Category: Earthquakes

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Earthquakes in Iceland, a short overview

I have seen a lot of people worrying about earthquakes and earthquake swarms that take place in Iceland on regular basic. Those worries are not needed as Iceland gets about one to two earthquake swarms on average over the course of one week. Most of the earthquakes that take place in Iceland are tectonic in nature. There are also volcano related earthquakes. But they can be spotted by there location in connection with the volcano in question (Katla, Grímsfjall, etc..).

The reasons for the earthquake swarms in Iceland is geological and is because Iceland sits on a rift zone. This can be shown clearly on this picture here.


Click on picture to get better resolution.

This map clearly shows all the zones in Iceland. In this areas most of Iceland earthquakes happens. But also a big part of Iceland earthquakes happen in areas like SISZ and TFZ.

On the normal week there are about 150 to 400 earthquakes in Iceland over the week. Most of them are in the size ML0.0 and up to ML2.8. Most week have one or two earthquakes that are ML3.0 to ML3.8 in size. On a quiet week there are about 50 to 100 earthquakes, most of them less then ML2.5 in size. When there is a busty week in Iceland the earthquakes numbers can easily go over 2000 and sometimes well over 5000 earthquakes. When that happens IMO doesn’t even bother in classifying and locating all the earthquakes that take place. But they are saved anyway in IMO database.

Picture taken from this blog: Earthquake in Iceland (2008); This blog has more images about the tectonic process in Iceland.

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A ML3.4 earthquake at Grímsfjall volcano

At 03:19 UTC there was a ML3.4 earthquake at 2,5km depth at Grímsfjall volcano according to the automatic SIL system that Icelandic Met Office has. This earthquake does not appear to be a after effect of the ML4.0 earthquake at Blöndulón few moments before that. Currently there have not been any other earthquake in Grímsfjall volcano. But that might change soon if this is a start of a eruption in Grímsfjall volcano. But it is going to take few moments to be clear on what is happening.

Currently there are no indicators that a eruption is starting in Grímsfjall volcano.

Update!

This earthquake was when reviewed size ML2.3 at the depth of 2.8 km.

Text updated at 14:40 UTC on the 31st of October 2010.

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Magnitude ML4.0 earthquake hits Blöndulón

Over the past few days (since 26th of October 2010) there have been earthquakes happening at Blöndulón. This earthquakes are intraplate earthquakes and it unclear why these earthquakes are happening.

At 02:35 UTC a earthquake with the size of ML4.0 did hit Blöndulón according to automatic SIL system that Icelandic Met Office has. So far this is the strongest earthquake to hit this area since the earthquake swarm did start. This earthquake appears to be a start of new earthquake sequence in this area. But several smaller earthquakes have happened as a result of the ML4.0 earthquake. The depth of the main earthquake was 1km. I do expect that it was felt in nearby farms that are closest to Blöndulón.

I am expecting more earthquakes in this area over the next few days. It remains to be seen if they grow in size or not.

Update!

When reviewed the size of this earthquake was ML3.8 at the depth of 21.1 km.

Text updated at 14:41 on the 31st of October 2010.

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More intraplate earthquakes north of Langjökull / Hofsjökull volcanoes

Earlier this night (around 19:19 UTC 28th of October) more intraplate earthquake did start happening north of Langjökull / Hofsjökull volcanoes. The earthquakes are in the same place as before. But please see my earlier post for information about the earlier earthquake swarm at the same location.

Currently it seems that the earthquake swarm is growing in size and frequency of earthquakes. But the earthquakes appears clearly on my Hvammstangi station. The web page for my geophones can be viewed here. The distance of this earthquakes from my Hvammstangi station is about 40 to 80 km. But no more then that I think.

So far all the earthquakes have been less then ML3.0 in size. But if the swarm gets stronger that might change with out any warning. This area of Iceland is unpopulated so it is unlikely that anyone is going to feel those earthquakes at current size levels.

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Strong earthquake swarm on Reykjanes Ridge

Few moments ago (around 20:15 UTC) a strong earthquake swarm started on Reykjanes Ridge. This earthquake swarm is deep on the Reykjanes Ridge. Strongest earthquakes so far are ML3,1 on Reykjanes Ridge.

I am going to post updates as the swarm progresses. Some of the earthquakes can be seen on my webicoders here. But the distance is great so only strongest earthquakes are going to appear there.

