+- Earthwaves Earth Sciences Forum (http://www.earthwaves.org/forum)
+-- Forum: Earthwaves (http://www.earthwaves.org/forum/forumdisplay.php?fid=16)
+--- Forum: Earth Sciences (http://www.earthwaves.org/forum/forumdisplay.php?fid=11)
+--- Thread: re-rupturing recently ruptured fault (/showthread.php?tid=98)
re-rupturing recently ruptured fault - Island Chris - 04-30-2014
The abstract at the link is interesting; we have had these sorts of discussions on Earthwaves before. I've likely posted that a subduction zone that just had a M9 quake is not going to have another one for some (long) time. But, parts of faults that break in earthquakes may not release all the differential stress. For example, the 2004 Sumatra M9.2(?) had very large slips in the southern few hundred km but not very much in the north.
The abstract is about the Nov 17 2013 Scotia Sea quake. I think we had a thread on old Earthwaves that both sides of the Scotia plate ruptures not to long apart:
http://onlinelibrary.wiley.com/doi/10.1002/2014GL059465/abstract
Geophysical Research Letters is an AGU journal so the paper will be available in 2 years.
Chris
RE: re-rupturing recently ruptured fault - Skywise - 04-30-2014
(04-30-2014, 03:19 PM)Island Chris Wrote: The abstract at the link is interesting; we have had these sorts of discussions on Earthwaves before. I've likely posted that a subduction zone that just had a M9 quake is not going to have another one for some (long) time. But, parts of faults that break in earthquakes may not release all the differential stress. For example, the 2004 Sumatra M9.2(?) had very large slips in the southern few hundred km but not very much in the north.
I recall seeing a visualization somewhere once to represent how earthquakes work. It used a brick being dragged up an inclined board pulled by a bungee cord being wound up on a pulley. As you crank the pulley at a steady rate, the tension slowly increases until it overcomes the stiction of the interface between the brick and board, allowing the brick to slide. As you keep steadily winding up the pulley, more 'quakes' happen, some big, some small.
And this is where the demonstration ends.
But it's obvious not all the tension is not released even in the largest of quakes. There is still some tension on the bungee. It never goes slack. This to me is obviously because of the friction between the surfaces eventually overcomes the remaining stress on the bungee even as the brick is moving. The tension could only possibly be completely relieved if the friction also lowered as the slip progressed and went to zero as the tension goes to zero. Obviously, it does not.
But I can envision a more complicated system that illustrates what may be happening in the context of this paper.
Now imagine a second brick behind the first one. This not only has it's own bungee pulling it up the inclined plane, but is also tied to the first brick, being in tow in a sense. As the pulley is cranked, it pulls on both bricks. Each brick can move independently of the other, but not always because they are also tied together.
I can envision a scenario where one brick may have moved, but when the second brick moves, the interlinking between them causes the first one to move again even though it just had most of it's tension relieved. This could either be because one brick adds more tension on it's bungee to the brick behind it, or it relieves tension on the bungee in front of it.
I bet it would scale quite well up to several bricks. You can't just tie all the bricks in a chain. They also have to be tied directly to the pulley as well as this would represent the mantle flow under the crust that drives their movement.
Wish I had a video camera. This would make an interesting experiment.
Elastic rebound stress I don't think is 100% relieved during each quake, and each segment of a fault IS connected to the others. Although we like to talk about this segment and that segment, it's really a very large complex interactive system.
Brian
RE: re-rupturing recently ruptured fault - Island Chris - 05-01-2014
I've seen a brick and bungee experiment also. I don't remember if there was one or two bricks and bungees. But, I do recall that sometimes you would get small slips closely-spaced in time, and sometimes large slips with longer time intervals.
Mark Zoback and others published a paper on aftershocks of Loma Prieta (1989 Santa Cruz Mountains; I know the regulars know this but maybe some readers do not?). There were left-lateral aftershocks on faults parallel to the San Andreas. The idea (I think) was that most of the expected differential stress was released by the main shock, so that stresses associated with the quake itself could dominate. I would assume this would only have happened over part of the fault. I probably did not read the paper.
Chris