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Seismic map nigeria& Study Of Nigeria
Seismic map nigeria& Study Of Nigeria
Seismic map nigeria& Study Of Nigeria
Seismic map nigeria& Study Of Nigeria
Seismic map nigeria& Study Of Nigeria
Seismic map nigeria& Study Of Nigeria
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Seismic map nigeria& Study Of Nigeria

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This paper describes the the Seimic Studies Of Nigeria

This paper describes the the Seimic Studies Of Nigeria

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  1. Seismic Activity in Nigeria. Edward O. Osagie, Ph.D. Savannah State University, Savannah, Georgia, U.S.A. 9400 Abercorn Ext # 301, Savannah, GA 31406ABSTRACT generally inadequate to explain all known observations, so that other as yet unknownThis paper presents an account of the earthquake sources may also be active.activities in Nigeria. It includes a discussion of thepossible origin and mechanism of theearthquakes. These developments in the nation’s RECENT SEISMIC ACTIVITIESgeological history bring to question the age longbelief that Nigeria is seismically safe. It is difficult On June 27, 1990, an earth tremor occurred into overlook the incidence of earth tremors in the Ibadan, West Africa’s largest city, in Oyo Statecountry because recurring tremors could be a (Figure 1 ). The nation lacks seismic equipment tobuild-up to a major earthquake. measure tremors or to monitor movement in the Earth’s crust. An unscientific method of (Keywords: earthquake, tremors, geological history, measuring the intensity of the quake is to have seismic activity) the testimony of eye- (or sense-) witnesses who were at or near the area of greatest intensity. For it is they who can describe the effects on theINTRODUCTION infrastructure. In comparing numerous accounts from witnesses of the same events, one canThis paper presents a discussion of the notice that there is a general agreement on majorearthquake activities in Nigeria (Figure 1). This and minor details of the earthquake. Buildingsinformation is non-instrumental. It includes a vibrated to their foundation, braking louver bladesdiscussion of the possible origin and mechanism of windows and stopping clocks. When wholeof the earthquakes. These developments in the buildings go into sudden violent vibrations,nation’s geological history bring to question the washing basins and plates tumbled, spilling theirage long belief that Nigeria is seismically safe. It contents. The tremor sent people into the streets,is difficult to overlook the incidence of earth though no one was killed.tremors in the country because recurring tremorscould be a build-up to a major earthquake.Earthquakes result from stresses whichaccumulate within the outer 700 km shell of theearth. The origin of these stresses are stillobscure, both as to the source of energy and asto the mechanism by which this energy isconverted to strain energy. The energy source isgenerally assumed to be of thermal origin(radioactivity, cooling, etc.), although othersources such as gravitational forces may also beactive. The mechanisms which have beensuggested for transferring thermal energy intomechanical energy or elastic strain areconvection currents, change of phase or state,diffusion processes, expansion, or contraction. Figure 1: Map of Nigeria. Areas with SeismicGravitational return to equilibrium from Activity are Shaded.disturbance produced in the past may also play arole. However, these mechanisms appear to beThe Pacific Journal of Science and Technology –546–http://www.akamaiuniversity.us/PJST.htm Volume 9. Number 2. November 2008 (Fall)
  2. Residents of Oluyole Estate Extensions, Apata, volcanic eruptions, were noticed in SeptemberOdoowa and Felele, an area covering about 16 1988 in Osererun hills in Gombe council area ofkilometers radius, experienced the highest Gongola State threatening about 10,000vibration. If the quake had lasted more than 10 inhabitants. Two hectares of farm land and manyseconds, it could have resulted in the collapse of animals were lost. In April 1988, panic gripped thesome houses. In fact, in a country where inhabitants of Amauzu Ede-Obela in Edemabuildings are as collapsible as bubbles, repeated council area of Anambra State where about 12tremors could have a devastating