Saturday, April 19, 2014

PLANETARY TREMORS: Major Global Seismic Uptick - Powerful 7.5 Magnitude Earthquake Strike Southwest Of Panguna, Papua New Guinea! [MAPS+ESTIMATES+TECTONIC SUMMARY]

April 19, 2014 - PAPUA NEW GUINEA - An earthquake with a magnitude 7.5 struck off Papua New Guinea on Saturday and a tsunami warning was briefly issued for the Pacific Island nation and neighboring Solomon Islands, but there were no immediate reports of damage.


Powerful 7.5 Magnitude Earthquake Strike Southwest Of Panguna, Papua New Guinea.
USGS earthquake location map.

The quake, at a depth of 10 km (6 miles), struck 68 km southwest of Panguna on the island of Bougainville, the U.S. Geological Survey said, revising down the magnitude from an initial 7.8.

The Pacific Tsunami Warning Center later cancelled a tsunami warning for Papua New Guinea and the Solomon Islands and there was no threat to neighboring Australia or across the Pacific Ocean.

At least six strong tremors have hit near Bougainville in the past week or so, including a magnitude 7.3 on April 11, but there have been no reports of major damage.

"Certainly it has been very active, more active than usual,"

said Jonathan Bathgate, a seismologist at Geoscience Australia. "(The spate of earthquakes) is relieving some pressure on this faultline, but we can't rule out another large earthquake."


Powerful 7.5 Magnitude Earthquake Strike Southwest Of Panguna, Papua New Guinea.
USGS earthquake shakemap intensity.

The quake would have been felt strongly on Bougainville and nearby islands, but given its position on the so-called "Pacific Ring of Fire" where earthquakes are frequent, extensive damage was unlikely, Bathgate said. However, a local tsunami may have been generated, he added. Readings showed a small wave had been generated, the Pacific Tsunami Warning Center said.

In 1998, a magnitude 7 earthquake triggered a tsunami that smashed into villages near Aitape on Papua New Guinea's north coast and killed more than 2,000 people.

Resource-rich Bougainville, which neighbors the Solomon Islands, fought a war for independence from Papua New Guinea in the 1990s, leading to the closure of the Panguna copper mine, majority-owned by Rio Tinto Ltd. Bougainville is now an autonomous region of Papua New Guinea. - Reuters.


Tectonic Summary
The M 7.5 April 19, 2014 earthquake southwest of Panguna, Papua New Guinea, occurred as the result of thrust faulting on or near the subduction zone interface between the subducting Australia plate and overriding Pacific plate. At the location of the earthquake, the Australia plate moves towards the east-northeast at a velocity of 102 mm/yr with respect to the Pacific, and begins its subduction into the mantle beneath Bougainville Island at the New Britain Trench south of the earthquake. The moment tensor and depth of the event are consistent with thrust-type motion on the interface between these two plates. Note that at the location of the earthquake, some researchers divide the edge of the Australia plate into several microplates that take up the overall convergence between Australia and the Pacific. Here the Solomon Sea plate moves slightly faster and more northeasterly with respect to the Pacific plate than does Australia due to sea-floor spreading in the Woodlark Basin several hundred kilometers to the south of the April 19 earthquake.

This event is the latest in an ongoing sequence of seismicity in the same region over the past week, which began with M 7.1 and 6.5 earthquakes on April 11, just to the northeast and southeast of the April 19 earthquake, respectively. Over the intervening eight days, 45 earthquakes of M 4.5 or greater have occurred nearby, including a M 6.6 event about 12 hours before the April 19 earthquake.

In the Papua New Guinea region, the boundary between Australia and Pacific plates is very active seismically; 35 M 7+ events have occurred within 250 km of the April 19, 2014 earthquake over the past century. None are known to have caused any shaking-related fatalities. The largest was an M 8.0 175 km to the northwest of the April 19, 2014 earthquake, one of two M8+ earthquakes 140 km apart in July 1971. The M 8.1 Solomon Islands earthquake in April 2007, which caused a devastating tsunami, was 300 km southeast of the April 19, 2014 event.


Seismotectonics of the New Guinea Region and Vicinity
The Australia-Pacific plate boundary is over 4000 km long on the northern margin, from the Sunda (Java) trench in the west to the Solomon Islands in the east. The eastern section is over 2300 km long, extending west from northeast of the Australian continent and the Coral Sea until it intersects the east coast of Papua New Guinea. The boundary is dominated by the general northward subduction of the Australia plate.

