Frozen in time, cracks reveal earthquake history

Apr 30, 2013 by Anne Ju
Frozen in time, cracks reveal earthquake history
Cracks produced during the 1995 magnitude 8.1 Antofagasta earthquake in northern Chile. Foreground: former graduate student Francisco Gomez. Credit: Rick Allmendinger

(Phys.org) —Northern Chile's Atacama Desert is an earthquake scientist's dream – the hyper-arid plain keeps a visible record of cracks caused by a million year's worth of earthquakes.

Using and analysis of surface frozen in time, Cornell researchers have created a million-year record of several thousand "great" earthquakes – magnitude 8 or more – that have occurred in northern Chile, one of the world's most -prone places.

Their work has not only defined the size of the area's average rupture, but also has shown that widely used earthquake modeling may not account for when the crust sometimes deforms permanently, rather than snapping back to its original position.

The work, led by Rick Allmendinger, professor of earth and atmospheric sciences, was published online April 28 in the journal Nature Geoscience. First author and former Cornell graduate student Amanda Baker did the work as part of her thesis, which involved years of in northern Chile in an area called the Iquique Gap.

Typical earthquake modeling follows the elastic rebound theory, which assumes that energy accumulates in the rocks on either sides of a via slow deformation, and an earthquake is the result of a sudden "rebound" – like a stress ball suddenly springing to its normal shape after years of slow squeeze. The rebound theory contends that the earth soon locks back to that original squeezed shape, until it slips again.

The Cornell researchers have concluded that up to 10 percent of the surface of South America that overlies the , which is responsible for the great earthquakes and runs along the western coast of the continent through much of Chile, has actually deformed permanently due to earthquakes. If that's the case in other places too, elastic rebound theory-based earthquake modeling might be too simple, Allmendinger said.

Frozen in time, cracks reveal earthquake history
Former graduate student Amanda Baker and Brad Lipovsky '08 investigate a surface crack. Credit: Rick Allmendinger

The researchers discovered this by looking at geodetic GPS data that records, down to a sub-centimeter scale, changes in the earth's surface in real time – a technology that has revolutionized all of earth sciences, Allmendinger said.

The field team spent much of 2008 and 2009 documenting surface deformation due to several thousand earthquakes in Iquique Gap. They surveyed about 11 kilometers (almost 7 miles) of scan lines across cracks in the area, measuring their width and orientation. They used a method called cosmogenic nuclide dating, which analyzes aluminum and beryllium isotope levels in quartz clasts, to determine the ages of the surface of the earth on both sides of the cracks. They then calculated the strain rate of the area, which allowed them to compare it to the modern GPS record.

"By using these cracks in this very dry area, we actually now have a statistically significant sample of thousands of earthquakes, because these cracks are the records of thousands of earthquakes," Allmendinger said.

The Iquique Gap area hasn't had a major earthquake since 1877; it will probably get one in the next several decades, Allmendinger said.

"This area has been particularly highly monitored in the last few years because people are expecting the earthquake," he said.

The paper is titled "Permanent deformation caused by subduction earthquakes in northern Chile."

Explore further: Clean air: Fewer sources for self-cleaning

More information: www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1789.html

Related Stories

GPS data reveals more on mega-thrust earthquakes

Apr 29, 2011

(PhysOrg.com) -- New GPS data of the 2010 earthquake that devastated parts of Chile and killed over 500 people is revealing new clues about large earthquakes such as the quake in Chile and the magnitude 9.0 ...

Geological evidence for past earthquakes in Tokyo region

Jan 31, 2012

In 1923, a magnitude 7.9 earthquake devastated the Tokyo area, resulting in more than 100,000 deaths. About 200 years earlier, in 1703, a magnitude 8.2 earthquake struck the same region, causing more than 10,000 deaths.

Ill. earthquake a wake-up call

Apr 20, 2008

A U.S. seismologist said the earthquake that jolted the Midwest Friday is a reminder of the risks seismic events pose outside familiar quake areas.

Recommended for you

Six Nepalese dead, six missing in Everest avalanche

2 hours ago

At least six Nepalese climbing guides have been killed and six others are missing after an avalanche struck Mount Everest early Friday in one of the deadliest accidents on the world's highest peak, officials ...

Clean air: Fewer sources for self-cleaning

16 hours ago

Up to now, HONO, also known as nitrous acid, was considered one of the most important sources of hydroxyl radicals (OH), which are regarded as the detergent of the atmosphere, allowing the air to clean itself. ...

There's something ancient in the icebox

16 hours ago

Glaciers are commonly thought to work like a belt sander. As they move over the land they scrape off everything—vegetation, soil, and even the top layer of bedrock. So scientists were greatly surprised ...

Image: Grand Canyon geology lessons on view

23 hours ago

The Grand Canyon in northern Arizona is a favorite for astronauts shooting photos from the International Space Station, as well as one of the best-known tourist attractions in the world. The steep walls of ...

First radar vision for Copernicus

Apr 17, 2014

Launched on 3 April, ESA's Sentinel-1A satellite has already delivered its first radar images of Earth. They offer a tantalising glimpse of the kind of operational imagery that this new mission will provide ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

rwinners
not rated yet Apr 30, 2013
The earth's crust is dynamic.

More news stories

Six Nepalese dead, six missing in Everest avalanche

At least six Nepalese climbing guides have been killed and six others are missing after an avalanche struck Mount Everest early Friday in one of the deadliest accidents on the world's highest peak, officials ...

China says massive area of its soil polluted

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

There's something ancient in the icebox

Glaciers are commonly thought to work like a belt sander. As they move over the land they scrape off everything—vegetation, soil, and even the top layer of bedrock. So scientists were greatly surprised ...

Clean air: Fewer sources for self-cleaning

Up to now, HONO, also known as nitrous acid, was considered one of the most important sources of hydroxyl radicals (OH), which are regarded as the detergent of the atmosphere, allowing the air to clean itself. ...

Scientists tether lionfish to Cayman reefs

Research done by U.S. scientists in the Cayman Islands suggests that native predators can be trained to gobble up invasive lionfish that colonize regional reefs and voraciously prey on juvenile marine creatures.

Leeches help save woman's ear after pit bull mauling

(HealthDay)—A pit bull attack in July 2013 left a 19-year-old woman with her left ear ripped from her head, leaving an open wound. After preserving the ear, the surgical team started with a reconnection ...