Seismicity in Ireland
In 2022 the Irish Examiner reported that Ireland was had one of the lowest seismic impact risks in Europe based on the potential for ground shaking and the impact the earthquake can have in terms of loss of life and property damage. Based on European Facilities for Earthquake Hazard and Risk modelling, even if an earthquake occurred in Ireland, which they emphasize can happen without warning even in an area of seismic quiet, the destructiveness of the shaking would be mitigated by the ground and soil conditions, building and infrastructure construction quality and low population density.[1]
Background edit
There is relatively little overland seismic activity in Ireland. Offshore, there is more significant activity in the English Channel and the North Sea off the coast of Humberside. Data may not be complete for smaller offshore events. The 7 June 1931 North Sea earthquake occurred off the east coast of England. It's magnitude is estimated at 5.8 MW. It was felt as far away as east Ireland and all the countries with North Sea coastline. The damage along Ireland's east coast was minor.[2]
Some parts of the UK are more seismically active than Ireland. Some of the worst effected places in the United Kingdom are the Northwest corner of Wales, which experiences many earthquakes and aftershocks. Other areas have a historic record of repeated activity: the Swansea area, Hereford-Shropshire and the Pennine Hills.
There are several interpretative factors for the historical evidence of earthquakes. The epicentres or foci and magnitudes of historical earthquakes are subject to interpretation. It is possible that 5-6mw earthquakes described in the historical record were larger offshore events felt moderately in populated areas. Documentation in the historic period is sparse and may not give a full picture of the geographic scope of an earthquake presenting an obstacle to interpretation. The historical record may have earthquake records spanning a few centuries, a very short time frame in a seismic cycle. This is not a reliable method to establish a maximum magnitude for intraplate earthquakes in any country, even those with a longer historical record. Fault length alone may not give a full picture either—seismic cycles in which faults zones mature and evolve are dynamic.[3][4]
Nicholas Ambraseys wrote in 1985:[3]
"The seismicity of the UK is clearly different from that of eastern USA or W Africa in that either (i) no earthquakes of M ≥ 6.0 occur of (ii) 700 years is not long enough to reveal such events in the UK, whereas 100 years is more than adequate in the eastern USA and W Africa ... Is there anywhere on the continents seismically quieter than the UK?"
Scientists began gathering more data to study the seismic activity in Ireland to gain more insight on intraplate earthquake distributions. They think Ireland gets fewer earthquakes because the lithosphere is thicker. In Britain, fewer quakes seem to occur where the lithosphere is stronger.[5]
Leannan fault edit
Ireland is a slow lithospheric deformation region. The Leannan fault runs through County Donegal which is the only seismically active area in Ireland. It is a proposed possibility but not confirmed that it is a north-west continuation of the Great Glen fault.[6][7]
Seismomenters edit
Until recently earthquake data from Ireland has been limited.
- ^ https://www.irishexaminer.com/news/arid-40863605.html
- ^ Geological Hazards in the UK (2020) Their Occurrence, Monitoring and Mitigation Engineering Group Working Party Report Geological Society of London.
- ^ a b Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes(2008) Springer Netherlands
- ^ Thakur, Prithvi; Huang, Yihe (2021). "Influence of Fault Zone Maturity on Fully Dynamic Earthquake Cycles". Geophysical Research Letters. 48 (17). doi:10.1029/2021GL094679.
- ^ "Why earthquakes happen more frequently in Britain than Ireland". phys.org.
- ^ "The micro-seismicity of Co. Donegal (Ireland): Defining baseline seismicity in a region of slow lithospheric deformation". Terra Nova. 36 (1): 62–76. 6 November 2023. doi:10.1111/ter.12691. Retrieved 11 February 2024.
Regions of slow lithospheric deformations are characterized by a low seismicity rate and limited accumulation and release of tectonic energy, leaving open the question if such deformation is 'diffusely' accommodated along a wide fault system (or even across the whole crust) rather than clusterized along specific faults. In particular, the sparsity of the seismic networks (common in region with low seismic risk) makes it appear, in current catalogue, that seismicity is generally diffuse, but it could also be grossly mislocated due to the small amount of seismic data available.
- ^ Burk, C. A.; Drake, C. L. (1974). The Geology of Continental Margins. Springer. p. 345.
Southwest of Mull, the Great Glen Fault splits into two branches; one continues west-southwest to the offset in the margin near 56°N and the other continues through northern Ireland as the Leannan Fault (Riddihough, 1968; Roberts, 1969b; Holgate, 1969; Pitcher, 1969; Bailey et al., 1974). The Highland Boundary Fault seems to continue to the west of Ireland but its offshore continuation is less certain. On Porcupine Bank, Vogt et al. (1971) show a west-southwest-trending magnetic lineament that lies a little north of the projected line of the fault, possibly because of sinistral strike-slip displacement by the Leannan Fault