Update at 21:06 UTC.

EMSC reports that the strongest earthquake was Mb4.8 while USGS is reporting that earthquake at Mb4.9 in size. The earthquake activity in this area is ongoing when this is written.

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Earthquakes in Esjufjöll volcano

There is always surprises in Iceland once in a while when it comes to volcanoes. This evening there was one. This time for a little known volcano named Esjufjöll. But since the year 2002 there have been regular earthquake swarms in Esjufjöll volcano since that year. But this indicates that magma is pushing up the volcano. But it is quite hard to know if that is going to lead to a eruption. It might happen. But so far nothing indicates that it is going to do so at present time.

Here (Week 43 also) are details of the earthquakes in Esjufjöll in the year 2002. But this earthquake activity in 2002 lasted until week 45 (a small earthquake swarm was also in Week 51) before it stopped completely.

So far this are the years that earthquake swarms have happened in Esjufjöll volcano. The year 2002 (swarms, see links above), 2006 (minor swarm, see here), 2008 (small swarm, see here), 2009 (small swarm, see here), 2010 (small swarm ?). Currently the only thing to do now is to wait and see what happens with the 2010 earthquakes in Esjufjöll. But this is unlikely to lead to a eruption. But with volcanoes with rather unknown eruption history it is hard to know for sure.

Last suspected eruption in Esjufjöll took place in 1927 on 5th of September (+- 5 days). But that is unclear eruption as it was not seen and did only create a minor glacier flood. This information is from Global Volcanism Program and can be found in the link at the top.

There is a web camera online that points to Esjufjöll, it can be viewed here.

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Deep earthquake in Katla volcano

Yesterday (18th October 2010) at 03:34 UTC there was a deep earthquake under Katla volcano. This earthquake was on a 14,8 km depth and had the size of ML0.7 according to reviewed earthquake data from IMO (this is too small for my Hekla geophone to detect at this distance). This was a single earthquake and does not indicate anything special at current time. However this earthquake might possibility signal a change inside Katla volcano and might be a start of a longer process that is in the end going to lead to a eruption in Katla some time in the future.

Currently it is unclear how the path to volcano eruption starts in Katla. But in 1918 there where no instruments to record that eruption.

This type of deep earthquake have sometimes created harmonic tremor signals in Katla volcano. But that happens due to dike event inside the volcano. This has happened regularly over the last few years. But has not been big enough to start a eruption.


Picture of the earthquake as it appears on IMO web site in the “EWIS (Icelandic)” that IMO has. Currently this earthquake is not on the weekly reviewed charts.

This is not the only earthquake that has been happening in Katla volcano over the past few weeks.


Week 41 earthquakes in Mýrdalsjökull and Eyjafjallajökull volcanoes.

The wait for Katla eruption is going to end one day. But that day is not today far as I know so far.

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How to spot a earthquakes on my helicorders

Many people don’t know how to spot a earthquakes on my helicorders web site (you can view it here). Here is a quick how-to. The earthquake used is a Mw6.3 earthquake that did happen in 2008 in Iceland.


The second the earthquake did hit the sensor. The green line is when the power did go down in my apartment, just moment before the earthquake. Before that you can see background noise. That is people, cards and stuff like that. The earthquake is the big black-red line on the helicorder. After that you see smaller earthquakes happening (mag 3+ in size). This Hvammstangi geophone


Same earthquake, different location. This station actually was low-gain at the time of the earthquake. But meant that it was less sensitive to smaller earthquakes then larger. But the aftershock can be seen clearly on the helicorder at the time.


This is how my earthquake computer screen looked like at the time. The top line is currently not in use, as it is for a long period seismometers and I was just testing it at the time (it is also unclear on the signals as can be seen). The second and the third line in use is my geophone. But it clearly showed the earthquake and all it’s waves.


The Mosfellsbær station. That I had connection to at the time. But this is rather crazy view, as this is earthquakes and it is a lot of earthquakes in short space of time. I soon gave up trying to collect them.


This is how I finally work out the earthquakes. I put in location and depth from IMO data, as I can’t plot them my self.

I hope that this examples help people to see when there is a earthquake on my helicorder and just noise from human movement. Harmonic tremors are different and so far I have not been able to get any good example of it. But during the Eyjafjallajökull eruption a wind was problematic and I was unsure if I was recording wind into the harmonic tremors of that eruption or not. So that is going to have to wait a better time.