Tuncay Taymaz

Consolidation patterns during initiation and evolution of a plate-boundary decollement zone: Northern Barbados accretionary prism

Borehole logs from the northern Barbados accretionary prism show that the plate-boundary decollement initiates in a low-density radiolarian claystone. With continued thrusting, the decollement zone consolidates, but in a patchy manner. The logs calibrate a three-dimensional seismic reflection image of the decollement zone and indicate which portions are of low density and enriched in fluid, and which portions have consolidated. The seismic image demonstrates that an underconsolidated patch of the decollement zone connects to a fluid-rich conduit extending down the decollement surface. Fluid migration up this conduit probably supports the open pore structure in the underconsolidated patch.

The geodynamics of the Aegean and Anatolia: introduction

The complexity of the plate interactions and associated crustal deformation in the Eastern Mediterranean region is reflected in many destructive earthquakes that have occurred throughout its recorded history, many of which are well documented and intensively studied. The Eastern Mediterranean region, including the surrounding areas of western Turkey and Greece, is indeed one of the most seismically active and rapidly deforming regions within the continents (Fig. 1). Thus, the region provides a unique opportunity to improve our understanding of the complexities of continental tectonics in an actively collisional orogen. The major scientific observations from this natural laboratory have clearly been helping us to better understand the tectonic processes in active collision zones, the mode and nature of continental growth, and the causes and distribution of seismic, volcanic and geomorphological events (e.g. tsunamis) and their impact on societal life and civilization. The tectonic evolution of the Eastern Mediterranean region is dominated by the effects of subduction along the Hellenic (Aegean) arc and of continental collision in eastern Turkey (Anatolia) and the Caucasus. Northward subduction of the African plate beneath western Turkey and the Aegean region is causing extension of the continental crust and volcanism in the overlying Aegean extensional province. Eastern Turkey has been experiencing crustal shortening and thickening as a result of northward motion of the Arabian plate relative to Eurasia and the attendant postcollisional magmatism (Taymaz et al. 1990, 1991a, b; McClusky et al. 2000, 2003; Dilek & Pavlides 2006, and references therein; Fig. 2). The resulting combination of forces (the ‘pull’ from the subduction zone to the west and ‘push’ from the convergent zone to the east) is causing the Turkish plate to move southwestward, bounded by strike-slip fault zones: the North Anatolian Fault Zone (NAFZ) to the north and the East Anatolian Fault Zone (EAFZ) to the south. Interplay between dynamic effects of the relative motions of adjoining plates thus controls large-scale crustal deformation and the associated seismicity and volcanism in Anatolia and the Aegean region (Taymaz et al. 2004).

Understanding tsunamis, potential source regions and tsunami-prone mechanisms in the Eastern Mediterranean

Abstract Historical tsunamis and tsunami propagation are synthesized in the Eastern Mediterranean Sea region, with particular attention to the Hellenic and the Cyprus arcs and the Levantine basin, to obtain a better picture of the tsunamigenic zones. Historical data of tsunami manifestation in the region are analysed, and compared with current seismic activity and plate interactions. Numerical simulations of potential and historical tsunamis reported in the Cyprus and Hellenic arcs are performed as case studies in the context of the nonlinear shallow-water theory. Tsunami wave heights as well as their distribution function are calculated for the Paphos earthquake of 11 May 1222 and the Crete earthquake of 8 August 1303 as illustrative examples depicting the characteristics of tsunami propagation, and the effects of coastal topography and near-shore amplification. The simulation studies also revealed that the long-normal distributions are compatible with reported damage. Furthermore, it is necessary to note that high-resolution bathymetry maps are a crucial component in tsunami wave simulations, and this aspect is rather poorly developed in the Eastern Mediterranean. The current study also demonstrates the role of bottom irregularities in determining the wave-height distribution near coastlines. Assuming the probability of occurrence of destructive tsunamigenic earthquakes, these studies will help us to evaluate the tsunami hazard for the coastal plains of the Eastern Mediterranean Sea region. We suggest that future oceanographic and marine geophysical research should aim to improve the resolution of bathymetric maps, particularly for the details of the continental shelf and seamounts.