effect. While km of land had cracked. Houses built with zincsome people impute supernatural cause to these also had cracks. There are reports of annualquakes, others regard them as some sort of tremors in some areas of Rivers State, especiallypenance imposed for group sins. The effect of during the month of April. These incidents havethis tremor would suggest a micro-quake of aggravated the fear of a possible earthquakemagnitude m 3-4. across the nation.An earthquake was first reported in Ibadan in The relative movement of plates give rise to1949. On July 28, 1984, another tremor occurred earthquakes. The slip on the fault generates thein Ibadan but many people did not take it earthquakes, according to plate tectonics.seriously. Some people though it was thunder or However, it is widely held that the African platethe sound of a heavy vehicle passing near their has not moved in the past 200 years.residence. Unlike the 1990 event, the tremor left Stratigraphic evidence and K/Ar dates from widelyno casualties or significant damage to property. separately areas on the African plate indicates aHowever, five days after the 1984 tremor, in roughly simultaneous upsurge in volcanic activityIbadan, Ijebu-Ode and Abeokuta, (Figure 1 ), two about 25 m.y. ago (Burke and Wilson, 1972). Ifmain settlements 68 km to the southeast and 77 this volcanism was generated over plumes andkm to the southwest, respectively, were hit by a the African plate has moved laterally over themmore ferocious tremor that left cracks in buildings. during the past 25 m.y., then the volcanoesThe tremor which lasted for only two seconds should form parallel lines across Africa. If theaffected Sobo, Porogun, Oliworo quarters, the motion averaged 1 cm/yr, the lines of volcanoesOndo-Benin road, and neighboring villages. Thus would be 250 km long and all would becomethe Ijebu-Ode tremor spread very far. younger in the same direction. Although African Neogene volcanoes are commonly arranged inThe local geology of the region around Ibadan, lines the lines are not parallel and there is nowhich is the main area of interest, is underlain by evidence of consistent age variations from onerocks belonging to the migmatite-gnesiss- end to another. This pattern of volcanism isquatrzite complex which constitutes the essential consistent with the hypothesis that the Africanpart of the Precambrian basement complex of plate halted and has been virtually at rest for theNigeria. The migmatite-gneissess are past 25 m.y. with each Neogene volcanic areaheterogeneous rock made up of several distinct overlying a different plume (Burke and Wilson,petrologic units (Rahaman and Ocan, 1978; 1972).Rahaman, Olarewaju, Ocan and Oshin, 1983).The two main petrologic units in the area are grey The affected areas do not lie on any plategneiss and the granite gneiss. The granite gneiss boundaries. What then could be the possiblewhich forms the hills in addition to a few level origin of these earth tremors in these areas? Weoutcrops is intrusive into the grey gneiss. All the want to attempt plausible causes for these earthrocks have undergone strong deformation and as tremors. One thing is certain, that is, the eartha result show microfolds, and microfaults and tremors that have occurred in Nigeria havelinear fabrics. occurred in the same area. Thus, these earthquakes do not occur randomly either in timeThe first earth tremors in Nigeria were in Warri or in space on the surface of the earth. There are(Delta part of Nigeria ) in 1923. It also occurred in distinct earthquake belts in Nigeria. Then thereOhafia (eastern part of Nigeria) in 1933. On must be some interesting features in theseDecember 8, 1984, a tremor was reported in particular areas. Certainly, the earthquakes in theYola, Gongola State (Figure 1). In April 1990, different parts of Nigeria can not be ascribed tothere were reports of strange shaking of the earth the same cause. The seismically active zones arein Jere town, Kaduna State (Figure 1). Some (Figure 1).cracks, suspected to have been caused byThe Pacific Journal of Science and Technology –547–http://www.akamaiuniversity.us/PJST.htm Volume 9. Number 2. November 2008 (Fall)
