Soil classification for seismic site effect using MASW and ReMi methods: A case study from western Anatolia (Dikili -İzmir)

Abstract

The study area is located in the northern part of Izmir, Western Turkey, prone to an active tectonic extensional regime and includes typical features of sedimentary basins, horst-grabens surrounded by a series of normal and strike-slip faults. In September 1939 the Dikili (Kabakum) earthquake with a magnitude of Mw: 6.6 occurred and after this phenomenon, residents moved from the west of Dikili to the east (i.d. soft sediments to relative to rock area). A proper estimate of the earthquake-related hazard for the area is the main objective of this study. The site effect and soil engineering problems for estimating hazard parameters at the soil surface need to be carefully analyzed for seismic site classification and geo-engineering problems like soil liquefaction, soil settlement, soil bearing capacity and soil amplification. To solve the soil static and dynamic problems, shear-wave velocities have been used in a joint interpretation process; Multichannel Analysis of Surface Waves (MASW) and Refraction Microtremor (ReMi) analyses were conducted on 121 sites with 300×300 m grid size in an area of 60km2. It has been proposed that the probability of an earthquake with a magnitude of Mw: 6 occurring within 10years is 64%, when considering the Gutenberg-Richter model. This puts the region under an important earthquake risk. The estimated Vs30 values are ≤180m/s in the central and the northernmost part of the study area are showing an E type soil after the classification of NEHRP, where alluvial deposits are dominant. Vs30 values in the north and central part are between 180≤Vs≤360m/s suggesting a D type soil. In the southernmost part of the study area where volcanic rocks are widely distributed, Vs30 values range between 360 and 908m/s, corresponding to a C type and B type soil. The results show that soil liquefaction induced settlement and soil amplification are the most important problems in the south and the northernmost part of the study area, which is densely populated and encompasses the urbanized part of the study region.