Primary-level Site Effect Zoning in Developing Urban Areas Through the Geomorphic Interpretation of Landforms
Authors: Pak Tarmani Zahra , Masoumi Zohre , Shabanian Esmaeil 
Published: March 2022

&lt;p&gt;The site effect has a great impact on seismic hazard assessment in urban and industrial regions.&lt;br&gt;For instance, a layer of soft soil with a thickness of several meters amplifies seismic waves from&lt;br&gt;1.5 to 6 times relative to the underlying bedrock. Therefore, investigating the main characteristics&lt;br&gt;of Quaternary deposits such as the granulometry and mechanical layering is crucial in site effect&lt;br&gt;studies. These parameters are directly related to the local geologic/geomorphic setting and genesis&lt;br&gt;processes of the Quaternary deposits. Nevertheless, large cities in development countries have&amp;#160;&lt;br&gt;rapidly been enlarged covering Quaternary terrains before being evaluated for the site effect. This&lt;br&gt;rather rapid growth in urbanization interested us to take advantage of ancient aerial photographs&lt;br&gt;reprocessed with new image processing techniques in order to provide 3D terrain models from&lt;br&gt;such kind of areas before the recent urbanization. It helped us in the geomorphic terrain&lt;br&gt;classification and the detection of regions with different site effects originally caused by the&lt;br&gt;geomorphic setting and genesis of the Quaternary terrains. For example, site effect in a river flood&lt;br&gt;plain will be different from surrounding areas underlined by alluvial conglomerates or bedrock.&lt;br&gt;The main target of this study is investigating the primary-level site effect in Urmia city using 3D&lt;br&gt;geomorphic models derived from ancient aerial photos taken in 1955. Urmia in NW Iran is one of&lt;br&gt;the populated high-risk areas according to the standard regulations of earthquake in Iran, and&lt;br&gt;covers a wide region from mountainous areas to the ancient coast of Lake Urmia, with the Shahr&lt;br&gt;Chai River as the axial drainage. We created the 3D terrain model through the Structure from&lt;br&gt;Motion (SfM) algorithm. We have provided a detailed geomorphic map of Plio-Quaternary terrains&lt;br&gt;using the 3D Anaglyph view, Digital Elevation Model (DEM), and orthophoto-mosaic of the&lt;br&gt;region. It was complemented by granulometry and mechanical layering information from the&lt;br&gt;available geotechnical boreholes to reconstruct a shallow soil structure model for the area. It&lt;br&gt;allowed us establishing a primary-level site effect zoning for Urmia. Our results reveal the&lt;br&gt;presence of five distinct geomorphic zones, with different genesis processes and soil characteristics&lt;br&gt;from piedmont to coastal zones, which represent different soil structures and probable site effects.&lt;br&gt;This zoning paves the way for performing complementary site effect investigations with lower&lt;br&gt;time consummation and cost. The developed method, proposes a sophisticated tool to evaluate&lt;br&gt;primary site effect in areas covered by urbanization subjected to future natural hazards like&lt;br&gt;earthquake, landslide and flood before designing geophysical networks for the measurement of&lt;br&gt;quantitative site effect parameters such as Nakamura microtremor H/V and Multichannel Analysis&lt;br&gt;of Surface Waves.&lt;br&gt;Key words: Earthquake hazard, Site effect, Image Processing, Aerial photos, Quaternary geology, Structure from&lt;br&gt;Motion&amp;#160;&lt;/p&gt;