  3. 1) South-west zone stretching from the Ijebu the whole city. Groundwater behavior is now areas to the Ibadan areas. acknowledged to be an important factor in 2) The Cross Rivers Basin, earthquake prediction especially since Nur 3) Gongola Trough, proposed a dilatancy-diffusion hypothesis of 4) Benue Valley. precursor behavior (Nur, 1972). Many reports concerning groundwater behavior accompanyingIn the southern part of the country such as Warri earthquakes have been recorded (Shimamura,and Rivers State (Figure 1), the earthquakes may 1980; Shimamura and Watenbe, 1981;be due to sediments. In areas where the earth is Shimamura et al., 1985; Wakita, 1981). However,overloaded, the plate is upset. This could much remains unknown about the role ofprecipitate earth movement because the groundwater in earthquake generation.application of stress to a rock mass having astructural weakness produces a fracture. Once a Gravity and structural geology of the Benue valleyfracture has occurred, movements will continue indicate a combined effect of a zone of intrusion,on it. However, sedimentation alone is generally a thin crust and possibly a shallow basementinadequate to induce earthquakes. This is (Ajakaiye and Burke, 1972). This conclusion isbecause the large sediment loads have generally consistent with the hypothesis that a spreadingbeen in place long enough that the stress had ridge underlay the southwestern part of therelaxed. Benue trough in part of Cretaceous times with closure of the embryo Benue ocean at the time ofWarri and Rivers State are in the Niger Delta. The a major Santonian folding episode (Burke et al.,Niger Delta is underlain by an RRR (Ridge- 1971). On this hypothesis the thick sedimentaryRidge-Ridge) triple junction (Burke et al., 1971) sequences mark the suture along whichand lies on an oceanic crust (Hospers, 1971). continental crust has rejoined after the short-lived spreading episode. Rex, et al. (1971), haveReyment (1969) published a map showing an suggested that the Neogene volcanism of the 87 86estimate of the former position of the edge of the Benue trough with its low Sr/ Sr ratios maySouth American continent under the Niger Delta have been localized along this suture. Thisbased on the distribution of marine Upper localized volcanism may be responsible for theCretaceous rocks. The northern limit of growth seismic activities in the Benue Valley.faults (Short and Stauble, 1967; Merki, 1970) inthe Niger Delta roughly coincides with the same The reactivation of pre-existing faults or weakline, that is, the Cretaceous margin of South zones has been observed in the ocean and inlandAmerica and this seems consistent with the (Wetmilla and Forsyth, 1978) and this process isgeneral observation that the deltas are pushing proposed for the Ibadan area. This intra-plateinto waters of oceanic depths and which have area constitutes a localized weakness zone in thebeen suggested to represent the results of a crust. The cause of this weakness is unknown. Itshort-lived subduction episode (Burke et al., is possible that the stressed rock becomes1971) which could trigger earth tremors in these weakened by water corrosion and the pushingareas. apart of the forces of the fault by abnormally high pressures. There is the possibility regarding theCities such as Warri and Rivers State which are concentration of strain in relatively narrow strainlocated on water-logged unconsolidated zones along the faults. Thus, the major portionssediments, that is, loose gravel, sand, dirt, and of the blocks between faults are relativelyclay and near major faults are more vulnerable to unstrained and so act principally as stressearthquake damage than those that are not. transmitting members of narrow strain zones atUnconsolidated sediments are at much greater their margins, where the strain is accumulated forrisk for seismic shaking than rock. intermittent release in earthquakes. However, we do not know the nature of the forces whichSome areas of the country are sinking because of produce the stresses. Perhaps, the forcesthe rate at which the nation’s underground water originate from within the whole block masses asresources are being tapped. Thousands of body forces and are applied horizontally fromboreholes in Lagos State, for example, are from a outside the affected region, or are generated bysingle source, the Abeokuta rocks in Ogun State. coupling to many structures below. We do notAn earth tremor occurred in Abeokuta in 1986. know the depth to which the faults and their strainThe water collects underground and literally floats zones extend.The Pacific Journal of Science and Technology –548–http://www.akamaiuniversity.us/PJST.htm Volume 9. Number 2. November 2008 (Fall)
