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We integrated satellite imagery (Landsat-8) with ground-truth data to produce a detailed and complete geological map of the Farasan Islands, off the Red Sea coast of Saudi Arabia at a scale of 1:100,000. This new map improves upon past efforts by expanding the mapped lithologies on the islands into four categories. We used different techniques to enhance this lithological differentiation, including band combination with ratio stretching and supervised classification techniques based on direct field validation. The former was used to distinguish differences in reflectance values across sets of bands to create a classification image from typical reflectance patterns. The geological feature boundaries were constrained by opensource high-resolution satellite imagery (WorldView-2) as well as field observations. The resulting map clearly distinguishes between different geomorphic and geologic features, including lineaments and lithologies. As the Farasan Islands are relatively remote and not easily accessible, with an area of 739 km 2 , these imagery-analysis techniques were an effective tool for using remote sensing data to produce new and better mapping products of this important area.

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Microtremor measurements become one of the widely accepted tools to evaluate the site response characteristics since the last two decades. These measurements have been conducted at four sites inside King Abdulaziz City for Science and Technology (KACST), Riyadh city, Saudi Arabia to estimate the resonance frequency and the associated amplitude of sediments. Microtremor measurements have been recorded for 24 h with a sampling frequency of 100 Hz in the range from 0.2 to 25 Hz band-pass filter. Origin of the identified peaks has been tested. The estimated peaks are correlated with borehole geotechnical data: (1) the first peak with an average frequency of 8.25 Hz that reflects the impedance contrast between the uppermost surface soil and the underlying completely weathered limestone and (2) the second peak of 1.43 Hz which corresponds to the impedance contrast between the completely weathered limestone and the underlying limestone rocks. In addition, the relation between sediment thickness and resonance frequency has been assessed. Based on the results of this study, it can be stated that microtremor measurements are capable to estimate thickness of sedimentary overburden. These results will support for seismic safety in case of civil engineering constructs in KACST area.