Intraplate Earthquakes

[damienpaul]

As many of you are aware, the Earth's crust is cracked like an eggshell and moved around by convection (heating -cooling circulation like peas boiling in a pot) in the mantle. The majority of earthquake and volcanic activity occurs in these regions. Thus the plate boundaries can be traced with a degree of certainty, such as shown below:


USGS - image source
(It ought to be noted that the Indo-Australian plate is actually two plates)

Notice on the map, the Hawaiian Islands - which are a volcanic hotspot, away from a plate boundary... this is somewhat, but not totally analogous to intraplate earthquakes. Essentially, they are earthquakes that occur away from plate boundaries - in places such as Hawaii (as occurred recently), and other areas away from volcanic influences such as Australia and China, a very famous example is the New Madrid Fault Zone in the US.

More information:

Wikipedia
Berkeley - mainly about the New Madrid and Charleston quakes
AGU - a south west Pacific example

[korjik]

Those are just active faults. There are thousands to millions of inactive or barely active faults scattered all through the continents. My mother actually discovered a fault in Waukesha county Wisconsin while she was working on her masters in geophysics

[damienpaul]

Those are just active faults. There are thousands to millions of inactive or barely active faults scattered all through the continents. My mother actually discovered a fault in Waukesha county Wisconsin while she was working on her masters in geophysics

Precisely, as they are away from plate boundaries they are termed Intraplate. That sounds totally cool about your mother's discovery!!! - anymore information possible?

[Frog march]

As many of you are aware, the Earth's crust is cracked like an eggshell and moved around by convection (heating -cooling circulation like peas boiling in a pot) in the mantle.

that's what I used to think but according to my geology book it isn't to do with convection but to do with subductive zones, the subducted part of the crust pulling the rest of the plate down into the Earth.

if that ain't the answer I would sure like to know.

[damienpaul]

that's what I used to think but according to my geology book it isn't to do with convection but to do with subductive zones, the subducted part of the crust pulling the rest of the plate down into the Earth.

if that ain't the answer I would sure like to know.

true - but what is moving the plates to start with .... what I have read is that the colder crustal material sinks through the mantle, heating up near to the bottom and rsing elsewhere.

Here is a University of Leeds page on mantle convection. Mind you, I would not mind learning more about other theories

[hhEb09'1]

that's what I used to think but according to my geology book it isn't to do with convection but to do with subductive zones, the subducted part of the crust pulling the rest of the plate down into the Earth.

if that ain't the answer I would sure like to know.

Which geology book is that? I'd be surprised if a recent text asserted that.
At one time, there were discussions about whether it was ridge push or slab pull--but both are a form of mantle convection. It looks like the slabs cool until they reach a certain age, and then they sink--that's the idea behind slab pull.

[Frog march]

Which geology book is that? I'd be surprised if a recent text asserted that.

This is still controversial, but most geologists would agree on two things, at least. The first is that, attractive as the idea might seem, plate motions are not the direct surface expressions of mantle convection... <snip>.... The plates seem to be moving around more or less independently of this deeper process...<snip>...Perhaps the most likely driving mechanism is that the old, cold edge of a subduction slab, sinking because it is negatively buoyant, drags the rest of the plate with it.

it was first published in 1997.

[hhEb09'1]

Ah. The counterexample to that is the Atlantic--where there are no subduction zones "pulling" the plates. So, I would say that that interpretation is an oversimplification.

[damienpaul]

Ah. The counterexample to that is the Atlantic--where there are no subduction zones "pulling" the plates. So, I would say that that interpretation is an oversimplification.

Also the East African Rift System.... the Sea floor spreading between Australia and Antarctica, between the Pacific and Nazca plates