  4. Kennedy (1965) recognized that Cretaceous and As further evidence that the west African nation isTertiary marine sediments were confined to the unstable, earthquakes were reported in Accra,reactivated areas in the Pan African orogency Ghana, west of Nigeria. Several seismic eventsaround the West African craton. Burke and have occurred in Accra extending along theDewey (1971) and Dewey and Burke (1973) in Akwapin faults to the Volta River (Burke, 1969).attempting to apply unformitarian principles to the Ghana does not belong to any of the knownPan African events, emphasized that these mobile zones, rather it belongs to a stable area,terraces resembled, in their vast areal extent, the the craton. However, the history of earthquakes inkind of orogenic environment presently resulting Ghana suggest that everything is but quiet. In thefrom continental collision in the Himalaya and past 120 years, Accra has on three occasionsTibet. They suggested, therefore, that Pan African been damaged by major earthquakes in 1906,reactivation might have resulted from continental 1939, and 1941 (Junner, 1941). Continued micro-collision seismic activity to date indicates that earthquake activity is far from over. The seismicity which occurred on the Volta river in 1971 was attributedDISCUSSION to the Chain fracture zone which reaches Africa at Accra (Burke, 1971). Bouguer anomaliesThe Atlantic-type continental margin of Nigeria (Rechenmann et al., 1960 ) in the Accra areawas generally regarded as aseismic until these indicate a change in crustal structure within thetremors. This suggests that the crust in the west continent across the eastern boundary of theAfrican portion of the African plate may not be West African craton. This change which resultedstable. Before the acceptance of plate from the development of the Dahomy suture in andisplacement, it seemed appropriate to relate early Palaeozoic paratectonic orogeny, localizedsurface structures directly to those of the the Cretaceous transform that split Gondwanaunderlying asthenosphere but this is no longer continent and became the Chain fracture zonerealistic unless a plate can be shown to be (Burke and Dewey, 1971). Differential lateraltemporarily at rest. motion across the Chain fracture zone at the continental margin is unlikely because the coastThe basin and swell structure which are peculiar of Africa lies beyond the mid-Atlantic ridge offset.to Africa are linked to the rift valley formation(Krenkel, 1957). Burke and Whiteman (1970) The seismicity of the Volta Dam is more probablyhave postulated a genetic sequence, discernible related to an abrupt change from crust ofin Africa, from uplift, through rifting and triple continental thickness to crust of oceanic thicknessjunction formation to continental separation. They at the edge of the Ghana continental shelf (Burke,suggested that these peculiarities of Neogene 1971). This does not seem to be a plausibleAfrican structure (in no other continent are they explanation for the occurrence of the earthquakesso prominent) may be a consequence of the in Ghana. The correspondence between thestandstill of the African plate over asthenosphere. offset of the continental margin and the mid- Atlantic ridge on the Chain fracture zone is furtherThe Nigerian continental shelf lies between evidence that Africa and the south Atlantic east of 0 0longitude 30 west and 80. 40 east and latitude the mid-Atlantic ridge may be considered as part 0 060.20 N and 40.20 N. It evolved about 180 of the same rigid block (Burke, 1969). Themillion years ago when Africa began to separate occurrence, however, of seismicity near Accrafrom south America (Junner, 1941). The mantle in with recently active faults indicates somethe ridges is jutting to the surface, thereby comparatively differential motion across thecausing fractures along the ridge. Some of these fracture zone.fractures have been found to cut into the Africancontinent, although the precise location in West On December 22, 1983, a large earthquakeAfrica has not been determined. Rock movement occurred in Guinea further west of Nigeria in analong