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Friday, August 17, 2007

337 Die in Strong Peru Quake

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The death toll from a powerful earthquake rose to at least 337 Thursday, a day after the magnitude-7.9 temblor shook Peru's coast, toppled buildings and shattered roads, officials said.

More than 827 people were reported injured and the Red Cross said the toll was expected to rise.

Rescue workers struggled to reach the center of the destruction, the port city of Pisco about 125 miles southeast of the capital, Lima. Pisco's mayor said at least 200 people were buried in the rubble of a church where they had been attending a service.

"The dead are scattered by the dozens on the streets," Mayor Juan Mendoza told Lima radio station CPN.

"We don't have lights, water, communications. Most houses have fallen, churches, stores, hotels, everything is destroyed," he said, sobbing.

An AP Television News cameraman who reached the city of Chincha, about 100 miles southeast of Lima, said he counted 30 bodies under bloody sheets on the floor of the badly damaged hospital.

Another church collapsed Wednesday evening in the city of Ica, 165 miles south of Lima, killing 17, according to cable news station Canal N.

The government rushed police, soldiers, doctors and aid to the stricken areas along the coast south of the capital but hundreds of vehicles were paralyzed on the Pan American Highway by giant cracks in the pavement and fallen power lines, the AP Television News cameraman reported from Chincha.

Giorgio Ferrario, head of the Peruvian International Federation of the Red Cross and Red Crescent, said teams from the Peruvian Red Cross arrived in Ica and Pisco after 7 1/2 hours, about three times as long as it would normally have taken because the earthquake had destroyed the roads to these areas.

He said that he expected the death toll to climb as rescue teams worked in the daylight.

News reports said dozens of people in Ica crowded hospitals that suffered cracks and other structural damage. The quake also knocked out telephone and mobile phone service in the capital and to the provinces, making it impossible to communicate with the Ica area.

Electricity also was cut to Ica and smaller towns along the coast south of Lima.

An Associated Press photographer said that some homes had collapsed in the center of Lima and that many people had fled into the streets for safety. The quake shook Lima furiously for more than two minutes.

"This is the strongest earthquake I've ever felt," said Maria Pilar Mena, 47, a sandwich vendor in Lima. "When the quake struck, I thought it would never end."

Antony Falconi, 27, was desperately trying to get public transportation home as hundreds of people milled on the streets flagging down buses in the dark.

"Who isn't going to be frightened?" Falconi said. "The earth moved differently this time. It made waves and the earth was like jelly."

Firefighters were called to put out a fire in a shopping center. Police reported that large boulders shook loose from hills and were blocking the country's Central Highway, which heads east into the Andes mountains.

State doctors called off a national strike that began on Wednesday to handle the emergency. President Alan Garcia also said public schools would be closed Thursday because the buildings may be unsafe.

The Civil Defense death toll of 337 first appeared on its Web site, but the organization's spokesman, Dario Ariola, refused to confirm the figure, which was much higher than the numbers provided by the health minister. But minutes later Civil Defense Commander Aristides Mussio confirmed the toll on Peru's state television station, saying one person was killed in Lima and 336 in the region of Ica.

The U.S. Geological Survey said Wednesday's earthquake hit at 6:40 p.m. about 90 miles southeast of Lima at a depth of about 25 miles. Four strong aftershocks ranging from magnitudes of 5.4 to 5.9 were felt afterward.

The Hawaii-based Pacific Tsunami Warning Center issued a tsunami warning for the coasts of Peru, Chile, Ecuador, Colombia, Costa Rica and Panama. A tsunami watch was issued for the rest of Centra

l America and Mexico and an advisory for Hawaii.

The center canceled all the alerts after about two hours, but it said the quake had caused an estimated 10-inch tsunami near the epicenter.

The last time a quake of magnitude 7.0 or larger struck Peru was in September 2005, when a 7.5-magnitude earthquake rocked the country's northern jungle, killing four people. In 2001, a 7.9-magnitude quake struck near the southern Andean city of Arequipa, killing 71 people.

The region sits on two plates that are constantly shifting and Thursday's earthquake, like most earthquakes in the area, occurred when one plate dove under the other quickly, according to Amy Vaughan, a USGS geophysicist at the National Earthquake Information Center in Golden, Colo.

The plates are always "moving slowly, but this was a sudden shift," Vaughan said.

Some of the world's biggest quakes, including the catastrophic Indian Ocean temblor in 2004 that generated deadly tsunami waves, are caused by a similar movement of plates.

AP Writer Monte Hayes reported from Lima, Peru. Associated Press writers Leslie Josephs in Lima, Alicia Chang in Los Angeles and Sarah DiLorenzo in New York contributed to this report.

Quake Matter

An earthquake is the result of a sudden release of stored energy in the Earth's crust that creates seismic waves. Earthquakes are accordingly measured with a seismometer, commonly known as a seismograph. The magnitude of an earthquake is conventionally reported using the Richter scale or a related Moment scale (with magnitude 3 or lower earthquakes being hard to notice and magnitude 7 causing serious damage over large areas).

