Analysis of Izmit Aftershocks

We investigate structural variation along the Izmit rupture zone analyzing recordings obtained by a 36-station seismic network. The network consists of a nucleus of 15 stations operated permanently since 1996 (SABONET, black triangles in Fig 1) which was then upgraded by another 21 stations within only four days after the mainshock by the German Task Force for Earthquakes of GFZ Potsdam (red triangles in Fig 1). The combined network allowed locating ~10000 aftershocks at a threshold of magnitude completeness of 1.1 (Fig 1.). The distribution allows identifying two main clusters of activity, named Akyazı and Karadere-Düzce cluster hereafter. At the eastern termination of the rupture, a sharp steeply dipping boundary of activity is observed exactly where the subsequent Düzce mainshock initiated 87 days after the Izmit event (Fig 2). The Double-difference technique is used to improve spatial resolution identifying small-scale structures that otherwise remain hidden in cloud-like clusters. Refined resolution of aftershock locations allowed us to better identify the lateral variations of seismotectonic setting along the İzmit-Düzce segment of the NAFZ.


Fig. 1