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.
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.
Predicting earthquakes
"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
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