or the point deep beneath Earth's surface where rocks first break apart. Scientists are using the borehole to pull up samples of rock from the fault. Geologists will examine the samples to see what types of rocks line the fault and look for clues as to how they deform under the high pressures and temperatures that occur deep underground. Scientists also lowered an array of sensors into the hole. For example, seismometers positioned in the borehole will record vibrations during an earthquake. Other sensors will measure the temperature and deformation of rocks along the fault and send the data to recorders at the surface. By constantly monitoring these conditions, scientists hope to spot patterns in the way the rocks behave before breaking apart in a quake. If they do notice patterns, scientists might be able to predict when a quake will occur.
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Article Details
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Author:Gaidos, Susan
Publication:Science World
Geographic Code:1U9CA
Date:Dec 12, 2005
Words:1112
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