Seismic interaction and delayed triggering along the North Anatolian Fault

Abstract : The deformation of northwestern Turkey is the result of the encounter of the westward extrusion of the Anatolian plate with the north-south extension of the Aegean domain. While the North Anatolian Fault localizes the former type of deformation and has been the site of more large earthquakes (9 events of magnitude ≥7) than any other continental fault over the past 100 years, the extension is diffuse and is characterized by spatial clusters of smaller earthquakes and near-continuous activity. We study the evolution of seismicity along the fault and in the clusters neighboring the fault before and after the two large earthquakes of 1999. We observe that the un-ruptured section of the fault and the extension clusters respond very differently to the earthquakes. While significant aftershock activity on the fault segments adjacent to the rupture only occurs at relatively short distance from the rupture (≤30 km), the clusters can be activated at much larger distances (300 km). Remarkably their triggering is not immediate after the earthquake but is delayed in time. Their peak seismic activation may occur weeks or months after the earthquake. This distant and delayed triggering, which is consistent with recent GPS observations, may help resolve some of the previously unexplained characteristics of the 1939-1999 sequence of large earthquakes along the fault.