Strong Earthquake - No Damage
Friday, 28. August 2009, 09:07:06
A 6.8-magnitude quake occurred in the Banda Sea, Indonesia, on Friday 28 August at 09:51 local time. It caused no severe damage, and although it was under sea it triggered no tsunami.
If you wonder why? the answer is simple, it was far too deep. And by deep I mean really deep - at a depth of 633.2 km. It is about as deep as earthquakes go. The deepest earthquake ever recorded is 705 km deep, under the Fiji Islands in the Southwest Pacific, on 6 May 2007.
Such deep earthquakes only occur in subduction zones - and only in some old subduction zones.
Looking at a map of historic seismicity from USGS we can see that the quake occurred in a band of former deep earthquakes (marked in red) at a certain distance from the surface frontier of the subduction zone marked as a purple line. In this area it is in fact relatively easy (even though the plate tectonics in the area are rather complex) to follow the inclination of the Benioff zone from shallow earthquakes, 0 – 36 km deep, to the deepest earthquakes 500 – 800 km deep. The earthquake foci normally plot along a dipping plane at an angle of 33 to 60 degrees and such a plane is called a Benioff zone. Earthquakes along Benioff zones define a lithospheric plate that descends into the mantle beneath another, overlying plate. The zone is named after Hugo Benioff, a US seismologist who first described this feature.
In Danish:
If you wonder why? the answer is simple, it was far too deep. And by deep I mean really deep - at a depth of 633.2 km. It is about as deep as earthquakes go. The deepest earthquake ever recorded is 705 km deep, under the Fiji Islands in the Southwest Pacific, on 6 May 2007.
Such deep earthquakes only occur in subduction zones - and only in some old subduction zones.
Looking at a map of historic seismicity from USGS we can see that the quake occurred in a band of former deep earthquakes (marked in red) at a certain distance from the surface frontier of the subduction zone marked as a purple line. In this area it is in fact relatively easy (even though the plate tectonics in the area are rather complex) to follow the inclination of the Benioff zone from shallow earthquakes, 0 – 36 km deep, to the deepest earthquakes 500 – 800 km deep. The earthquake foci normally plot along a dipping plane at an angle of 33 to 60 degrees and such a plane is called a Benioff zone. Earthquakes along Benioff zones define a lithospheric plate that descends into the mantle beneath another, overlying plate. The zone is named after Hugo Benioff, a US seismologist who first described this feature.-
http://www.etaiwannews.com/etn/news_content.php?id=1043099&lang=eng_news
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http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009kwae.php#details
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http://my.opera.com/nielsol/blog/2007/05/09/deep-fiji-eartquake
In Danish:
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