7.0 Quake Off Japan; Aftershocks Hit Russia In Third Major Quake This Week
A 7.0 quake off Japan sent aftershocks as far away as eastern Russia, with no major damage or casualties reported in what is now the third major earthquake reported this week. On Monday, a 7.8 quake blasted Iran and Pakistan, sending aftershocks as far as Dubai and India and killing 40 people. Then, on Wednesday morning, a 6.8 earthquake erupted off the coast of Papua New Guinea. Fortunately no casualties were reported.
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Today's 7.0 quake off Japan occurred at midday and the epicenter was located in the Pacific Ocean. The nearest land masses are the volcanic islands of Urup, Iturup and Sumushir, and officials told USA Today they are not under Japanese control. No tsunami warning was issued from today's 7.0 quake off Japan even though it occurred at a fairly shallow depth. Tsunamis are generated by earthquakes under the sea floor, so when an earthquake, like today's 7.0 quake off Japan, has a shallow depth it increases the chance of a tsunami because more kinect energy makes its way into the sea.
Here is the tectonic summary from the U.S. Geological Survey:
The April 19, 2013 M 7.2 earthquake ENE of Kuril'sk, Russia, occurred as a result of oblique normal faulting at intermediate depths within the subducting lithosphere of the Pacific plate. At the latitude of this earthquake, the Pacific plate converges with the North America plate (and the smaller Okhotsk microplate) towards the west-northwest at a velocity of approximately 82 mm/yr, and subducts beneath the Kuril Islands at the Kuril-Kamchatka trench, some 160 km to the southeast of the April 19 event. The depth of this earthquake, and its oblique-faulting mechanism, indicate that it involved intraplate faulting within the subducting slab, rather than being an interplate thrust event on the shallower seismogenic zone between the two tectonic plates.
The Kuril-Kamchatka arc has frequent moderate-to-large earthquakes, and has hosted over three-dozen M 6.5+ events within 250 km of the April 19 earthquake over the past 40 years. None are known to have caused shaking-related fatalities. The largest of these was the November 2006 M 8.3 interplate thrust event, approximately 200 km to the east of the April 19 earthquake. However, while the Pacific slab is seismically active in this region to depths of almost 700 km, just one of these nearby M 6.5+ events has occurred at depths greater than 70 km - a M 6.7 event in October 1994, 130 km to the southwest.
Intermediate depth (70 - 300km) and deep-focus (depth > 300 km) earthquakes are distinguished from shallow earthquakes (depth < 70 km) by the nature of their tectonic setting, and are in general much less hazardous than their shallow counterparts, though they may be felt at great distances from their epicenters.
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