Nigerian seismologists are all agreed that Nigeria is no longer an earthquake-free zone (aseismic) as previously believed following the series of earth tremors in different parts of the country in recent times. This development requires that measures be put in place to mitigate the devastating effects when a major earthquake occurs in Nigeria. In this report, Vanguard Features presents the solutions as proffered by experts.
By Ebele Orakpo
INCREASING seismic activities
You may not have come to terms with its threatening reality. But some experts are convinced that there is a real possibility of an earthquake occurring somewhere within our shores.
It all began with Mr. Umar Afegbua of the Centre for Geodesy and Geodynamics, National Space Research and Development Agency. According to him: “The recent trend of earthquakes/tremors in Nigeria is an indication that seismic activities within the country are increasing and urgent measures need to be adopted to avert devastating consequences of big earthquakes in the most populous black nation in the world.
The seismic events whose vibrations were felt heavily close to epicenters at the respective communities are now causing the entire country and indeed, the global seismological community a great concern” .
Professor Alexander Lar of the Department of Geology, University of Jos took it up from there. “Geologically, Nigeria is located in a so-called stable Pre-Cambrain–Paleozoic age Basement terrain believed to be seismically safe. However, records have shown that earth tremors (minor earthquakes) have occurred in Nigeria from 1933-2016. An overview of these events would leave us with no other explanation than to question the previous assertion that Nigeria is seismically safe,” he submitted.
Timeline: Nigeria experienced tremor in 1933, 1939, 1964, 1984, 1985 (in Komba Yaya), 1987 (in Akko) near Gombe; 1990, 1994, 1997, 2000, 2006, 2009 and 2016.
Most of these occurrences were not instrumentally recorded because there were no functional seismological observatories in Nigeria but those of 1984 at Ijebu-Ode, 1990 at Ibadan and 2000 at Jushi Kwari were recorded.
South-West as epicentre
“Earth tremors with different magnitudes and intensities have been observed or instrumentally recorded in Nigeria over the past 70 years. The epicenters of most of these events were mainly located in South-West Nigeria. However, no loss of lives or noticeable damages to property was recorded until recently in 2016,” said Afegbua. In their publication inwww.researchgate.net/publication/227304964_A_review_of_earthquake occurrences_and_observations_ n_Nigeria, Ajakaiye et al. 1988; Akpan, Yakubu 2010; Tsalha et al. 2015 noted that “the most frequent earthquakes were observed in the South-West of Nigeria, near Warri, Lagos, Ibadan and Akure. There are also records of earthquakes in Upper Benue Trough near Gombe, as well as Yola (in 1984 and 2005).”
“In 2016 alone, series of events with scary shakings were observed in Shaki community of Oyo State. Although the tremors were not recorded by the closest seismic station located in Ile-Ife, however, from the field observation and well-structured questionnaires data gathered by a team of experts from the Centre for Geodesy and Geodynamics under the National Space Research and Development Agency, NASRDA, the intensity of the tremors was established to range from three to four on the Modified Mercalli, MM, Intensity Scale, and the magnitudes subsequently estimated from the Ritcher Intensity-Magnitude Scale table,” stated Afegbua.
Bayelsa/Rivers: She continued: “While residents in the ancient community of Shaki were trying to come to terms with the tremors some residents described as strange and mysterious, the border communities of Bayelsa and Rivers states were hit with yet another tremor on July 10, 2016, and structures were seriously damaged in this case, but no loss of lives. The tremors were widely felt within Bayelsa and Rivers states and this has changed the age-long belief that Nigeria is not active or free from earthquakes; and consequently, paving way for a new thinking and new focus on occurrence of earth tremors in the most populous Black nation.
“Swiftly tailing the Bayelsa/Rivers states’ slip-up, were the Kaduna earthquakes, especially those that were witnessed at Kwoi and surrounding villages of Nok, Sanbang Daji and Chori, all in Jaba Local Government Area of Kaduna State on Sunday, 11th and Monday, 12th September, 2016. Damages to structures were noticed in the affected communities. The earthquakes at Kwoi were recorded by the seismic station at Kujama, Kaduna State and also operated by the Centre for Geodesy and Geodynamics, with magnitudes ranging from 2.6 to 3.0.”
