Seismic coupling for the Aegean - Anatolian region

Abstract

Seismic coupling helps define how large the earthquake potential of a region is, as well as the presence of asperities along plate zones. This work seeks to provide an improved picture of the seismic coupling for the Aegean-Anatolian region by taking advantage of extensive seismic and geodetic datasets. To estimate coupling, we compiled a series of by-products that are specific ingredients also for seismic hazard studies. With these by-products, we found that the seismogenic thickness is thinner (10–15 km) or thicker (20 to 30 km) to the east and to the west, respectively and even deeper along the Hellenic subduction zone. The b-value ranges between 0.9 and 1.1 for the entire area with high values concentrated at locations of Late Miocene to -recent volcanism whereas low b-values (<0.8) concentrate along most of the Northern Anatolian fault zone that may suggests stress accumulation. Seismic coupling is low (<35%) or intermediate (35% - 70%) in most of the area, while the Karliova triple junction, on a N-S-oriented belt along the boundary between western and central Anatolia, and the southeastern Peloponnese are fully coupled, suggesting a full seismic release of the entire deformation budget. An intermediate value of seismic coupling is observed for the eastern and central segments of the Northern and Eastern Anatolian Fault zones, for part of the Hellenic volcanic arc, the Kefalonia Transform Fault and the Corinth gulf active faults. Considering historical earthquake data, these intermediate coupling values indicate either aseismic deformation or catalog incompleteness. Furthermore, the time period since large magnitude earthquakes clearly raises the possibility of impending earthquakes on the Northern and Eastern Anatolian Fault zones. A broad seismic gap is evidenced along the Hellenic subduction zone, because of the reduced coupling and the absence of ~M8 earthquakes in the last 700 years, at least. We conclude that in most of the central Aegean Sea aseismic deformation prevails as suggested by the small value of coupling and the modest seismic release over the last millennium.