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Tuesday, August 14, 2012

7.7 quake in sea near Japan and few questions to plate tectonics

hi
To days quake of 7.7 deep in sea ,near Japan ,have posed two questions
1) The quake was very deep 620Kms,ie in side mantle,ie below crust and upper mantle,
 How do we explain such a huge quake at such a depth?
 Can any body(who supports plate tectonics )can answer this?

2) There are two false quake anouncement in california (5+).The beauty of these quakes is ,it was announced by ,none other than USGS ,and later canceled as below

--This event has been deleted after review by a seismologist----

Can anybody explain how such things happen? that too with USGS?

Amit

6 comments:

Roger Hunter said...

Amit;

Deep quakes happen when the subducting edge of the plate undergoes a phase change.

The USGS publishes computer generated locations initially. These may be calculated by the computer software from later phases of a large quake or random noise in some cases.

It takes a human to straighten things out when that happens.

Roger

AMIT said...

Roger
By phase change ,if we mean,plates changing dtate from solid to liquid,such huge quake may not be possible.besides phase chage is a slow process and may not induce jeeks to this extent

How far we can trust a software which gives false indications.several times the issue of anomaly in magnitude(by usgs and local seismologydept) have arised.
Amit

Roger Hunter said...

Amit;

No, the phase change is from one type of rock to another. Google it or look on the NEIC website.

We don't trust it very far, that's why it's reviewed. Mag is a different question. It relates more to the amount of data available.

Roger

Jazzman said...

Hi Amit

Deep quakes make up 20% of all quakes.

Deep quakes are formed when the lithospheric plates are pushed down, into the mantle, they become slabs.

These slabs then proceed downwards, sometimes meeting cooler harder mantle, rubbing which then cause deeper quakes...
Continuing downwards, the slabs reach the depth of 160km, we then see changes in the minerals, resulting in water... this water build takes up more room than is available.

As the slab goes deeper, it goes through many changes, temperature and water plays big parts in this change, along with many unknowns.

Shallow quakes need cold, brittle rocks storing up elastic strain along the fault, held in check by friction, until the strain lets loose in a violent rupture.

As for your other question, iv seen quite a few quakes called, then suddenly vanish... mainly Washington.

Jazzman

tremor-activity.blogspot.co.uk/

:)

AMIT said...

Jazzman
The whole idea is confusing.following points not clear
1)how the desity of crust increases as it goes down,may be cacluim changng to aother ,harder form?Waht about other elements?Do those elemnt melts?;eaving a thin crust decending?
2)How can we find cooler mantle as we go down
3) what exacly happens ,as the rock goes down.
4) Do phase change and water vapour produce ,so much energy?
5) Any one have calculated the energy requared to produced.recent 7.7 quake?and do we get this energy from water vapour and phase change?

How many grey areas are thare?Seems ,no one have correct picture
Amit

Jazzman said...

Hi Amit

Minerals in the slab begin to change under pressure. Metamorphosed basalt and gabbro changes to the blueschist mineral suite, then into eclogite . Water is released and the rocks become more compact and grow more brittle.
serpentine minerals change to olivine and enstatite plus water. 160 km depth.


at roughly 410 km, olivine begins to change to a different crystal form identical to that of the mineral spinel... phase change ... Olivine-spinel changes again to a perovskite form at around 650 km.

410km-650km... the mantle's transition zone.)

Enstatite-to-ilmenite and garnet-to-perovskite at depths below 500 km.... and so on.

You mention the power... What needs to be remembered is that deep quakes have one-tenth as many aftershocks as shallow quakes do, they move most their energy in one motion.... the pressure must be tremendous.

once there is enough lubricant between two surfaces, you will get the movement, its a process over many years.

Melting points rise with pressure, different elements have there own melting points, magnesia-rich spinel is stable at very high temperature (melting point 2135°C [3875°F])

Ilmenite and perovskite higher still.

In the mantle, temperatures range between 500 to 900 °C (932 to 1,652 °F) at the upper boundary with the crust; to over 4,000 °C (7,230 °F) at the boundary with the core.

For me personally, magnetics has a large part to play.

what's known and what's told to us is another thing ; )

tremor-activity.blogspot.co.uk/

Have a nice day

:)