Large-magnitude (M>7) earthquakes do occur along subduction margins and have devastating effects in the forearc regions. Understanding the spatial and temporal distribution of forearc deformation from deep to surface processes, over different timescales ranging from the earthquake cycle to millions of years, is therefore crucial to access subduction dynamics and contribute to the time-dependent seismic hazard.

The fast-retreating Hellenic subduction zone is the most seismically active margin of the Mediterranean realm and the source of the most devastating tsunamis in the area. It appears as an ideal study case because of the abundant geological, seismic and geodetic observations, which contribute to accurately constrain the forearc dynamics.

The work of GFZ over the last 7 years, encompassing the study of uplifted paleoshorelines on Crete (southern Hellenic forearc region) has revealed a recurrence of large magnitude earthquakes during the last 50,000 years and a rapid uplift of the margin primarily achieved by slip released on spatially and temporally clustered upper-plate reverse faults (Mouslopoulou et al., 2015). In addition, active faults on Crete have been mapped to quantify the kinematics of the upper-crust in the last 16,000 years (Veliz et al., 2018) and to constrain the upper-crust earthquake processes, fault growth over intermediate timescales and earthquake parameters (i.e. recurrence intervals and single event displacements).

Active deformation on Crete is currently monitoring by a permanent and survey-mode GNSS network that record surface deformation during the last ~10 years. Such dataset provides information of the current pattern of interseismic strain accumulation along the Hellenic margin, which is crucial, as it controls the locus and timing of future large earthquakes. The analysis of this observation dataset, together with empirical fault slip-rate information, has shown a strong variability in the interseismic strain accumulation, along the southern Hellenic margin, which is consistent with the millennial uplift pattern revealed from uplifted paleoshorelines (Saltogianni et al., in review).

References:

• Mouslopoulou, V., Nicol, A., Begg, J.,Oncken, O., Moreno, M. (2015). Clusters of mega-earthquakes on upper plate faults control the Eastern Mediterranean hazard. Geophysical Research Letters, 42, 10,282–10,289, doi:10.1002/2015GL066371.
• Veliz, V., Mouslopoulou, V., Nicol, A., Fassoulas, B., Begg, J., Onkcen, O. (2018). Millenial to million normal-fault interactions on the forearc of a subduction margin, Crete, Greece. Journal of Structural Geology, 113, 225-241.
• Saltogianni, V., Mouslopoulou, V., Oncken, O., Nicol, A., Gianniou, M., Mertikas, S. (2020). Elastic fault interactions and earthquake-rupture along the southern Hellenic subduction plate-interface zone in Greece (under review in GRL).

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