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Author: Timothy H. Dixon Publisher: Columbia University Press ISBN: 9780231138666 Category : Computers Languages : en Pages : 696
Book Description
Subduction zones, one of the three types of plate boundaries, return Earth's surface to its deep interior. Because subduction zones are gently inclined at shallow depths and depress Earth's temperature gradient, they have the largest seismogenic area of any plate boundary. Consequently, subduction zones generate Earth's largest earthquakes and most destructive tsunamis. As tragically demonstrated by the Sumatra earthquake and tsunami of December 2004, these events often impact densely populated coastal areas and cause large numbers of fatalities. While scientists have a general understanding of the seismogenic zone, many critical details remain obscure. This volume attempts to answer such fundamental concerns as why some interplate subduction earthquakes are relatively modest in rupture length (greater than 100 km) while others, such as the great (M greater than 9) 1960 Chile, 1964 Alaska, and 2004 Sumatra events, rupture along 1000 km or more. Contributors also address why certain subduction zones are fully locked, accumulating elastic strain at essentially the full plate convergence rate, while others appear to be only partially coupled or even freely slipping; whether these locking patterns persist through the seismic cycle; and what is the role of sediments and fluids on the incoming plate. Nineteen papers written by experts in a variety of fields review the most current lab, field, and theoretical research on the origins and mechanics of subduction zone earthquakes and suggest further areas of exploration. They consider the composition of incoming plates, laboratory studies concerning sediment evolution during subduction and fault frictional properties, seismic and geodetic studies, and regional scale deformation. The forces behind subduction zone earthquakes are of increasing environmental and societal importance.
Author: Timothy H. Dixon Publisher: Columbia University Press ISBN: 9780231138666 Category : Computers Languages : en Pages : 696
Book Description
Subduction zones, one of the three types of plate boundaries, return Earth's surface to its deep interior. Because subduction zones are gently inclined at shallow depths and depress Earth's temperature gradient, they have the largest seismogenic area of any plate boundary. Consequently, subduction zones generate Earth's largest earthquakes and most destructive tsunamis. As tragically demonstrated by the Sumatra earthquake and tsunami of December 2004, these events often impact densely populated coastal areas and cause large numbers of fatalities. While scientists have a general understanding of the seismogenic zone, many critical details remain obscure. This volume attempts to answer such fundamental concerns as why some interplate subduction earthquakes are relatively modest in rupture length (greater than 100 km) while others, such as the great (M greater than 9) 1960 Chile, 1964 Alaska, and 2004 Sumatra events, rupture along 1000 km or more. Contributors also address why certain subduction zones are fully locked, accumulating elastic strain at essentially the full plate convergence rate, while others appear to be only partially coupled or even freely slipping; whether these locking patterns persist through the seismic cycle; and what is the role of sediments and fluids on the incoming plate. Nineteen papers written by experts in a variety of fields review the most current lab, field, and theoretical research on the origins and mechanics of subduction zone earthquakes and suggest further areas of exploration. They consider the composition of incoming plates, laboratory studies concerning sediment evolution during subduction and fault frictional properties, seismic and geodetic studies, and regional scale deformation. The forces behind subduction zone earthquakes are of increasing environmental and societal importance.
Author: Jeanne Sauber Publisher: Birkhäuser ISBN: 3034886799 Category : Science Languages : en Pages : 373
Book Description
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.
