Investigation of the site properties of Urla town and its surroundigs by using microtremor method

The microtremor method is in the last decade widely used for microzonation and site effects studies. Urla town which is located in western end of the İzmir Gulf, Türkiye, is one of the most populated, touristic and cultural city in the Aegean region. This region is sorrounded by the strike-slip faults of Urla, Karaburun and Gülbahçe of which the potantial of seismic activitiy have very high.Free-field Measurements HVSR analyses of 200 free-field microtremor measurements in the area of Urla showed that most of them fulfill the criteria defined by the European SESAME project (SESAME, 2004). In the Urla town, measurements of ambient vibrations were performed by using portable seismograph Guralp CMG-6TD velocity sensor during at least 30 min. The microtremor horizontal-to-vertical spectral ratio (HVSR) method was applied to a 250 m dense grid of free-field measurements over an extended area and to a 500 m grid in the outer part of the town area in order to assess the fundamental frequency of the sediments.The microtremor study has shown that local geological conditions can have important effects on seismic ground motion in the Urla region. Finally, the interpretation of the map of fundamental soil frequency derived from free-field microtremor measurements have been enhanced and validated by independent information from boreholes, from geophysical investigations, and from earthquake recordings. Since the interpretation of microtremors is limited to identifying the resonance frequency and gives no reliable indication of the amplification of seismic ground motion.