Akademik Veri Yönetim Sistemi
TURKIYE JEOLOJI BULTENI-GEOLOGICAL BULLETIN OF TURKEY, cilt.52, sa.2, ss.217-238, 2009 (ESCI, TRDizin)
Izmir city and its surroundings are located in the strike-slip dominated zone of weakness known as the Izmir-Balikesir Transfer Zone. The latest activity of the zone was evidenced by the October-2005 Sigacik earthquakes. In this study, we merge the seismic geomorphological features of the Izmir earthquakes with the active faults and stress field of the region. Three main shocks (17 October 2005 at 05: 45, Mw = 5.4; 17 October at 09: 46, Mw = 5.8 and 20 October at 21: 40, Mw = 5.9) occurred in the Gulf of Sigacik synsedimentary structures to form. These structures have been mapped and evaluated with respect to their seismo-geomorphological features. The syn-sedimentary deformational structures occur around Demircili village and Yumlu Farm to the south of the Urla Basin. These structures developed in recent sediments which comprise beach gravels and sands that interfinger with the river deposits. The seismites are composed of NE- and E-W-trending fractures and sand volcanoes due to liquefaction. NE-trending cracks are from tens of centimetres up to several metres long and display an en-echelon pattern that locally forms an anastomosing geometry. They trend N40-70 degrees E in accordance with main fault segments. E-W-trending cracks are oriented parallel to the coastline of the Sigacik Bay and have a dip-slip displacement up to a maximum of 8 cm. At Yumlu Farm, the shaking created a linear fissure that extends NNE in direction. To the north of the Urla Basin, we also observed a small-scale landslide that developed in the stepover area of the western margin of the basin. Although syn-sedimentary deformational structures can be attributed to a simple seismic shaking, they appear to display a close spatial and temporal relationship with the tectonic framework of the region, shaped by NE/NW-trending strike-slip faults and E-W-trending oblique-slip normal faults of Quaternary age. The main events and aftershocks of the Izmir earthquakes clustered on this fault pattern, indicating a negative flower structure that is real evidence of earthquake related tectonic framework. This flower structure is characterized by an arrray of upward-diverging strike-slip dominated zone that shaped the Quaternary Urla Basin.