Author: Harold Kuehn Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The largest and most destructive earthquakes nucleate on the seismogenic parts of megathrust faults along subduction zones. Understanding the controls of rupture propagation in along-trench and dip direction is a key factor to estimate size and location of future megathrust earthquakes. Various geologic features and subduction-related processes have been proposed to affect megathrust segmentation along the plate boundary zone, however, inaccessibility due to its deep location makes a detailed investigation challenging. The ALEUT project aims to overcome these difficulties by acquisition of state-of-the-art deep penetrating multichannel seismic reflection data combined with coinciding ocean bottom seismometer refraction data for a large section of the eastern Alaska-Aleutian subduction zone (AASZ). This thesis discusses results based on the ALEUT dataset and provides unique insights into possible morphological controls on along-strike rupture organization of the subduction thrust and new constraints on its seismogenic down-dip limit. Plate interface reflections recorded throughout the survey area were used to construct a 3D model of the interplate interface, on which two major crest-like have been identified. The spatial coincidence of these geometrical highs, interpreted to represent subducted seamounts chains, with boundaries of the region's great earthquake ruptures indicates that the megathrust geometry is the primary factor controlling the segmentation of the eastern AASZ. Furthermore, the plate interface reflection signatures appear to increase significantly with depth and have been correlated to 1) seismogenic, 2) conditionally stable and, 3) aseismic slip behavior. The results confirm the spatial extent of rupture areas derived from existing information, such as aftershock locations, inverse tsunami waveform modelling and the intersection of a serpentinized mantle wedge. However, contrary to recent geodetic dislocation models that suggest a widely free slipping segment along the ASSZ (Shumagin Gap), the results suggest a seismogenic plate interface for this area that extents from the trench up to 100 km landward. A partially seismogenic Shumagin Gap area could become part of a great future megathrust event as shallow rupture is propagating into this area and exposing it to strong ground shaking and large tsunami waves, as it might have happened in the 18th and 19th century.
Author: Katja Stanislowski Publisher: ISBN: Category : Languages : en Pages :
Book Description
Many regions that are prone to experience strong earthquakes and tsunamis are densely populated, such as the coastlines of the Pacific Ocean and some of the Indian Ocean. These regions are subduction zone settings, where one tectonic plate subducts beneath another, which produces a gigantic fault - a megathrust fault. Subduction zone earthquakes largely occur on such megathrust faults. They have cost an incredible number of lives, and future events pose a constant threat to many more. Especially those megathrust earthquakes that nucleate in or propagate to very shallow depths can cause large damage and tsunamis. In general, the seismicity in the shallow portion of subduction zone megathrusts is low, but recent events such as the 2004 Aceh-Andaman earthquake and tsunami offshore North Sumatra have tragically shown the potential of shallow seismicity. Despite extensive investigations of multiple geoscientific disciplines, the shallow extent of earthquake rupture and slip of subduction zones around the world is still poorly constrained. Reasons for this lie in the challenging nature of such investigations, because the shallow extent of subduction zone earthquakes lies at sea and well below the ocean floor. Limited knowledge of this shallow earthquake extent reduces the chance of meaningful earthquake and tsunami hazard assessment and thus damage mitigation. Because earthquakes are friction phenomena, a large body of work in earthquake research is based on laboratory friction experiments. Early friction experiments have shown that repetitive frictionally unstable stick-slip sliding on artificial faults in the laboratory represents the small-scale equivalent of earthquakes on faults in nature. Friction on a fault evolves with velocity, slip, and time (rate- and state-dependent friction) and thus can lead to unstable sliding. Unstable sliding includes periods of fault locking and accumulation of elastic energy, with intermittent periods of fault rupture and slip, which releases the stored energy. The depth interval on the megathrust fault that is capable of unstable frictional sliding and thus earthquake nucleation is called the seismogenic zone. Crucial to estimating the extent of the seismogenic zone is knowledge of the variation of the velocity-dependent frictional behavior with depth. Especially the velocity-dependent frictional behavior at plate tectonic rate has shown to be crucial. This information can be derived from laboratory friction experiments and application of so-called rate- and state-friction laws. Ideally, such experiments should be conducted on fault-zone material. However, such material is difficult to obtain and its availability is very limited. Subduction zone input materials, which are the