Source characteristics of the 6 June 2000 Orta–Çankırı (central Turkey) earthquake: a synthesis of seismological, geological and geodetic (InSAR) observations, and internal deformation of the Anatolian plate

Abstract This paper is concerned with the seismotectonics of the North Anatolian Fault in the vicinity of the Orta–Çankırı region, and consists of a study of a moderate-sized (Mw=6. 0) earthquake that occurred on 6 June 2000. The instrumental epicentre of this earthquake is far from the North Anatolian Fault Zone (NAFZ), and rapid focal mechanism solutions of USGS–NEIC and Harvard-CMT also demonstrate that this earthquake is not directly related to the right-lateral movement of the North Anatolian Fault. This earthquake is the only instrumentally recorded event of magnitude (Mw) >5.5 since 1900 between Ankara and Çankırı, and therefore provides valuable data to improve our understanding of the neotectonic framework of NW central Anatolia. Field observations carried out in the vicinity of Orta town and neighbouring villages immediately after the earthquake indicated no apparent surface rupture, but the reported damage was most intense in the villages to the SW of Orta. We used teleseismic long-period P- and SH-body waveforms and first-motion polarities of P-waves, broadband P-waves, and InSAR data to determine the source parameters of the 6 June 2000 (Orta–Çankırı, to=02:41:53.2, Mw=6. 0) earthquake. We compared the shapes and amplitudes of long-period P- and SH-waveforms recorded by GDSN stations in the distance range 30–90°, for which signal amplitudes were large enough, with synthetic waveforms. The best-fitting fault-plane solution of the Orta–Çankırı earthquake shows normal faulting with a left-lateral component with no apparent surface rupture in the vicinity of the epicentre. The source parameters and uncertainties of this earthquake were: Nodal Plane 1: strike 2°±5°, dip 46°±5°, rake –29°±5°; Nodal Plane 2: strike 113°, dip 70°, rake –132°; principal axes: P=338° (48°), T=232° (14°), B=131° (39°); focal depth 8±2 km (though this does not include uncertainty related to velocity structure), and seismic moment Mo=(140–185)×1016 N m. Furthermore, analysis of a coseismic interferogram also allows the source mechanism and location of the earthquake to be determined. The InSAR data suggest that the north–south fault plane (Nodal Plane 1 above) was the one that ruptured during the earthquake. The InSAR mechanism is in good agreement with the minimum misfit solution of P- and SH-waveforms. Although the magnitude of slip was poorly constrained, trade-off with the depth range of faulting accurred such that solutions with a large depth range had small values of slip and vice versa. The misfit was small and the geodetic moment constant for fault slips greater than c. 1 m. The 6 June 2000 Orta–Çankırı earthquake occurred close to a restraining bend in the east–west-striking rightlateral strike-slip fault that moved in the much larger earthquake of 13 August 1951 (Ms=6.7). The faulting in this anomalous earthquake could be related to the local geometry of the main strike-slip system, and may not be a reliable guide to the regional strain field in NW central Turkey. We tentatively suggest that one possible explanation for the occurrence of the 6 June 2000 Orta–Çankırı earthquake could be localized clockwise rotations as a result of shear of the lower crust and lithosphere.

The Geodynamics of the Aegean and Anatolia

The complexity of plate interactions and associated crustal deformation in the Eastern Mediterranean region is reflected by the numerous destructive earthquakes that have occurred throughout its history. Many of these have been well documented and studied. In addition, the Aegean region provides examples of core-complex formation, synchronous basin evolution and subsequent graben formation and continental extensional deformation following orogenic contraction. It is therefore considered to be a perfect natural laboratory for the study of these mechanisms. The region has been the subject of intensive research for several decades. This book contains current results and ideas regarding the geodynamics of the Aegean and Anatolia. It will be essential reading for all geoscientists with an interest in the structural evolution of the Eastern Mediterranean.

Fault slip source models for the 2014 Mw 6.9 Samothraki‐Gökçeada earthquake (North Aegean Trough) combining geodetic and seismological observations

The 24 May 2014, Mw 6.9, Samothraki-Gokceada shallow (depth: 11 km) earthquake along the North Aegean Trough (NAT), at the westward extension of the North Anatolian Fault Zone (NAFZ), is investigated using constraints from seismological and geodetic data. A point source solution based on teleseismic long-period P and SH waveforms suggests an essentially strike-slip faulting mechanism consisting of two subevents, while from a finite fault inversion of broadband data the rupture area and slip history were estimated. Analysis of data from 11 permanent GPS stations indicated significant coseismic horizontal displacement but no significant vertical or postseismic slip. Okada-type inversion of horizontal slip vectors, using the new TOPological INVersion algorithm, allowed precise modeling of the fault rupture both as single and preferably as double strike-slip faulting reaching the surface. Variable slip models were also computed. The independent seismological and geodetic fault rupture models are broadly consistent with each other and with structural and seismological data and indicate reactivation of two adjacent fault segments separated by a bend of the NAT. The 2014 earthquake was associated with remote clusters of low-magnitude aftershocks, produced low accelerations, and filled a gap in seismicity along the NAT in the last 50 years; faulting in the NAT seems not directly related to the sequence of recent faulting farther east, along the NAFZ and the seismic gap in the Marmara Sea near Istanbul.

