Thursday, April 14, 2016

PLANETARY TREMORS: Very Strong 6.4 And 6.0 Magnitude Earthquakes Strike Japan - Tsunami Warning Issued, But Later Cancelled; Several AFTERSHOCKS; Rescuers Battle To Free People Trapped Under Rubble; Fires Breakout; At Least 19 HOMES COLLAPSED! [MAPS + TECTONIC SUMMARY + PHOTOS + VIDEOS]

USGS earthquake location.

April 14, 2016 - JAPAN - A 6.4 magnitude earthquake has struck east of Kumamoto, Japan, according to the Japan Meteorological Agency. It had a depth of 10 kilometers (6.2 miles).

The quake hit at 9:26 p.m. local time (12:26 GMT), eight kilometers (4.97 miles) from the city of Tamana.

USGS shakemap intensity.

The earthquake left behind damage to buildings, as well as a fire.

Keisukei Urata, an official in Uki, told AP that he saw walls around houses collapsing.

"Papers, files, flower vases and everything fell on the floor," Kasumi Nakamura, an official in the village of Nishihara, located near the epicenter, told NHK. He said the rattling started small but then grew violent, lasting about 30 seconds, adding that there were aftershocks.

One aftershock measuring 5.7 struck about 40 minutes after the quake, according to the Japan Meteorological Agency.

The US Geological Survey (USGS) put the quake at a 6.2 magnitude.

The Japan Meteorological Agency originally issued a tsunami warning, but later canceled it.

WATCH: Dozens injured after 6.4-strong earthquake hits east of Kumamoto.

Second large earthquake hits Japan measuring 6.0 in magnitude as rescuers battle to free people trapped in rubble

Fires burn after a second quake hit Japan.
© Sky News

A second huge earthquake has hit Japan measuring 6.0 in magnitude.

This comes as the nation was coming to terms with the destruction caused by the 6.4 tremor which struck earlier today.
It is unclear how much damage the latest quake has caused but there is reportedly, currently no tsunami warning in place.

Fires were seen breaking out after nineteen homes reportedly collapsed near to the site of the tremor.

Rescue workers are currently battling to free those trapped in the rubble. After the first tremor, the Nuclear Regulation Authority said there were no irregularities at three nuclear plants on the southernmost island of Kyushu and nearby Shikoku.

Some high-speed trains were halted as a precaution. Japanese media showed watermelons falling from shelves at asupermarket in Kumamoto.

A quake of magnitude 9 struck offshore north of Tokyo in March 2011, causing tsunami waves along the coast which killed nearly 20,000 people and triggered a meltdown at a nuclear powerplant.

The first tremor caused widespread damage.
© Getty

The earlier quake struck 11 km (7 miles) east of the city of Kumamoto, the U.S. Geological Survey reported. It initially said the magnitude was 6.2 but revised it down. Japanese public broadcaster NHK said the quake registered 6.4.

There was no tsunami warning, but Japan's chief government spokesman, Yoshihide Suga, said several buildings had collapsed. He gave no more details. Footage captured some dramatic scenes during the earlier quake with one camera catching officer workers diving for cover as the quake hit.

Watermelons fell from store shelves and lay crushed on the floor of a supermarket in Kumamoto city, near the epicentre, NHK footage showed.

Objects fell from shelves and staff ducked under desks as the quake shook the NHK office in Kumamoto, video showed.

Tectonic Summary

The April 14, 2016 M 6.4 earthquake north of Kumamoto, on the island of Kyushu in southwest Japan, occurred as the result of strike-slip faulting at shallow depth. Focal mechanisms for the earthquake indicate slip occurred on either a left-lateral fault striking to the northwest, or on a right-lateral fault striking northeast. While the earthquake occurred several hundred kilometers northwest of the Ryukyu Trench, where the Philippine Sea plate begins its northwestward subduction beneath Japan and the Eurasia plate, the shallow depth and faulting mechanism of this earthquake indicate it occurred on a crustal fault within the upper Eurasia plate. At the location of this event, the Philippine Sea plate converges with Eurasia towards the northwest at a velocity of 58 mm/yr.

Moderate-to-large, shallow earthquakes in Kyushu are infrequent – most seismicity in the region is related to the subduction of the Philippine Sea plate at depth. Thirteen M 5+ earthquakes have occurred at shallow depths (> 50 km) within 100 km of the April 2016 event over the past century. In January and April of 1975, two shallow events with magnitudes of M 5.8 and M 6.1 - 40 km and 65 km to the northwest of the April 2016 earthquake, respectively – caused injuries, but no known fatalities. A shallow M 6.6 earthquake in March 2005, just off the north coast of Kyushu and 110 km north of the April 2016 event, caused over 1000 injuries and at least one fatality.

Mapped faults in the region generally trend east-west or northeast-southwest, in agreement with the right-lateral plane of preliminary focal mechanisms, and the trend of early aftershocks. In the first three hours after the M 6.4 event (12:26:36 UTC), 7 aftershocks have been located, the largest of which is a M 6.0 event at 15:03:47 UTC.

