Strong offshore quake kills 1 in the Philippines
By Joe Sterling, CNN
August 31, 2012 -- Updated 1913 GMT (0313 HKT)
The 7.6-magnitude quake, which was about 20 miles deep, struck just before 8:50 p.m., authorities said.
STORY HIGHLIGHTS
- NEW: Damage is reported to houses and bridges
- The quake struck on Friday night
- At least one person has died as a result of the earthquake
- Tsunami waves ranging from an inch to a foot and a half were reported
Manila, Philippines (CNN) -- A major earthquake offshore of the Philippines sent people scrambling toward higher ground, generated a small tsunami and killed at least one person Friday, authorities said.
The 7.6-magnitude quake struck Friday evening, with its epicenter about 65 miles southeast of the coastal town of Guiuan, in the Philippine province of Eastern Samar, the U.S. Geological Survey said. It was about 20 miles deep.
Tsunami waves ranging from 6 to 7 inches to a foot and a half were recorded in the province of Surigao del Norte, with waves of an inch reported near the cities of Davao and Legaspi, the National Disaster Risk Reduction and Management Council said.
Those waves did no known damage, but the earthquake triggered a landslide that killed one person and injured another, the council said.
"The quake occurred amid a strong rain, so the earth shook loose and there was a landslide," the country's civil defense chief, Benito Ramos, said, The Manila Times reported.
The quake was centered in the Marianas Trench in the western Pacific Ocean and was felt in the country's east, said Aimee Menguilla, a spokeswoman for the council.
Ed Serrano, the head of security at the Marco Polo Hotel in the city of Davao, about 250 miles south of Guiuan, said he felt the ground shake.
"The hotel guests were panicking," he said. "Most of them went outside."
Marie Elairon, working at the front desk at Hotel Dona Vicenta in the city of Borongan, said some people headed to mountainous areas and others took shelter in a church.
The Pacific Tsunami Warning Center said tsunami waves were possible in a vast arc of the Pacific, but the alerts were soon canceled. The Philippines canceled an advisory urging people to evacuate early Saturday.
Ricky Carandang, President Benigno Aquino's press secretary, said there has been minor damage to roads in six provinces authorities were monitoring: Eastern and Northern Samar, Leyte, Southern Leyte, Surigao del Norte, Surigao del Sur. The government also reported damage to bridges and houses.
Paul Earle, a U.S. Geological Survey seismologist, said the quake was "fairly far off the coast, so it likely won't cause severe shaking damage." But, he said, an earthquake "this large could cause a lot of damage" if it were inland.
The U.S. Geological Survey initially said the quake had a magnitude of 7.9 but later revised that figure.
http://edition.cnn.com/2012/08/31/world/asia/philippines-earthquake/index.html ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Philippines Earthquake Tsunami Alert Explained
The large earthquake near the Philippines sparked tsunami warnings across a large swath of the neighboring Pacific region, yet those warnings were canceled not long after.
-
- Fri Aug 31, 2012
Content provided by Andrea Mustain, OurAmazingPlanet
The large earthquake that struck off the eastern coast of the Philippines today (Aug. 31) at 8:47 p.m. local time sparked tsunami warnings across a large swath of the neighboring Pacific region, yet those warnings were canceled not long after.
The magnitude-7.6 earthquake hit about 58 miles (63 kilometers) from shore along a tectonic boundary known as a subduction zone, where an oceanic plate is diving beneath a continental plate.
Earlier reports put the quake's magnitude at 7.9, but after more data from global networks of seismometers arrived, officials at the U.S. Geological Survey downgraded the magnitude to 7.6.
"There's a significant difference, but they're both really big earthquakes that can generate tsunamis, and if they occur on land they can kill lots of people," said Paul Caruso, a geophysicist with the U.S. Geological Survey in Golden, Colo.
In this case, the oceanic Philippine plate shoved deeper below the Sunda plate, a continental plate home to the Philippines, and portions of Indonesia, Malaysia, Thailand and Vietnam.
The quake ruptured at a depth of about 22 miles (35 km). That's fairly shallow, Caruso said, and shallower earthquakes are more likely to cause tsunamis.
"When you get a really deep quake, a lot of the energy is absorbed before it reaches the seafloor, and what causes a tsunami is the seafloor being pushed up," he told OurAmazingPlanet.
However, tsunami warnings that were in effect for the Philippines, Indonesia and Belau were cancelled by the Pacific Tsunami Warning Center in Hawaii at around 11 a.m. ET.
So-called subduction quakes — those that occur when an oceanic plate suddenly jolts deeper beneath a continental plate — are the most powerful type of earthquakes that occur on our planet.
They're also very good at shoving the seafloor, and the sheer area of the seafloor that is thrust upward — the length of the rupture, and its horizontal and vertical displacement — determines the size of the tsunami that follows.
Data from sensors in the ocean near the site of the quake indicate a tsunami was generated, and waves are coming between 10 and 14 minutes apart, but it appears the waves aren't packing so much energy that they'll take a significant toll once they reach land.
In deep water, tsunami waves appear small, and only reach a massive size once they make it into shallower waters close to shore.
So, although today's quake was a significant one, it appears it didn't move the seafloor enough to cause a large tsunami.
However, Caruso warned that earthquakes can also trigger undersea landslides, which can, in turn, cause tsunamis.
It appears the earthquake has caused at least one death after a house collapsed, and Philippine authorities are warning residents to remain vigilant, in case any further earthquakes occur, the AP reported.
The tectonic region that ruptured today has a long history of shallow, strong earthquakes.
http://news.discovery.com/earth/tsunami-alert-explained-120831.html#mkcpgn=rssnws1 --
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