After the earthquake and tsunami that struck north eastern Japan last Friday, the question on the lips of most Nigerians is “can such happen in the country?”
A REVIEW of earthquake occurrences and observations in Nigeria by Ofonime Umo Akpan and Tahir Abubakar Yakubu published recently in EARTHQUAKE SCIENCE indicates that although Nigeria is not located within the major seismic zones of the world; several minor earthquakes have been experienced in some parts of the country, over the years.
The first widely reported occurrence of an Earth tremor in Nigeria was in 1933. Other events were reported in 1939, 1964, 1984, 1990, 1994, 1997, 2000 and 2006. The intensities of these events ranged from III to VI based on the Modified Mercalli Intensity Scale. Of these events, only the 1984, 1990, 1994 and 2000 events were instrumentally recorded. They had body wave magnitudes ranging from 4.3 to 4.5, local magnitudes between 3.7 and 4.2, and surface wave magnitudes of 3.7 to 3.9.
Last year, Nigerian scientists at the National Space Research and Development Agency (NARSDA) warned that Nigeria should be prepared for earthquake experience.
In a publication in a journal, the scientist said:
“At exactly 3:10 GMT on September 11, 2009, an earth tremor occurred in the Abeokuta environs, Ogun State. This earthquake was felt mainly in most parts of Ogun State and some parts of Lagos State.”
The NARSDA researchers said the tremor is a sign that Nigeria is not immune from earthquake occurrence. In fact, one of the researchers from the Geology Department of Obafemi Awolowo University (OAU), Ile Ife, Osun State, Dr. Abraham Adekunle Adepetumi told The Guardian that the country is not in the earthquake-safe region.
“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.
On the possibility of a tsunami in the country, a Director from the Earth Science Education Unit, Department of Education, Keele University, Mr Chris King, told reporters in Abuja, after a lecture at the Nigerian Geological Survey Agency (NGSA) that Nigeria is a safe haven. He argued that since there had been tsunamis in South East Asia and the Atlantic Ocean and Niger Delta could cause tsunami in Nigeria. He explained: “Let us talk that Nigeria is not about tsunami; yes, it is possible one of the island is the Atlantic Ocean that can produce a tsunami and with the Niger Delta there could be a tsunami.”
King said because there was a major volcanic eruption in Nigeria in the past, the nation is also likely to experience it. He said: “And also there will be major volcanic eruption in Nigeria in the past. And that is possible in the future as well.”
However, researchers have discovered new details of how the Earth’s continental crust is tearing apart in Ethiopia, which will one day give birth to a new ocean.
In the final throes of breakup, it turns out, the crust thins dramatically, allowing a flood of magma to rise from deep in the Earth and erupt onto the surface, The Scientists reported online March 13 in Nature Geoscience on Sunday. The work revealed how an old continent gives way to a young ocean.
A seismologist at the University of Bristol in England who was not involved in the research, James Hammond, said: “It shows that we’re starting to understand some of the processes of how we go from continental to oceanic crust.”
Earth’s surface is broken into more than a dozen large tectonic plates, which drift around, collide and create geological phenomena such as earthquakes and volcanoes. The plates are driven by magma that wells up from within the planet, then cools and solidifies to form fresh oceanic crust. Older, lighter crust makes up the continents.
In East Africa, continental crust is losing its battle for existence. Tugged by tectonic forces from either side, the crust here is destined to rip apart and create a new ocean, like the neighboring Red Sea and Gulf of Aden.
According to the review of earthquake occurrences in Nigeria, when these events occurred, there were no functional seismological observatories in Nigeria. However, that has now changed with the establishment of a seismographic network managed by the Centre for Geodesy and Geodynamics (CGG), Toro, Nigeria. Presently, the network has four operational stations equipped with 24-bit 4-channel recorders and broadband 30-second seismometers.
The researchers said efforts are being made to establish more stations and migrate to real-time collection of seismic data using the general packet radio service (GPRS) technology as well as automatic location of events. Remote sensing, geological and geophysical studies have revealed the presence of a NNE-SSW trending Ifewara-Zungeru fault zone which has been shown to be linked with the Atlantic fracture system. The dynamics of the Atlantic fracture zones have been suggested to be responsible for the seismic activities experienced in the areas.
To geologists, eastern Africa shows plate tectonics in the raw. “Ethiopia is an ideal natural laboratory because we can see all these things happening,” says Ian Bastow of the University of Bristol, a coauthor of the new paper
Bastow and Derek Keir, a geologist at the University of Southampton, reanalyzed data from the 1970s, collected when other scientists set off explosive charges and watched how the resulting vibrations traveled through the ground. How fast those waves travel through the crust allows researchers to determine how thick the crust is.
Of particular interest, says Bastow, is a region in northernmost Ethiopia where the crust is so thin that much of the ground has dropped below sea level. Here earthquakes shake the ground constantly, and volcanoes pour out lava across the hot, flat landscape.
The new analysis shows that this lava erupts because of the recent stretching of the plate. “This very abrupt thinning is what is causing the melting,” Bastow says. “If that thinning had occurred slowly, you couldn’t explain this large magma pulse and the voluminous young lava flows at the surface.”
Bastow says the work explains not only why northern Ethiopia looks the way it does, but also what might have happened at other places where continents tore apart. The Atlantic Ocean, for instance, started to form about 200 million years ago when Europe and North America pulled away from each other.
Scientists might now be able to use what they have learned about Ethiopia’s split to better understand what happened as Europe and North America ripped asunder.