Thursday, February 28, 2013

PLANETARY TREMORS: 5.1 Magnitude Earthquake Strikes Off The Coast Of Oregon And 4.0 Magnitude Tremor Rocks Central Oklahoma, Causes Some Damage!

February 28, 2013 - UNITED STATES - A 5.1 magnitude earthquake occurred Wednesday afternoon about 114 miles west of Bandon, according to the U.S. Geological Survey.

USGS earthquake map and location.
The earthquake hit the ocean floor far off the Southern Oregon coast, but there were no immediate reports of anyone feeling it on land.  USGS spokeswoman Leslie Gordon says there were no immediate reports to the agency’s website from people feeling the quake on shore.

USGS earthquake shakemap.

The U.S. Geological Survey reports the magnitude 5.1 quake was 114 miles west northwest of Port Orford at 2:14 p.m. Wednesday.

USGS historical seismicity for the region.

The temblor struck in the Pacific Ocean about 6.1 miles deep. No tsunami warning has been issued by the Pacific Tsunami Warning Center.


4.0 Magnitude Tremor Rocks Central Oklahoma, Causes Some Damage.
Two earthquakes rattled nerves in the metro and caused damage to some homes in the southeast suburbs. 

The first hit Choctaw Wednesday morning. The second was recorded as a 4.0 magnitude earthquake centered in Nicoma Park Wednesday afternoon.

In November 2011, the largest earthquake in Oklahoma history shook Sooner soil just as News 9's Ed Murray was beginning to report the news. It was a 5.6 magnitude earthquake. The damage then was much more significant than what Oklahomans experienced Wednesday.

"My animals all took off in different directions," Midwest City resident Michelle Davis said. "I really thought somebody was coming through the back wall."

Davis says there's no damage at her Midwest City home, but just across the street, Melissa Haynie showed News 9 cracks in her walls and paint. Pictures sent in from viewers showed similar damage to other homes in the area.

"This house isn't really that old, and it's pretty sturdy … so it kind of surprises me that it got cracks," Haynie said.

Moments before the second earthquake, Haynie says her dogs were scared and whining. She believes they were sensing what was to come.

"My dogs started barking and my cats went and ran behind the furniture [when the second earthquake hit]," Haynie said.

No injuries were reported following the earthquakes. Residents say the shaking lasted less than 5 seconds following the Nicoma Park earthquake. - News9.

WATCH: Earthquakes Rattle OKC Metro, Cause Some Damage.

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PLANETARY TREMORS: 6.9 Magnitude Earthquake Strikes Off Kuril Islands, Eastern Russia!

February 28, 2013 - RUSSIA - A magnitude 6.9 earthquake has hit the Kuril Islands, south of Russia’s Kamchatka peninsula, according to the United States Geological Survey (USGS). The quake had a depth of 18 miles.

USGS earthquake map and location.

There are no reports of damage.

It's the second quake to hit the Kuril Islands this year.  A magnitude 5.5 earthquake struck the Isles on January 1. The Islands were also hit with two earthquakes in November 2012, which measured magnitudes of 6.8 and 5.3.

USGS earthquake shakemap.

USGS earthquake shakemap.

The Kuril Islands are located 90 kilometers (56 miles) from Severo-Kuril'sk, Russia. Tokyo is located 2,204 kilometers (1,369 miles) away from the Isles.

The population of the Islands is around 19,000 people, and the total land area is about 15,600 square kilometers (6,000 square miles).

USGS earthquake population exposure.


USGS earthquake population exposure.

The Pacific Tsunami Warning Center issued a statement saying, “Based on all available data, a destructive Pacific-wide tsunami is not expected, and there is no tsunami threat to Hawai’i.” - RT.


Tectonic Summary - Seismotectonics of the Kuril-Kamchatka Arc.
The Kuril-Kamchatka arc extends approximately 2,100 km from Hokkaido, Japan, along the Kuril Islands and the Pacific coast of the Kamchatka Peninsula to its intersection with the Aleutian arc near the Commander Islands, Russia. It marks the region where the Pacific plate subducts into the mantle beneath the Okhotsk microplate, part of the larger North America plate. This subduction is responsible for the generation of the Kuril Islands chain, active volcanoes located along the entire arc, and the deep offshore Kuril-Kamchatka trench. Relative to a fixed North America plate, the Pacific plate is moving towards the northwest at a rate that increases from 75 mm/year near the northern end of the arc to 83 mm/year in the south.

