Irish Earthquake

 Earthquakes  1 Response »
May 072010
 

An interesting event in the world of seismology yesterday, an Irish earthquake. The British Geological Survey report a magnitude 2.7 tremor felt in County Clare yesterday evening.

Irish earthquakes are as rare as hen’s teeth, which is really quite curious. The geology of Ireland is very similar to that of the rest of the British Isles and many of the geological structures in the UK can be traced into the Republic. However, whilst Great Britain has a modest level of seismicity, ‘Lesser’ Britain virtually has none.

Historical seismicity of the UK (yellow) from 1832 to 1970 for earthquakes of magnitude above 3.0 and instrumental seismicity (red) from 1970 to present for earthquakes with ML >2.0. Source BGS

Image source BGS.

One of the most sensible reasons for the lack of Irish earthquakes is that St Patrick banished them from Ireland at the same time he banished the snakes!

 Posted by hypocentre at 17:07  Tagged with:

Gnosall, Staffordshire Earthquake M1.3 20/04/2010

 Earthquakes  Comments Off
Apr 202010
 

An intriguing little earthquake from the south of the county this morning, a magnitude 1.3 tremor southwest of Gnosall (west of Stafford). This is the recording from Keele University.

The region is underlain by Mercia Mudstone so it could be salt collapse related, but most of the salt extraction is the other side of Stafford. Nearby is the enigmatically named “Coal Pit Bank Coverts” but there are no mines to my knowledge at the ‘pit’ is almost certainly a ‘marl-hole’ (marl being spread on the local fields to aid agriculture).

The ‘quake does lie between the epicentres of the Dudley 2002 M4.7 and the Stafford 1916 M4.6 earthquakes so could be related to a structure running north-south between the two, possibly an extension of the Malvern Line, but this event has been located very shallow by the BGS where as the larger events were at about 10km down.

Update: The BGS in their infinite wisdom have relocated the event to northeast of Gnosall and upped the magnitude to 1.4. However, the geology is broadly similar and most of the above comments still hold.


View Gnosall Quake in a larger map

 Posted by hypocentre at 15:13  Tagged with:

Qinghai Earthquake M6.9 13/04/2010 Recorded at Keele

 Earthquakes  Comments Off
Apr 142010
 

Another large earthquake recorded on our seismometer overnight, this time from Southern Qinghai in China, with a magnitude of 6.9. In common with the a few earthquakes we have recorded recently, because one of the nodal planes of the source (which I’m guessing to be the fault plane at the minute) is directed towards us here at Keele, the P-wave is nodal so we don’t see it well (it should arrive at about 40 seconds past midnight on the 14th here). We do, however, see the S-wave and the Love and Rayleigh wave trains quite well.

More details from the USGS here.

Recorded as part of the UK School Seismology Project.

 Posted by hypocentre at 07:55  Tagged with:

Deep Spanish Earthquake M6.3 11/04/2010 Recorded at Keele

 Earthquakes  3 Responses »
Apr 122010
 

An unusual earthquake has just occurred deep below southern Spain. Deep earthquakes are associated with subduction systems and earthquakes extend down to about 660km. This earthquake at magnitude 6.3 and a depth of 617km appears to have occurred on a relict subduction system from the Alboran plate between Spain and North Africa that was subducted beneath southern Spain during the Tertiary. There are suggestions that the subducted Alboran plate has become detached and we are just looking at its death throws as it enters the lower mantle.

Keele is only about 16° away so there are clear P and S arrivals but little in the way of surface waves as the event is so deep.

More information from the USGS here.

 Posted by hypocentre at 10:51  Tagged with:

Northern Sumatra Earthquake M7.7 06/04/2010 Recorded at Keele

 Earthquakes  Comments Off
Apr 072010
 

Another day, another large earthquake, this time in Northern Sumatra. This is 24 hour record that I saw when I broke my holiday for the second time this week.

Extracting the record shows a very strong body wave phase and surface wave train …

Matching this to the travel-time curves show that the strong phase is S, not P. Note that around 95° epicentral distance, Keele is not quite in the core shadow…

The P-wave is not visible because the path of the earthquake waves to Keele lies along the strike direction of the fault (northwestwards) and so P is nodal. S, however, is antinodal so we get a strong S-wave.

Full details of this earthquake are available from the USGS here.

 Posted by hypocentre at 10:13  Tagged with:
 Older Entries  Newer Entries
© 2012 Hypo-theses Suffusion theme by Sayontan Sinha