Surface soil assessment in the Ubhur area,north of Jeddah,western Saudi Arabia,using a multichannel analysis of surface waves method |
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| Authors: | Maher Aldahri Saad mogren Kamal Abdelrahman Hani Zahran Sherif El Hady Mahmoud El-Hadidy |
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| Institution: | 1.Saudi Geological Survey,Jeddah,Saudi Arabia;2.Geology and Geophysics Dept.,King Saud University,Riyadh,Saudi Arabia;3.Seismology Dept.,National Research Institute of Astronomy & Geophysics,Cairo,Egypt;4.Geophysics Dept.,King Abdul-Aziz University,Jeddah,Saudi Arabia |
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| Abstract: | Ten boreholes drilled in Ubhur area up to the depth of bedrock indicted the shallow depth of bedrock where the average depth ranges between 10 and 15 m. The standard penetration test N-values of these boreholes were measured and averaged. Based on N-values to the depth of bedrock, Ubhur area can be classified as site class C and D. Multichannel analysis of surface waves technique has been applied along seventy six profiles using 24-channel geophone array and 4.5Hz vertical geophones with 1m geophone spacing and sledgehammer and/or weight drop as seismic energy sources. Values of shear wave velocity to 30 m are calculated and then averaged (Vs30) where it ranges between 310.08 m/s and 1139.8 m/s. Therefore, Ubhur area can be classified into site class B, C and D based on site classification of the national earthquake hazards reduction program (NEHRP) recommendations. Accordingly, the greatest part of the study area falls in site class C while class B and D covered limited areas in the western and the eastern parts respectively. Depending on the shallow depth of bedrock in the study area, the Vs30 parameter is not applicable in the study area so the average values of Vs for the soil thickness, excluding the bedrock, have been calculated and mapped for site class C and D only. So Vs30 approach is not applicable for areas with shallow depth of bedrock which gives higher classification. |
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