Data Services Newsletter

Volume 15 : No 3 : Winter 2013

The New Nigerian Network of Seismographic Stations

The Center for Geodesy and Geodynamics under the National Space Research and Development Agency (NASRDA), has been managing Nigerian National Network of Seismographic Stations (NNNSS) since 2006 after it was handed over by the National Agency for Science and Engineering Infrastructure (NASENI). The NNNSS presently has five operational stations equipped with 24-bit 4-channel recorders (digitizer and data logger) and broadband seismometers. The recorders and seismometers were manufactured by Eentec Company. The Five operational stations in Nigeria are located in Kaduna, Nsukka, Ile-Ife, Awka, and Toro (Fig. 1). Five other proposed stations in Oyo, Abuja, Minna, Ibadan and Abakiliki have been constructed. However, no seismic equipment are installed.

Figure 1  - Nigeria Map
Figure 1: Map of Nigeria showing operational stations (blue triangles) and proposed ones (yellow triangles). Note: Instruments are presently not installed at Oyo station.

The equipment at each station are: DR-4000 data acquisition system, EP-105 broadband (30 seconds period) seismometer or SP-400 medium period (16 seconds period) seismometer, manufactured by Eentec (Fig. 2). New sets of equipment have also been procured: the DR-4050 data acquisition system, EP-300 broadband sensor (100 seconds & 60 seconds period respectively). For time synchronization, the equipment at the stations are connected with Global Positioning System (GPS), while solar panels and 100 AH battery are provided as power source, at the remote stations. Serious efforts are being made to network all the remote stations (Kaduna, Ife, Awka and Nsukka) to Toro Central station for real time data transmission within Nigeria and robust sharing amongst neighbouring countries and other international agencies. Although, there exit pockets of challenges to transmit data from Toro station in real time due to absence of a seedlink server, even with the installation of VSAT (Fig. 3), nonetheless, it is now possible to download data from the station through ftp in anywhere in the world. Many thanks to IRIS-DMC that made this initial step to provide internet connectivity to all the stations a reality. This indeed is a milestone achievement. The Center for Geodesy and Geodynamics is working tirelessly to see that all the stations are provided with internet connectivity in the nearest future, to make data sharing stress-free. Below are pictures from TORO station including equipment installed.

Figure 2 - Toro station
Figure 2: (A) Toro station on stable immobile rock hosting other monitoring equipment like GPS; (B) Vault; (C) Digitizers: yellow box is Eentec DR4000 and the red box is DR4050; (D) Insulated Eentec EP105 in a vault at Toro.

Figure 3 - VSAT unit
Figure 3: (A) Newly acquired 1.2m Dish VSAT outdoor unit; (B) Low Profile Database server hosting seismic data installed at Toro station (Courtesy IRIS-DMS).

Nigeria is not located in regions that are seismically active in the world; the question readily posed by experts who are aware of this fact is always, why does Nigeria need a network of seismographic stations? Before I will attempt to provide incisive answer to this query, let me give a brief account of the geological setting of Nigeria.

Apart from being located within the intraplate area, Nigeria’s land mass is made of Precambrian to Early Paleozoic crystalline basement rocks, about half of which is covered by sedimentary rocks of Cretaceous to recent age (Fig. 4). About two-thirds of the country’s landmass is underlain by the Pre-cambrian basement complex consisting of gneisses, migmatites, schist, and various metamorphic rocks and granites (Eze et al., 2011). These are in places intruded and interspersed by the “Older granites” which originated in the Pan-Africa Orogeny (Olujide and Udoh, 1989). Basement Complex rocks outcrop in four main areas of the country: North of Rivers Niger and Benue, covering parts of Kaduna, Plateau, Bauchi, Kano and Sokoto States; southern Nigeria, covering the greater parts of Kwara, Oyo, Ogun; and Ondo States; southeast Nigeria, spanning the northern parts of Cross Rivers State and as far north as Yola; and north of Benue River in Gongola State (Eze C.L et al, 2011). These crystalline basement rocks have been subjected to deformation of different intensities throughout the geological period. Consequently, North-South (N-S), Northeast-Southwest (NE-SW), Northwest-Southeast (NW-SE), North northeast-South southwest (NNE-SSW), North northwest-South southeast (NNW-SSE) and to a lesser extent, East-West (E-W) fractures have developed (Olujide and Udoh, 1989). See Fig. 4.

