Updates April-August 2012: seismic swarm and tremor in June-July

Deflation recorded, few earthquakes
Update Wed 22 Aug 18:00
Deformation charts of El Hierro (IGN)
Deformation charts of El Hierro (IGN)
So far, only 4 quakes occurred at El Hierro today. In addition, some deflation of about 2 cm has been registered over the past few days, suggesting that magma is withdrawing from under the island.
Update Tue 21 Aug 17:37
Only 5 very weak quakes have been recorded today so far. It seems that the swarm is ending.
Seismic swarm decreasing, but size of quakes increase
Update Mon 20 Aug 14:39
Location of recent quakes under El Hierro (IGN)
Location of recent quakes under El Hierro (IGN)
The seismic swarm at El Hierro continues, but the number of quakes has been decreasing. Yesterday, 8 quakes (all below M2) were recorded and today there have been 5 weak quakes so far. The strength of the earthquakes has however increased, and the latest quake was a M2.7 event at 20 km depth under the western tip of the island.
Update Sun 19 Aug 11:20
Location of the recent earthquake swarm at El Hierro (IG)
Location of the recent earthquake swarm at El Hierro (IG)
The earthquake swarm seems to be ending or is at least decreasing. No quakes have been listed so far for today (although a few seem to be visible on the seismic recording) while there were about 25 small quakes yesterday.
Update Fri 17 Aug 18:29
The swarm continues in the same area at aroud 10 km depth beneath the western El Golfo coast, but seems to be decreasing. Yesterday, 58 quakes occurred, today so far 18 although this number is likely to rise.
Tremor is low.
New seismic swarm at 10 km depth near the coast of El Golfo
Update Thu 16 Aug 12:42
Seismic signal with a cluster of small quakes today (IGN)
Seismic signal with a cluster of small quakes today (IGN)
Location of recent quakes under the El Golfo coast (IGN)
Location of recent quakes under the El Golfo coast (IGN)
A new earthquake swarm has started yesterday just north off the western El Golfo coast. So far, more than 50 (mostly very small around magnitude 1) quakes have been registered since yesterday. The quakes are clustered at around 10 km depth, i.e. only half the distance to the surface than the previous swarms. A small increase in tremor is visible as well.
Update Mon 13 Aug 16:54
A total of 5 earthquakes (between M1.3-2.4) at 10-19 km depth has occurred today so far. This is the highest number in many days.
Slightly increased number of earthquakes, M2.4 quake at 3 km depth on 8 Aug
Update Thu 09 Aug 12:26
Earhtquake locations during the past 2 days under El Hierro
Earhtquake locations during the past 2 days under El Hierro
During the past days, the number of quakes beneath El Hierro has shown an increase. Since 7 Aug, 10 small quakes have been recorded at depths mostly between 10-22 km, i.e. significantly shallower than during the seismic swarm in late June-early July. The largest quake was a M2.4 yesterday at only 3 km depth beneath the western ridge of the island under the Tanganasoga volcanic system.
There is currently no significant tremor signal visible suggesting magma movements.
Update Wed 25 Jul 15:35
Recent quakes on El Hierro (IGN)
Recent quakes on El Hierro (IGN)
El Hierro volcano (Canary Islands, Spain) reported 11 earthquakes today and yesterday mostly SW off the island. This is a significant number compared to the many preceeding days of relative calm.
Seismic swarm with about 50 quakes >M2.5 on 8 July
Update Sun 08 Jul 17:02
Seismic swarm today between 9-13 am UTC (IGN)
Seismic swarm today between 9-13 am UTC (IGN)
Another swarm of earthquakes with about 50 quakes between M2-3.3 occurred today under the Las Calmas Sea SW of El Hierro. The quakes were at depths mostly between 20-25 km, i.e. slightly deeper than most previous quakes and could indicate a new intrusion from depth. Also, the quakes are continuing to migrate now eastwards closer towards the area of the 2011-12 submarine vent south of La Restinga. It is also a clear sign that the seismic crisis on El Hierro is far from over.
Earhtquake locations during the past 2 days, showing the migration eastwards towards the former eruption area
Earhtquake locations during the past 2 days, showing the migration eastwards towards the former eruption area
Seismic activity decreases
Update Sat 07 Jul 15:06
Location of the quakes during the past 48 hours (IGN)
Location of the quakes during the past 48 hours (IGN)
The seismic activity has calmed down since 4 July, after several pulses of intense earthquake activity, sometimes accompanied by an elevated tremor signal, in particular during 29 June - 1 July, and 2-3 July. During 1-7 July, there were 680 earthquakes, mostly between M1.5-3, but also 56 quakes >M3 and 3 larger than M4, the largest a M4.4 on 2 July, were recorded.
The epicenters have remained at about 18-21 km depth at or near the SW tip of the island, suggesting that magma has accumulated there.
Uplift of the island has continued and reached peak values of up to 10 cm total, but also stagnated in the past days.
The next days to weeks will show whether the magmatic process is coming to a halt or continues and still leads to a new eruption.
Activity burst with strong tremor and frequent quakes
Update Fri 29 Jun 15:33
Burst of seismic activity after 12:40 (IGN)
Burst of seismic activity after 12:40 (IGN)
Since 12:40 UTC, a strong tremor signal and many stronger quakes have been recorded. A series of about 10 strong volcanic quakes (probably well >M2.5) occurred between about 13:00-13:10. Magma is moving again, but we have to wait to see the location of the quakes.
As the quakes get listed, it seems that they are in the Las Calmas Sea south of the El Julan coast at about 20 km depth.
Seismic activity decreases
Update Fri 29 Jun 11:09
Decreasing seismic activity (IGN)
Decreasing seismic activity (IGN)
Depth of quakes during the past 10 days (AVCAN)
Depth of quakes during the past 10 days (AVCAN)
Since about 2am today, the seismic activity has dropped markedly. Quakes continue, but at lower rate and most of them are weak (
Animated visualization of the hypocenters of the recent earthquake swarm (www.avcan.org)
New shallower quakes (16 km), press release (PEVOLCA) admits strong deformation of up to 5 cm
Update Thu 28 Jun 18:29
Some of the latest quakes were measured at 16 km depth. It becomes clearer and clearer that some magma has probably started to rise!