At the Earth's surface, earthquakes may manifest themselves by a shaking or displacement of the ground. Sometimes, they cause tsunamis, which may lead to loss of life and destruction of property. An earthquake is caused by tectonic plates getting stuck and putting a strain on the ground. The strain becomes so great that rocks give way by breaking and sliding along fault planes.

Earthquakes may occur naturally or as a result of human activities. Smaller earthquakes can also be caused by volcanic activity, landslides, mine blasts, and nuclear tests. In its most generic sense, the word earthquake is used to describe any seismic event-whether a natural phenomenon or an event caused by humans-that generates seismic waves.

An earthquake's point of initial ground rupture is called its focus or hypocenter. The term epicenter means the point at ground level directly above this.

Naturally occurring earthquakes

Fault types

Fault types

Most naturally occurring earthquakes are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes. The Earth's lithosphere is a patchwork of plates in slow but constant motion caused by the release to space of the heat in the Earth's mantle and core. The heat causes the rock in the Earth to become flow on geological timescales, so that the plates move slowly but surely. Plate boundaries lock as the plates move past each other, creating frictional stress. When the frictional stress exceeds a critical value, called local strength, a sudden failure occurs. The boundary of tectonic plates along which failure occurs is called the fault plane. When the failure at the fault plane results in a violent displacement of the Earth's crust, the elastic strain energy is released and seismic waves are radiated, thus causing an earthquake. This process of strain, stress, and failure is referred to as the Elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth and is converted into heat, or is released to friction. Therefore, earthquakes lower the Earth's available potential energy and raise its temperature, though these changes are negligible.[1]

The majority of tectonic earthquakes originate at depths not exceeding tens of kilometers. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, Deep focus earthquakes may occur at much greater depths (up to seven hundred kilometers). These seismically active areas of subduction are known as Wadati-Benioff zones. These are earthquakes that occur at a depth at which the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.[2]

Earthquakes may also occur in volcanic regions and are caused there both by tectonic faults and by the movement of magma in volcanoes. Such earthquakes can be an early warning of volcanic eruptions.

A recently proposed theory suggests that some earthquakes may occur in a sort of earthquake storm, where one earthquake will trigger a series of earthquakes each triggered by the previous shifts on the fault lines, similar to aftershocks, but occurring years later, and with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the North Anatolian Fault in Turkey in the 20th century, the half dozen large earthquakes in New Madrid in 1811-1812, and has been inferred for older anomalous clusters of large earthquakes in the Middle East and in the Mojave Desert.

Size and frequency of occurrence

Small earthquakes occur nearly constantly around the world in places like California and Alaska in the U.S., as well as in Peru, Indonesia, Iran, the Azores in Portugal, New Zealand, Greece and Japan.[3] Large earthquakes occur less frequently, the relationship being exponential; for example, roughly ten times as many earthquakes larger than magnitude 4 occur in a particular time period than earthquakes larger than magnitude 5. In the (low seismicity) United Kingdom, for example, it has been calculated that the average recurrences are:

  • an earthquake of 3.7 or larger every year

  • an earthquake of 4.7 or larger every 10 years

  • an earthquake of 5.6 or larger every 100 years.

The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, many more earthquakes are reported than in the past because of the vast improvement in instrumentation (not because the number of earthquakes has increased). The USGS estimates that, since 1900, there have been an average of 18 major earthquakes (magnitude 7.0-7.9) and one great earthquake (magnitude 8.0 or greater) per year, and that this average has been relatively stable.[4] In fact, in recent years, the number of major earthquakes per year has actually decreased, although this is likely a statistical fluctuation. More detailed statistics on the size and frequency of earthquakes is available from the USGS.[5]

Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-km-long, horseshoe-shaped zone called the circum-Pacific seismic belt, also known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate.[6][7] Massive earthquakes tend to occur along other plate boundaries, too, such as along the Himalayan Mountains.

Effects/impacts of earthquakes

Chūetsu earthquake.

Chūetsu earthquake.

Smoldering after the 1906 San Francisco earthquake.

Smoldering after the 1906 San Francisco earthquake.

Man walking around in Ruins after Tsunami.

Man walking around in Ruins after Tsunami.

There are many effects of earthquakes including, but not limited to the following:

Shaking and ground rupture

Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings or other rigid structures. The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from epicenter, and the local geological and geomorphological conditions, which may amplify or reduce wave propagation. The ground-shaking is measured by ground acceleration.

Specific local geological, geomorphological, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the seismic motion from hard deep soils to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical setting of the deposits.

Landslides and avalanches

Earthquakes can cause landslides and avalanches, which may cause damage in hilly and mountainous areas.


Following an earthquake, fires can be generated by break of the electrical power or gas lines.

Soil liquefaction

Soil liquefaction occurs when, because of the shaking, water-saturated granular material temporarily loses their strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, as buildings or bridges, to tilt or sink into the liquefied deposits.


Undersea earthquakes and earthquake-triggered landslides into the sea, can cause Tsunamis. See, for example, the 2004 Indian Ocean earthquake.

Human impacts

Earthquakes may result in disease, lack of basic necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage, and collapse of buildings or destabilization of the base of buildings which may lead to collapse in future earthquakes.

Preparation for earthquakes

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