6.2 magnitude earthquake strikes off east coast of Japan
October 2, 2012 – JAPAN – The U.S. Geological Survey reports that early Tuesday morning local time, a magnitude 6.2 earthquake hit off of Japan’s eastern coast. Originating from a depth of 9.7 kilometers (6 miles), it was centered about 96 kilometers (60 miles) off the coast of Miyako, Iwate Prefecture, in the northeast region of the country that was struck by the devastating earthquake and tsunami on March 11th, 2011. There have been no reports of damages or signs of approaching tsunami. In comparison from Tokyo, the 6.2 magnitude quake was about 550 kilometers (342 miles) from the capital city. Neither the Japan Meteorological Agency or the Pacific Tsunami Warning Center issued tsunami warnings or advisories on Tuesday as it wasn’t necessary. Geophysicist Gerard Fryer, with the Pacific Tsunami Warning Center, says the quake was too small to generate any kind of tsunami, but the residents of northeastern Japan would surely have felt it. The quake probably gave some frightful flashbacks to those of Japan’s Tohoku region who survived last year’s disaster. The tsunami disaster that took tens of thousands of lives and washed away entire coastal cities was caused by a magnitude 9.0 earthquake just over a year and a half ago, and led to the world’s worst nuclear crisis in 25 years in Fukushima Prefecture.
Powerful 7.3 earthquake strikes along the coast of Colombia: the fifth 7.0 magnitude quake to strike in 45 days
September 30, 2012 – COLOMBIA – A strong 7.3 magnitude earthquake struck along the coast of Colombia at a depth of 162.1 km (100.7 miles). The epicenter of the earthquake was 62 km (39 miles) S (176°) from Popayan, Colombia and 345 km (214 miles) from QUITO, Ecuador. According to USGS statistics, about fifteen 7.0 magnitude earthquakes occur each year but there have been five such high intensity earthquakes reported across the planet in the last 45 days, provided the USGS does not downgrade today’s quake further. On August 14, a 7.7 magnitude earthquake was reported in Sea of Okhotsk near NE Russia; on August 27, a 7.3 magnitude earthquake struck off the coast of El Salvador; on August 31, a 7.6 magnitude earthquake struck near the Philippine Islands, and on September 5, a 7.6 magnitude earthquake struck off the coast of Costa Rica. Today’s earthquake was originally registered as a 7.4 by the USGS. The director of Colombia’s disaster relief service, Carlos Ivan Marquez, said that there were only reports of minor damage to homes in one village. The temblor shook buildings and rattled windows in 10 central and western provinces, but despite police and firefighters reported no damage. The quake also shook Ecuador’s capital Quito and other parts of the country for about 30 seconds, and was felt particularly in tall buildings in the capital.
SCIENCE: Large 2012 earthquake triggered temblors worldwide for nearly a week
This year’s largest earthquake, a magnitude 8.6 temblor on April 11 centered in the East Indian Ocean off Sumatra, did little damage, but it triggered quakes around the world for at least a week, according to a new analysis by seismologists from the University of California, Berkeley, and the U.S. Geological Survey.
The April 11 quake was unusually large – the tenth largest in the last 100 years and, similar to a few other recent large quakes, triggered small quakes during the three hours it took for seismic waves to travel through Earth’s crust.
The new study shows, however, that some faults weren’t rattled enough by the seismic waves to fail immediately, but were primed to break up to six days later.
The findings are a warning to those living in seismically active regions worldwide that the risk from a large earthquake could persist – even on the opposite side of the globe – for more than a few hours, the experts said.
“Until now, we seismologists have always said, ‘Don’t worry about distant earthquakes triggering local quakes,’” said Roland Burgmann, professor of earth and planetary science at UC Berkeley and coauthor of the study. “This study now says that, while it is very rare – it may only happen every few decades – it is a real possibility if the right kind of earthquake happens.”
“We found a lot of big events around the world, including a 7.0 quake in Baja California and quakes in Indonesia and Japan, that created significant local shaking,” Burgmann added. “If those quakes had been in an urban area, it could potentially have been disastrous.”
Burgmann and Fred F. Pollitz, Ross S. Stein and Volkan Sevilgen of the USGS will report their results online on Sept. 26 in advance of publication in the journal Nature.
Burgmann, Pollitz, a research seismologist, and their colleagues also analyzed earthquake occurrences after five other recent temblors larger than 8.5 – including the deadly 9.2 Sumatra-Andaman quake in 2004 and the 9.0 Tohoku quake that killed thousands in Japan in 2011 – but saw only a very modest increase in global earthquake activity after these quakes.
