Near-surface site characterization at Quriyat City, Sultanate of Oman using HVSR and MASW techniques
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ORIGINAL PAPER
Near-surface site characterization at Quriyat City, Sultanate of Oman using HVSR and MASW techniques A. M. E. Mohamed 1,3 & I. El-Hussain 1 & A. Deif 1,3 & K. Al-Jabri 2 & Z. Al-Habsi 1 & S. El-Hady 3,4
Received: 8 May 2015 / Accepted: 10 September 2015 # Saudi Society for Geosciences 2015
Abstract It is well known that the effects of near-surface structures on ground shaking represent an important factor in earthquake ground motion amplification; in particular, soft sedimentary cover could strongly amplify the seismic motion. The parameters of the soft layer that controls the amplification most are the fundamental frequency and the shear-wave velocity. The frequency band of the ground motion that is affected by such factors depends on the thickness and the velocity of the sedimentary layers. In order to investigate and characterize the near-surface structures beneath Quriyat coastal city in the Sultanate of Oman, Nakamura’s technique which was characterized by the horizontal-to-vertical spectral ratio (HVSR) of the ambient noise measurements was used to estimate the fundamental frequency of the soft soil at 70 sites. The shearwave velocity is an important tool in the design of buildings for site-specific conditions and is a much more diagnostic tool for engineering properties. The multichannel analysis of surface waves (MASW) was carried out at 40 sites at Quriyat City in order to evaluate the near-surface shear-wave velocities. The fundamental frequencies were found to be in the range of 2.0 Hz (occupying the coastal soft soil area) and 23.3 Hz (occupying the area close to the hard rock). The
* A. M. E. Mohamed [email protected]
1
Earthquake Monitoring Center, Sultan Qaboos University, Muscat, Sultanate of Oman
2
Department of Civil and Architectural Engineering, Sultan Qaboos University, Muscat, Sultanate of Oman
3
National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt
4
Earth Science department, King Abdull Aziz University, Jeddah, Saudi Arabia
average shear-wave velocities down to 30 m depth (Vs30) ranged from 225 m/s (class D according to NEHRP standard for site classification and covering the coastal area) to 1058 m/ s (class B covering the area in vicinity of hard rock). The results demonstrate that the HVSR of ambient vibrations were in a good agreement with the values of VS30. Areas of lower VS30 values exhibit lower fundamental frequency and cover areas with considerable soft soil thickness and vice versa. Keywords Quriyat City . HVSR . MASW . Seismic Refraction . VS30 . Site classification
Introduction The damage figures of infrastructures due to large earthquakes and their associated events have increased in recent times. The importance of site characterization for construction purposes has become crucial in order to prevent loss of structures and lives. Most of the reasons why buildings may be susceptible to collapse include poor quality of building materials, salinity, and old age of buildings. Less frequently mentioned is the subsurface condition
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