Friday, March 18, 2016

PLANETARY TREMORS: Strong 6.0 Magnitude Earthquake Strikes Off Atka Island, Southwest Alaska - USGS! [MAPS + TECTONIC SUMMARY]

USGS earthquake location.

 March 18, 2016 - ALASKA - A strong earthquake with a preliminary magnitude of 6.0 has struck off Atka Island in the Andreanof Islands, which are part of the Aleutian Islands in southwest Alaska, seismologists say. No tsunami alerts have been issued.

The earthquake, which struck at 01:35 a.m. local time on Friday, was centered about 47 miles (76 km) south of Atka, which is a small town located on the eastern side of Atka Island. It struck about 10.6 miles (17 km) deep, making it a shallow earthquake.

The U.S. Tsunami Warning Center said the earthquake was not strong enough to generate a tsunami, and no tsunami alerts have been issued, but the earthquake was likely felt on islands across the region.

Other details about Friday's earthquake were not immediately available, and there were no immediate reports of damage or casualties from the sparsely-populated region.

Seismotectonics of Alaska

The Aleutian arc extends approximately 3,000 km from the Gulf of Alaska in the east to the Kamchatka Peninsula in the west. It marks the region where the Pacific plate subducts into the mantle beneath the North America plate. This subduction is responsible for the generation of the Aleutian Islands and the deep offshore Aleutian Trench.

The curvature of the arc results in a westward transition of relative plate motion from trench-normal (i.e., compressional) in the east to trench-parallel (i.e., translational) in the west, accompanied by westward variations in seismic activity, volcanism, and overriding plate composition. The Aleutian arc is generally divided into three regions: the western, central, and eastern Aleutians. Relative to a fixed North America plate, the Pacific plate is moving northwest at a rate that increases from roughly 60 mm/yr at the arc's eastern edge to 76 mm/yr near its western terminus. The eastern Aleutian arc extends from the Alaskan Peninsula in the east to the Fox Islands in the west. Motion along this section of the arc is characterized by arc-perpendicular convergence and Pacific plate subduction beneath thick continental lithosphere. This region exhibits intense volcanic activity and has a history of megathrust earthquakes.

USGS plate tectonics for the region.

The central Aleutian arc extends from the Andreanof Islands in the east to the Rat Islands in the west. Here, motion is characterized by westward-increasing oblique convergence and Pacific plate subduction beneath thin oceanic lithosphere. Along this portion of the arc, the Wadati-Benioff zone is well defined to depths of approximately 200 km. Despite the obliquity of convergence, active volcanism and megathrust earthquakes are also present along this margin.

The western Aleutians, stretching from the western end of the Rat Islands in the east to the Commander Islands, Russia, in the west, is tectonically different from the central and eastern portions of the arc. The increasing component of transform motion between the Pacific and North America plates is evidenced by diminishing active volcanism; the last active volcano is located on Buldir Island, in the far western portion of the Rat Island chain. Additionally, this portion of the subduction zone has not hosted large earthquakes or megathrust events in recorded history. Instead, the largest earthquakes in this region are generally shallow, predominantly strike-slip events with magnitudes between M5-6. Deeper earthquakes do occur, albeit rather scarcely and with small magnitudes (Magnitude less than 4), down to approximately 50 km.

Most of the seismicity along the Aleutian arc results from thrust faulting that occurs along the interface between the Pacific and North America plates, extending from near the base of the trench to depths of 40 to 60 km. Slip along this interface is responsible for generating devastating earthquakes. Deformation also occurs within the subducting slab in the form of intermediate-depth earthquakes that can reach depths of 250 km. Normal faulting events occur in the outer rise region of the Aleutian arc resulting from the bending of the oceanic Pacific plate as it enters the Aleutian trench. Additionally, deformation of the overriding North America plate generates shallow crustal earthquakes.

The Aleutian arc is a seismically active region, evidenced by the many moderate to large earthquakes occurring each year. Since 1900, this region has hosted twelve large earthquakes (Magnitude greater than 7.5) including the May 7, 1986 M8.0 Andreanof Islands, the June 10, 1996 M7.9 Andreanof Islands, and the November 17, 2003 M7.8 Rat Islands earthquakes. Six of these great earthquakes (M8.3 or larger) have occurred along the Aleutian arc that together have ruptured almost the entire shallow megathrust contact. The first of these major earthquakes occurred on August 17, 1906 near the island of Amchitka (M8.3) in the western Aleutian arc. However, unlike the other megathrust earthquakes along the arc, this event is thought to have been an intraplate event occurring in the shallow slab beneath the subduction zone interface.