Plate motion is predominantly convergent along the Kuril-Kamchatka arc with obliquity increasing towards the southern section of the arc. The subducting Pacific plate is relatively old, particularly adjacent to Kamchatka where its age is greater than 100 Ma. Consequently, the Wadati-Benioff zone is well defined to depths of approximately 650 km. The central section of the arc is comprised of an oceanic island arc system, which differs from the continental arc systems of the northern and southern sections. Oblique convergence in the southern Kuril arc results in the partitioning of stresses into both trench-normal thrust earthquakes and trench-parallel strike-slip earthquakes, and the westward translation of the Kuril forearc. This westward migration of the Kuril forearc currently results in collision between the Kuril arc in the north and the Japan arc in the south, resulting in the deformation and uplift of the Hidaka Mountains in central Hokkaido.

USGS historical seismicity.

The Kuril-Kamchatka arc is considered one of the most seismically active regions in the world. Deformation of the overriding North America plate generates shallow crustal earthquakes, whereas slip at the subduction zone interface between the Pacific and North America plates generates interplate earthquakes that extend from near the base of the trench to depths of 40 to 60 km. At greater depths, Kuril-Kamchatka arc earthquakes occur within the subducting Pacific plate and can reach depths of approximately 650 km.

This region has frequently experienced large (Magnitude greater than 7) earthquakes over the past century. Since 1900, seven great earthquakes (M8.3 or larger) have also occurred along the arc, with mechanisms that include interplate thrust faulting, and intraplate faulting. Damaging tsunamis followed several of the large interplate megathrust earthquakes. These events include the February 3, 1923 M8.4 Kamchatka, the November 6,1958 M8.4 Etorofu, and the September 25, 2003 M8.3 Hokkaido earthquakes. A large M8.5 megathrust earthquake occurred on October 13, 1963 off the coast of Urup, an island along the southern Kuril arc, which generated a large tsunami in the Pacific Ocean and the Sea of Okhotsk, and caused run-up wave heights of up to 4-5 m along the Kuril arc. The largest megathrust earthquake to occur along the entire Kurile-Kamchatka arc in the 20th century was the November 4, 1952 M9.0 event. This earthquake was followed by a devastating tsunami with run-up wave heights as high as 12 m along the coast of Paramushir, a small island immediately south of Kamchatka, causing significant damage to the city of Severo-Kurilsk.

On October 4,1994, a large (M8.3) intraplate event occurred within the subducted oceanic lithosphere off the coast of Shikotan Island causing intense ground shaking, landslides, and a tsunami with run-up heights of up to 10 m on the island.

The most recent megathrust earthquake in the region was the November 15, 2006 M8.3 Kuril Island event, located in the central section of the arc. Prior to this rupture, this part of the subduction zone had been recognized as a seismic gap spanning from the northeastern end of the 1963 rupture zone to the southwestern end of the 1952 rupture. Two months after the 2006 event, a great (M8.1) normal faulting earthquake occurred on January 13, 2007 in the adjacent outer rise region of the Pacific plate. It has been suggested that the 2007 event may have been caused by the stresses generated from the 2006 earthquake. - USGS.



PLANETARY TREMORS: Magnitude 6.1 Earthquake Sways Buildings In South Pacific Nation Of Vanuatu - No Major Damage Seen!

February 28, 2013 - VANUATU - A strong earthquake has shaken the South Pacific island nation of Vanuatu without causing major damage.

USGS earthquake map and location.
The magnitude-6.1 quake struck Thursday afternoon. The Pacific Tsunami Warning Center did not issue a tsunami warning.

Godwin Ligo, a reporter at the Trading Post newspaper, said he felt his office building in the capital Port Vila shake and sway. He said he wasn't aware of any major problems caused by the quake.

USGS earthquake shakemap.

The U.S. Geological Survey reported the epicenter was 104 kilometers (64 miles) west of the capital at a relatively shallow depth of 15 kilometers (9 miles).

USGS earthquake population exposure.
Vanuatu is on the "Ring of Fire" — an arc of earthquake and volcanic zones that stretches around the Pacific Rim. It's where most of the world's seismic activity occurs. - FOX News.