Along the South Solomon trench, the Australia plate converges with the Pacific plate at a rate of approximately 95 mm/yr towards the east-northeast. Seismicity along the trench is dominantly related to subduction tectonics and large earthquakes are common: there have been 13 M7.5+ earthquakes recorded since 1900. On April 1, 2007, a M8.1 interplate megathrust earthquake occurred at the western end of the trench, generating a tsunami and killing at least 40 people. This was the third M8.1 megathrust event associated with this subduction zone in the past century; the other two occurred in 1939 and 1977.


Strong 6.1 Magnitude Earthquake Strikes Southeast Of Lorengau, Papua New Guinea!
USGS plate tectonics for the region.

Further east at the New Britain trench, the relative motions of several microplates surrounding the Australia-Pacific boundary, including north-south oriented seafloor spreading in the Woodlark Basin south of the Solomon Islands, maintain the general northward subduction of Australia-affiliated lithosphere beneath Pacific-affiliated lithosphere. Most of the large and great earthquakes east of New Guinea are related to this subduction; such earthquakes are particularly concentrated at the cusp of the trench south of New Ireland. 33 M7.5+ earthquakes have been recorded since 1900, including three shallow thrust fault M8.1 events in 1906, 1919, and 2007.

The western end of the Australia-Pacific plate boundary is perhaps the most complex portion of this boundary, extending 2000 km from Indonesia and the Banda Sea to eastern New Guinea. The boundary is dominantly convergent along an arc-continent collision segment spanning the width of New Guinea, but the regions near the edges of the impinging Australia continental margin also include relatively short segments of extensional, strike-slip and convergent deformation. The dominant convergence is accommodated by shortening and uplift across a 250-350 km-wide band of northern New Guinea, as well as by slow southward-verging subduction of the Pacific plate north of New Guinea at the New Guinea trench. Here, the Australia-Pacific plate relative velocity is approximately 110 mm/yr towards the northeast, leading to the 2-8 mm/yr uplift of the New Guinea Highlands.

Whereas the northern band of deformation is relatively diffuse east of the Indonesia-Papua New Guinea border, in western New Guinea there are at least two small (less than 100,000 km²) blocks of relatively undeformed lithosphere. The westernmost of these is the Birds Head Peninsula microplate in Indonesia's West Papua province, bounded on the south by the Seram trench. The Seram trench was originally interpreted as an extreme bend in the Sunda subduction zone, but is now thought to represent a southward-verging subduction zone between Birds Head and the Banda Sea.

There have been 22 M7.5+ earthquakes recorded in the New Guinea region since 1900. The dominant earthquake mechanisms are thrust and strike slip, associated with the arc-continent collision and the relative motions between numerous local microplates. The largest earthquake in the region was a M8.2 shallow thrust fault event in the northern Papua province of Indonesia that killed 166 people in 1996.

The western portion of the northern Australia plate boundary extends approximately 4800 km from New Guinea to Sumatra and primarily separates Australia from the Eurasia plate, including the Sunda block. This portion is dominantly convergent and includes subduction at the Sunda (Java) trench, and a young arc-continent collision.

In the east, this boundary extends from the Kai Islands to Sumba along the Timor trough, offset from the Sunda trench by 250 km south of Sumba. Contrary to earlier tectonic models in which this trough was interpreted as a subduction feature continuous with the Sunda subduction zone, it is now thought to represent a subsiding deformational feature related to the collision of the Australia plate continental margin and the volcanic arc of the Eurasia plate, initiating in the last 5-8 Myr. Before collision began, the Sunda subduction zone extended eastward to at least the Kai Islands, evidenced by the presence of a northward-dipping zone of seismicity beneath Timor Leste. A more detailed examination of the seismic zone along it's eastern segment reveals a gap in intermediate depth seismicity under Timor and seismic mechanisms that indicate an eastward propagating tear in the descending slab as the negatively buoyant oceanic lithosphere detaches from positively buoyant continental lithosphere. On the surface, GPS measurements indicate that the region around Timor is currently no longer connected to the Eurasia plate, but instead is moving at nearly the same velocity as the Australia plate, another consequence of collision.

Large earthquakes in eastern Indonesia occur frequently but interplate megathrust events related to subduction are rare; this is likely due to the disconnection of the descending oceanic slab from the continental margin. There have been 9 M7.5+ earthquakes recorded from the Kai Islands to Sumba since 1900. The largest was the great Banda Sea earthquake of 1938 (M8.5) an intermediate depth thrust faulting event that did not cause significant loss of life. - USGS.



Friday, April 18, 2014

PLANETARY TREMORS: Global Seismic Uptick - Strong 6.6 Magnitude Earthquake Strike Southwest Of Panguna, Papua New Guinea! [MAPS+ESTIMATES+TECTONIC SUMMARY]

April 18, 2014 - PAPUA NEW GUINEA - A strong 6.6-magnitude earthquake has struck off Papua New Guinea's Bougainville Island but there is no risk of a widespread tsunami, seismologists say.


