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SHAKE AND BLOW
Hope fading for survivors as Mexico search enters third day
By Yussel GONZALEZ, Jean ARCE
Mexico City (AFP) Sept 22, 2017


Mexico City, supremely vulnerable to quake threats
Paris (AFP) Sept 21, 2017 - Built in a natural basin filled with the sediment of a former lake, Mexico City has proved particularly vulnerable to the devastating effects of earthquakes, seen once again with a 7.1-magnitude tremor on Tuesday that killed at least 233 people in the capital.

The quake was "medium strong" according to Yann Klinger, an expert at the Global Physics Institute in Paris.

By comparison, the 8.2-magnitude quake that rocked southern Mexico on September 7 was "a monster", Klinger said -- yet resulted in fewer, about 100, deaths.

"The fact that there were a lot of victims this time is mainly due to the specific configuration of Mexico City," he said.

Mexico as a whole sits along the edges of several huge tectonic plates, though generally their movements produce quakes along the country's western coast, through more common "interplate" shiftings deep below the earth, which is what caused the massive quake that hit Mexico in 1985, killing an estimated 10,000 people.

Tuesday's quake occurred farther to the east and involved the Cocos, a so-called microplate "stuck" between the Pacific and the North American plates, Klinger said.

Such phenomena, which also caused the quake that hit on September 7, are known as "intraplate" quakes that happen within plates, and not when the edges of separate plates grind against each other.

"Fortunately this occurred deep down (about 50 kilometres) so the shaking at ground level was not as bad as it might have been," said David Rothery, a geosciences professor at the Open University in Britain.

"The deformation builds up by flexing and bending until enough stress has been built up to release the blockage, allowing many year's worth of movement to occur in a few seconds," he said.

- 'Like quicksand' -

But no matter the type of tectonic activity, the resulting vibrations can be especially deadly in Mexico City because it is built on the packed sediment of a dried-up lake.

"There are two very dangerous effects coming together: The seismic waves are trapped in the basin and amplified," Klinger said.

"And furthermore, the unconsolidated sediments (clay, sand) lose their coherence in the shaking and become like liquid, a little like quicksand."

Taller buildings in the capital are especially susceptible to the resulting vibrations on shaky ground, posing bigger risks for residents.

Rescuers were focusing their efforts in particular on Thursday on a school in the south of Mexico City, where 21 children and five adults were crushed to death, and where many might still be trapped in the rubble.

"The Enrique Rebsamen elementary school where many children died looks like a modern building, and ought to have had in-built earthquake resilience," Rothery said.

"Had it been properly constructed it should not have collapsed, and I expect questions will be asked about whether the appropriate building codes were adhered to," he added.

Scientists are also expecting aftershocks in the coming days or weeks.

"In the most common scenario, the magnitudes are lower than the initial earthquake. But we can't exclude other strong shocks," Klinger said.

Mexico waited anxiously on Thursday for signs of life in the rubble of collapsed buildings as a desperate search for survivors of a devastating earthquake entered a third day.

Authorities put the death toll from Tuesday's 7.1 magnitude quake at 272 people, with the number expected to rise.

Volunteer rescue workers who have been seeking survivors since Tuesday fought off growing fatigue to continue removing tons of rubble at dozens of flattened buildings in the capital and across several central states.

But time is running out. Experts say the average survival time in such conditions and depending on injuries is 72 hours.

Some 200 people were still reported missing in Mexico City and feared trapped in the rubble.

In the central neighborhood of Roma, rescue workers scrambled to locate 23 people believed to be in the wreckage of a collapsed seven-storey office building.

They have already pulled 28 survivors from the mountain of rubble. No deaths have been reported at the site so far.

Relatives of the missing waited in anguish for news.

Aaron Flores's sister Karen and friend Paulino Estrada were both trapped inside.

Estrada has managed to contact his family by cell phone, even making a video call. But there has been no news from Karen Flores.

"We're feeling disoriented and desperate because we haven't heard anything from her," said her brother, 30.

- Phantom schoolgirl -

Authorities put the overall death toll at 137 people in Mexico City, 73 in Morelos state, 43 in Puebla, 13 in Mexico state, five in Guerrero and one in Oaxaca.

However, the situation on the ground was chaotic, and the figures were rising -- and sometimes falling.

Highlighting the confusion that still reigned two days after the quake, one story that gripped the world's attention turned out to be false: that of a girl supposedly trapped alive beneath the rubble of a school that collapsed in Mexico City.

Authorities denied Thursday that the girl existed.

"We have carried out a full count with the directors of the school and we are sure that all the children are either safe at home, in the hospital or unfortunately died," Angel Sarmiento, a top officer in the Mexican marines, told journalists at the ruins of the Enrique Rebsamen school on the capital's south side.

"There are indications there may be an (adult) still alive in the rubble. There are traces of blood in the photographs, as if the person had dragged him or herself and may still be alive."

Rescue workers had told journalists they were certain a girl was trapped beneath the rubble, but the different versions of the story varied widely.

The story had made headlines around the world after the quake, injecting a ray of hope into a tragedy that killed 19 children and six adults at the school.

- Not giving up -

But real stories of hope continued to emerge from ruined buildings across the city, where more than 10,000 people lost their lives in a devastating earthquake in 1985.

In the north of the city, a man who had been trapped for 26 hours and a 90-year-old woman were pulled alive from the rubble.

President Enrique Pena Nieto said authorities were not giving up the search.

"The rescue and support effort in the buildings that collapsed is still on. We are not suspending it. We have to keep up the rescue effort to keep finding survivors in the rubble," he said during a visit to the state of Puebla, where the epicenter was.

More than 50 people had been rescued from collapsed buildings in the capital as of late Wednesday, he said.

US President Donald Trump called Pena Nieto and offered assistance. A US search-and-rescue team was deployed to Mexico, the American embassy said.

Rescue teams have also flown in from Israel, El Salvador and Panama and more were expected from Costa Rica, Ecuador, Honduras, Colombia and Spain.

Rescuers said the Israeli teams came with equipment enabling them to detect cell phone signals in the rubble.

Tuesday's tragedy struck just two hours after Mexico held a national earthquake drill, as it does every year on the 1985 anniversary.

A system of quake sensors was set up in 1993 along the Pacific coast, where tremors are more common.

People in Mexico City were not warned by the system on Tuesday because the epicenter was only 120 kilometers (75 miles) outside the capital and thus outside the main area of sensor coverage, said Carlos Valdes of the National Center for Disaster Prevention.

Adding to the national sense of vulnerability, the earthquake struck just 12 days after another quake that killed nearly 100 people in southern Mexico.

SHAKE AND BLOW
Rescuers in grim search for survivors of Mexico quake
Mexico City (AFP) Sept 20, 2017
Rescuers dug frantically Wednesday for survivors of a 7.1- magnitude earthquake that killed more than 200 people in Mexico, as the nation watched anxiously for signs of life at a collapsed school in the capital. The death toll stood at 225, the head of the national disaster response agency, Luis Felipe Puente, wrote on Twitter. President Enrique Pena Nieto warned the figure would likely rise ... read more

Related Links
Bringing Order To A World Of Disasters
When the Earth Quakes
A world of storm and tempest


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