Figure 4 - Nigeria Geological Map
Figure 4: Map of Nigeria showing Geology of the Country. Courtesy Afegbua et al., 2011.

There exist, some confirmed and others not, faults, like the SW-NE Ifewara-Zungeru trending which is believed to be responsible for the various earth tremors experienced in the South Western Nigeria. Several minor tremors had also been experienced in other parts of the country in 1933, 1939, 1964, 1984, 1990, 1994, 1997, 2000 and 2006 with intensities ranging from III to VI based on the Modified Mercalli Intensity Scale. But only few of these tremors like the 1990, 1994 and 2000 events were recorded instrumentally (Akpan and Yakubu, 2010; Afegbua et al,. 2011). Earthquakes that occurred on 28th July and 2nd August, 1984 whose vibrations were felt in south-western Nigeria towns of Ijebu-Ode, Ibadan, Abeokuta etc., prompted the Federal Government of Nigeria through the Federal Ministry of Science and Technology to set up the National Technical Committee on Earthquake Phenomena (NTCEP) to advise it on measures to adopt to mitigate the effects of such occurrences. In 1995, The NTCEP recommended the establishment of the NNNSS with a central station initially planned for Abuja (but now in Toro) and 9 remote stations. The remote stations were to be sited at Abuja, Kaduna, Minna, Ile-Ife, Ibadan, Oyo, Nsukka, Awka and Abakiliki. In the same vein, in 1989, Nigeria through the effort of the NTCEP indicated her interest to participate in global co-operative programme in Space Geodesy with the aim of providing insight into African plate tectonics, global geodynamics and the study of earthquake mechanisms. The central and remote stations were subsequently constructed in 2001 and 2002.

Apart from the earthquake monitoring exigencies, Nigeria also aims to use its network to explore collaboration opportunities with other agencies involved in hazard monitoring; mitigate losses that might result due to hazards, and to establish an Integrated Seismic hazard monitoring scheme since the country is seriously considering the deployment of critical facilities that require seismic hazard investigations as part of its developmental plans. The overall goal is to see data from all functioning stations in Nigeria streamed real-time to interested users through SEEDLink server, which would in turn assist Nigeria realize seismic hazard monitoring scheme indirectly.

Figure 5 - Kaduna and Awka Stations
Figure 5: (A) Kaduna Station on a basement complex in the northern part of Nigeria; (B) Awka on sediments in the south respectively; (C) Vault at Awka station.

References

Afegbua et al, (2011): Towards an Integrated Seismic Hazard Monitoring in Nigeria using Geophysical and Geodetic Techniques; International Journal of the Physical Sciences Vol. 6(28), pp. 6385-6393

Akpan O.U and Yakubu T.A, (2010): A Review of Earthquake Occurrences and Observations in Nigeria; Earthquake Science; Vol. 23, no. 3 Pp 289-294.

Eze CL, Sunday VN, Ugwu SA, Uko ED, Ngah SA (2011). Mechanical Model for Nigerian Intraplate Earth Tremors. Disaster Management, Earth Observation

Olujide, P. O. and Udoh A. N. (1989). Preliminary comments on the fracture systems of Nigeria. In Proceedings of the National Seminar on earthquakes in Nigeria (Ed.) Ajakaiye D. E; Ojo S. B. and Daniyan M. A. 97-109

Appendix

Table 1: Showing some properties of the equipment installed at the stations

Parameters EP105 (Broadband) SP400 (Medium period)
Operating principle Proprietary Electrochemical Sensors; force-balanced Proprietary Electrochemical Sensors; force-balanced
Output signals 2 horizontal, 1 vertical; velocity flat response 2 horizontal, 1 vertical; velocity flat response
Output swing ±20 V differential; (40 V p-p) ±20 V differential; (40 V p-p)
Dynamic Range 142 dB 142 dB
Passband 0.033 – 50 Hz 0.067 – 50 Hz
Generator constant 2000 V/m/s 2000 V/m/s
Maximum installation tilt ±10° ±10°
Mechanical resonances none none
Environmental Waterproof, submersible (1m) Waterproof, submersible (1m)
Temperature range -12 to +55°C -12 to +55°C
Housing material Aluminum Aluminum
Weight ~8kg ~8kg
Power 10-15 Vdc; (Nominal 12Vdc);
30 mA
10-15 Vdc; (Nominal 12 Vdc);
30 mA (12Vdc); 30mA

by Kadiri Umar Afegbua (National Space Research and Development Agency (NARSDA))

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