Deterministic seismic hazard assessment close to a gas field in northern Oman

The Northern Oman region has one of the most important on-land gas reservoirs in Oman, which has been exploited since 1979. Earthquakes with small magnitude and shallow depth that have been induced by gas exploitation were proved to cause light damage to structures on gas and gas fields in the region. Therefore, a long-term (unfortunately intermittent) monitoring program for the seismicity of this area was started in 1999 in order to contribute to the seismic risk reduction. The main aim of the current study is to conduct a deterministic seismic hazard assessment in order to provide the maximum ground-motion spectra at 12 selected sites inside the area of interest and to recommend the elastic design response spectra of any intended structures at each of the selected sites. The 5 % critical damping spectra were calculated at the median and 84th percentile levels. The site effect considered in all the used ground-motion prediction equations was evaluated based upon the value of the average shear-wave velocity in the upper most 30 m (V_S30) at each of the selected 12 sites. Shear-wave velocity (V_s) was evaluated using the multichannel analysis of surface waves. The 12 sites were investigated with survey lines of 40 m length. 1-D and interpolated 2-D shear-wave velocity profiles have been generated up to a depth range of 25–40 m. The median PGA ranges from 54 cm/s² at site no. 4 to 72 cm/s² at site no. 9, which resulted from an earthquake with magnitude 3.6 at 4.45 and 2.92 km distance respectively from the interested sites. High frequency ground motions are found to be controlled by nearby seismic zones, whereas the low frequency ones are controlled by the distant western Makran large magnitude earthquakes. Finally, the hazard results were used to calculate the elastic design response spectra at each site of interest.