Broadband Earthquake Monitoring at OAUIFE Station, Nigeria Dr Adepelumi, A. A Department of Geology, Obafemi Awolowo University, Ile-Ife, Osun State Email: adepelumi@gmail.com or aadepelu@oauife.edu.ng Phone: +234-08067163658 29th September, 2009

Seismology In November 2007, Guralp system was installed at OAUIFE seismic station through the funding provided by UNESCO office in Italy. Inverter and Solar Panel were installed in November 2008 for the smooth running of the seismic station.

Some of the Events Recorded at OAUIFE Earthquake station

Mexico Event- 2008

Tonga Event- 2008

OAUIFE Observatory

Earthquake Facilities at OAUIFE

Properties of the Seismometer

11th September 2009-NIGERIA An earth tremor occurred on 11th September, 2009 in Southwest Nigeria. This event was one of the largest tremors in this region and the in country. Since it was the first to be recorded instrumentally within the country, it was an opportunity to carry out interpretation of the event. For the location of the event using flat six-layered earth model, the result gave epicentre location of latitude 6.6° and longitude 2.5°, focal depth 10.0 km and origin time 3:10.23 GMT with rms 0.7 . Also the moment magnitude is 4.2 and the P wave to S wave velocity ratio is 1.73. An analysis of the event provided a normal fault mechanism with median solution of strike 180°, dip 45° and rake -90°.

Interpretation of the Event The result of the analysis of the September 11, 2009 earth-tremor in the southwest Nigeria, showed that the fault that resulted into the tremor rupture at about 10 km within the upper crust with a stress drop of about 0.265 bar and a 3.07 km radius rupture. Considering the areas where the tremor was felt, the rupture process propagated up to north-east and down to south-west. The majority of the fault plane solutions for the rupture process suggested a normal dip-slip mechanism.

Iceland Earthquake (OAUIFE)

Iceland Earthquake - Sandpoint, USA

Nigeria as a case study

Recent Seismicity in Nigeria Although, no active faults have been established in Nigeria, however, a careful review of seismicity record in Nigeria had showed that Nigeria may not be aseismic as has hitherto been believed. Recent events in Nigeria: Ijebu-Ode (July and August, 1984); Gulf of Guinea (December, 1984). Warri (1933), Lagos (1939); Umuahia (July, 1961); Kundunnu, Bauchi (1981); Dambatta, Kano (July, 1975); Yola ( December, 1984) and Gombe (June, 1985). Thus monitoring and prediction of earthquake hazards could begin by a proper documentation of the pathways through which they emanate, using seismological data.

Short Term Earthquake Prediction: Southwestern Nigeria The Empirical Earthquake Recurrence Model – a time-dependent model, was employed to predict the probabilistic occurrences of earthquakes in the Ijebu-Ode and environs between the year 2008 and 2028. This probability model takes the mean recurrence intervals and standard deviation of historic earthquake events in this area in order to determine the probability of earthquakes occurrence for the predicted years.

Probability of Recurrence of Earthquake of Intensity V-VII in Southwestern Nigeria

Probability of Recurrence of Earthquake of Intensity V-VII in Southwestern Nigeria The results of the model showed that the probability of earthquake occurrence in the study area between the year 2008 and 2028 increased from 2.8% to 91.1%. The result also showed that the probability of 2 events occurring has the highest likelihood within the predicted years.

Conclusion Therefore, it is instructive as a necessary measure to henceforth incorporate seismic criteria in the site investigations for design and construction of major and sensitive structures like Nuclear power plants the country is seriously considering as alternative source of energy for electricity generation, whose sudden damage can lead to disruption of major essential services, loss of lives and property and general degradation of the environment. Long Term Earthquake Monitoring should be embraced by Nigeria.

Future Plans Expand OAUIFE network to a comprehensive and effective earthquake Information System Center; Acquire more sensitive seismometers; Study the Crustal and Mantle structure beneath Southwestern Nigeria.

Acknowledgments ORFEUS for the financial support. Dr. Eck van, Torild for the encouragement.