The first megathrust event along the arc during the 20th century was the November 10, 1938 M8.6 Shumagin Island earthquake. This event ruptured an approximately 300 km long stretch of the arc from the southern end of Kodiak Island to the northern end of the Shumagin Islands and generated a small tsunami that was recorded as far south as Hawaii.

The April 1, 1946 M8.6 Unimak Island earthquake, located in the central Aleutian arc, was characterized by slow rupture followed by a devastating Pacific-wide tsunami that was observed as far south as the shores of Antarctica. Although damage from earthquake shaking was not severe locally, tsunami run-up heights were recorded as high as 42 m on Unimak Island and tsunami waves in Hilo, Hawaii also resulted in casualties. The slow rupture of this event has made it difficult to constrain the focal mechanism and depth of the earthquake, though it is thought to have been an interplate thrust earthquake.

The next megathrust earthquake occurred along the central portion of the Aleutian arc near the Andreanof Islands on March 9, 1957, with a magnitude of M8.6. The rupture length of this event was approximately 1200 km, making it the longest observed aftershock zone of all the historic Aleutian arc events. Although only limited seismic data from this event are still available, significant damage and tsunamis were observed on the islands of Adak and Unimak with tsunami heights of approximately 13 m.

The easternmost megathrust earthquake was the March 28, 1964 M9.2 Prince William Sound earthquake, currently the second largest recorded earthquake in the world. The event had a rupture length of roughly 700 km extending from Prince William Sound in the northeast to the southern end of Kodiak Island in the southwest. Extensive damage was recorded in Kenai, Moose Pass, and Kodiak but significant shaking was felt over a large region of Alaska, parts of western Yukon Territory, and British Columbia, Canada. Property damage was the largest in Anchorage, as a result of both the main shock shaking and the ensuing landslides. This megathrust earthquake also triggered a devastating tsunami that caused damage along the Gulf of Alaska, the West Coast of the United States, and in Hawaii.

The westernmost Aleutians megathrust earthquake followed a year later on February 4, 1965. This M8.7 Rat Islands earthquake was characterized by roughly 600 km of rupture. Although this event is quite large, damage was low owing to the region's remote and sparsely inhabited location. A relatively small tsunami was recorded throughout the Pacific Ocean with run-up heights up to 10.7 m on Shemya Island and flooding on Amchitka Island.

Although the Aleutian arc is highly active, seismicity is rather discontinuous, with two regions that have not experienced a large (Magnitude greater than 8.0) earthquake in the past century: the Commander Islands in the western Aleutians and the Shumagin Islands in the east. Due to the dominantly transform motion along the western arc, there is potential that the Commander Islands will rupture in a moderate to large strike-slip earthquake in the future. The Shumagin Islands region may also have high potential for hosting a large rupture in the future, though it has been suggested that little strain is being accumulated along this section of the subduction zone, and thus associated hazards may be reduced.

East of the Aleutian arc along the Gulf of Alaska, crustal earthquakes occur as a result transmitted deformation and stress associated with the northwestward convergence of the Pacific plate that collides a block of oceanic and continental material into the North America plate. In 2002, the Denali Fault ruptured in a sequence of earthquakes that commenced with the October 23 M6.7 Nenana Mountain right-lateral strike-slip earthquake and culminated with the November 3, M7.9 Denali earthquake which started as a thrust earthquake along a then unrecognized fault and continued with a larger right-lateral strike-slip event along the Denali and Totschunda Faults.

More information on regional seismicity and tectonics

For More Information
Additional earthquake information for Alaska



GEOLOGICAL UPHEAVALS: Massive Sinkhole Opens Up Overnight In Lanarkshire, UK - Measured 30-FOOT-WIDE!

The enormous sinkhole suddenly developed just yards from the front doors of three detached properties.© Presstream Scotland

March 18, 2016 - UNITED KINGDOM - The enormous hole suddenly developed just yards from the front doors of three detached properties in Plains, Lanarkshire

Homes have been evacuated after a massive sinkhole appeared in their street overnight. The enormous hole suddenly developed just yards from the front doors of three detached properties in Plains, Lanarkshire. The crater covers a large section of road in Moffat View in the village and is estimated to be 30ft wide and 10ft deep.

Residents have been told to stay away from their £130,000 properties until work is carried out to assess and fix the damage. Locals have speculated a former mineshaft had collapsed following heavy rains. The cul-de-sac had been closed off since Wednesday morning and was being inspected by workers today. However homeowners have blasted North Lanarkshire Council and claimed they had highlighted concerns over the area last month.

John Riley, 61, said he was now living in a hotel as work was carried out. He took to Facebook to complain, adding: "All three residents evacuated at short notice by Fire Service. "Emergency team told us we usually get the evacuees into the local school for a few hours and give them telephone and Internet access, refreshments and any other support until they can be safely rehoused or make other arrangements."

"My insurance has put us up in Premier inn for two weeks," John continued. "I refused the 4th floor flat in Holehills whose condition was "unknown". "After seven weeks of pleading with North Lanarkshire Council, including the offer of sharing the geo-tech info I had obtained and was refused.

John Lowe, 60, a former resident in the street, said issues with water had been raised before. He added: "When I stayed in the middle house I spent three years complaining about the water coming out the ground. "It was a rusty colour and causing damage to the pavements, I even had to channel it away. "The council did nothing about it and when I came to sell my house it took me seven months to get it sold. People had obviously read the water reports and thought against it," John continued.

© Pressstream Scotland

© Pressstream Scotland

"I always feared something like this would happen because water shouldn't be running like that. "There has been water bubbling up for five or six weeks here just at the bit where the hole now is. "Something should have been done much, much sooner to try and avoid this."

"Because it is a quiet street with a dead end, it is very popular with young kids playing," he added. "I dread to think what would have happened had it collapsed while the kids were all on bikes playing or whatever. "The families living there must be very angry because it has been a long term issue which just hasn't been addressed by the council and they've been left with this massive hole.

"The whole field in front of the houses is absolutely soaking so there is obviously a real problem with water here. "A new estate was also built recently and that can't have helped the situation at all. "Hopefully they get it fixed and the families get back to their houses soon, it must be terrible for them. "The council should have done something much quicker rather than letting this happen." Workers had sealed off the cul-de-sac today and council bosses said they did not believe homes had been put at risk by the hole. A North Lanarkshire Council spokesman said: "We have taken the decision to evacuate the three properties at the end of Moffat View to ensure the safety of the residents of those properties. "Our partners at Scottish Fire and Rescue and Scottish Gas Networks are satisfied that there is no risk from gas and we have consulted with Scottish Water.

"We have fenced off the end of Moffat View to ensure no-one can approach the area of the hole in the road. "We are consulting with technical specialists about our next course of action. Once they have completed their work we will act quickly on their findings." Last October 20 residents were evacuated and dozens more left stranded after a 66ft sinkhole opened up overnight in a suburban street in Hertfordshire. The gaping hole was discovered in St Albans, after spreading across the quiet cul-de-sac and swallowing two front gardens. - Mirror.

PLANETARY TREMORS: Unsually Strong Gulf Of Bothnia Earthquake Felt In Finland And Sweden - The Biggest Tremor In 100 YEARS For Northern Sweden!

The earthquake took place around 45 kilometres off the coast. Photo: Google Maps

March 18, 2016 - GULF OF BOTHNIA, SWEDEN - The earthquake was measured as 3.9 on the Richter scale, although the European-Mediterranean Seismological Centre (EMSC) measured the quake at 4.2.

According to the Swedish national seismic network, the Gulf of Bothnia "has relatively high seismic activity but has not experienced a quake of this size in the last 100 years."

According to northern Swedish regional newspapers, there were no injuries and only minor damage to property has been reported.

Paul Connolly, The Local's northern Sweden correspondent, who lives in the affected area, said that the earthquake struck at around 10.55pm.

"The whole house shook but I thought it was our old washing machine going a bit mad in the basement. However, I know people who were out at the time and they said the ground vibrated beneath their feet for up to 30 seconds. That would have terrified me."

Ice on the Bay of Bothnia. © Rista Degerman/YLE

Another northern Swede from Piteå told the EMSC that, "The whole house trembled and was shaking for a good 30 seconds. It was a dark, rumbling noise. After that it slowly wore off. I have felt earthquakes before, but never this heavy and long. Scared the crap out of both me and the cat!"

Another witness from Umeå said, "It felt like a tractor had driven into the house. The house swayed and the roof creaked loudly."

Earthquakes that are powerful enough to be felt are a rare occurrence in Sweden.

The country sees around three earthquakes measuring around 3.0 in magnitude scale every year and most of them go unnoticed. - The Local.