Slip and strain partitioning across subparallel strands of the north Anatolian fault in the Marmara Region

Abstract

Marmara Region hosts a substantial part of the inhabitants in Turkey, more than 30% of the total population in the cities of Istanbul, Bursa, and Kocaeli. This region has experienced a number of large earthquakes in the past and still under threat of de structive earthquakes in the future. There, subparallel strands of the North Anatolian Fault (NAF) expand into the region distributing the earthquake hazards across the whole region. In this context, it is a key issue to investigate how the tectonic process is distributed between these sub-parallel strands in order to discriminate their indi vidual earthquake hazards. In this context, we jointly used historical earthquakes and GPS slip rates to quantify the slip and strain partitioning of the subparallel strands of the fault system. In addition to all available slip rates, we analyzed 50 new GPS sites (38 continuous and 12 campaign-based) to intensify the GPS network in the re gion. Historical earthquake records since 100 AD shows that 76.4% of the total slip is stored on the northern strand. The rest of the slip is partitioned between middle and southern strands as 11.8% and 11.8% respectively. These ratios are almost confirmed by GPS observations with 76.8%, 12.7%, and 10.5% slip ratios for northern, middle, and southern strands respectively. In conclusion, the northern strand of the NAF is the most active compared to the middle and southern strands and therefore accommo dates the highest earthquake hazards in the Marmara region. As middle and southern strands deform at substantially slower slip rates, they accommodate relatively much lower earthquake hazards.