Determine Site Effect of Zarqa City and Hashemite University Campus Based on Microtremors Field Measurements: a microzonation Stud

Waleed Eid Olimat

Jordan Seismological Observatory (JSO); Natural Resources Authority (NRA), Jordan

waleedolimat@yahoo.com; w.olimat@gmail.com

Zarqa governorate is one of the important governorates in Jordan. It is the second populated after the capital Amman, the location of Zarqa gives the city a great importance because it lies on the main high ways leading to Syria, Iraq and Saudi Arabia, most of Jordan's industries, power plants and strategic projects are located in Zarqa, which gives this city a special importance.

The Nakamura's technique is applied in this study for both areas; Zarqa city and Hashemite University Campus in order to determine the resonance frequencies and amplification factors for each site then draw there maps which will be of a great use in the field of civil and structural engineering by enriching the building codes.

The results of our study show that; values of resonance frequency F are not affected by the time of recording. While values of amplification factor A can vary accordingly. Results also show that the amplification factor A varies from 0.8 to 8.55 in Zarqa city and varies from 0.4 to 9.36 in Hashemite University Campus, the resonance frequency (F) also varies between 0.37 Hz and 2.98 Hz in Zarqa city and varies from 0.59 Hz to 1.77 Hz in Hashemite University Campus, that means some constructions in the study area, in case of a major earthquake, may experience minor damages respectively.

Geophysics Shallow subsurface investigation using 2-d seismic refraction tomography

Ahmed I.I ¹, Osazuwa I.B. ²

1Department of Geology, Ahmadu Bello University Zaria, Nigeria; 2Department of Physics, Federal University of Petroleum Efurun, Nigeria

Iiahmed@abu.Edu.Ng

Geophysical investigation involving seismic refraction tomography (SRT) was conducted at a sewage treatment site at Ahmadu Bello University Zaria with the objectives of determining the overburden thickness and velocity of the subsurface layers in the area, and delineating any geological structures, such as fractures, that may pose a threat to the safe running of the Sewage lagoon system in the area.

Five seismic profiles, with three running N-S and two running E-W, were acquired over the earthen-dikes separating the lagoons with the aid of a 24-channel digital Seismograph and a 10 kg sledge hammer striking a rubber plate. Shots were fired at 2.5 m interval within the offset and the geophone spread.

Tomography models were then generated for each of the profiles with the aid of ray tracing through a wave-front inversion method that is based on finite difference approximation of the eikonal equation. Geological artifacts, as a result of noise observed in the tomography models of some of the profiles, were removed by filtrations that include manual editing of model’s physical parameters and iterative model updating through simultaneous iterative reconstruction techniques (SIRT).

The result of the investigation shows that the area consists of three subsurface layers; an undifferentiated overburden layer with a P-wave velocity range of 891 m/s to 1.421 km/s, a partially weathered zone with P-wave velocity range of 3.010 km/s to 5.129 km/s and underlying fresh granitic basement with P-wave velocity range of 5.704 km/s to 7.762 km/s, while the overburden thickness in the area varies from an average of about 18 m in the northern part to about 55 m in the southern part. The investigation also revealed a fracture zone within the underlying granitic basement, which occurs at about 60 m below the earthen-dike located at the centre of the study area.

References

1. Ike, E. C. (1988), Late-stage Geological Phenomena in the Zaria Basement Granites, In Precambrian Geology of Nigeria, Geological Survey of Nigeria Spec. Pub. pp. 83-89.

2. Ososami, A. I. (1968), Assessment of the Groundwater in the Kubanni valley, Zaria. An Unpublished M.Sc. Thesis, Department of Civil Engineering, A. B. U. Zaria.

3. Shemang, E.M., Ajayi, C.O. and Osazuwa, I.B. (1992). The Basement Rocks and Tectonism in the Kubanni River Basin, Zaria Nigeria: Deductions from D.C. Resistivity Data. Journal of Mining and Geology, Vol. 28; No.1, pp. 119-124.