Abstract
The stress regime across the Hellenic subduction zone was investigated by performing stress inversion on 100 intermediate-depth moment tensor solutions. In this study, the slab was divided into four sectors based on earthquake distribution, trench geometry, and the results of a previous study of slab geometry. For the Peloponnese sector, moment tensors reaching 80 km depth were inverted, and the slab stresses were compatible with a possible slab tear. For the Kithira-Western Crete and Crete sectors, homogeneity was observed at depths up to 100 and 80 km, respectively. For these two areas, the subvertical σ3 and along-strike σ1 justify slab rollback as the driving mechanism. The differences in the stress regime and azimuth of the maximum compression of these two sectors may reflect a bulge in the slab. For the fourth sector, Karpathos-Rhodes, two distinct subsectors were defined along a depth gradient (50–90 km and 90–180 km, respectively). The strong heterogeneity observed at both depths and changes in the stress regime from slab pull to extension may be an indication of a doubleWadati-Benioff zone. The membrane strain model presented here can provide a possible explanation for the along-strike compression observed at the top 90 km in three of the four sectors.
Highlights
The Southern Aegean is located on the convergent boundary of two tectonic plates, namely, the Eurasian and African plates (e.g., Jackson and McKenzie, 1988) (Fig. 1)
If the σ3 axis is steeper than the slab, a component of slab-pull force is unbalanced by the subduction resistance
The main conclusions that can be drawn from this study are: 1. The Hellenic subduction zone can be divided from west to east into four sectors based on differences in the stress regime, slab geometry, earthquake depth distribution: (1) Peloponnese; (2) Kithira-Western Crete; (3) Crete; (4) Karpathos-Rhodes
Summary
The Southern Aegean is located on the convergent boundary of two tectonic plates, namely, the Eurasian and African plates (e.g., Jackson and McKenzie, 1988) (Fig. 1). A Wadati-Benioff zone (WBZ) identified by seismicity down to a depth of 150–180 km, is created by the subduction of the African lithosphere at a rate of about 1 cm/year and the motion of the upper Aegean plate towards the SW at a rate of 3.3 cm/year (e.g., Reilinger et al, 2006; Rontogianni, 2010). Seismic tomography data show that the subducting lithosphere can be traced down to about 1200 km (e.g., Bijwaard and Spakman, 1998). On the basis of seismicity and moment tensor data, they showed that the angles at which T -axes dip to the inner side of the Hellenic arc are generally steeper than that of the slab dip. Benetatos et al (2004) used 22 intermediate-depth focal mechanisms and concluded that the distribution of T -axes shows shortening roughly parallel to the arc. The P-axes followed the trend of the arc in Copyright c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB
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