Strong 6.6 Magnitude Earthquake Strike Southwest Of Panguna, Papua New Guinea
USGS earthquake location map.

The quake hit at 0104 GMT (1104 AEST) on Saturday and was centred 62km southwest of the town of Panguna on Bougainville at a depth of 45km, the US Geological Survey said.

In its initial estimate, the USGS said there was a low likelihood of casualties and damage.

According to the Hawaii-based Pacific Tsunami Warning Centre there was no threat of a destructive widespread tsunami based on historical data.

Geoscience Australia measured the quake at magnitude 7.0 and said it was probably felt within a wide radius, with the potential for localised shaking damage.

"Because it's such a large event there's a possibility of damage in that area," seismologist Emma Mathews told AFP.

"But it's nothing out of the ordinary for such an earthquake-prone country."

Mathews said it was the latest in a recent cluster of earthquakes in the Panguna region, with five events recorded in the past week including powerful magnitude 7.6 and 7.5 tremors that triggered a local tsunami alert.


Strong 6.6 Magnitude Earthquake Strike Southwest Of Panguna, Papua New Guinea
USGS earthquake shakemap intensity.


Those jolts were felt locally but there were no reports of significant damage from remote and isolated Bougainville, which sits between the island of New Guinea and the Solomons.

The rumblings sparked panic in the Solomons capital Honiara, reeling from floods earlier this month that claimed at least 21 lives.

"This is quite an active area, an active tectonic area that receives a high frequency of earthquake activity," Mathews said.

Quakes of such magnitude are common in PNG, which sits on the so-called Pacific "Ring of Fire", a hotspot for seismic activity due to friction between tectonic plates.

In October, a 7.1-magnitude quake struck in the same area -- around 65 kilometres west of Panguna.

Last year in February the remote town of Lata in the Solomons was hit by a devastating tsunami after an 8.0-magnitude earthquake. The tsunami left at least 10 people dead, destroyed hundreds of homes and left thousands of people homeless. - Brisbane Times.


Tectonic Summary - Seismotectonics of the New Guinea Region and Vicinity.
The Australia-Pacific plate boundary is over 4000 km long on the northern margin, from the Sunda (Java) trench in the west to the Solomon Islands in the east. The eastern section is over 2300 km long, extending west from northeast of the Australian continent and the Coral Sea until it intersects the east coast of Papua New Guinea. The boundary is dominated by the general northward subduction of the Australia plate.

Along the South Solomon trench, the Australia plate converges with the Pacific plate at a rate of approximately 95 mm/yr towards the east-northeast. Seismicity along the trench is dominantly related to subduction tectonics and large earthquakes are common: there have been 13 M7.5+ earthquakes recorded since 1900. On April 1, 2007, a M8.1 interplate megathrust earthquake occurred at the western end of the trench, generating a tsunami and killing at least 40 people. This was the third M8.1 megathrust event associated with this subduction zone in the past century; the other two occurred in 1939 and 1977.


Strong 6.1 Magnitude Earthquake Strikes Southeast Of Lorengau, Papua New Guinea!
USGS plate tectonics for the region.

Further east at the New Britain trench, the relative motions of several microplates surrounding the Australia-Pacific boundary, including north-south oriented seafloor spreading in the Woodlark Basin south of the Solomon Islands, maintain the general northward subduction of Australia-affiliated lithosphere beneath Pacific-affiliated lithosphere. Most of the large and great earthquakes east of New Guinea are related to this subduction; such earthquakes are particularly concentrated at the cusp of the trench south of New Ireland. 33 M7.5+ earthquakes have been recorded since 1900, including three shallow thrust fault M8.1 events in 1906, 1919, and 2007.

The western end of the Australia-Pacific plate boundary is perhaps the most complex portion of this boundary, extending 2000 km from Indonesia and the Banda Sea to eastern New Guinea. The boundary is dominantly convergent along an arc-continent collision segment spanning the width of New Guinea, but the regions near the edges of the impinging Australia continental margin also include relatively short segments of extensional, strike-slip and convergent deformation. The dominant convergence is accommodated by shortening and uplift across a 250-350 km-wide band of northern New Guinea, as well as by slow southward-verging subduction of the Pacific plate north of New Guinea at the New Guinea trench. Here, the Australia-Pacific plate relative velocity is approximately 110 mm/yr towards the northeast, leading to the 2-8 mm/yr uplift of the New Guinea Highlands.

