Bench Mark Stability in Nigeria

The Use of Geodetic Leveling For Crustal Motion and Deformation Studies: A 30-Year Case Study in Ahmadu Bello University, Zaria

“…Benchmarks located upland are covered by another network, where about 70% of the benchmarks were displaced upward (uplifted) between 1976 and 2002 with a maximum value of 8.03mm between 1976 and 2002 at a ground station name CP13. These results when compared to those obtained by Ebong and Musa (1992) show that more movements have occurred over the last 14 years. The causes of these movements are investigated in this paper.…”

“…Henceforth, in this study the network around the University dam shall be tagged network A, while benchmarks upland form network B. It is important to note that the levelling networks reported in this paper do not include those already reported in Ebong and Musa (1992). It was reported in the latter paper that the first levelling network for the study of deformation on the University campus was established in 1976.…”

“…The major difference between the two networks lies in their locations. The type of benchmarks and monitoring stations used in this paper are the same as those already reported by Ebong and Musa (1992), except those of the 2006 survey in which a new type of benchmark (GSES series) was introduced; The GSES series of benchmarks are pre-cast concrete pillars measuring 15cm x 15cm in section and 76cm long. They consist of a 5mm diameter iron rod of length 74cm, with a galvanized metal plate measuring 10cm x 10cm embedded on the top surface of the pillars.…”

“…In Ebong and Musa (1992), the height differences of five benchmarks (BM3, BM9, BM10, BM11, and BM19) between 1976 and 1983 were analysed. It was revealed that the maximum and minimum movements recorded during this interval of time were 0.67mm and 0.08mm.…”

“…No great value was attached to these results because of the inherent weakness in the structure of the 1990 levelling loop from which the apparent movements were deduced. Benchmarks between 1976and 1983(after Ebong and Musa, 1992 Benchmarks Year (1979) and Other Epochs (after Ebong and Musa, 1992) Test Benchmarks 1979Benchmarks -1980Benchmarks (mm) 1979Benchmarks -1983Benchmarks (mm) 1979Benchmarks -1990 It is important to note that observational procedures adopted for the surveys reported in this paper are as described in Ebong and Musa (1992). The first complete measurement is usually referred to as the reference measurement.…”