Seismotectonics of the Philippine Sea and Vicinity

The Philippine Sea plate is bordered by the larger Pacific and Eurasia plates and the smaller Sunda plate. The Philippine Sea plate is unusual in that its borders are nearly all zones of plate convergence. The Pacific plate is subducted into the mantle, south of Japan, beneath the Izu-Bonin and Mariana island arcs, which extend more than 3,000 km along the eastern margin of the Philippine Sea plate. This subduction zone is characterized by rapid plate convergence and high-level seismicity extending to depths of over 600 km. In spite of this extensive zone of plate convergence, the plate interface has been associated with few great (Magnitude greater than 8.0) ‘megathrust’ earthquakes. This low seismic energy release is thought to result from weak coupling along the plate interface (Scholz and Campos, 1995). These convergent plate margins are also associated with unusual zones of back-arc extension (along with resulting seismic activity) that decouple the volcanic island arcs from the remainder of the Philippine Sea Plate (Karig et al., 1978; Klaus et al., 1992).

South of the Mariana arc, the Pacific plate is subducted beneath the Yap Islands along the Yap trench. The long zone of Pacific plate subduction at the eastern margin of the Philippine Sea Plate is responsible for the generation of the deep Izu-Bonin, Mariana, and Yap trenches as well as parallel chains of islands and volcanoes, typical of circum-pacific island arcs. Similarly, the northwestern margin of the Philippine Sea plate is subducting beneath the Eurasia plate along a convergent zone, extending from southern Honshu to the northeastern coast of Taiwan, manifested by the Ryukyu Islands and the Nansei-Shoto (Ryukyu) trench. The Ryukyu Subduction Zone is associated with a similar zone of back-arc extension, the Okinawa Trough. At Taiwan, the plate boundary is characterized by a zone of arc-continent collision, whereby the northern end of the Luzon island arc is colliding with the buoyant crust of the Eurasia continental margin offshore China.

USGS plate tectonics.

Along its western margin, the Philippine Sea plate is associated with a zone of oblique convergence with the Sunda Plate. This highly active convergent plate boundary extends along both sides the Philippine Islands, from Luzon in the north to the Celebes Islands in the south. The tectonic setting of the Philippines is unusual in several respects: it is characterized by opposite-facing subduction systems on its east and west sides; the archipelago is cut by a major transform fault, the Philippine Fault; and the arc complex itself is marked by active volcanism, faulting, and high seismic activity. Subduction of the Philippine Sea Plate occurs at the eastern margin of the archipelago along the Philippine Trench and its northern extension, the East Luzon Trough. The East Luzon Trough is thought to be an unusual example of a subduction zone in the process of formation, as the Philippine Trench system gradually extends northward (Hamburger et al., 1983). On the west side of Luzon, the Sunda Plate subducts eastward along a series of trenches, including the Manila Trench in the north, the smaller less well-developed Negros Trench in the central Philippines, and the Sulu and Cotabato trenches in the south (Cardwell et al., 1980). At its northern and southern terminations, subduction at the Manila Trench is interrupted by arc-continent collision, between the northern Philippine arc and the Eurasian continental margin at Taiwan and between the Sulu-Borneo Block and Luzon at the island of Mindoro. The Philippine fault, which extends over 1,200 km within the Philippine arc, is seismically active. The fault has been associated with major historical earthquakes, including the destructive M7.6 Luzon earthquake of 1990 (Yoshida and Abe, 1992). A number of other active intra-arc fault systems are associated with high seismic activity, including the Cotabato Fault and the Verde Passage-Sibuyan Sea Fault (Galgana et al., 2007).

Relative plate motion vectors near the Philippines (about 80 mm/yr) is oblique to the plate boundary along the two plate margins of central Luzon, where it is partitioned into orthogonal plate convergence along the trenches and nearly pure translational motion along the Philippine Fault (Barrier et al., 1991). Profiles B and C reveal evidence of opposing inclined seismic zones at intermediate depths (roughly 70-300 km) and complex tectonics at the surface along the Philippine Fault.

Several relevant tectonic elements, plate boundaries and active volcanoes, provide a context for the seismicity presented on the main map. The plate boundaries are most accurate along the axis of the trenches and more diffuse or speculative in the South China Sea and Lesser Sunda Islands. The active volcanic arcs (Siebert and Simkin, 2002) follow the Izu, Volcano, Mariana, and Ryukyu island chains and the main Philippine islands parallel to the Manila, Negros, Cotabato, and Philippine trenches.

Seismic activity along the boundaries of the Philippine Sea Plate (Allen et al., 2009) has produced 7 great (Magnitude greater than 8.0) earthquakes and 250 large (Magnitude greater than 7) events. Among the most destructive events were the 1923 Kanto, the 1948 Fukui and the 1995 Kobe (Japan) earthquakes (99,000, 5,100, and 6,400 casualties, respectively), the 1935 and the 1999 Chi-Chi (Taiwan) earthquakes (3,300 and 2,500 casualties, respectively), and the 1976 M7.6 Moro Gulf and 1990 M7.6 Luzon (Philippines) earthquakes (7,100 and 2,400 casualties, respectively). There have also been a number of tsunami-generating events in the region, including the Moro Gulf earthquake, whose tsunami resulted in more than 5000 deaths.

More information on regional seismicity and tectonics

- RT | Daily Mirror | USGS.

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