[KathyKeegan]

Is that close enough to India yet? It just had a 4.9 southwest of India.

[Skywise]

(05-18-2015, 06:48 AM)KathyKeegan Wrote: Is that close enough to India yet? It just had a 4.9 southwest of India.

If you're asking, is the quake on the Carlsberg Ridge related to the Nepal quake? Nothing wrong with questions. It's how we learn.

But really, no relation. It's over 2,000 miles away.

The Carlsberg ridge is a spreading center where the crust pulls apart and mantle magma wells up to form new crust. Quakes like this are pretty typical of mid ocean ridges. They can get quite big, too, especially along all the transform faults that break up the ridge line.

The Nepal quake, and the Himalaya in general, are on the other side of the Indian Plate. The tectonics there are cause by the subduction of the plate. It's a whole different ball game.

This picture is from: http://en.wikipedia.org/wiki/Mid-ocean_ridge


The quake you ask about would be on the ridge in the center of the diagram, whereas the Nepal quakes and Himalaya are on either of the trenches off to the side - on the other side of the tectonic plate they are on.

Brian

[KathyKeegan]

(05-18-2015, 09:51 PM)Skywise Wrote:

(05-18-2015, 06:48 AM)KathyKeegan Wrote: Is that close enough to India yet? It just had a 4.9 southwest of India.

If you're asking, is the quake on the Carlsberg Ridge related to the Nepal quake? Nothing wrong with questions. It's how we learn.

But really, no relation. It's over 2,000 miles away.

The Carlsberg ridge is a spreading center where the crust pulls apart and mantle magma wells up to form new crust. Quakes like this are pretty typical of mid ocean ridges. They can get quite big, too, especially along all the transform faults that break up the ridge line.

The Nepal quake, and the Himalaya in general, are on the other side of the Indian Plate. The tectonics there are cause by the subduction of the plate. It's a whole different ball game.

This picture is from: http://en.wikipedia.org/wiki/Mid-ocean_ridge


The quake you ask about would be on the ridge in the center of the diagram, whereas the Nepal quakes and Himalaya are on either of the trenches off to the side - on the other side of the tectonic plate they are on.

Brian

Ok, do the mid ocean ridges usually have such a cocktail party as they are having now? Mid Atlantic, South Atlantic, Mid Indian, North Pacific, West Chile Rise, somewhere south of Tonga, Western Indian-antarctic Ridge, the Galapagos, are all reeling around as if drunk on their ass in numbers as high as mid to upper 5's in some cases. It's just that they seem to be adjusting to the big ones in Nepal with some staggering around themselves. I'm not talking about the volcanoes puffing away this time.

[KathyKeegan]

(05-25-2015, 11:13 PM)KathyKeegan Wrote:

(05-18-2015, 09:51 PM)Skywise Wrote:

(05-18-2015, 06:48 AM)KathyKeegan Wrote: Is that close enough to India yet? It just had a 4.9 southwest of India.

If you're asking, is the quake on the Carlsberg Ridge related to the Nepal quake? Nothing wrong with questions. It's how we learn.

But really, no relation. It's over 2,000 miles away.

The Carlsberg ridge is a spreading center where the crust pulls apart and mantle magma wells up to form new crust. Quakes like this are pretty typical of mid ocean ridges. They can get quite big, too, especially along all the transform faults that break up the ridge line.

The Nepal quake, and the Himalaya in general, are on the other side of the Indian Plate. The tectonics there are cause by the subduction of the plate. It's a whole different ball game.

This picture is from: http://en.wikipedia.org/wiki/Mid-ocean_ridge


The quake you ask about would be on the ridge in the center of the diagram, whereas the Nepal quakes and Himalaya are on either of the trenches off to the side - on the other side of the tectonic plate they are on.

Brian

Ok, do the mid ocean ridges usually have such a cocktail party as they are having now? Mid Atlantic, South Atlantic, Mid Indian, North Pacific, West Chile Rise, somewhere south of Tonga, Western Indian-antarctic Ridge, the Galapagos, are all reeling around as if drunk on their ass in numbers as high as mid to upper 5's in some cases. It's just that they seem to be adjusting to the big ones in Nepal with some staggering around themselves. I'm not talking about the volcanoes puffing away this time.

http://earthquakestoday.info/

[KathyKeegan]

(05-25-2015, 11:24 PM)KathyKeegan Wrote:

(05-25-2015, 11:13 PM)KathyKeegan Wrote:

(05-18-2015, 09:51 PM)Skywise Wrote:

(05-18-2015, 06:48 AM)KathyKeegan Wrote: Is that close enough to India yet? It just had a 4.9 southwest of India.

