Evolving plate boundaries in the Aegean–Anatolian region

My thesis focuses on evolving and (geologically) short-lived plate boundary segments, their segmentation processes and geological imprints in the eastern Mediterranean. In Chapter 2, I investigate the nature/type of the plate boundary between the eastern Aegean region and the Africa plate. The work involves an integrative analysis of geological and geophysical information. I conclude that these surface observations document that the “Pliny-Strabo trench” is a predominantly strike-slip plate boundary. My interpretation is that this plate boundary represents an expression of slab tearing related to an active STEP (c.f. Figure 1.1). The paper represents the first detailed account of surface deformation related to a STEP fault, and constitutes a novel contribution to the understanding of the relation between deep processes and (near-) surface deformation, a key topic in geodynamic research. In Chapter 3, I investigate the location and nature of currently active plate boundaries and other major faults in the southern Anatolia-Aegean region, in the transition region from the Hellenic Arc to the Cyprus Arc. The question is particularly relevant for accessing earthquake hazard. I use mechanical models based on the finite element method. I explore various options for these faults, most of them proposed in the scientific literature, to explore how they would affect the deformation at locations where there are actual observations. The (mis)fit between model predictions and observations allows us to conclude that the active plate boundary is located offshore. The research question that I address in Chapter 4 is what the cause is of deformation in one of the seismically most active fault zones in Europe, the Kefalonia Transform Fault. I present results from a recent full-waveform tomographic model which particularly improves our understanding of the structure of the upper few hundred kilometers of the Earth. The cause of the deformation along the Kefalonia Transform Fault is likely rooted in a fragmented slab that we image for the first time. The geometry of the slab fragment leads me to conclude that it became disconnected from the larger Hellenic slab around 5 Ma, at about the time of opening of the Gulf of Corinth in the overriding plate, which suggests a highly interesting causal relation

Evolving plate boundaries in the Aegean–Anatolian region

My thesis focuses on evolving and (geologically) short-lived plate boundary segments, their segmentation processes and geological imprints in the eastern Mediterranean. In Chapter 2, I investigate the nature/type of the plate boundary between the eastern Aegean region and the Africa plate. The work involves an integrative analysis of geological and geophysical information. I conclude that these surface observations document that the “Pliny-Strabo trench” is a predominantly strike-slip plate boundary. My interpretation is that this plate boundary represents an expression of slab tearing related to an active STEP (c.f. Figure 1.1). The paper represents the first detailed account of surface deformation related to a STEP fault, and constitutes a novel contribution to the understanding of the relation between deep processes and (near-) surface deformation, a key topic in geodynamic research. In Chapter 3, I investigate the location and nature of currently active plate boundaries and other major faults in the southern Anatolia-Aegean region, in the transition region from the Hellenic Arc to the Cyprus Arc. The question is particularly relevant for accessing earthquake hazard. I use mechanical models based on the finite element method. I explore various options for these faults, most of them proposed in the scientific literature, to explore how they would affect the deformation at locations where there are actual observations. The (mis)fit between model predictions and observations allows us to conclude that the active plate boundary is located offshore. The research question that I address in Chapter 4 is what the cause is of deformation in one of the seismically most active fault zones in Europe, the Kefalonia Transform Fault. I present results from a recent full-waveform tomographic model which particularly improves our understanding of the structure of the upper few hundred kilometers of the Earth. The cause of the deformation along the Kefalonia Transform Fault is likely rooted in a fragmented slab that we image for the first time. The geometry of the slab fragment leads me to conclude that it became disconnected from the larger Hellenic slab around 5 Ma, at about the time of opening of the Gulf of Corinth in the overriding plate, which suggests a highly interesting causal relation