the fractures are rampant and so builds up area which was previously considered aseismictension and force which at a point snaps or yields (USGS location 11.93 S and 13.60 W). Theto cause vibration to the landmass in what is magnitude of the Guinean earthquake was M =experienced as tremors. However, no evident 8.2 and was followed by about 1,000 aftershocks.oceanic fracture seems to be related to this The main shock was felt over an area of about 15epicentral region. The shelf does not extend that km. Several lives and property were lost on thatfar from the coast. occasion. The epicenter of the earthquake wasThe Pacific Journal of Science and Technology –549–http://www.akamaiuniversity.us/PJST.htm Volume 9. Number 2. November 2008 (Fall)
  5. located in a region bordering the West African question is the relationship of small to largecraton at the southern end of the Mauritanides earthquakes. Can observations of micro-fold belt and at the edge of the Bowe basin earthquakes (defined as those of magnitude lesscharacterized by non-metamorphic sedimentary than 4) give information about large destructivelayers (Dorbarth et al., 1983). Earthquakes have earthquakes (of magnitude 7 or 8)? Smallbeen reported in Guinea during the century earthquakes are now monitored in several partsmainly in the area and to the north of Cape Verde of the world. Unfortunately, neither fixed orIslands. temporary seismic arrays have been installed in Nigeria to monitor these micro-earthquakes. It isFurther east, Seiberg (1932) reported five therefore extremely necessary to deploy seismicearthquakes from Cameroon of which two were instruments in order to catalogue epicenters andassociated with the Cameroon mountain volcano magnitudes of these micro-earthquakes inand two including the largest had epicenters at Nigeria. Such masses of data need to be 0 0Kribi (10 E, 4 N), 200 km to the south. Many collected and painstakingly analyzed before avolcanic eruptions have been observed in recent thorough understanding of the tectonics of thesetimes in the Cameroons which is adjacent to the regions could be made.northeastern and southeastern parts of Nigeriasuch as Gongola State. On August 21, 1986, thelake Nyos erupted. Cattle were killed and the flow ACKNOWLEDGEMENTSof gas down the river caused 1,700 deathsamong the local population. Lake Nyos volcano Thanks to the many individuals who willinglyhas been very active in the past. Similar gas provided information during this investigation.explosions had taken place in 1954, 1982, and This work was carried out when the author was at1984. The outburst may be associated with a the University of Benin, Benin City, Nigeria andphenomenon in which the lake turns over under he is grateful to the University for funding thethe influence of a minor external stimulus such as study. I thank Prof. C.A. Kogbe for his detaileda storm or earthquakes. review, corrections, and thoughtful constructive comments on the manuscript and in particular, forThe Cameroon volcanic zone which developed in drawing my attention to previous works. Thethe Neogene times is characterized by alkaline, paper is significantly improved because of him.mainly basaltic volcanics, is more than 1,100 km Thanks are due to Prof. Kelvin Burke for hislong, half on land and half in the ocean and is a support and assistance in making his papersmajor structural feature of the Gulf of Guinea, but available to me.the fracture zones because they seem to havecontrolled the distribution of Cretaceous andTertiary sedimentary basins may be more REFERENCESfundamental (Burke, 1969). The Cameroon linecuts across a sedimentary basin and although 1. Ajakaiye, D.E. and Burke, K. 1973. “A Bouguerthere is a continuous history of Cenozoic Gravity Map of Nigeria”. Tectonophysics. 16:103-magmatic activity in Cameroon, the volcanoes 115.which make up the line are very young. The 2. Ashwal, L. and Burke, K. 1989. “AfricanCameroon structures appear to be tensional Lithospheric Structure, Volcanism andfeatures related to the contact of oceanic Topography”. Earth and Planetary Science Letters.fractures with the continent. 96:8-14. 3. Burke, K. 1969. “Seismic Areas of the GuineaCONCLUSION Coast where Atlantic Fracture Zones Reach Africa”. Nature. 222(5194):655-657.Cenozoic volcanism may be ascribed as the 4. Burke, K. 1971. “Recent Faulting near the Voltatriggering mechanism for the earthquakes in Dam”. Nature. 