Although Nigeria is not located within the major seismic zones of the world; over the years, several minor earthquakes have been experienced in some parts of the country. The first widely reported occurrence of an Earth tremor in

The evaluation of an intra-plate earthquake that occurred on Friday, 11 th September, 2009 and felt in parts of Abeokuta, Ago-Iwoye, Ajambata, Ajegunle, Imeko, Ijebu-Ode, Ilaro and Ibadan, all in south western Nigeria is presented. This event has been the largest inland earthquake recorded since the inception of digital seismological recording in Nigeria in 2008 was incepted. The event was recorded by three seismological stations operated by Centre for Geodesy and Geodynamics (CGG), Toro. Data obtained from the CGG stations and others distributed around the world were analysed to determine precise earthquake locations and focal mechanism and to assess the regional tectonic stress. The data recorded in MiniSEED format at a sampling rate of 40 samples per second (sps) were analyzed using the SEISAN earthquake analysis software. The result showed an epicentral location situated about 108 km west of Lagos, a focal depth of 10.0 km and an origin time of 03:10:21.60 GMT. The local and moment magnitudes were 4.5 and 4.2 respectively. The P-wave to S-wave velocity ratio was 1.72. The fault plane solutions obtained for the rupture process indicated that a normal dip-slip fault with median solution of strike 325˚, dip 40˚ and rake −90˚ was the probable trigger mechanism for this earthquake. It suggested that the event was a reactivation of a buried high-angle fault in the Precambrian basement represented by the contemporary northeast-southwest trending regional horizontal compressive stress. Generally, the seismotectonics of the region was linked to the fracture zones in the Atlantic Ocean.

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This article presents the results of a study carried out to relate the frequency of pavement failures, the engineering indices of the ? .')grade materials and the underlying geology. The results show a high variability in the indices such as the liquid limit, LL, the pidsticity index, PI, the maxirnum dry density, MDD, the optimum moisture content, OMC, compressibility and the California Yearing Ratio, CBR, between the different geologic units. Engineering indices having significant correlation with CBR (the major criteria for assessing the quality of subgrade materiais), are used to develop a scheme for evaluating the materials at different failure points along the Calabar-ltu Highway in Nigeria. The evaluation shows that locations exhibiting high failure rates are underlain by shaly or marly subgrade whereas locations characterised by low failure rates are underlain by weathered basement or sandy unit as subgrade. It is recommended that .maintenance and provision of drainage facilities will go a long way to reducing the rate of fsilure.

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