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Seismic background information

Irish National Seismic Network (INSN) – Background information

Tom Blake, the director of the INSN, can be heard on the following links with regard to the devasting earthquake and subsequent tsunami in Japan on the 11th March 2011.

The expansion of the Irish National Seismic Network (INSN) is an important development as a monitoring tool for recording local, regional and global earthquakes, particularly in the circum-North Atlantic region. At the local level, Irish seismicity levels are known well in relatively few localities. The Irish National Seismic Network (INSN) will help us to understand Irish seismicity more fully. Regionally, there is unequivocal historical evidence that Ireland has been affected by tsunamis generated by strong earthquakes in the Atlantic, such as the Great Lisbon earthquake of 1755.  Similar waves were recorded at Newlyn, England after earthquakes west of Portugal in 1941 (8.2 Ms), and 1975 (7.9 Ms). The development and expansion of the Irish National Seismic Network will play an important role in monitoring for such events and feeding data to the North East Atlantic and Mediterranean Tsunami Warning Centre, which is currently under discussion under the auspices of the Intergovernmental Oceanographic Commission (IOC) and UNESCO.

The largest earthquake felt in Ireland in recent times occurred off the coast of Wales, in the Irish Sea, on 19th July, 1984 and measured 5.4 on the Richter Scale. It caused some structural damage along the east coast of Ireland. The most recent earth tremor, measuring 2.6 on the Richter Scale, occurred in North Clare, on 6th May 2010, in an area previously thought to be aseismic.  Although there are difficult constraints available in relation to the focus of the earthquake, initial data suggests a depth of 33km.  This is the largest recorded recorded onshore earth tremor by the Irish National Seismic Network (INSN), since records began in 1978.

It is fitting that the expansion of the Irish National Seismic Network occurred in 2010, as this was the bicentenary year of the birth of a very important Irish Engineer and Scientist, Robert Mallet, 1810 – 1881, who is also known as the “father of controlled source seismology” from seismic experiments he carried out on Killiney Beach, Dublin, in 1849.

The broadband station (DSB) has a wide spectral response which allows the study of all kinds of seismic waves and it is part of a rapid response system for major world seismic events. The data available in realtime at http://geofon.gfz-potsdam.de/geofon//gfn_liveseis.html.

Sumatra Earthquake  26th Dec 2001The seismogram to the left is from DSB station in the Dublin mountains. This is the earthquake that occurred off the west coast of northern Sumatra, Indonesia on the 26th December 2004, which caused a devasting tsunami. The origin time was 00:58:53 UTC, Location 3.30N, 95.95E, Magnitude 9.0, and Depth 30km. This was the fourth largest recorded earthquake since 1900 and is the largest since the 1964 Prince William Sound, Alaska earthquake. In addition to the death and destruction in the East Asia/Indian Ocean region by the tsunami generated by the earthquake, the tsunami crossed into the Pacific and Atlantic Oceans and was recorded in New Zealand and along the west and east coasts of South and North America. The earthquake was felt (intensity VII) at Banda Aceh and (intensity V) at Medan, Sumatra and (intensities II-IV) in parts of Bangladesh, India, Malaysia, Maldives, Myanmar, Singapore, Sri Lanka and Thailand. Subsidence and landslides were observed in Sumatra, Indonesia.

This screen shot is an example of 3 component data recorded in real-time and displayed at DIAS on the seedlink server.  The epicentre of the earthquake was Offshore Honduras on 28th May 2009 and had a magnitude Mw 7.1.  Station names from top to bottom are: VAL Valentia, Co. Kerry, Ireland;  EPON Northwestern Spain; HTL Hartlands, UK; MCH1 Michaelchurch, UK; PVAQ, Southern Portugal.

Tom Blake gave the following interviews regarding regional seismicity and our Irish Seismic Network which can be heard when you click the following: