Near Büyükılıca Village, İvrindi District of Balıkesir is geologically composed of pre-Tertiary basement units, Tertiary volcanics and clastic units and Quaternary deposits such as travertine, debris sediments and alluviums. Quaternary deposits outcrop along the NE extending Kocaçay valley.
In the light of field studies and measurements around Büyükılıca village, the faults are identified along morphological scarp in the south of İvrindi through elongated ridges and the lines forming deep valleys. It is seen these faults that cause complex stratigraphic relationships in the region, consist of main and secondary faults developed in the shear regime.
The main component of these lines, which have NE-SW and NW-SE trend, is Kocaçay fault that is a right lateral strike-slip fault with a reverse slip component, which limits the project area from the east. It is seen that this fault is divided into semi-parallel conjugate faults especially at the west part of the study area.
Fracture sets, releasing and restraining bends are developed by the shear regime in the areas with block movement between the splayed and combined secondary branches, in the western part of the Kocaçay fault. The hot water outlets that provide the travertine formation in the study area are provided along the fractures which are the product of this deformation.
Another fault line in the study area is the left lateral strike-slip fault, where intense deformation and slickensides are observed in the south entrance of Büyükılıca village, and this NW trending fault cuts the ridges that the village is located. It is seen that the secondary components of the fault presenting the vertical components along the fracture planes form the flower structures (positive-negative flower).
Paleoseismological studies were carried out in 5 trenches perpendicular to the specified fault planes; no discontinuity, surface rupture or changes were observed that could indicate deformation of alluvial units, slope debris sediments, and flood deposits as well as soil coverings, which were thought to be formed during the Holocene period.
Although the faults do not provide surface rupture, the slip of the river because of the Balıkesir fault in the north of the region reveal the potential to produce a 7.2 magnitude earthquake. The fact that no surface rupture during the 2000 year period in the Gökçeyazı segment could be seen in the previous studies suggests that there is a seismic gap which could affect the study area.
Anahtar Kelimeler: Geology of the Buyukılıca, Kocacay Fault, Paleoseismology, Earthquake
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