Tectonic Summary - Seismotectonics of the Eastern Margin of the Australia Plate.
The eastern margin of the Australia plate is one of the most sesimically active areas of the world due to high rates of convergence between the Australia and Pacific plates. In the region of New Zealand, the 3000 km long Australia-Pacific plate boundary extends from south of Macquarie Island to the southern Kermadec Island chain. It includes an oceanic transform (the Macquarie Ridge), two oppositely verging subduction zones (Puysegur and Hikurangi), and a transpressive continental transform, the Alpine Fault through South Island, New Zealand.

Since 1900 there have been 15 M7.5+ earthquakes recorded near New Zealand. Nine of these, and the four largest, occurred along or near the Macquarie Ridge, including the 1989 M8.2 event on the ridge itself, and the 2004 M8.1 event 200 km to the west of the plate boundary, reflecting intraplate deformation. The largest recorded earthquake in New Zealand itself was the 1931 M7.8 Hawke's Bay earthquake, which killed 256 people. The last M7.5+ earthquake along the Alpine Fault was 170 years ago; studies of the faults' strain accumulation suggest that similar events are likely to occur again.

North of New Zealand, the Australia-Pacific boundary stretches east of Tonga and Fiji to 250 km south of Samoa. For 2,200 km the trench is approximately linear, and includes two segments where old (>120 Myr) Pacific oceanic lithosphere rapidly subducts westward (Kermadec and Tonga). At the northern end of the Tonga trench, the boundary curves sharply westward and changes along a 700 km-long segment from trench-normal subduction, to oblique subduction, to a left lateral transform-like structure.

USGS historical seismicity.

Australia-Pacific convergence rates increase northward from 60 mm/yr at the southern Kermadec trench to 90 mm/yr at the northern Tonga trench; however, significant back arc extension (or equivalently, slab rollback) causes the consumption rate of subducting Pacific lithosphere to be much faster. The spreading rate in the Havre trough, west of the Kermadec trench, increases northward from 8 to 20 mm/yr. The southern tip of this spreading center is propagating into the North Island of New Zealand, rifting it apart. In the southern Lau Basin, west of the Tonga trench, the spreading rate increases northward from 60 to 90 mm/yr, and in the northern Lau Basin, multiple spreading centers result in an extension rate as high as 160 mm/yr. The overall subduction velocity of the Pacific plate is the vector sum of Australia-Pacific velocity and back arc spreading velocity: thus it increases northward along the Kermadec trench from 70 to 100 mm/yr, and along the Tonga trench from 150 to 240 mm/yr.

The Kermadec-Tonga subduction zone generates many large earthquakes on the interface between the descending Pacific and overriding Australia plates, within the two plates themselves and, less frequently, near the outer rise of the Pacific plate east of the trench. Since 1900, 40 M7.5+ earthquakes have been recorded, mostly north of 30°S. However, it is unclear whether any of the few historic M8+ events that have occurred close to the plate boundary were underthrusting events on the plate interface, or were intraplate earthquakes. On September 29, 2009, one of the largest normal fault (outer rise) earthquakes ever recorded (M8.1) occurred south of Samoa, 40 km east of the Tonga trench, generating a tsunami that killed at least 180 people.

Across the North Fiji Basin and to the west of the Vanuatu Islands, the Australia plate again subducts eastwards beneath the Pacific, at the North New Hebrides trench. At the southern end of this trench, east of the Loyalty Islands, the plate boundary curves east into an oceanic transform-like structure analogous to the one north of Tonga.

Australia-Pacific convergence rates increase northward from 80 to 90 mm/yr along the North New Hebrides trench, but the Australia plate consumption rate is increased by extension in the back arc and in the North Fiji Basin. Back arc spreading occurs at a rate of 50 mm/yr along most of the subduction zone, except near ~15°S, where the D'Entrecasteaux ridge intersects the trench and causes localized compression of 50 mm/yr in the back arc. Therefore, the Australia plate subduction velocity ranges from 120 mm/yr at the southern end of the North New Hebrides trench, to 40 mm/yr at the D'Entrecasteaux ridge-trench intersection, to 170 mm/yr at the northern end of the trench.

Large earthquakes are common along the North New Hebrides trench and have mechanisms associated with subduction tectonics, though occasional strike slip earthquakes occur near the subduction of the D'Entrecasteaux ridge. Within the subduction zone 34 M7.5+ earthquakes have been recorded since 1900. On October 7, 2009, a large interplate thrust fault earthquake (M7.6) in the northern North New Hebrides subduction zone was followed 15 minutes later by an even larger interplate event (M7.8) 60 km to the north. It is likely that the first event triggered the second of the so-called earthquake "doublet". - USGS.