The earthquake registered at 10:59:54 UTC (coordinates 27.7110, -18.2727) : magnitude 4.9 mbLg according to IGN. It is the largest since the beginning of the activity ... in 2011!
Computed depth is 20 km.
As usual in such cases, the website of the IGN is currently overloaded.
Sunday, March 31, 2013
Friday, March 29, 2013
Fictional El Hierro...
A bit of geological fiction (or not?)
Imagine you want to push a whole volcano up. Now imagine that, instead of a typical, conical volcano, the volume is more complex and globally looks like a triangle, like, for instance, say, El Hierro.
If you mentally divide a island like that using a North/South line, it is obvious that the amount of mass in the West part is much less than the amount of mass in the East part. Take into account that the overall high is 4 km above the see bottom in the area. This is a lot to move.
If then the pressure centre is near the centre and a bit westwards from this N/S line, then it is probable that the West part will move more than the East part. Less mass in this area means it is "easier" to move. After a certain time, it is probable that a break-up will occur, around that North/South line, with lots of earthquakes, then propagating outwards. Now, if the West part continues to go up faster than the East part, a constraints field will start to build-up, and after a while this constraints field will need to be relaxed.
This new activity will start where the constraints are maximized, so near the centre of pressure. Then, this will propagate outwards. For an analogy, try to bend a plank of wood, you'll see cracks occurring. This cracks can happen everywhere, but will preferentially occur near a point of previous failures.
Now, the triangular shape is supposed to be a triple-junction set-up, and one branch extends in the North-West direction. So, cracks will propagate in that direction.
After a while, the cracks will reach a distance where the field of constraints no longer propagate outwards, but rather propagates laterally at the same distance from the pressure centre.
However, there are less pre-existing failures because now the activity is moving outside of the old failure area. The constraints needed to break the rocks are higher, and instead of frequent, but lower intensity earthquakes, you get less frequent, but more powerful ones.
By the way, magma is probably following the cracks...
Sounds familiar?
Imagine you want to push a whole volcano up. Now imagine that, instead of a typical, conical volcano, the volume is more complex and globally looks like a triangle, like, for instance, say, El Hierro.
If you mentally divide a island like that using a North/South line, it is obvious that the amount of mass in the West part is much less than the amount of mass in the East part. Take into account that the overall high is 4 km above the see bottom in the area. This is a lot to move.
If then the pressure centre is near the centre and a bit westwards from this N/S line, then it is probable that the West part will move more than the East part. Less mass in this area means it is "easier" to move. After a certain time, it is probable that a break-up will occur, around that North/South line, with lots of earthquakes, then propagating outwards. Now, if the West part continues to go up faster than the East part, a constraints field will start to build-up, and after a while this constraints field will need to be relaxed.
This new activity will start where the constraints are maximized, so near the centre of pressure. Then, this will propagate outwards. For an analogy, try to bend a plank of wood, you'll see cracks occurring. This cracks can happen everywhere, but will preferentially occur near a point of previous failures.
Now, the triangular shape is supposed to be a triple-junction set-up, and one branch extends in the North-West direction. So, cracks will propagate in that direction.
After a while, the cracks will reach a distance where the field of constraints no longer propagate outwards, but rather propagates laterally at the same distance from the pressure centre.
However, there are less pre-existing failures because now the activity is moving outside of the old failure area. The constraints needed to break the rocks are higher, and instead of frequent, but lower intensity earthquakes, you get less frequent, but more powerful ones.
By the way, magma is probably following the cracks...
Sounds familiar?
El Hierro; major earthquake: mbLg 4,7
A major earthquake was detected near El Hierro today at 17h10 UTC. More info later.
El Hierro, set of huge earthquakes today
Since 21h50 UTC, a set of powerful earthquake are occurring near El Hierro.
Short summary:
Fortunately, they are located in the same area, at deep depth, so no serious danger for the people there.
Hope they will be able to sleep tonight!
Short summary:
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| Data © IGN |
Hope they will be able to sleep tonight!
Wednesday, March 27, 2013
El Hierro: what a day !
The activity is amazing today. For the first time since long ago, multiple earthquakes with a magnitude greater than 4 were recorded in a very short period. This activity continues so far with no end in sight.
Other earthquakes with lower magnitude were recorded as well. They are too numerous to be displayed here.
The interesting point also, is that the evolution is rather scary, as more higher magnitude are recorded as time passes:
At the beginning, few earthquake with a magnitude greater than 3 were recorded (see the lack of purple bars). Now even magnitude 4 and above are becoming common.
Fortunately, the activity is located far at see:
There is also a tendency of the last earthquake to move a bit south. We'll see later if this is confirmed.
Stay tuned !
 |
| © IGN |
The interesting point also, is that the evolution is rather scary, as more higher magnitude are recorded as time passes:
 |
| © IGN |
Fortunately, the activity is located far at see:
 |
| © IGN |
There is also a tendency of the last earthquake to move a bit south. We'll see later if this is confirmed.
Stay tuned !
Update 22h00 UTC
The situation forced the PEVLCA to raise the alert level to yellow for the western part of the island.Tuesday, March 26, 2013
El Hierro follow-up, restarted
I'll restart the follow-up concerning the seismic activity on El Hierro, and time permitting, other informations.
I'll try to translate the other posts from my French blog, when appropriate.
I'll try to translate the other posts from my French blog, when appropriate.
Wednesday, September 19, 2012
El Hierro update
Updated (18:00 UTC)
This value is normal again. To be continued...
Potentially important update (17:20 UTC)
The concentration of sulfur dioxide (SO2), as measured by the mobile station located at La Restinga, rose sharply to nearly 900 micrograms per cubic meter (µg/m3). This value is more than 100 times the usual value.
It can be a technical problem. If this is not the case, the source of this increase must be determined and analyzed, as if it is of volcanic origin, the risk of eruption increases significantly (it is a known precursor).
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