Chile Earthquake: Is Mother Nature Out of Control?

Jeanna Bryner, livescience.com 27 Feb 10;

Chile is on a hotspot of sorts for earthquake activity. And so the 8.8-magnitude temblor that shook the capital region overnight was not a surprise, historically speaking. Nor was it outside the realm of normal, scientists say, even though it comes on the heels of other major earthquakes.

One scientist, however, says that relative to a time period in the past, the Earth has been more active over the past 15 years or so.

The Chilean earthquake, and the tsunami it spawned, originated on a hot spot known as a subduction zone, where one plate of Earth's crust dives under another. It's part of the very active "Ring of Fire," a zone of major crustal plate clashes that surround the Pacific Ocean.

"This particular subduction zone has produced very damaging earthquakes throughout its history," said Randy Baldwin, a geophysicist with the U.S. Geological Survey (USGS).

The world's largest quake ever recorded, magnitude 9.5, occurred along the same fault zone in May 1960.

Even so, magnitude-8 earthquakes occur globally, on average, just once a year. Since magnitudes are given on a logarithmic scale, an 8.8-magnitude is much more intense than a magnitude 8, and so this event would be even rarer, said J. Ramón Arrowsmith, a geologist at Arizona State University.

Is Earth shaking more?

The Ryukyu Islands of Japan were hit with a 7.0-magnitude quake just last night. News of this, the Haiti quake and now Chile make it seem Earth is becoming ever more active. But in the grand scheme of things, geologists say this is just Mother Nature as usual.

"From our human perspective with our relatively short and incomplete memories and better and better communications around the world, we hear about more earthquakes and it seems like they are more frequent," Arrowsmith said. "But this is probably not any indication of a global change in earthquake rate of significance."

Coupled with better communication, as the human population skyrockets and we move into more hazardous regions, we're going to hear more about the events that do occur, Arrowsmith added.

However, "relative to the 20-year period from the mid 1970's to the mid 1990's, the Earth has been more active over the past 15 or so years," said Stephen S. Gao, a geophysicist at Missouri University of Science & Technology. "We still do not know the reason for this yet. Could simply be the natural temporal variation of the stress field in the earth's lithosphere." (The lithosphere is the outer solid part of the Earth.)

And while the Chilean earthquake wasn't directly related to Japan's 7.0-magnitude temblor, the two have some factors in common.

For one, any seismic waves that did make their way from Japan to the Chilean coast could play a slight role in ground-shaking.

"It is too far away for any direct triggering, and those distances also make the seismic waves as they would pass by from the Haiti or Japan events pretty small because of attenuation," Arrowsmith told LiveScience. (Attenuation is the decrease in energy with distance.) "Nevertheless, if the Chilean fault surface were close to failure, those small waves could push it even closer."

In addition, both regions reside within the Ring of Fire, which is a zone surrounding the Pacific Ocean where the Pacific tectonic plate and other plates dive beneath other slabs of Earth. About 90 percent of the world's earthquakes occur along this arc. (The next most seismic region, where just 5 to 6 percent of temblors occur, is the Alpide belt, which extends from the Mediterranean region eastward.)

Colliding plates

The Chilean earthquake occurred at the boundary between the Nazca and South American tectonic plates. These rocky slabs are converging at a rate of 3 inches (80 mm) per year, according to the USGS. This huge jolt happened as the Nazca plate moved down and landward below the South American plate. This is called a subduction zone when one plate subducts beneath another.

(Over time, the overriding South American Plate gets lifted up, creating the towering Andes Mountains.)

The plate movement explains why coastal Chile has such a history of powerful earthquakes. Since 1973, 13 temblors of magnitude 7.0 or greater have occurred there, according to the USGS.

In fact, today's earthquake originated about 140 miles (230 km) north of the source region of the magnitude 9.5 earthquake of May, 1960, considered the largest instrumentally recorded earthquake in the world.

The 1960 earthquake killed 1,655 people in southern Chile, unleashing a tsunami that crossed the Pacific and killed 61 people in Hawaii, Japan, and the Philippines.