Earthquake-causing faults: Earthquakes are said to occur along tectonic boundaries, faults, etc, as a result of sudden release of energy from strain failure. “Studies in Nigeria have suggested and in some cases, confirmed the existence of earthquake-causing faults within the country. Whether these intra faults are active or not, is a big question yet to be answered,” said Afegbua.
Seismic data: To correctly answer the question of the causes of earthquakes in Nigeria, Afegbua says seismologists need enough and reliable seismic data and other geological information which unfortunately, is not the case. “This is really not the case as the existing seismic stations in Nigeria are grossly inadequate for a robust research to ascertain and appraise the seismicity scenario of the country, delineate known and yet-to-be discovered faults, appraise their active nature or otherwise. The existing seismic network operated by the Centre for Geodesy and Geodynamics are located in triangulation-like fashion in Nsukka, Awka, Abakaliki, Ife, Kaduna, Toro and Minna. The broadband equipment installed at the stations have recorded prominent distant events that occurred around the world and researchers from Nigeria and abroad have used the recordings for ingenious scientific studies for the benefit of Nigeria and the world at large.”
“Now that it is a foregone conclusion that earthquakes are here with us, and Nigeria will continue to witness more of them in future, the country has to do the needful by adopting measures that will assist the agency saddled with natural hazard monitoring and investigation to carry out its mandate effectively and efficiently.
Earthquakes here with us
As it is the convention worldwide, Nigeria needs to immediately adopt a healthy and sustained monitoring of seismic activities within the country and its environs to avert the devastating impact of earthquakes in future. This is so because an earthquake is a natural phenomenon and nobody can stop its occurrence or even correctly predict it before it occurs,” said Afegbua.
Getting more equipment: Afegbua believes that Nigeria needs to immediately acquire more recording and monitoring sensors, especially the short-period sensors specifically designed for local earthquakes recordings, seismicity and seismic hazards studies. “Although the broadband sensors will continue to play their role in the overall recording capacity of the seismic equipment in Nigeria, the short-period sensors deployment would not only help in the delineation of faults and prompt recording of local earthquakes in Nigeria, with real-time/near-real-time analysis for micro-earthquake detection, they are also suitable for site effects studies prior to the siting of critical infrastructural facilities like dams, power plants, military installations, rail lines, bridges and high-rise buildings whose damage from earthquakes’ vibrations would lead to monumental economic loss.
Many permanent and temporary stations of these short-period sensors can also be used fordetermination of site response, determination of crustal structure, volcanic studies, after-shock studies and for microzonation investigation and develop therein, seismic hazard maps showing seismic hazard potentials at each site for each region and the entire country.
“With densification of the short-period sensors and co-located with Global Positioning System-monitoring equipment in Nigeria, it would help in predicting strain build-up and probable rupture time, if not precisely, but to a large extent. By and large, the timely intervention will undeniably help in planning purposes, as a precursor for the establishment of seismic building codes, in demographic studies, and for enhanced earthquakes’ disaster mitigation in Nigeria,” said Afegbua.
Prof. Lar notes that a successful prediction of earthquakes will come to reality in the future. “This is because despite the volume of information gathered by the Geologists about the causes of earthquakes, they have not been able to predict when exactly one will occur. An earthquake before it strikes, gives little or no warning and once it begins, little or nothing can be done to reduce the damage.”
Disaster preparedness/prevention strategies
Said Lar: “In Nigeria, seismic hazard assessment maps can be produced from available information on previous tremors and the distribution of faults in the country. Such maps would indicate the likelihood and potential severity of future earthquakes based on the intensity/magnitude of previous recorded earth tremors in Nigeria. Such maps are useful in anticipating future earthquakes and helping people plan for the event.
*Those living in earthquake-prone areas must be sensitized on the geologic hazards of the areas where they live and work or are visiting.
*Houses should be built in adherence to conventional building code that can withstand shocks and prevent their falling apart and or breakages.
*In a poorly built house, it may be better to leave before the earthquake with the understanding that earthquakes don’t kill, but it is the collapsing buildings due to the ground shaking that kill.
*Avoid tall buildings, high tension power lines, bridges and falling debris if possible.
*Provide for several days of food, water supply, batteries for radio/torch light, fire extinguisher etc.
*Have a basic first aid kit and a working knowledge of first aid procedures