Whereas the northern band of deformation is relatively diffuse east of the Indonesia-Papua New Guinea border, in western New Guinea there are at least two small (less than 100,000 km²) blocks of relatively undeformed lithosphere. The westernmost of these is the Birds Head Peninsula microplate in Indonesia's West Papua province, bounded on the south by the Seram trench. The Seram trench was originally interpreted as an extreme bend in the Sunda subduction zone, but is now thought to represent a southward-verging subduction zone between Birds Head and the Banda Sea.

There have been 22 M7.5+ earthquakes recorded in the New Guinea region since 1900. The dominant earthquake mechanisms are thrust and strike slip, associated with the arc-continent collision and the relative motions between numerous local microplates. The largest earthquake in the region was a M8.2 shallow thrust fault event in the northern Papua province of Indonesia that killed 166 people in 1996.

The western portion of the northern Australia plate boundary extends approximately 4800 km from New Guinea to Sumatra and primarily separates Australia from the Eurasia plate, including the Sunda block. This portion is dominantly convergent and includes subduction at the Sunda (Java) trench, and a young arc-continent collision.

In the east, this boundary extends from the Kai Islands to Sumba along the Timor trough, offset from the Sunda trench by 250 km south of Sumba. Contrary to earlier tectonic models in which this trough was interpreted as a subduction feature continuous with the Sunda subduction zone, it is now thought to represent a subsiding deformational feature related to the collision of the Australia plate continental margin and the volcanic arc of the Eurasia plate, initiating in the last 5-8 Myr. Before collision began, the Sunda subduction zone extended eastward to at least the Kai Islands, evidenced by the presence of a northward-dipping zone of seismicity beneath Timor Leste. A more detailed examination of the seismic zone along it's eastern segment reveals a gap in intermediate depth seismicity under Timor and seismic mechanisms that indicate an eastward propagating tear in the descending slab as the negatively buoyant oceanic lithosphere detaches from positively buoyant continental lithosphere. On the surface, GPS measurements indicate that the region around Timor is currently no longer connected to the Eurasia plate, but instead is moving at nearly the same velocity as the Australia plate, another consequence of collision.

Large earthquakes in eastern Indonesia occur frequently but interplate megathrust events related to subduction are rare; this is likely due to the disconnection of the descending oceanic slab from the continental margin. There have been 9 M7.5+ earthquakes recorded from the Kai Islands to Sumba since 1900. The largest was the great Banda Sea earthquake of 1938 (M8.5) an intermediate depth thrust faulting event that did not cause significant loss of life. - USGS.



PLANETARY TREMORS: Major Global Seismic Uptick - Powerful Magnitude 7.2 Earthuake Rattles Mexico City, Shakes Buildings! [PHOTOS+MAPS+ESTIMATES+TECTONIC SUMMARY]

April 18, 2014 - MEXICO - A powerful earthquake struck Mexico on Friday, shaking buildings in the capital and sending people running out into the street, although there were no early reports of major damage.


Powerful 7.2 magnitude earthquake rattles Mexico, shakes buildings.
USGS earthquake location map.


The magnitude 7.2 quake was centered in the southwestern state of Guerrero, close to the Pacific beach resort of Acapulco, the U.S. Geological Survey (USGS) said.

Some residents of the capital ran outdoors in their pajamas after the quake. Electricity was cut off in parts of the city and some residents said paintings fell off the walls and small parts of masonry crumbled inside apartment buildings.

Luis Felipe Puente, head of the Mexican government's emergency services, said there were no immediate reports of damage and the U.S. Pacific Warning Center said it did not expect the quake to trigger a destructive tsunami.

Nevertheless, residents of the capital were shaken by the quake, one of the biggest to hit Mexico in several years.

"I had to hold on to a tree, like a drunk," said Pedro Hernandez, 68, a doorman working in central Mexico City.


Powerful 7.2 magnitude earthquake rattles Mexico, shakes buildings.
USGS earthquake shakemap intensity.

Powerful 7.2 magnitude earthquake rattles Mexico, shakes buildings.
USGS earthquake population exposure.


The USGS said the quake was centered some 37 km (23 miles) north of the municipality of Tecpan de Galeana in Guerrero. It was relatively shallow, at a depth of about 24 km (15 miles).

Emergency services in Guerrero, which is frequently struck by earthquakes, said there were no immediate reports of major damage, but that checks were still being made.

An employee of the Fairmont hotel in Acapulco, said the situation was calm and that guests had returned to the building.

"The structure is fine," the woman, who identified herself only as Ana, said by telephone.


Powerful 7.2 magnitude earthquake rattles Mexico, shakes buildings.
People stand at a staircase after evacuating a building following an earthquake in Mexico City April 18, 2014.
Credit: REUTERS/Claudia Daut

Powerful 7.2 magnitude earthquake rattles Mexico, shakes buildings.
People stand along a street after evacuating a hospital following an earthquake in Puebla April 18, 2014.
Credit: REUTERS/ Imelda Medina

Cesar Sanchez, 24, a student living in Guerrero's capital Chilpancingo said he got a big shock when the tremors began.

"I was in bed, and some things fell that have never fallen. The dogs outside were barking and barking," Sanchez said.

A devastating 8.1-magnitude earthquake in 1985 killed thousands of people in Mexico City. In March 2012, a 7.4 magnitude quake hit Mexico but did not cause major damage. - Reuters.



Tectonic Summary
The April 18, 2014 M 7.2 earthquake near the western coast of Mexico occurred in the state of Guerrero, 265 km southwest of Mexico City. The earthquake occurred as the result of thrust motion at shallow depths. The initial location, depth, and mechanism of the April 18 earthquake are broadly consistent with slip on or near the plate boundary interface between the subducting Cocos oceanic sea plate and the North America plate.

The broad scale tectonics of the west coast of Mexico are controlled by the northeastward subduction of the Cocos plate beneath the North America plate at a rate of approximately 65 mm/yr. Earthquakes are a common occurrence along the Middle American subduction zone; the August 2013 earthquake occurred just northwest of the rupture area of the 1957 M 7.8 Guerrero Earthquake.  Since 1975, 23 events of M > 6.0 have occurred within 200 km of the April 2014 earthquake, including events of M 8.0 and M 7.6 (September 1985), M 7.2 (October 1981), and M 7.5 (March 1979), all to the northwest. The 1981 and 1979 events caused 9 and 5 shaking-related fatalities, respectively. The 1985 M 8.0 earthquake, 195 km to the northwest of the April 2014 event, led to more than 9,500 fatalities, mostly in Mexico City, and generated small, local tsunamis. That event was influential in initiating efforts to establish earthquake early warning systems in Mexico City.

The April 2014 earthquake occurred within the “Guerrero Seismic Gap” – an approximately 200 km long segment of the Cocos-North America plate boundary identified to have experienced no significant earthquakes since 1911 (M 7.6). The plate interface in this region is known to be locked, with an earthquake of M 8.1-8.4 thought possible should the entire gap rupture in a single event.


Seismotectonics of Mexico
Located atop three of the large tectonic plates, Mexico is one of the world's most seismologically active regions. The relative motion of these crustal plates causes frequent earthquakes and occasional volcanic eruptions. Most of the Mexican landmass is on the westward moving North American plate. The Pacific Ocean floor south of Mexico is being carried northeastward by the underlying Cocos plate. Because oceanic crust is relatively dense, when the Pacific Ocean floor encounters the lighter continental crust of the Mexican landmass, the ocean floor is subducted beneath the North American plate creating the deep Middle American trench along Mexico's southern coast. Also as a result of this convergence, the westward moving Mexico landmass is slowed and crumpled creating the mountain ranges of southern Mexico and earthquakes near Mexico's southern coast. As the oceanic crust is pulled downward, it melts; the molten material is then forced upward through weaknesses in the overlying continental crust. This process has created a region of volcanoes across south-central Mexico known as the Cordillera Neovolcánica.


USGS plate tectonics for the region.

The area west of the Gulf of California, including Mexico's Baja California Peninsula, is moving northwestward with the Pacific plate at about 50 mm per year. Here, the Pacific and North American plates grind past each other creating strike-slip faulting, the southern extension of California's San Andreas fault. In the past, this relative plate motion pulled Baja California away from the coast forming the Gulf of California and is the cause of earthquakes in the Gulf of California region today.

Mexico has a long history of destructive earthquakes and volcanic eruptions. In September 1985, a magnitude 8.1 earthquake killed more than 9,500 people in Mexico City. In southern Mexico, Volcán de Colima and El Chichón erupted in 2005 and 1982, respectively. Paricutín volcano, west of Mexico City, began venting smoke in a cornfield in 1943; a decade later this new volcano had grown to a height of 424 meters. Popocatépetl and Ixtaccíhuatl volcanos ("smoking mountain" and "white lady", respectively), southeast of Mexico City, occasionally vent gas that can be clearly seen from the City, a reminder that volcanic activity is ongoing. In 1994 and 2000 Popocatépetl renewed its activity forcing the evacuation of nearby towns, causing seismologists and government officials to be concerned about the effect a large-scale eruption might have on the heavily populated region. Popocatépetl volcano last erupted in 2010. - USGS.