I'm pretty sure Donna Eberhart-Philips is one of you guys; I think she's still with GNS. Here's a nice, short poster that she co-authored re: the TVZ. It's a damn interesting place.

As for your question, Qp is generally considered P-wave attenuation, that is, the rate at which the P-wave dies out. This is generally measured over distance. The lower value for Qp reflects higher attenuation values. So, (here's two disclaimers- I haven't seen her video and I'm not a practicing seismologist) the water will tend to attenuate P-waves. I would imagine they are able to image the amount of water volatilizing off the slab by the P-wave attenuation.

WOW! I simply must go there. Thanks for the link!

Geo, I'm getting my p's and q's muddled up..well that's overstating it..

just watched the USGS video from Eberhard-Philips UC Davis on the TVZ and tried to understand it.. She was talking of all the water coming off the subducted Pacific slab resulting in low Q... what is Q? Is this a seismic signal? (waves moving slowly in water-rich environments?)

.. and is there is still a lot of melt at shallow levels under the TVZ?

NoEnz,

For the most part the slip (at depth) is converted to plastic deformation (folding) near the surface. As the fault slips (earthquake) the fold grows so there actually is deformation at the surface, it's just not discrete but more broadly distributed.

There are a couple types of blind thrust faults, fault propagation folds and fold bend folds. We have both types up here in northern coastal CA. They are also what occur in LA (that was the cause of the Northridge earthquake in 1994) and parts of New Zealand.

Here's a couple of pictures I use to illustrate basic blind thrusts in class. The first is a schematic diagram. The second is from a seismic section in the LA basin. Hopefully you can see the similarities. There's a lot of work being done on these structures right now (part of the reason I'm going to NZ soon).

Hope this helps.



Blind Thrust Schematic




Seismic section (the blue lines are deep wells used to confirm the seismic interpretation).

Geo I have another stupid question:

in a blind thrust earthquake, where do the rocks go? I mean you're not getting any surface rupture but you do have movement along the fault line.. Do the rocks just compress and stretch? I realize we are normally talking about a couple of miles here for them to do it but it still sounds kind of counter-intuitive.

PS thanks for the link to the aftershock.. that's also quite a heavy shake and shallower than the first.

WOW! I simply must go there. Thanks for the link!

The latest quake in Chile was centered in the Atacama Desert. Fortunately a very sparsely populated region and one of the most beautiful places on the planet.

Click through for one of the better slideshows in the net. It's worth it!

Karst topography is a landscape shaped by the dissolution of a soluble layer or layers of bedrock, usually carbonate rock such as limestone or dolomite. These landscapes display distinctive surface features and underground drainages, and in some examples there may be little or no surface drainage. Some areas of karst topography, such as southern Missouri and northern Arkansas in the USA, are underlain by thousands of caves.

think I have to read up on karstic...

There also appears to be quite a lot of weathering expoiting what may be joints and bedding planes in the rock - the course of the stream is very straight. Water (or at least CO2 dissolved in the water to make a very mild acid) moving along such lines would make them stand out. Chemical weathering will also tend to round off and soften features. If they are in a cool enough climate, then freez-thaw might act further on the joints. Although if of a karstic nature, the rock probably wouldn't hold enough standing water.

NoEnz, I'm not sure what's going on. I've looked through several records and have not found these events... curious.

Here's a realtime plot from the IRIS (Incorporated Research Institutions for Seismology) site. Although they get their data from the USGS it is comprehensive and verified. Are you getting your event data from geonet?

Reference Number 2818146/G
Universal Time November 6 2007 at 22:17
NZ Daylight Time Wednesday, November 7 2007 at 11:17 am
Latitude, Longitude 42.10°S, 172.89°E
Focal Depth 60 km
Richter magnitude 5.4