İzmir Fault

The fault trending east-west, located in the east of  İzmir bay and limiting the bay morphologivally from south, is called as İzmir fault (Emre and Barka, 2000). When the studies on the fault are examined, it is seen that the fault is named as İzmir Fault (IF) or İzmir Fault Zone (IFZ). The İzmir Fault is mentioned in the geological studies carried out for different purposes in İzmir and its surroundings (Kaya, 1979, 1981), but the first evaluations of the fault zone's activity were made by studies conducted after 2000 (Emre and Barka, 2000, Emre et al., 2005, Sözbilir et al., 2008). The İzmir fault is a normal fault with 2-4 km width and 40 km length between Güzelbahçe and Pınarbaşı (Emre et al., 2005, Sozbilir et al., 2008, Uzel et al., 2012). The southern part of the inner bay is considered as a tectonic pit located to the north of the fault in İzmir bay. With this feature, the inner bay is similar to the Gediz graben system, which forms one of the largest depression basins formed in the West Anatolian extensional tectonic regime (Hakyemez et al., 1999). The fault, which is the continuation of the northern branch of the Kemalpaşa Fault at the western end of the Gediz graben, starts from Pınarbaşı in the east and continues to Güzelbahçe. Balçova geothermal field is located on this fault system. However, there is no research on the continuation of the fault in the open sea from Balçova-Narlıdere to the west (Coskun et al., 2017). D-B trending İzmir Fault consists of two segments. The section extending between Güzelbahçe in the west and Konak in the east is named as the Balçova-Narlıdere segment, and the section between Konak and Pınarbaşı is named as the Pınarbaşı segment (Figure 1, Emre et al., 2005). On the MTA map, the Balçova-Narlıdere segment of the fault is shown as Holocene (active fault), and Pınarbaşı segment as Quaternary fault (possible active fault). In the area between the two segments (between Konak and Üçkuyular), the fault is thought to continue under the sea.

When the instrumental period records are examined, it is seen that there is an intense earthquake activity in the close to İzmir city center. However, micro-earthquakes that have occurred on the İzmir fault throughout history are concentrated in the Pınarbaşı segment, which forms the eastern part of the fault (Akıncı et al., 2000). Sözbilir et al. (2008) stated that the fault has an oblique slip component and is kinematically linked with the Seferihisar Fault Zone (SFZ). Drahor and Berge (2017) showed that the fault split into many parts to the west of the Ilıca creek in their studies in which they investigated the secondary faults connected to the IF. In the study, using Ground Penetrating Radar (GPR), Electrical Resistant Tomography (ERT) and Seismic Refraction Tomography (SRT) methods, it was stated that the width of the main fault is 250 m and it extends in the NE-SW direction (Dragor and Berge, 2017). It is known that İzmir Bay is a tectonic depression basin and there is a thick and problematic soil structures due to sedimentation by the rivers flowing into this basin. This structure magnifies the ground motions and increases the damages in the earthquake (Gok et al., 2014; Eyidoğan, 2020).

 There are two major studies in the literature called as "İzmir Earthquake Scenario and Earthquake Master Plan (IBBDMP, 1999)" and MTA report by Emre et al., (2005). In both studies, the İzmir fault was considered among the active faults that could cause a major earthquake for İzmir metropolis. The fact that, the fault passes through Konak, Balçova and Narlıdere, which are the most crowded and highly dense central districts in the city center, having a risk in terms of material and non-material damages to be caused by a major earthquake. It is stated in both literatures that the  field (in situ) studies could haven't been carried out in and around the İzmir Fault (IF) due to heavily urbanization.