In November 1922, a magnitude-8.5 earthquake occurred about 540 miles (870 km) to the north of the Feb. 27 earthquake, triggering a local tsunami that inundated the Chile coast and crossed the Pacific to Hawaii.

Because the recent one was such a huge earthquake, the shaking would likely have caused just as much damage had a similar-sized event occurred elsewhere, said Baldwin, the USGS scientist.

"If [the quake] were in Los Angeles you'd probably have massive destruction too," Baldwin said in a telephone interview.

Andrea Thompson contributed reporting to this story.

Chile quake wave racing to Asia at jet speed: scientist
Yahoo News 28 Feb 10;

WASHINGTON (AFP) – A tsunami triggered by the powerful quake that rocked Chile was Saturday racing across the Pacific Ocean towards Hawaii and Asia at around 450 miles per hour, a quake expert said.

Estimating the depth of the wave's water column to be around four kilometers (2.4 miles) on average, Roger Bilham, a professor of geological sciences at the University of Colorado, calculated that at mid-ocean, the mass of water would be hurtling toward Hawaii at 200 meters per second, or 720 kilometers per hour (446 mph).

"Mid-ocean, the wave is traveling at around the speed of a jet plane," Bilham told AFP.

"The amplitude of the wave is small when it's mid-ocean, but it may rise to five to 10 meters when it reaches Japan or the Philippines," he said.

A huge arc of nations around the Pacific, from New Zealand to Japan, have gone on tsunami alert, while sirens sounded warnings of destructive waves around Hawaii for the first time in 16 years.

The powerful 8.8-magnitude quake that rattled Chile in the early hours of Saturday occurred offshore in a subduction zone -- the point where two tectonic plates meet and one plunges beneath the other.

The undersea earthquake that set off the 2004 Asian tsunami, which killed some 200,000 people and left hundreds of thousands homeless, was also a subduction earthquake.

"Subduction zone earthquakes produce the world largest tsunamis because the sea floor moves like a piston, heaving 100 kilometer by 50 kilometer (60 miles x 30 miles) or larger regions of sea floor water up or down," Bilham told AFP.

Walls of water of up to four meters (13 feet) crashed ashore in French Polynesia and the Marquesas Islands hours after the quake had rattled Chile.

But the tsunamis caused only minor damage and no casualties as they rampaged across the Pacific, where authorities had sounded warning sirens and urged residents of coastal areas to move to higher ground.

The tidal waves that devastated parts of southern Asia in 2004 struck without warning. It was after that deadly series of monster waves that the Pacific Tsunami Warning Center, set up after a tsunami unleashed by a 9.5-magnitude earthquake in Chile in 1960, beefed up its warning system.

"This time, we're ready for the tsunamis. When the waves hit Hawaii, there will be cameras there to catch them," said Bilham.

"This is a huge success," he said.

Tsunami spares US, takes aim at Japan
Mark Niesse and Audrey McAvoy Associated Press Google News 28 Feb 10;

HONOLULU — With a rapt world watching the drama unfold on live television, a tsunami raced across a quarter of the globe on Saturday and set off fears of a repeat of the carnage that caught the world off guard in Asia in 2004.

The tsunami delivered nothing more than a glancing blow to the U.S. and most of the Pacific, but Japan was still bracing for a direct hit and waves up to 10 feet high (3 meters). Scientists worried the giant wave could gain strength as it rounds the planet and consolidates, though the first wave to hit Japan's outlying island's was just 4 inches (10 centimeters) high.

The tsunami was spawned by a ferocious magnitude-8.8 earthquake in Chile that sent waves barreling north across the Pacific at the speed of a jetliner. But Pacific islands had ample time to prepare because the quake struck several thousand miles away.

By the time the tsunami hit Hawaii — a full 16 hours after the quake — officials had already spent the morning ringing emergency sirens, blaring warnings from airplanes and ordering residents to higher ground.

The islands were back to paradise by the afternoon, but residents endured a severe disruption and scare earlier in the day: Picturesque beaches were desolate, million-dollar homes were evacuated, shops in Waikiki were shut down, and residents lined up at supermarkets to stock up on food and at gas stations.