If you're asking, is the quake on the Carlsberg Ridge related to the Nepal quake? Nothing wrong with questions. It's how we learn.

But really, no relation. It's over 2,000 miles away.

The Carlsberg ridge is a spreading center where the crust pulls apart and mantle magma wells up to form new crust. Quakes like this are pretty typical of mid ocean ridges. They can get quite big, too, especially along all the transform faults that break up the ridge line.

The Nepal quake, and the Himalaya in general, are on the other side of the Indian Plate. The tectonics there are cause by the subduction of the plate. It's a whole different ball game.

This picture is from: http://en.wikipedia.org/wiki/Mid-ocean_ridge


The quake you ask about would be on the ridge in the center of the diagram, whereas the Nepal quakes and Himalaya are on either of the trenches off to the side - on the other side of the tectonic plate they are on.

Brian

Ok, do the mid ocean ridges usually have such a cocktail party as they are having now? Mid Atlantic, South Atlantic, Mid Indian, North Pacific, West Chile Rise, somewhere south of Tonga, Western Indian-antarctic Ridge, the Galapagos, are all reeling around as if drunk on their ass in numbers as high as mid to upper 5's in some cases. It's just that they seem to be adjusting to the big ones in Nepal with some staggering around themselves. I'm not talking about the volcanoes puffing away this time.

http://earthquakestoday.info/

Ok, I missed the story about the volcano in the Galapagos till just now.

[Skywise]

(05-25-2015, 11:13 PM)KathyKeegan Wrote: Ok, do the mid ocean ridges usually have such a cocktail party as they are having now?

I've been staring at the quake maps daily (usually several times a day) for going on 20 years. I personally don't see anything out of the ordinary. But perhaps I'm missing something.

Why do you think the activity that's occurring is unusual? I turn the question around for two reasons - one so I can understand what you're thinking, and two for you to justify your reasoning. It's a good exercise to question yourself once in a while. Think of it as a teacher questioning the student.

Maybe a simple statistical analysis is in order. Roger? You've been quiet lately. Anything you can tell us? You'd have to create bounding boxes for all the ridges. If you're not busy.

Brian

[Island Chris]

I also don't see anything unusual at the ridges or anywhere else. I also have been looking at global seismicity daily for more than 20 years (probably almost 30 years), but not in a scientific way. Indeed, Roger has capability to graph earthquake occurrence at Ridges over time: could be M4/4+ or M5.0+. But, sounds like a lot of work for him, and I doubt it is worth his time at this time (but of course he will do it if he wants).

There are quakes that are obviously related to each other: Nepal M7.3 time was advanced by Nepal M7.8, and I posted on the swarms of M7 quakes at 2 locations on same subduction zone (New Britain in NW; I forget for the SE).

Just pointing out earthquakes without some context on why they are interesting/related soon becomes background noise to me.

Chris

[KathyKeegan]

(05-18-2015, 06:48 AM)KathyKeegan Wrote: Is that close enough to India yet? It just had a 4.9 southwest of India.

I just was thinking that if there was an increase in quakes around the plate that is shoving Nepal into China it would have to have repercussions both on the ridges and boundaries of plates elsewhere. There is no action without reaction sort of thing.

[Skywise]

(05-26-2015, 10:04 PM)KathyKeegan Wrote:

(05-18-2015, 06:48 AM)KathyKeegan Wrote: Is that close enough to India yet? It just had a 4.9 southwest of India.

I just was thinking that if there was an increase in quakes around the plate that is shoving Nepal into China it would have to have repercussions both on the ridges and boundaries of plates elsewhere. There is no action without reaction sort of thing.

There is something known as the elastic rebound theory which explains how stresses build in the Earth's crust along a fault line and are then released. Here's a couple of videos:







As you can see the ground deforms as the stress builds up, and springs back during the earthquake. Just like a pebble in a pond, when the ground snaps back (the earthquake), ripples spread out. These are the earthquake waves, the ground motions that we feel.

