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A Mw 7.4 Quake S of Tonga occurred at 17:19 UT, 23-5-2013
still visible on my seismo for ~ another 24 Hrs till it scrolls off
http://www.sydneystormcity.com/sydln.gif
it was quite a deep event at 171km and within the boundary area of the down going Pacific seafloor slab along the Tonga - Kermadec Trench
Its depth meant that it didnt have high amplitude surface waves
P arrival at my station ( Sydney) @ ~ 17:25 UT and the S wave arrival just before 17:30
This trench is well known for very deep events that occur from under the North Island of New Zealand and right up via Tonga to Fiji. Events up 600+ km are not uncommon.
One of the main reasons for the quakes at great depth in this region is because of the high subduction rate along this plate boundary of up to 8cm / year. This allows the Pacific Plate to subduct to great depth before it heats and softens too much to allow fracturing to occur.
Its quite a complex process where the outer edges of the subducting slab are warming faster than its core and allowing the core to continue to fracture causing quakes long after the outer edges are softly deforming.
Dave
still visible on my seismo for ~ another 24 Hrs till it scrolls off
http://www.sydneystormcity.com/sydln.gif
it was quite a deep event at 171km and within the boundary area of the down going Pacific seafloor slab along the Tonga - Kermadec Trench
Its depth meant that it didnt have high amplitude surface waves
P arrival at my station ( Sydney) @ ~ 17:25 UT and the S wave arrival just before 17:30
This trench is well known for very deep events that occur from under the North Island of New Zealand and right up via Tonga to Fiji. Events up 600+ km are not uncommon.
One of the main reasons for the quakes at great depth in this region is because of the high subduction rate along this plate boundary of up to 8cm / year. This allows the Pacific Plate to subduct to great depth before it heats and softens too much to allow fracturing to occur.
Its quite a complex process where the outer edges of the subducting slab are warming faster than its core and allowing the core to continue to fracture causing quakes long after the outer edges are softly deforming.
Dave
