Subduction Zones

Subduction is a major process that plays a first-order role in the dynamics of the Earth. The sinking of cold lithosphere into the mantle is thought by many authors to be the most important source of energy for plates driving forces. It also deeply modifies the thermal and chemical structure of the mantle, producing arc volcanism and is responsible for the release of most of the seismic energy on Earth. There has been considerable achievements done during the past decades regarding the complex interactions between the various processes acting in subduction zones. This volume contains a collection of contributions that were presented in June 2007 in Montpellier (France) during a conference that gave a state of the art panorama and discussed the perspectives about "Subduction Zone Geodynamics". The papers included in this special volume offer a unique multidisciplinary picture of the recent research on subduction zones geodynamics. They are organized into five main topics: Subduction zone geodynamics, Seismic tomography and anisotropy, Great subduction zone earthquakes, Seismogenic zone characterization, Continental and ridge subduction processes. Each of the 13 papers collected in the present volume is primarily concerned with one of these topics. However, it is important to highlight that papers always treat more than one topic so that all are related lighting on different aspects of the complex and fascinating subduction zones geodynamics.

This volume highlights the career of Dr. Gaku Kimura, professor emeritus of geosciences at the University of Tokyo, by showing the spectrum of research required to understand these dynamic environments and the range of research he has inspired. The first three chapters provide context for the growth of accretionary prisms by examining the thermal structure of the ocean crust, and the sedimentary facies and potential fluid pathways in the Shikoku Basin. Next, two chapters look at the regional-scale structure of the plate boundary and the rheology and hysteresis of the hanging wall of the subduction zone in SW Japan. The following five chapters discuss the progressive deformation and thermal maturation of sediments along accretionary margins from Japan to New Zealand to western North America. The final two chapters look at the deformation processes near the subducting plate interface with the last chapter proposing a link between outcrop-scale observations and seismic slip.

Subduction zones consume oceanic lithosphere and are an indispensible part of plate tectonics. Unlike the oceanic lithosphere production system which can be linked as a nearly continuous, albeit sinuous, strand around the earth, subduction zones are a rather dissociated group and are found in several isolated corners of the world. While plate tectonics can predict that subduction zones are required along certain plate boundaries, it does not stipulate how subduction zones initiate and develop. The preservation of newly created oceanic lithosphere and the propensity for spreading centers to fragment continents leaves a wealth of geological informa tion on the initiation and evolution of spreading. On the other hand, the subject of subduction initiation has little observational basis. To find such observations, we need to look at some muddled tectonic regimes. The Macquarie Ridge complex presents a natural laboratory for studies of subduction initiation. 2. Tectonics of the Macquarie Ridge Complex The Macquarie Ridge complex is a complicated physiographic feature that trends approximately north-south between South Island, New Zealand and the Pacific-Antarctica spreading center. This feature consists of a sequence of troughs and ridges, with Macquarie Island as the only exposed expression. The seismically active Macquarie Ridge complex (hereafter: MRC) is crudely continuous with the Tonga-Kermadec-New Zealand seismic activity. The basic physiographic features and seismicity of the MRC are shown in Figure I. The earthquake epicenters generally cluster about the bathymetric expression of the MRC.

Earthquakes in shallow subduction zones account for the greatest part of seismic energy release in the Earth and often cause significant damage; in some cases they are accompanied by devastating tsunamis. Understanding the physics of seismogenic and tsunamigenic processes in such zones continues to be a challenging focus of ongoing research. The seismologic and geodetic work reported in this volume highlights the recent advances made toward quantifying and understandig the role of shallow plate coupling in the earthquake generation process. The relation between regional seismotectonics, features in the downgoing plate, and the slip distribution in earthquakes are examined for recent and great historical events. In addition to papers reporting new results, review articles on tsunami and tsunamigenic earthquakes and depth dependent plate interface properties are presented. These observational results, along with complementary laboratory and theoretical studies, can assist in assessing the seismic potential of a given region.

Reprint from Pure and Applied Geophysics (PAGEOPH), Volume 140 (1993), No. 2

Reprint from Pure and Applied Geophysics (PAGEOPH), Volume 142 (1994), No. 1

The Mediterranean and northern Arabian regions provide a unique natural laboratory to constrain geodynamics associated with arc-continent and continent-continent collision and subsequent orogenic collapse by analysing regional and temporal distributions of the various elements in the geological archive. This book combines thirteen new contributions that highlight timing and distribution of the Cretaceous to Recent evolution of the Calabrian, Carpathian, Aegean and Anatolian segments of the Africa-Arabia-Eurasia subduction zone. These are subdivided into five papers documenting the timing and kinematics of Cretaceous arc-continent collision, and Eocene and Miocene continent-continent collision in Anatolia, with westward extrusion of Anatolia as a result. Eight papers provide an overview and new data from stratigraphy, structure, metamorphism and magmatism, covering the geological consequences of the largely Neogene collapse that characterizes the segments of interest, in response to late stage reorganization of the subduction zone, and the roll-back and break-off of (segments of) the subducting slab.

This thesis is remarkable for the wide range of the techniques and observations used and for its insights, which cross several disciplines. It begins by solving a famous puzzle of the ancient world, which is what was responsible for the tsunami that destroyed settlements in the eastern Mediterranean in 365 AD. By radiocarbon dating of preserved marine organisms, Shaw demonstrates that the whole of western Crete was lifted out of the sea by up to 10 meters in a massive earthquake at that time, which occured on a previously unknown fault. The author shows that the resulting tsunami would have the characteristics described by ancient writers, and uses modern GPS measurements and coastline geomorphology to show that the strain build-up near Crete requires such a tsunami-earthquake about every 6.000 years - a major insight into Mediterranean tsunami hazard. A detailed seismological study of earthquakes in the Cretan arc over the last 50 years reveals other important features of its behaviour that were previously unknown. Finally, she provides fundamental insights into the limitations of radiocarbon dating marine organisms, relating to how they secrete carbon into their skeletons. The thesis resulted in three major papers in top journals.