231:439-440.certain parts of Nigeria such as the Benue Valley,although this process is not well understood. 5. Burke, K., Dessauvagie, T. F., and Whiteman, A.J.Similarly, it is uncertain as to the cause of the 1971. “The Opening of the Gulf of Guinea and theearthquakes in other parts of the country. In any Geological History of the Benue Trough and theregion, micro-earthquakes are much more Niger Delta”. Nature (Phys. Sci ). 233:51-55.frequent than larger events. A fundamentalThe Pacific Journal of Science and Technology –550–http://www.akamaiuniversity.us/PJST.htm Volume 9. Number 2. November 2008 (Fall)
  6. 6. Burke, K. and Dewey, J. 1971. “The Lost Oceans 20. Seiberg, A. 1932. Handbuck der Geophysik. of Africa”. J. Min. Geol. Nigerian Min. Geol. Metall. Berlin, Germany. 4, 687. Soc. 6:75. 21. Shimamura, H. 1980. “Precision Quartz7. Burke, K. and Wilson, J.T. 1972. “Is the African Thermometers for Borehole Observations”. J. Plate Stationary”. Nature. 239:387-390. Phys. Earth. 25:243-260.8. Dewey, J. and Burke, K. 1973. “Tibetan, Variscan 22. Shimamura, H. and Waterembe, H. 1981. and Precambrian Basement Reactivation: “Coseismic Changes in Groundwater Temperature Products of Continental Collision”. J. Geol. 81: of the Usu Volcanic Region”. Nature. 251:137- 683-692. 147.9. Dorbarth, L., R. Caulon, T. George, and P. 23. Shimamura, H., Ino, M., Hilcawa, H., and Iwasaki, Mougue. 1983. “Guinean Earthquake of December T. 1985. “Groundwater Microtemperature in 22, 1983”. Tectonophysics. 82:112-124. Earthquake Region”. Pageoph. 122: 937-946.10. Hospers, J. 1971. “The Geology of the Niger Delta 24. Short, K.C. and Stauble, A.J. 1967. “Outline of the Area”. In: Geology of the East Atlantic continental Geology of the Niger Delta”. Am. Assoc. Pet. Geol. Margin. F.M. Delany (ed). Africa Inst. Geol. Sci. Bull. 51 761-779. Rep; 70/16 :209. 25. Wakita, H. 1981. “Precursory Changes in11. Junner, N.R. 1941. “The Accra Earthquake of 22nd Groundwater Prior to the 1978 IZU- Oshima-Kinkui June, 1939”. Gold Coast Geological Survey. Earthquake”. In: Earthquake Prediction. An Bulletin 13. International Review. Maurice Ewing Series. Simpson, D. W. and Richards, P. G. (eds.)12. Kennedy, W.Q. 1965. The Influence of Basement American Geophysical Union: Washington, D.C. Structure on the Evolution of the Coastal 527-532. (Mesozoic and Tertiary) Basins, in Salt Basins Around Africa. The Institute of Petroleum: London, 26. Wetmiller, R.J and Forsyth, D.A. 1978. “Seismicity UK. 7-16. of the Artic”. Geophysical Review Pub. Earth Phys. Branch. 45:15 -24.13. Krenkel, E. 1957. Geologie and Bodenschatze Africas, second ed. Akad. Verlag: Leipzip, Germany. ABOUT THE AUTHOR14. Merki, P.J. 1970. “Structural Geology of the Cenozoic Niger Delta. African Geology”. Proc. Dr. Edward O. Osagie currently serves as an Ibadan Conf. Afr. Geol; Ibadan, Nigeria. Assistant Professor of Physics at Savannah State University. He had been teaching at the15. Nur, A. 1972. “Dilatancy, Porefluid and University of Benin in Nigeria. Dr. Osagie earned Premonitory Variations in Ts/Tp travel times”. Bull. his bachelor’s from the University of Lagos in Seis. Soc. AA. 62:1217-1222. Nigeria, master’s degrees from the University of Lagos and Princeton University, and his doctorate16. Rahaman, M.A. and Ocan, O. 1978. “On from St. Louis University. Relationships in the Precambrian Migmatitic Gneises of Nigeria”. Journal of Mining and Geology (Nigeria). 15:23-32. SUGGESTED CITATION17. Rahaman, M.A., Olarewaju, V.O., Ocan, O., and Oshin, I.O. 1983. “Crystal Evolution During the Osagie, E.O. 2008. “Seismic Activity in Nigeria”. Proterozoic in Southwestern Nigeria”. Bulletin of Pacific Journal of Science and Technology. the Science Association of Nigeria. 9:135-136. 9(2):546-551.18. Rechenmann, J., Blot, C., and Crenn, Y. 1960. “Measures Gravimetriques et A.O.F.”. Pacific Journal of Science and Technology O.R.S.T.O.M.: Paris, France.19. Rex, D.C., Grant, N.K., and Freeth, S.J. 1971. “K/ 87 86 Ar ages and Sr / Sr Ratios from Igneous Rocks in the Benue Trough”. Conf. Afr. Geol. 6th Leicester. Abstr.The Pacific Journal of Science and Technology –551–http://www.akamaiuniversity.us/PJST.htm Volume 9. Number 2. November 2008 (Fall)

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