Thursday, April 28, 2016

PLANETARY TREMORS: Strong 4.2 Magnitude Earthquake Strikes Lima, Peru - Experts Say The Capital Is Overdue For A Major Earthquake! [MAPS + TECTONIC SUMMARY]

The quake hit last night at 11:02 p.m.
El Comercio/AP

April 28, 2016 - LIMA, PERU - The earthquake's epicenter was located 46 km west of San Vicente de Cañete and registered late last night.

An earthquake of 4.2 magnitude on the Richter scale struck Cañete in the region of Lima last night, according to the Geophysical Institute of Lima (IGP).

The quake was registered at 11:04 p.m. with an epicenter located 46 kilometers west of San Vicente de Cañete.

The earthquake had a depth of 63 kilometers and had an intensity of III Cañete, II Lima.

Earlier this month, three earthquakes of the same magnitude hit the region of Lima within three days. Neither caused harm or damages.

The authorities have not reported personal or material damages due to the earthquakes.

Lima Overdue For A Major Earthquake - However, Peru Is Unprepared For Potential Devastation!

The earthquake all but flattened colonial Lima, the shaking so violent that people tossed to the ground couldn’t get back up. Minutes later, a 15-meter wall of Pacific Ocean crashed into the adjacent port of Callao, killing all but 200 of its 5,000 inhabitants. Bodies washed ashore for weeks.  Plenty of earthquakes have shaken Peru’s capital in the 266 years since that fateful night of Oct. 28, 1746, though none with anything near the violence. 

The relatively long “seismic silence” means that Lima, set astride one of the most volatile ruptures in the Earth’s crust, is increasingly at risk of being hammered by a one-two, quake-tsunami punch as calamitous as what devastated Japan last year and traumatized Santiago, Chile, and its nearby coast a year earlier, seismologists say.  Yet this city of 9 million people is sorely unprepared. From densely clustered, unstable housing to a dearth of first-responders, its acute vulnerability is unmatched regionally. Peru’s National Civil Defense Institute forecasts up to 50,000 dead, 686,000 injured and 200,000 homes destroyed if Lima is hit by a magnitude-8.0 quake.

“In South America, it is the most at risk,” said architect Jose Sato, director of the Center for Disaster Study and Prevention, or PREDES, a non-governmental group financed by the charity Oxfam that is working on reducing Lima’s quake vulnerability.  Lima is home to a third of Peru’s population, 70 percent of its industry, 85 percent of its financial sector, its entire central government and the bulk of international commerce. 

“A quake similar to what happened in Santiago would break the country economically,” said Gabriel Prado, Lima’s top official for quake preparedness. That quake had a magnitude of 8.8.  Quakes are frequent in Peru, with about 170 felt by people annually, said Hernando Tavera, director of seismology at the country’s Geophysical Institute. A big one is due, and the chances of it striking increase daily, he said. The same collision of tectonic plates responsible for the most powerful quake ever recorded, a magnitude-9.5 quake that hit Chile in 1960, occurs just off Lima’s coast, where about 3 inches of oceanic crust slides annually beneath the continent.  A 7.5-magnitude quake in 1974 a day’s drive from Lima in the Cordillera Blanca range killed about 70,000 people as landslides buried villages. Seventy-eight people died in the capital.

In 2007, a 7.9-magnitude quake struck even closer, killing 596 people in the south-central coastal city of Pisco. A shallow, direct hit is the big danger.  More than two in five Lima residents live either in rickety structures built on unstable, sandy soil and wetlands, which amplify a quake’s destructive power, or in hillside settlements that sprang up over a generation as people fled conflict and poverty in Peru’s interior. Thousands are built of colonial-era adobe.  Most quake-prone countries have rigorous building codes to resist seismic events. In Chile, if engineers and builders don’t adhere to them they can face prison. Not so in Peru. 

“People are building with adobe just as they did in the 17th century,” said Carlos Zavala, director of Lima’s Japanese-Peruvian Center for Seismic Investigation and Disaster Mitigation.  Environmental and human-made perils compound the danger.  Situated in a coastal desert, Lima gets its water from a single river, the Rimac, which a landslide could easily block. That risk is compounded by a containment pond full of toxic heavy metals from an old mine that could rupture and contaminate the Rimac, said Agustin Gonzalez, a PREDES official advising Lima’s government.  Most of Lima’s food supply arrives via a two-lane highway that parallels the river, another potential chokepoint.

Lima’s airport and seaport, the key entry points for international aid, are also vulnerable. Both are in Callao, which seismologists expect to be scoured by a 6-meter tsunami if a big quake is centered offshore, the most likely scenario.  Mayor Susana Villaran’s administration is Lima’s first to organize a quake-response and disaster-mitigation plan. A February 2011 law obliged Peru’s municipalities to do so. Yet Lima’s remains incipient. 

“How are the injured going to be attended to? What is the ability of hospitals to respond? Of basic services? Water, energy, food reserves? I don’t think this is being addressed with enough responsibility,” said Tavera of the Geophysical Institute.  By necessity, most injured will be treated where they fall, but Peru’s police have no comprehensive first-aid training. Only Lima’s 4,000 firefighters, all volunteers, have such training, as does a 1,000-officer police emergency squadron.  But because the firefighters are volunteers, a quake’s timing could influence rescue efforts. “If you go to a fire station at 10 in the morning there’s hardly anyone there,” said Gonzalez, who advocates a full-time professional force. 