A new press release by the government admits that deformation of the island due to magma pressure is strong. It was kindly translated by Earthquake-Report:

"We have observed a deformation of the entire island. The center of the deformation originates in the present earthquakes area (see below)
The energy release and ground deformation show an acceleration of the active magmatic process on the island of El Hierro, according to information forwarded by the National Geographic Institute at the direction of the Civil Protection Plan for Volcanic risk (PEVOLCA)
The GPS network solution, measuring the surface strain on the island shows that there is a clear process of inflation, marking an apparent center of pressure in the area where the seismicity is located. The total cumulative displacement from 24 June to 24 hours yesterday, is about 3-4 cm in the horizontal components and 4-5 cm in the vertical component.
Since the beginning of the new magmatic process on June 24, there have been over 750 earthquakes. An earthquake with a Magnitude 4.0, occurred yesterday at 18:55 pm in the Las Calmas Sea, 2 km from the coast and 20 km deep.
Be remembered as the seismicity started in the El Golfo bay, then moved to the center of the island, coinciding with the point of intersection of the ridges, and later migrated to the west. Since the 25th of June the seismicity is concentrated in the west and El Julan. From 12:00 hours. On 27th of June, seismicity began to migrate towards the Las Calmas sea."
Quakes continue, often depths now at 17 km
Update Thu 28 Jun 16:20
Location of earthquakes today since 09:00 (AVCAN)
Location of earthquakes today since 09:00 (AVCAN)
Seismic recording (IGN) showing frequent quakes and a phase of elevated tremor (IGN)
Seismic recording (IGN) showing frequent quakes and a phase of elevated tremor (IGN)
The intense quake swarm continues underneath the El Julan coast, with about 90 quakes > M1.5 so far today. Some of the quakes are now measured to be at 17 km rather than 19-20 km depth. It could indicate a weak trend of magma rising, but as for now, it is not very clear.
Tremor is mostly relatively low, but increases in phases typically lasting a few hours before decreasing again.
Update Thu 28 Jun 07:18
Location of quakes during the first 3 hours on 28 June (AVCAN)
Location of quakes during the first 3 hours on 28 June (AVCAN)
Ongoing quakes but low tremor signal on 28 June
Ongoing quakes but low tremor signal on 28 June
Earthquakes continue, but at slightly lower rate. In the first 3 hours, 19 quakes >M1.5 were recorded by IGN, all at 18-19 km depth beneath the El Julan coast.
Tremor is low, suggesting magma might be blocked in this area for the time being.
Total earthquakes on 27 June: 197 above M1.3, most of them between M2-3, one at M4 which was felt by most people on the island. Quake depths still at 20 km.
Quakes migrate southwards into Las Calmas Sea
Update Wed 27 Jun 20:09
Seismic signal on 27 June (IGN)
Seismic signal on 27 June (IGN)
Location of the latest quakes (AVCAN)
Location of the latest quakes (AVCAN)
Earthquakes are still at 20 km depth and continue at high rate (more than 150 >M1.5 today, mostly larger than M2). Accompanied by harmonic tremor, their location is migrating southwards into the Las Calmas Sea. In other words, magma continues to move southwards and the question is whether or not it will at some point start rising to the surface.
Strong deformation detected, yellow alert for El Julan area
Finally, INVOLCAN has published the important information that during the last 2 days significant and rapdid inflation was measured in the southern part of the island: At the El Pinar station, there has been horizontal eastward displacement of 2 cm and northward of 3 cm. The vertical displacement was 2 cm.
This deformation is most likely caused by the accumulating magma underneath, and it is much faster than those observed last year 2011 prior to the eruption south of La Restinga.
A "yellow alert" has been declared for the El Verodal or the western tip of the island and the southern area in the El Julan bay, where most quakes are located, and an eruption could be imminent.
Quakes continue beneath the El Julan coast
Update Wed 27 Jun 10:11
Location of the latest quakes since midnight (AVCAN)
Location of the latest quakes since midnight (AVCAN)
The quakes continue; up to now, 60 quakes (most of them between M2-3) were recorded and listed by IGN, still at around 20 km depth and in the EL Julan area. Tremor has decreased but is still present. Apparently, magma keeps moving somewhere.
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