[Geology2] New Seismic unrest at El Hierro Island (Canary Islands) from 9-13 to 9-16

Seismic unrest at El Hierro Island (Canary Islands) in 2011-12: updates

Update Sun 16 Sep 14:35

Current seismic signal (IGN)

The activity has been calming down, but it is probably to early to say that the swarm is over. IGN lists about 100 quakes (including smaller ones below M2) for today, the largest being a M3 at 08:48 about 3 km NW of El Pinar at 19 km depth.

Update Sun 16 Sep 11:48

The seismic swarm continues. Yesterday, a total of 167 quakes were registered and there are 50 so far during the first 5 hours of today. Most quakes are in the south-central part of the island at about 22 km depth and around magnitudes 2-2.6.

location of recent quakes (red=past 24 hours)

First earthquakes > magnitude 3

Update Sat 15 Sep 17:26

The increasing trend of quakes continues and the first quake above magnitude 3 has was recorded at 13:13 local time near El Pinar at 23 km depth. People around El Pinar might be starting to feel some of the quakes.

The M 3.2 quake near El Pinar today 13:13

Swarm continues - 88 earthquakes so far

Update Sat 15 Sep 14:32

The image below shows the quakes during the past 48 hours (red) and older ones from last week in yellow. The most recent quakes are in the southern part of the cluster, near El Pinar. The latest quake (with marker on map) was again a 2.8 event. The magnitudes are gradually increasing.

Location of recent quakes at El Hierro

Update Sat 15 Sep 13:57

The new seismic swarm continues with a high frequency of quakes and a weak tremor signal. So far, there have been more than 80 earthquakes today, mostly between magnitudes 2-2.8 at 20 km depth beneath the central part of the island (Tanganasoga volcanic vent area). There is a trend of a southward migration and increasing magnitudes as well. 

The strongest earthquake was a M2.8. The depth of the epicenters is still in the ""safe" area between 17 to 23 km, and the quakes are hardly felt at this stage. 

As the southwards migration of the quakes becomes more visible, the most plausible interpretation is that magma is moving in the underground this way, using fractures in the rock. Earthquakes are created when magma opens new fractures at depth. The more pressure it takes to open new paths, the larger the magnitude of the earthquake needed. At the moment, most quakes are beneath the El Pinar area. 

Vertical deformation values seem to be going up slightly at the Pinar and Restinga stations, but this needs to be confirmed. 

So far, there are no official statements from IGN, Involcan, Iter and Pevolca (who combines all of them), but if the seismic crisis increases, there will likely be one very soon.

Current seismic signal (IGN)		Location of recent quakes (IGN)

New seismic swarm with tremor under the central part of the island

Update Sat 15 Sep 01:04

A new seismic swarm with so far more than 50 quakes during the past 12 hours or so is under way. The quakes (mostly around magnitude 2) are located in the central part of the island at about 20 km depth and there is a tremor signal visible as well. Deformation measurements show no change (inflation or deflation).

Current seismic signal (IGN)		Current earthquakes (red) under the central part of the island

Update Fri 14 Sep 15:22

The current seismic swarm continues with 15 earthquakes so far today. The intensity has increased as well, most quakes are now between magnitudes 1-2 (while most were 0-1 during the past days). Another new observation is that a weak tremor signal is now visible, suggesting that there could be some (small) movement of magma. 

A third news is that the quakes are now clustered in 2 zones: one is where most recent quakes were before, at about 10 km depth beneath the western El Golfo bay, the second, new focal area is at about 20 km depth beneath the central part of the island. 

Time and depth of recent quakes		Location of recent quakes
Seismic signal showing some small earthquakes (IGN)		Spectrogram of current seismic signal showing a weak tremor signal (IGN)

Update Thu 13 Sep 10:00

The frequency of quakes has strongly increased today and it might be called a new swarm. There have been 10 quakes so far, in the western El Golfo area at 10 km depth.

Earthquake depth distribution over the past 3 days

Update Tue 11 Sep 16:58

The number of quakes remains elevated. There were 19 yesterday and 10 today so far. The quakes are mostly in the same area of the western El Golfo Bay at about 10 km depth.