They said this could be because the East Indian Ocean quake was a “strike-slip” quake that more effectively generates waves, called Love waves, that travel just under the surface and are energetic enough to affect distant fault zones.
Burgmann explained that most large quakes take place at subduction zones, where the ocean bottom sinks below another tectonic plate.
This was the origin of the Sumatra-Andaman quake, which produced a record tsunami that took more than 200,000 lives.
The 2012 East Indian Ocean quake involved lateral movement – referred to as strike-slip, the same type of movement that occurs along California’s San Andreas Fault – and was the largest strike-slip quake ever recorded.
“This was one of the weirdest earthquakes we have ever seen,” Burgmann said. “It was like the 1906 San Francisco earthquake, a strike-slip event, but it was huge – 15 times more energetic. This earthquake and an 8.3 that followed were in a very diffuse zone in an oceanic plate close to the Sumatra subduction zone, but it wasn’t a single fault that produced the quake, it was a crisscrossing of three or four faults that all ruptured in sequence to make such a big earthquake, and they ruptured deep.”
The seismologists analysis found five times the expected number of quakes during the six days following the April 11 quake and aftershock.
An unusually low occurrence of quakes during the 6-12 days before that 8.6 quake may have accentuated the impact, possibly because there were many very-close-to-failure faults sensitive to a triggering shock wave, Pollitz said.
One possible mechanism for the delayed action, Burgmann said, is that the East Indian Ocean quake triggered a cascade of smaller, undetectable quakes on these faults that led to larger ruptures later on.
Alternatively, large quakes could trigger nearly undetectable tremors or microquakes that are a sign of slow slip underground.
“One possibility is that the earthquake immediately triggers slow slip in some places, maybe accompanied by detectable tremor, and then that runs away into a bigger earthquake,” Burgmann speculated. “Some slow slip events take days to a week or more to evolve.”
The work was supported by the USGS.
Robert Sanders works for the University of California, Berkeley News Center.
Earthquake in California’s Silicon Valley could cause aftershocks across the globe
September 28, 2012 – CALIFORNIA – The San Andreas, Calaveras, and Hayward fault lines -which run underneath Silicon Valley – could set off tremors and aftershocks globally, according to a new study. Researchers at UC Berkeley and the U.S. Geological Survey found that fault lines of the “strike-slip” type, where plates of land slide past each other, were more likely to set off the worldwide aftershocks. As an example, the researchers found the 8.6 earthquake in Indonesia this April set off 16 earthquakes with a magnitude of 5.5 or greater within days. Not only could these “strike slip” faults like the San Andreas, Calaveras, and Hayward faults set off worldwide aftershocks, but the researchers indicate the faults could also be set off if another earthquake’s tremors struck when the fault was ready to rupture. However, the study indicates a quake powerful enough to do that only happens once every 50 years or so.
6.0 magnitude earthquake strikes Solomon Islands region
September 28, 2012 – SOLOMON ISLANDS – A quake measuring magnitude 6.0 hit off the Solomon Islands today, but Australian seismologists said there was little risk of a tsunami. The US Geological Survey put the quake at 6.0-magnitude some 272 kilometers west-northwest of the capital Honiara. With a depth of about 9 kilometers, it was about 112 kilometers southeast of the western city of Gizo. Geoscience Australia measured the quake at about 6.2-magnitude but said it was unlikely to create a tsunami or cause serious damage in the capital. “It’s just off the plate boundary so it’s a normal-sized earthquake and positioning for the area,” seismologist Hugh Glanville told AFP. “It’s not too close to Honiara. There’s a local city with a population of about 6,000 or so that might get a bit of damage,” he said in reference to Gizo. “But the majority of the population is a bit too far away to suffer more than a bit of shaking. And the population in the area is pretty sparse really.” Glanville also said the quake was too small to generate a tsunami. “Generally a local tsunami starts at about 6.5 (magnitude). It’s always possible, but it’s just extremely rare that it would generate a tsunami,” he said. “It’s just one of the plate boundary earthquakes along the Ring of Fire that normally happens in this area.” The Solomon Islands form part of the Ring of Fire, a zone of tectonic activity around the Pacific Ocean that is subject to earthquakes and volcanic eruptions. In 2007 a tsunami following an 8.1-magnitude earthquake killed at least 52 people in the Solomons and left thousands homeless.
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