Combination of Acceleration-Sensor and Broadband Velocity-Sensor Recordings for Attenuation Studies: The Case of the 8 January 2006 Kythera Intermediate-Depth Earthquake

On 8 January 2006, an intermediate-depth earthquake occurred at the western part of the Hellenic trench close to the island of Kythera (southern Greece). This is the first intermediate-depth earthquake in the broader Aegean area that has produced such an extensive set of useful recordings, as it was recorded by the main permanent seismological networks and numerous acceleration sensors operating in Greece, as well as by EGELADOS, a large-scale temporary amphibian broadband seismological network deployed in the southern Aegean area. An effort to combine all the available data (broadband velocity and acceleration sensor) was made to study the properties of ground-motion attenuation of this earth- quake. The combination of both types of data revealed interesting properties of the earthquake wave field, which would remain hidden if only one type of data was used. Moreover, the data have been used for a validation of existing peak ground-motion empirical prediction relations and the preliminary study of the very inhomogeneous attenuation pattern of the southern Aegean intermediate-depth events at both near- and far-source distances.

Toward a risk assessment of central Aegean volcanoes

Active tectonic processes along the African-Eurasian collision zone are associated with catastrophic events including earthquakes, major volcanic eruptions, and tsunamis. Understanding how these processes can affect the eastern Mediterranean is of increasing scientific and public interest. The region includes a frequently crossed international sea traffic corridor and dense population centers. Furthermore, most of the small volcanic islands in the Aegean are major tourist attractions that contribute significantly to the wealth of this region.

Recent Devastating Earthquakes in Turkey and Active Tectonics of the Aegean and Marmara Seas

The Eastern Mediterranean region, including the adjacent areas of western Turkey and Greece, is indeed one of the most seismically active and rapidly deforming regions within the continents. Thus, the wide range of active deformational processes observed in the Eastern Mediterranean means that this region provides a unique opportunity to improve our understanding of the complex dynamics of continental collision, including strike-slip faulting, subduction and crustal extension, as well as associated volcanism, intense seismic activity and geomorphological events (e.g. tsunamis) and their impacts on societal life and civilization. Recent devastating earthquakes along the North Anatolian Fault Zones (NAFZ) such as the August 17, 1999 Golcuk-I. zmit (Mw=7.4) and the November 12, 1999 Duzce (Mw=7.1) earthquakes confirm the complexity of the crustal deformations throughout the region. Furthermore, the source mechanisms and rupture histories of the moderate and large size earthquakes that occured in the last decades contribute to conceive the nucleation and growth of fault system in the region. In this article, we present novel seismological observations and briefly presented the source characteristics of the recent damaging earthquakes in Turkey and adjacent areas. The latter includes the Marmara and North Aegean Seas, the Lake districts region of SW Turkey, Orta-Cankin of central Turkey and the East Anatolian Fault Zone (EAFZ) in order to display the active tectonic structures associated with seismicity. Investigating and monitoring of the active seismogenic zones will provide a better understanding for predicting the occurences of future earthquakes and hence an improved physical basis for mitigation of their effects on environment and societies in this earthquake-prone region.

The Collaborative Seismic Earth Model: Generation 1

Abstract We present a general concept for evolutionary, collaborative, multiscale inversion of geophysical data, specifically applied to the construction of a first‐generation Collaborative Seismic Earth Model. This is intended to address the limited resources of individual researchers and the often limited use of previously accumulated knowledge. Model evolution rests on a Bayesian updating scheme, simplified into a deterministic method that honors todays computational restrictions. The scheme is able to harness distributed human and computing power. It furthermore handles conflicting updates, as well as variable parameterizations of different model refinements or different inversion techniques. The first‐generation Collaborative Seismic Earth Model comprises 12 refinements from full seismic waveform inversion, ranging from regional crustal‐ to continental‐scale models. A global full‐waveform inversion ensures that regional refinements translate into whole‐Earth structure.