Abstract
Dammam City was affected by strong earthquakes from Zagros fold-fault belt of subduction zone. These distant earthquakes of magnitude greater than 6.0 produced great site effects on the sedimentary layers that in turn significantly influenced earthquake ground motions in the area. Site effect in terms of fundamental frequency (f (0)) has been estimated using microtremor measurements and borehole geotechnical data. Microtremor measurements were carried out at 113 sites distributed well through Dammam City. These sites present two peaks of f (0). The 1st peak ranges from 0.25 to 3.0 Hz, while the 2nd one ranges from 4 to 8 Hz. The 1st peak is due to the impedance contrast between the limestone and the overlying sediments, while the 2nd peak originated from the upper most surface sediments and the underlying layer. Tests to ensure that natural origin of these peaks were conducted. The northwestern and southeastern parts of Dammam City have the lowest f (0) indicating great thickness of sediments. Whereas, the rest zones have higher f (0) values illustrating shallow depths of bedrock. In addition, the geotechnical data in terms of shear wave velocity, density, and soil thickness of different layers have been compiled at 30 boreholes where f (0) and average shear wave velocities up to 30 m depth have been calculated. Results of borehole data clarified that the fundamental frequencies range between 2.9 and 7 Hz, which correlated well with that of microtremor measurements. These results can be used for land use planning, preparedness purposes through improving of building design code in Dammam City.