Others parked their cars along higher ground to watch the ocean turbulence, and one brave soul stayed behind and surfed before being urged by an emergency helicopter pilot to get out of the water.

There were no immediate reports of widespread damage, injuries or deaths in the U.S. or in much of the Pacific, but a tsunami that swamped a village on an island off Chile killed at least five people and left 11 missing.

Waves hit California, but barely registered amid stormy weather. A surfing contest outside San Diego went on as planned.

Despite Internet rumors of significant problems in coastal areas of California, no injuries or major property damage occurred.

It was still possible that the tsunami would gain strength again as it heads to Japan. That's what happened in 1960, when a deadly tsunami killed dozens of people in Hilo, Hawaii, then went on to claim some 200 lives in Japan.

Japan and Russia were the only countries left on the Pacific Tsunami Warning Center's watch list, but some countries in Asia and the Pacific — including the Philippines, Australia and New Zealand — said their own warnings would remain in effect as a precaution.

Japan put all of its eastern coastline on alert for a "major" tsunami Sunday and ordered hundreds of thousands of residents in low-lying areas to seek higher ground. It was the first such alert for Japan's coasts in nearly 20 years.

Hawaii had originally prepared to bear the brunt of the damage, but the tsunami was smaller than anticipated.

"We dodged a bullet," said Gerard Fryer, a geophysicist for the Pacific Tsunami Warning Center in Hawaii.

The tsunami initially raised fears that the Pacific could fall victim to the type of killer waves that killed 230,000 people in the Indian Ocean in 2004 the morning after Christmas. During that disaster, there was little to no warning and much confusion about the impending waves.

Officials said the opposite occurred after the Chile quake: They overstated their predictions for the size of the waves and the threat.

"We expected the waves to be bigger in Hawaii, maybe about 50 percent bigger than they actually were," Fryer said. "We'll be looking at that."

The Navy moved more than a half dozen vessels to try to avoid damage from the tsunami. A frigate, three destroyers and two smaller vessels were being sent out of Pearl Harbor and a cruiser out of Naval Base San Diego, the Navy said.

The tsunami caused a series of surges in Hawaii that were about 20 minutes apart, and the waves arrived later and smaller than originally predicted. The highest wave at Hilo measured 5.5 feet (1.7 meters) high, while Maui saw some as high as 6.5 feet (2 meters).

Water began pulling away from shore off Hilo Bay on the Big Island just before noon, exposing reefs and sending dark streaks of muddy, sandy water offshore. Waves later washed over Coconut Island, a small park off Hilo's coast.

"We've checked with each county. There was no assessment of any damage in any county, which was quite remarkable," said Hawaii Gov. Linda Lingle. "It's just wonderful that nothing happened and no one was hurt or injured."

Officials in Tonga and the Samoas evacuated coastal residents and used radio, television and mobile phone text messages to alert residents.

Sea surges hit 6.5 feet (2 meters) at several places in New Zealand. Waters at Tutukaka, a coastal dive spot near the top of the North Island, looked like a pot boiling with the muddy bottom churning up as sea surges built in size through the morning, sucking sea levels below low water marks before surging back.

A nude photo shoot involving scores of people scheduled for the coastline near the capital, Wellington, was canceled by the tsunami threat before any of the volunteers could strip.

Past South American earthquakes have had deadly effects across the Pacific.

A tsunami after a magnitude-9.5 quake that struck Chile in 1960, the largest earthquake ever recorded, killed about 140 people in Japan, 61 in Hawaii and 32 in the Philippines. It was about 3.3 to 13 feet (1 to 4 meters) in height, Japan's Meteorological Agency said.

Associated Press writers Jaymes Song and Greg Small in Honolulu; Kristen Gelineau in Sydney, Chris Havlik in Phoenix, Ray Lilley in Wellington, New Zealand; Eric Talmadge in Tokyo; Alan Clendenning in Sao Paulo, Brazil; Tiphaine Issele in Papette, French Polynesia; Pauline Jelinek in Washington; and Charmaine Noronha in Toronto contributed to this report.