MODELLING OF BASIN STRUCTURES AND DETERMINATION OF WEST BLACK SEA FAULT IN THE AREA BETWEEN BUYUKCEKMECE AND KUCUKCEKMECE LAKES WITH USING DIFFERENT GEOPHYSICAL METHODS

Abstract

Two terrain-bounding major fault zones occur in the Marmara Sea and the northern onshore areas. The first of these is the dextral, E-W trending, North Anatolian Fault Zone which cuts through the deep basins within the Marmara Sea and is known to be one of the most seismically active fault zones on the Earth. The second is the inferred West Black Sea Fault Zone (WBFZ), a NNW-SSE trending, dextral boundary fault which separates the Istranca Massif to the west and the Istanbul Terrane to the east. The WBFZ is thought to have accommodated the opening of the east Black Sea basin. This fault zone and the two adjacent continental blocks are covered by Middle to Upper Eocene sediments and therefore the WBFZ is considered to be an inactive fault. Nevertheless, it forms a major crustal zone of weakness in the vicinity of Istanbul.

Istanbul established in an area which has been the influence of North Anatolian Fault Zone which occurred many great eartquakes and/or possible earthquakes in an area where there is a high danger today too. 3 deep basins determined (NE to SW trending) in the area between Küçükçekmece and Büyükçekmece Lakes by using microtremor measurements(Karabulut, 2012). Single station microtremor measurements at 326 points (with Guralp 6 TD seismometers) and gravity data (CG-5 autogravity meter) collected same measurement points from 2013 to 2015. Joint Inversion analysis were performed both them. Moreover, microtremor array measurements at 50 points were taken each 2 km gridding interval.

As results of microtremor measurements (H/V), we obtained soil fundamental frequency and sediment thickness map were calculated and plotted by using developed equation for these study. Lower soil fundamental frequences of the sediment thickness map shows the boundaries of the basin. Also boundaries of the Gurpinar formations to Oligocene age with Kirklareli limestones to Eocene age have been distinguished from each other. As result of gravity measurements determined some lineaments as faults and some basin. Basins structure and tectonic features of the study area are modeled by using three different data sets