Active tectonics and seismicity of Balçova district and surrounding: Comparison of geologic and seismological data

In this study, it is aimed that the Balçova district and surrounding area are studied by geological and geomorphological methods to discuss the activity and earthquake potential of the İzmir Fault. İzmir Fault is an approximatelly E-W-trending fault which forms the southern margin of the İzmir Bay. In study area, the İzmir Fault consists of a fault zone pattern that include several fault segments along the lenght of the fault. The Balçova Geothermal System is also located within the zone.According to field observations and interrelationship between the geological features, the southern segment of the fault zone is interprated as a main fault. Various antithetic and synthetic faults are mapped on the hangingwall block. Whereas the footwall block consists of Bornova Melange rocks of Upper Cretaseous-Paleocene in age, the hangingwall rocks of the İzmir Fault are Bornova Melange rocks and Quaternary deposits including alluvial and fluvial deposits with marine interbeds.To understand recent activity of the İzmir fault, it has been established jeomorphological nidices and related geological maps by using 1/25000 scaled topographic maps. Geomorphologic indices (such as hipsometric curve, asymetry of drainage basin, river length-gradian index, sinuosity rate of mountain front (Smf index, width of valley floor- rate of valley height(Vf index)) have been calculated from analyses of geomorplogical markers (drainage basins, ironflat structure, axial river, mountain front sinuosity). With respect to the asymetry factor, there is tilting on the basin. The sinuosity rate of mountain front represents mean value within the basin. This value shows that the region is raised by active tectonics having an approximately linear mountain front.In addition to the above studies, kinematic analysis has been applied to the İzmir fault to establish its characterictic. To do this, it is measured the parameters on the fault planes along the İzmir fault. This result shows that the İzmir fault is an oblique normal fault.In the light of geological, geomorphological and seismological data, the mapped İzmir fault is the main source for earthquake potential of the Balçova region. For that reason, to establish the relationships between historic earthquakes and İzmir fault, it should be made paleoseismologic-based trench studies , and finally it should be determined earthquake potential/period of the fault. In addition to that, 1/1000-scaled maps of suitability for settlement should be prepared and new building should be constructed with respect to these maps.