Active faults in the Anatolian-Aegean plate boundary region with Nubia

Convergence of the Africa, Arabia, and Eurasia plates and the westward escape of Anatolia have resulted in an evolving plate boundary zone in the Eastern Mediterranean. e current location and nature of the plate boundary between the Anatolian and the African plate is di cult to trace due to the scattered crustal earthquakes and the absence of deep ones. We examine various types and locations for the plate boundary as constrained by seismicity, seismic re ection studies, tomographic studies, and geodetic measurements and we use a spherical plane stress nite element model to test these possibilities. In our regional model, we impose the convergence of Africa, Arabia, and stable Eurasia by applying GPS-derived velocities in the far- eld, as well as the roll-back of the Hellenic trench to solve for regional deformation. Model velocity and stress elds are compared with GPS-derived velocities and stress directions from focal mechanism solutions. We nd that the plate boundary via the Pliny and Strabo trenches, the Anaximander Mountains, the Eratosthenes Seamount collisional segment, and the Latakia-Larnaka ridges gives the best t to the data. e Anaximander Mountains plate boundary has both down-dip and strike-slip motions, and the Latakia segment is pure strike-slip. e Cyprus subduction contact is 42% locked. From a combined analysis of indicators for long-term deformation (predominantly slip-rates on major faults) and model results we infer that this southern plate boundary con guration may have existed since the Late Pliocene

A new crustal model of the Anatolia–Aegean domain: evidence for the dominant role of isostasy in the support of the Anatolian plateau

International audienceThe engines of surface deformation in the Anatolia-Aegean region are a matter of debate, including the origin of the high elevations of the Anatolian plateau. Recent publications based on geological and thermomechanical modelling emphasize the role of dynamic topography in the plateau uplift. However, quantitative estimates of the contribution of dynamic topography are affected by large uncertainties due to insufficient knowledge of the crustal structure, in particular crustal thickness and density. To reduce these uncertainties, we provide a new accurate crustal thickness map of the Anatolia-Aegean domain computed from a large volume of broadband seismic data. In addition, we display high-resolution seismic sections of the internal structure of the crust in Western and Central Anatolia. Density contrasts are derived from the same seismic data set and Bouguer gravity anomaly computed from the EGM2008 model. Our crustal thickness model is highly correlated with the topography suggesting that the Anatolian plateau is close to isostatic equilibrium. The average density difference between crust and upper mantle computed from our crustal model and Bouguer gravity anomaly is low compared to the global average, ∼0.315 ×10 3 kg m −3. The ratio of surface elevation to crustal thickness is lower than average, 1/9.4, which also indicates a low-density crust. Differences between isostatic topography and observed topography are overall small (<500 m). The east-to-west gradients of crustal thickness and topography changes are nearly constant in between the Taurides and Pontides at the northern and southern borders of Anatolia. The observed constant crustal thickness gradient may indicate a low viscosity lower crust supported by the thin mantle lithosphere evidenced by seismic tomography beneath the Anatolian plateau. We propose that viscous flow in the lower crust has smoothed out lateral changes in the crustal structure expected for such a heterogeneous collage of continental fragments. This flow may originate from gravitational potential energy differences between Eastern Anatolia (thick crust, high elevations) and the Aegean Sea (thin crust, low elevations), suggesting that gravity plays an integral part in the westward escape of Anatolia

Active faults in the Anatolian-Aegean plate boundary region with Nubia

Convergence of the Africa, Arabia, and Eurasia plates and the westward escape of Anatolia have resulted in an evolving plate boundary zone in the Eastern Mediterranean. e current location and nature of the plate boundary between the Anatolian and the African plate is di cult to trace due to the scattered crustal earthquakes and the absence of deep ones. We examine various types and locations for the plate boundary as constrained by seismicity, seismic re ection studies, tomographic studies, and geodetic measurements and we use a spherical plane stress nite element model to test these possibilities. In our regional model, we impose the convergence of Africa, Arabia, and stable Eurasia by applying GPS-derived velocities in the far- eld, as well as the roll-back of the Hellenic trench to solve for regional deformation. Model velocity and stress elds are compared with GPS-derived velocities and stress directions from focal mechanism solutions. We nd that the plate boundary via the Pliny and Strabo trenches, the Anaximander Mountains, the Eratosthenes Seamount collisional segment, and the Latakia-Larnaka ridges gives the best t to the data. e Anaximander Mountains plate boundary has both down-dip and strike-slip motions, and the Latakia segment is pure strike-slip. e Cyprus subduction contact is 42% locked. From a combined analysis of indicators for long-term deformation (predominantly slip-rates on major faults) and model results we infer that this southern plate boundary con guration may have existed since the Late Pliocene