The area of deformation is local to the fault zone. So is the area of rebound after the quake. This deformation can be measured using something called InSAR (Interferometric Synthetic Aperture Radar), usually done with satellites. The resulting images show how the ground shifted during the quake. Here's an InSAR image of the Nepal quake:


from: http://www.travelinggeologist.com/2015/0...ke-searle/

The tight rings represent the area of ground displacement resulting from the quake. As you can see, it's concentrated in the local region where the fault slipped. There is some slight change at a distance, but some of this can be due to causes other than the quake. InSAR is amazingly sensitive. But looking at the map, the maximum displacement is near Kathmandu and by the time you move south to Hetauda, things are still normal. That's only a distance of 27 miles.

On the other hand, there is the idea of faults being affected by the passing earthquake waves and that has been studied. But that's an effect that occurs within minutes or hours after the quake.

Now, that isn't to say that the stress field doesn't have an effect. For example, here is the resulting cumulative stress field from the Landers (M7.3) and Hector Mine (M7.1) earthquakes in the southern California deserts. I then plotted on the map the locations of larger quakes in the years afterward. The red areas represent locations where ground stress has increased; blue is lower stress. As you can see, nearly all the quakes occurred in areas of increased stress.


from: http://www.skywise711.com/quakes/index.html#8

I made that image more than five years ago so it doesn't show more recent quakes.

It is widely conjectured that the Hector Mine quake was triggered by the Landers quake seven years earlier. The epicenter of Hector Mine is smack in the middle of a high stress lobe from the Landers quake. But again, this is within tens of miles.

Basically, the 'stress field' from a quake doesn't go far enough to affect faults thousands or even hundreds of miles away. The change in the stress field is just too small. The Earth's crust just isn't that solid. At these scales, rock is almost "spongy". Imagine pressing your finger into a sponge on one side. The other side doesn't deform.

Brian

[KathyKeegan]

(05-26-2015, 11:24 PM)Skywise Wrote:

(05-26-2015, 10:04 PM)KathyKeegan Wrote:

(05-18-2015, 06:48 AM)KathyKeegan Wrote: Is that close enough to India yet? It just had a 4.9 southwest of India.

I just was thinking that if there was an increase in quakes around the plate that is shoving Nepal into China it would have to have repercussions both on the ridges and boundaries of plates elsewhere. There is no action without reaction sort of thing.

There is something known as the elastic rebound theory which explains how stresses build in the Earth's crust along a fault line and are then released. Here's a couple of videos:







As you can see the ground deforms as the stress builds up, and springs back during the earthquake. Just like a pebble in a pond, when the ground snaps back (the earthquake), ripples spread out. These are the earthquake waves, the ground motions that we feel.

The area of deformation is local to the fault zone. So is the area of rebound after the quake. This deformation can be measured using something called InSAR (Interferometric Synthetic Aperture Radar), usually done with satellites. The resulting images show how the ground shifted during the quake. Here's an InSAR image of the Nepal quake:


from: http://www.travelinggeologist.com/2015/0...ke-searle/

The tight rings represent the area of ground displacement resulting from the quake. As you can see, it's concentrated in the local region where the fault slipped. There is some slight change at a distance, but some of this can be due to causes other than the quake. InSAR is amazingly sensitive. But looking at the map, the maximum displacement is near Kathmandu and by the time you move south to Hetauda, things are still normal. That's only a distance of 27 miles.

On the other hand, there is the idea of faults being affected by the passing earthquake waves and that has been studied. But that's an effect that occurs within minutes or hours after the quake.

Now, that isn't to say that the stress field doesn't have an effect. For example, here is the resulting cumulative stress field from the Landers (M7.3) and Hector Mine (M7.1) earthquakes in the southern California deserts. I then plotted on the map the locations of larger quakes in the years afterward. The red areas represent locations where ground stress has increased; blue is lower stress. As you can see, nearly all the quakes occurred in areas of increased stress.


from: http://www.skywise711.com/quakes/index.html#8

I made that image more than five years ago so it doesn't show more recent quakes.

It is widely conjectured that the Hector Mine quake was triggered by the Landers quake seven years earlier. The epicenter of Hector Mine is smack in the middle of a high stress lobe from the Landers quake. But again, this is within tens of miles.

Basically, the 'stress field' from a quake doesn't go far enough to affect faults thousands or even hundreds of miles away. The change in the stress field is just too small. The Earth's crust just isn't that solid. At these scales, rock is almost "spongy". Imagine pressing your finger into a sponge on one side. The other side doesn't deform.

Brian

Ok, thanks for taking the time to explain it.