Rapid series of shallow quakes rock T...

Rapid series of shallow quakes rock Taiwan

There are 2 comments on the Suria story from Jun 17, 2012, titled Rapid series of shallow quakes rock Taiwan. In it, Suria reports that:

Seven shallow earthquakes hit eastern Taiwan in rapid succession on Sunday afternoon, sparking panic, causing damage to buildings and shaking the capital Taipei.

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“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#1 Jun 18, 2012
An interesting report.

In particular as I have noticed the shallow quakes on monitoring of the NEIC earthquake list.

The quake series sits in the arc graben ans is likely a result of magma movement along relatively deep fractures in the arc graben toward one or other of the offshore volcanoes (E. of Taiwan island proper which is an uplifted forearc in collision with the South China block).

Movement of magma will initially cause dilation of the upper strata in the arc graben and shallow rifting, which should be traceable in location as the magma moves. This will then be followed by recompression of the near surface strata (which may occur decades after the passage of the magma filled fracture.

As Taiwan is a zygomorph, there are 2 megathrusts bordering the region (one W, and one E.) the W. megathrust broke last and is recompressing, it appears to have a fair amount of time left before the next rebound/long duration mercalli X event (acronym= r/lx, such as has recently occurred in Tohoku (another zygomorph) in NE. Honshu). The recurrence interval time for r/lx here appears to be on the order of 500 years (possibly to 700 or more), so there appears to be plenty of time to squeeze the deep crustal magma around in the arc graben.
The magma is a product of the last r/lx to hit Taiwan (which hith the E. Megathrust), the relaxation of the crust allowed ingress of magma from discs of ponded magma at the tightly compressed base of the crust into fractures which formedduring the r.lx. This process has just been observed at Tohoku (March 2011 and onward) with the arc graben region in Tohoku remaining aseismic to the present but magma ingress likely ended by May/June 2011.

Once magma ingress has occurred the only way for the magma to go once the megathrust has locked and its r/lx generated frictional melt solidified (a few months) is into the zone of least compression and from there directly upward (hence volcanism).

Keep watching that space, there may be some very interesting underwater volcanism offshore of E Taiwan within the decade.

Have a nice day: Ag


#2 Jun 21, 2012

one china only.

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