In the next two months, Lima will spend nearly $2-million on the three fire companies that cover downtown Lima, its first direct investment in firefighters in 25 years, Prado said. The national government is spending $18-million citywide for 50 new fire trucks and ambulances.  But where would the ambulances go?  A 1997 study by the Pan American Health Organization found that three of Lima’s principal public hospitals would likely collapse in a major quake, but nothing has been done to reinforce them.  And there are no free beds. One public hospital, Maria Auxiliadora, serves more than 1.2 million people in Lima’s south but has just 400 beds, and they are always full.  Contingency plans call for setting up mobile hospitals in tents in city parks. But Gonzalez said only about 10,000 injured could be treated. Water is also a worry. The fire threat to Lima is severe – from refineries to densely-backed neighborhoods honeycombed with colonial-era wood and adobe. Lima’s firefighters often can’t get enough water pressure to douse a blaze. 

“We should have places where we can store water not just to put out fires but also to distribute water to the population,” said Sato, former head of the disaster mitigation department at Peru’s National Engineering University.  The city’s lone water-and-sewer utility can barely provide water to one-tenth of Lima in the best of times.  Another big concern: Lima has no emergency operations center and the radio networks of the police, firefighters and the Health Ministry, which runs city hospitals, use different frequencies, hindering effective communication.  Nearly half of the city’s schools require a detailed evaluation to determine how to reinforce them against collapse, Sato said.  A recent media blitz, along with three nationwide quake-tsunami drills this year, helped raise consciousness. The city has spent more than $77-million for retention walls and concrete stairs to aid evacuation in hillside neighborhoods, Prado said, but much more is needed.

USGS Seismotectonics of South America (Nazca Plate Region)

The South American arc extends over 7,000 km, from the Chilean margin triple junction offshore of southern Chile to its intersection with the Panama fracture zone, offshore of the southern coast of Panama in Central America. It marks the plate boundary between the subducting Nazca plate and the South America plate, where the oceanic crust and lithosphere of the Nazca plate begin their descent into the mantle beneath South America. The convergence associated with this subduction process is responsible for the uplift of the Andes Mountains, and for the active volcanic chain present along much of this deformation front. Relative to a fixed South America plate, the Nazca plate moves slightly north of eastwards at a rate varying from approximately 80 mm/yr in the south to approximately 65 mm/yr in the north. Although the rate of subduction varies little along the entire arc, there are complex changes in the geologic processes along the subduction zone that dramatically influence volcanic activity, crustal deformation, earthquake generation and occurrence all along the western edge of South America.

Most of the large earthquakes in South America are constrained to shallow depths of 0 to 70 km resulting from both crustal and interplate deformation. Crustal earthquakes result from deformation and mountain building in the overriding South America plate and generate earthquakes as deep as approximately 50 km. Interplate earthquakes occur due to slip along the dipping interface between the Nazca and the South American plates. Interplate earthquakes in this region are frequent and often large, and occur between the depths of approximately 10 and 60 km. Since 1900, numerous magnitude 8 or larger earthquakes have occurred on this subduction zone interface that were followed by devastating tsunamis, including the 1960 M9.5 earthquake in southern Chile, the largest instrumentally recorded earthquake in the world. Other notable shallow tsunami-generating earthquakes include the 1906 M8.5 earthquake near Esmeraldas, Ecuador, the 1922 M8.5 earthquake near Coquimbo, Chile, the 2001 M8.4 Arequipa, Peru earthquake, the 2007 M8.0 earthquake near Pisco, Peru, and the 2010 M8.8 Maule, Chile earthquake located just north of the 1960 event.

USGS plate tectonics for the region.

Large intermediate-depth earthquakes (those occurring between depths of approximately 70 and 300 km) are relatively limited in size and spatial extent in South America, and occur within the Nazca plate as a result of internal deformation within the subducting plate. These earthquakes generally cluster beneath northern Chile and southwestern Bolivia, and to a lesser extent beneath northern Peru and southern Ecuador, with depths between 110 and 130 km. Most of these earthquakes occur adjacent to the bend in the coastline between Peru and Chile. The most recent large intermediate-depth earthquake in this region was the 2005 M7.8 Tarapaca, Chile earthquake.

Earthquakes can also be generated to depths greater than 600 km as a result of continued internal deformation of the subducting Nazca plate. Deep-focus earthquakes in South America are not observed from a depth range of approximately 300 to 500 km. Instead, deep earthquakes in this region occur at depths of 500 to 650 km and are concentrated into two zones: one that runs beneath the Peru-Brazil border and another that extends from central Bolivia to central Argentina. These earthquakes generally do not exhibit large magnitudes. An exception to this was the 1994 Bolivian earthquake in northwestern Bolivia. This M8.2 earthquake occurred at a depth of 631 km, which was until recently the largest deep-focus earthquake instrumentally recorded (superseded in May 2013 by a M8.3 earthquake 610 km beneath the Sea of Okhotsk, Russia), and was felt widely throughout South and North America.

Subduction of the Nazca plate is geometrically complex and impacts the geology and seismicity of the western edge of South America. The intermediate-depth regions of the subducting Nazca plate can be segmented into five sections based on their angle of subduction beneath the South America plate. Three segments are characterized by steeply dipping subduction; the other two by near-horizontal subduction. The Nazca plate beneath northern Ecuador, southern Peru to northern Chile, and southern Chile descend into the mantle at angles of 25° to 30°. In contrast, the slab beneath southern Ecuador to central Peru, and under central Chile, is subducting at a shallow angle of approximately 10° or less. In these regions of “flat-slab” subduction, the Nazca plate moves horizontally for several hundred kilometers before continuing its descent into the mantle, and is shadowed by an extended zone of crustal seismicity in the overlying South America plate. Although the South America plate exhibits a chain of active volcanism resulting from the subduction and partial melting of the Nazca oceanic lithosphere along most of the arc, these regions of inferred shallow subduction correlate with an absence of volcanic activity.

More information on regional seismicity and tectonics

- USGS | Living in Peru. | National Post.


No comments: