Seismic activity triggered by the 1999 Izmit earthquake and its implications for the assessment of future seismic risk

A serious question has remained as to the location of the western end of the main rupture zone associated with the 1999 Izmit, Turkey, earthquake. A clear answer to this question is extremely important for the assessment of future seismic risk in the eastern Marmara Sea region, Turkey. In this paper we show an effective approach to answering this important question, unifying different kinds of information such as seismic activity, focal mechanism solutions and stress changes caused by the main shock into a clear image. We first point out that the major moment release is 1.6 x 10(20) N m and covered the area between 29.7 degreesE and 30.5 degreesE and we then claim that the enhanced seismic activity after the main shock in the eastern Marmara Sea region should be regarded as activity triggered by the increase of stress, rather than as aftershock activity along the ruptured zone. We propose three fault segments with an average stress increase on each in the western extension of the main-shock rupture zone as potential sites for future large earthquakes, namely (i) the 50 km long Yalova-Hersek segment (0.45 MPa), (ii) the NW-SE-trending right-lateral strike-slip fault known as the Princes Islands segment (0.18 MPa), and (iii) the Cinarcik-Yalova segment (0.09 MPa) characterized by normal faulting, which was subject to rupture in 1963.