Paul Tregoning, Journal of Geophysical Research

Deformation from earthquakes bigger than magnitude 8.0 since 2000. The blue squares are GPS reference sites, and the red arrows are deformation from big earthquakes.

By Becky Oskin, LiveScience

Thirteen years of supersized earthquakes, such as Friday's magnitude-8.3 in Russia, have contaminated GPS sites around the world, a new study finds.

The Global Positioning System is a network of satellites and ground stations that provide location information anywhere on Earth. Except for spots in Australia, western Europe and the eastern tip of Canada, every GPS site on the ground underwent small but important shifts since 2000 because of big earthquakes, according to a study published May 6 in the Journal of Geophysical Research: Solid Earth.

The research confirms that great earthquakes, those bigger than magnitude 8.0, can have far-reaching effects on the Earth's crust. And because GPS is critical for everything from calculating satellite orbits to sea level rise to earthquake hazards, scientists can't ignore these tiny zigs and zags, the researchers conclude.

"We have to find a way to deal with it," said Paul Tregoning, lead study author and a geophysicist at Australia National University in Canberra. "The community needs to work out how to find all the offsets, estimate them accurately and get everyone to agree on how to correct them," he told LiveScience.

Tregoning and his colleagues modeled the sudden jolts in Earth's crust from each of the 15 biggest earthquakes since 2000. They discovered that crust thousands of miles away from the faults had moved horizontally by as much as a tenth of an inch (a few millimeters). The model was checked against a few spots around the planet. On average, the earthquakes deformed the crust by a hundredth of an inch every year (0.4 millimeters a year) — about the width of the lead in a mechanical pencil. [7 Craziest Ways Japan's Earthquake Affected Earth]

"It's quite amazing to us that we can see this and detect this," Tregoning said.

These tiny effects won't make a difference to the GPS in cars or phones, or the tough little units carried by hikers and mountaineers. But scientists who need precise measurements to calculate sea level rise or satellite orbits should be concerned, Tregoning said.

The changing Earth
Here's why these seemingly small changes matter. Scientists who rely on GPS need to compare one place to another. There are a handful of stable spots around the world, usually in the interior of continents, called the terrestrial reference frame. For example, a geologist measuring the speed of the Pacific plate would compare it with the North American reference frame. But Tregoning's study shows these stable spots were shifted by the massive earthquakes.

Disturbing the reference frame will introduce errors into GPS measurements, Tregoning said. It could also throw off calculations of satellite orbits. "If the coordinates of the tracking stations are wrong, then the orbit isn't right either," he said.

"I think he's identified a good problem," said Don Argus, a principal research scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., who was not involved in the study. Argus is part of a group that uses GPS to calculate satellite orbits and conduct research on the changing Earth.

"It's difficult to find a stable frame with these post-seismic transients," Argus said. "The earthquakes are making things a little hard for the people on our floor."

While Argus and his colleagues already account for the deformation caused by earthquakes, it takes computers at JPL 24 hours to churn through the calculations, Argus said. "I've got the best plate motion model out there," he told LiveScience.

Tregoning hopes that the next update to the International Terrestrial Reference Frame System, the internationally agreed upon reference for GPS research, will consider the wide-ranging effects of big earthquakes.

"We have to agree on how to improve the reference frame," he said. "People doing regional studies will find that they potentially get a different answer, and it will potentially be a more accurate answer."

Editor's note: This story was updated May 24 to include information about the May 24 Okhotsk earthquake.

Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on LiveScience.com.

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John Fletcher, CICESE

Ruptures along the trace of the magnitude-7.2 earthquake in Baja California, Mexico in 2010. The earthquake ruptured along a plate boundary, and is one of several which shows signs of foreshocks caused by slow movement prior to the earthquake, a new study finds.

After a destructive earthquake, scientists sifting through the rumbles that preceded the big event often find foreshocks.

Foreshocks are smaller temblors that strike in the days and hours before a moderate-to-large earthquake. They're puzzling. Not all earthquakes have foreshocks, and despite decades of effort, no one has successfully found a way to predict earthquakes using foreshocks.

Now, a new study may help explain some of the mysteries surrounding these enigmatic earthquakes.

At plate boundaries, the interface between two of Earth's tectonic plates, foreshocks result from slow, creeping movement between the two plates before big earthquakes rupture more rapidly, according to a study published today (March 24) in the journal Nature Geoscience. As the fault creeps, small, stuck zones resist this slow movement and eventually break, generating foreshocks, explained study co-author Virginie Durand, a graduate student in seismology at the Institute of Earth Science (ISTerre) in Grenoble, France.

Thus, foreshocks aren't triggers for earthquakes, as was once thought, Durand told OurAmazingPlanet. Instead, "these events can tell us how an earthquake begins," she said. "And if we understand better where and how earthquakes begin, we can better mitigate earthquake hazard."

Plate boundaries
For the study, Durand and her colleagues looked at earthquakes bigger than magnitude 6.5 along the edge of the Pacific Ocean, where Taiwan, Japan, the United States and Mexico operate dense seismic monitoring networks. Between 1999 and 2011, half of the earthquakes tested were on plate boundaries (22 subduction zone quakes and nine strike-slip) and half were so-called intraplate earthquakes. [ Video: What Does Earthquake 'Magnitude' Mean? ]

Subduction zones are collision zones between two plates, where one bends down and dives under the other. Strike-slip boundaries are where plates slide horizontally past one another. Intraplate quakes hit away from the massive faults that mark plate boundaries.

While the pattern for each plate boundary earthquake was unique, on average, the seismicity along the faults was nearly constant until about two months before a big earthquake, when there was a small but noticeable increase, the researchers found. Seismicity refers to the geographic and time distribution of earthquakes.

