My OperaSolomon Quake 2007
Monday, April 13, 2009 5:50:54 PM
As plate tectonics are the cause of most earthquakes, it is no wonder that those earthquakes tell us a lot about plate tectonics. Sometimes, however, it takes a long time to read the message.
Two years ago I wrote a minor post about Solomon earthquakes that occurred in April 2007. In the meantime these earthquakes have been thoroughly studied, and a paper on some of the findings has just been published in the journal Science. The earthquake is sort of special, a.o. because it occurred at a three-plate boundary, or triple junction. Below is a simple situation map.
The New Georgia Island Group of the Solomon Islands is one of four places where an active or recently active spreading ridge has subducted beneath an island arc. The spreading ridge pushing the small Solomon Sea Plate and the Australian Plate apart is being subducted beneath the Pacific Plate. The situation is rather complicated because the two plates descend beneath the overriding plate at different rates and directions.
According to the study the event began in the Australian Plate and moved across into the Solomon Sea Plate and had two centers of energy separated by lower energy areas, which is noticeable as we normally think earthquakes should stop at the plate boundaries. When the earthquake moved from one plate to the other, it quickly changed direction, mimicking the different plate motion directions of the plates involved. The authors are confident that the fault slip in the two main locations are different by 30 to 40 degrees. That behaviour during an earthquake has probably never been observed before, but it most certainly has happened here before, according to the authors.
Before about half a million years ago, the easternmost segment of the Woodlark Basin spreading ridge was subducting beneath the westernmargin of the Solomon Islands, and the ridgetrench triple junction migrated northwesterly at around 110 to 120 mm/year. The differences in plate subduction rates and directions produced a slab window, which today lies beneath the southern New Georgia Islands. (When a mid-ocean spreading ridge subducts, it typically splits apart at depth to form two tapered slab edges separated by asthenospheric mantle within an inter-slab gap called a slab window).
A cartoon in the paper shows how the Solomon Sea Plate and the Australian Plate subduct as two different layers (slabs) beneath the overriding Pacific plate, with a slab window at depth (shown as increasing empty space between the two coloured slabs). The surface subduction boundary is marked by a red line.
• http://www.sciencemag.org/cgi/content/short/324/5924/226
• http://news.yahoo.com/s/ap/20090409/ap_on_sc/sci_solomon_tsunami_1
• http://www.eurekalert.org/pub_releases/2009-04/ps-sie040609.php
• http://www.geologytimes.com/research/Solomon_Islands_earthquake_sheds_light_on_enhanced_tsunami_risk.asp
• http://earthquake.usgs.gov/eqcenter/eqinthenews/2007/us2007aqbk/finite_fault.php
• http://earthquake.usgs.gov/eqcenter/eqinthenews/2007/us2007aqbk/
• http://walrus.wr.usgs.gov/tsunami/solomon07/index.html
Two years ago I wrote a minor post about Solomon earthquakes that occurred in April 2007. In the meantime these earthquakes have been thoroughly studied, and a paper on some of the findings has just been published in the journal Science. The earthquake is sort of special, a.o. because it occurred at a three-plate boundary, or triple junction. Below is a simple situation map.
The New Georgia Island Group of the Solomon Islands is one of four places where an active or recently active spreading ridge has subducted beneath an island arc. The spreading ridge pushing the small Solomon Sea Plate and the Australian Plate apart is being subducted beneath the Pacific Plate. The situation is rather complicated because the two plates descend beneath the overriding plate at different rates and directions.
According to the study the event began in the Australian Plate and moved across into the Solomon Sea Plate and had two centers of energy separated by lower energy areas, which is noticeable as we normally think earthquakes should stop at the plate boundaries. When the earthquake moved from one plate to the other, it quickly changed direction, mimicking the different plate motion directions of the plates involved. The authors are confident that the fault slip in the two main locations are different by 30 to 40 degrees. That behaviour during an earthquake has probably never been observed before, but it most certainly has happened here before, according to the authors.
Before about half a million years ago, the easternmost segment of the Woodlark Basin spreading ridge was subducting beneath the westernmargin of the Solomon Islands, and the ridgetrench triple junction migrated northwesterly at around 110 to 120 mm/year. The differences in plate subduction rates and directions produced a slab window, which today lies beneath the southern New Georgia Islands. (When a mid-ocean spreading ridge subducts, it typically splits apart at depth to form two tapered slab edges separated by asthenospheric mantle within an inter-slab gap called a slab window).
A cartoon in the paper shows how the Solomon Sea Plate and the Australian Plate subduct as two different layers (slabs) beneath the overriding Pacific plate, with a slab window at depth (shown as increasing empty space between the two coloured slabs). The surface subduction boundary is marked by a red line.
• http://www.sciencemag.org/cgi/content/short/324/5924/226
• http://news.yahoo.com/s/ap/20090409/ap_on_sc/sci_solomon_tsunami_1
• http://www.eurekalert.org/pub_releases/2009-04/ps-sie040609.php
• http://www.geologytimes.com/research/Solomon_Islands_earthquake_sheds_light_on_enhanced_tsunami_risk.asp
• http://earthquake.usgs.gov/eqcenter/eqinthenews/2007/us2007aqbk/finite_fault.php
• http://earthquake.usgs.gov/eqcenter/eqinthenews/2007/us2007aqbk/
• http://walrus.wr.usgs.gov/tsunami/solomon07/index.html
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