Evolution of the Stress Field in the Northern Aegean Sea (Greece)

Abstract

Summary The evolution of the stress field in the area of the northern Aegean Sea during the 20th century has been studied. The area is dominated by dextral strike‐slip faulting and is characterized by frequent strong earthquakes. Coulomb stress changes (ΔCFF) were calculated assuming that earthquakes can be modelled as static dislocations in an elastic half‐space, and taking into account both the coseismic slip in large (M ≥ 7.0) earthquakes and the slow tectonic stress build‐up along the major fault segments. The stress change calculations were performed for strike‐slip faults of strike, dip, and rake appropriate to the large events. We evaluate whether these stress changes brought a given large earthquake closer to, or farther from, failure. It was found that each of the large events occurred in regions of increased calculated Coulomb stress. Moreover, the majority of smaller events for which reliable fault‐plane solutions are available were also located in areas of positive ΔCFF. By extending the calculations to 2020, and assuming that no additional large (M ≥ 7.0) earthquake occurs between 1999 and 2020, possible sites of future large earthquakes are identified.

The Evolution of the Stress Field in Eastern Macedonia and Thrace

“…Thus, the depth of the seismogenic layer in our calculations is taken to be in the range of 3-15 km for all of the events we modeled, in agreement with relevant previous studies (e.g. Papadimitriou and Sykes, 2001). The rupture models are approximated by rectangular surfaces with two edges parallel to the Earth's surface.…”

Forecasting seismicity rates in western Turkey as inferred from earthquake catalog and stressing history

“…Moreover, strong event influence (e.g., 1956 M = 7.7 in southern Aegean, 1967 M = 7.2 in NAF, 1970 M = 7.1 close to the borders of subareas 2 and 4) was not taken into account because of the insufficient data available before 1980 for a robust seismicity rate investigation. Therefore, it is inevitable that the state of stress remains unknown at the beginning of our analysis, since data adequacy and reliability reduce when going back in time (e.g., Papadimitriou and Sykes 2001). Nevertheless, note that we utilized nondeclustered datasets, which contain triggered events or seismicity depression that persist in time and are related to the stress perturbations produced by previous strong main shocks (Leptokaropoulos et al 2012).…”

“…The fault lengths, L, were estimated from the empirical relations of Papazachos et al (2004), as they were specifically obtained for Aegean and surrounding areas. Fault widths, w, were estimated from the dip angle of the fault and the distance measured down-dip from the surface to the upper and lower edges of the rectangular dislocation plane, respectively, assuming that the seismogenic layer in the study area extends from 3 to 15 km depth (Papadimitriou and Sykes 2001;Paradisopoulou et al 2010). Average coseismic slip, " u, was calculated from the formula: (Table 2).…”

Seismicity Rate Changes in Association With Time Dependent Stress Transfer in the Region of Northern Aegean Sea, Greece

“…ΔCFF is calculated from (5) with μ΄ set to 0.4 (Stein et al, 1997;Nalbant et al, 1998). Shear modulus G, is assumed to be 33GPa and Poisson ratio 0.25 (Papadimitriou & Sykes, 2001). The width of seismogenic layer, h in the region consider to extend down to 15km and calculations were done at the depth of 8km.…”