Mitigating future risk
The increase became more pronounced about 20 days before the main event. Earthquake frequency continued accelerating about two days before, then a few hours before, and kept increasing until the final convulsion, the study found.

"This observation suggests that an earthquake is preceded by the slow slip of the two plates in contact," Durand said."If confirmed, the relatively long duration of this nucleation phase may help mitigate earthquake risk in the future."

There was no clear pattern in earthquakes away from plate boundaries, on the intraplate quakes, an observation that could help explain the puzzling lack of foreshocks for some earthquakes.

Future research will confirm whether the pattern is present in other earthquake zones around the world, and if monitoring faults for creeping movements and foreshocks could be used to forecast future earthquakes on certain types of faults. It's not known if the pattern also appears along faults when there are no earthquakes, the researchers point out.

EmailBecky Oskinor follow her@beckyoskin. Follow us @OAPlanet,Facebook orGoogle+.Original article on LiveScience's OurAmazingPlanet.

• 7 Ways the Earth Changes in the Blink of an Eye
• Image Gallery: This Millennium's Destructive Earthquakes
• The 10 Biggest Earthquakes in History 

NOAA

Oregon's idyllic coastline, a region that may be due for a powerful earthquake that could do plenty of damage.

By Lauren Gambino, The Associated Press

SALEM, Ore. — More than 10,000 people could die when — not if — a monster earthquake and tsunami occur just off the Pacific Northwest coast, researchers told Oregon legislators Thursday.

Coastal towns would be inundated. Schools, buildings and bridges would collapse, and economic damage could hit $32 billion.

These findings were published in a chilling new report by the Oregon Seismic Safety Policy Advisory Commission, a group of more than 150 volunteer experts.

In 2011, the Legislature authorized the study of what would happen if a quake and tsunami such as the one that devastated Japan hit the Pacific Northwest.

The Cascadia Subduction Zone, just off the regional coastline, produced a mega-quake in the year 1700. Seismic experts say another monster quake and tsunami are overdue.

"This earthquake will hit us again," Kent Yu, an engineer and chairman of the commission, told lawmakers. "It's just a matter of how soon."

When it hits, the report says, there will be devastation and death from Northern California to British Columbia.

Many Oregon communities will be left without water, power, heat and telephone service. Gasoline supplies will be disrupted.

The 2011 Japan quake and tsunami were a wakeup call for the Pacific Northwest. Governments have been taking a closer look at whether the region is prepared for something similar and discovering it is not.

Oregon legislators requested the study so they could better inform themselves about what needs to be done to prepare and recover from such a giant natural disaster.

The report says that geologically, Oregon and Japan are mirror images. Despite the devastation in Japan, that country was more prepared than Oregon because it had spent billions on technology to reduce the damage, the report says.

Jay Wilson, the commission's vice chairman, visited Japan and said he was profoundly affected as he walked through villages ravaged by the tsunami.

"It was just as if these communities were ghost towns, and for the most part there was nothing left," said Wilson, who works for the Clackamas County emergency management department.

Wilson told legislators that there was a similar event 313 years ago in the Pacific Northwest, and "we're well within the window for it to happen again."

Experts representing a variety of state agencies, industries and organizations expanded on the report's findings and shared with lawmakers how they have begun planning.

Sue Graves, a safety coordinator for the Lincoln County School District, told lawmakers that high school students in her district take semester-long classes that teach CPR and other survival techniques in preparation for a giant earthquake. The class teaches students to "duck, cover and hold" when the ground starts shaking.

Maree Wacker, chief executive officer of the American Red Cross of Oregon, said it is important for residents to have their own contingency plans for natural disasters.

"Oregonians as individuals are underprepared," she said.

By Becky Oskin
Our Amazing Planet

The deadly earthquake and tsunami that hit the Solomon Islands Wednesday struck along a subduction zone, the same geologic setting responsible for the world's most powerful earthquakes.

In a subduction zone, two of Earth's tectonic plates meet and one slides beneath the other into the mantle, the deeper layer beneath the crust. The Solomon Islands sits above the collision between the Australia and Pacific plates. In the region of Wednesday's magnitude-8.0 earthquake, the Australia plates dives beneath the Pacific plate toward the east-northeast at a geologically speedy 3.7 inches (94 millimeters) per year, according to the Incorporated Research Institutions for Seismology (IRIS).

The earthquake hit at a depth of 17.8 miles (28.7 kilometers) and was the second-largest earthquake in the Solomon Islands region in almost 40 years, IRIS said in a statement. Several aftershocks followed, the largest measuring magnitude 6.6, according to the U.S. Geological Survey (USGS).

The tsunami generated by the quake, reported as 3 feet (0.9 meters) in height, hit villages on Santa Cruz Island, destroying structures and homes, according to news reports. A tsunami watch was issued for Australia, Indonesia and New Zealand, but not for the rest of the Pacific, according to the West Coast and Alaska Tsunami Warning Center.

Subduction zone quakes shove the seafloor in one sudden movement, which may generate a tsunami by pushing the ocean water above. However, depending on the depth and size of the earthquake, the actual seafloor surface may not move a significant amount, so a big earthquake doesn't always produce a massive wave. For example, a magnitude-7.6 subduction zone earthquake in the Philippines in August 2012, which started deep in Earth's crust, did not trigger a tsunami.

There were dozens of earthquakes around the Solomon Islands in the month leading up to Wednesday's massive quake, the USGS reported. More than 40 magnitude-4.5 quakes shook the islands in the past week alone, and seven of those temblors were larger than a magnitude-6.0, the USGS said.

Reach Becky Oskin at boskin@techmedianetwork.com. Follow her on Twitter @beckyoskin. Follow OurAmazingPlanet on Twitter @OAPlanet. We're also on Facebook and Google+.

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