marine sedimentary column on the subducting plate, are less difficult to recover and hold important information on where a megathrust forms or what intrinsic frictional behavior the fault-forming material has. Measurements on input material are therefore a valuable alternative to measurements on fault zone material. This thesis presents the results of laboratory friction experiments at room temperature, under relatively low pressure, and driven at velocities starting from plate rate. These experiments were designed to investigate the frictional behavior of subduction zone input sediments and its implications on the fault slip behavior and seismic potential of the shallow portions of two subduction zones. The first is the northern Cascadia subduction zone, located along the West coast of North America, where a major earthquake is about to be due. The second is the North Sumatra subduction zone, a region of the Sunda subduction zone and the location of recent destructive earthquakes and tsunamis. At northern Cascadia, the megathrust has so far not been sampled. Based on measurements of frictional strength contrasts in the input sedimenatry column, we propose that the megathrust fault will likely form in a weak illite-rich hemipelagic clay near the top of the oceanic basement. Because this inference is in good agreement with interpretations of seismic imaging, we focused on the frictional behavior of this specific material. The absence of shallow non-destructive slow slip events at northern Cascadia has recently been interpreted to result from a megathrust that is locked and potentially seismogenic all the way to the trench. In contrast, the results presented in this work indicate that the shallow part of the megathrust is not capable of producing slow slip events nor capable of locking and thus likely not seismogenic. However, our friction data also indicate low resistance to a propagating earthquake nucleating at greater depth. This low resistance is evident from substantially elevated pore pressure, low frictional strength, and low cohesion. Therefore, the northern Cascadia subduction zone holds the potential of shallow earthquake slip and tsunamigenesis. At North Sumatra, seismic slip during the 2004 Aceh-Andaman subduction zone earthquake was unexpectedly shallow and resulted in a devastating tsunami. Recent work suggested that the cause is a very shallow seismogenic zone that may be created by diagenetic strengthening of fault-forming input sediments prior to subduction. This thesis presents the results of laboratory friction experiments designed to test this hypothesis. We showed that input sediments to the North Sumatra subduction zone exhibit pronounced frictional instability, offering evidence for a frictionally unstable and thus seismogenic shallow megathrust and thus an explanation for shallow earthquake slip in the 2004 event. However, our measurements indicate that the shallow megathrust is not seated in frictionally strong, but in very weak sediments. The combination of weak and unstable sediments is striking because a large number of previous friction studies have established that weak materials under low temperature and pressure conditions are generally associated with stable frictional sliding. This relationship offers an explanation for the observed general lack of seismicity in the shallow portion of subduction zone megathrusts, where unconsolidated, clay-rich, weak materials are typically encountered. We proposed that threshold amounts of dispersed hydrous amorphous silica in otherwise weak and clay-rich sediments are responsible for an unstable sliding character, which can explain the shallow seismicity at North Sumatra. To test the hypothesis that small amounts of hydrous amorphous silica induce unstable sliding behavior, we designed friction experiments on artificial mixtures of weak shale and biogenic opal, a type of hydrous amorphous silica. These experiments revealed pronounced potentially unstable behavior in mixtures with ≥ 30 % opal that had low frictional strength. Based on our results, we proposed that potential unstable sliding at low frictional strength can be explained by the viscous behavior of frictional contacts of hydrous amorphous silica. This highlights the necessity to reevaluate the strength-stability relationship. Our findings support the hypothesis on the role of hydrous amorphous silica in unstable sliding behavior, which has important implications for the potential of shallow seismogenesis at other subduction zones where input sediments contain critical amounts of hydrous amorphous silica. This thesis demonstrates that the northern Cascadia and the North Sumatra subduction zone have very different intrinsic frictional fault slip behavior despite very similar extrinsic properties and attributes, such as temperature or pressure. Thus, intrinsic factors are found to be crucial to the estimation of the slip behavior of shallow megathrust faults, such as a mineral composition of fault material with threshold amounts of hydrous amorphous silica. Hydrous amorphous silica-bearing sediments could form megathrust faults due to intrinsically low strength and potential of overpressure. The shallow portion of megathrust faults formed in such sediments may thus be able to host large and slow earthquakes. This could for instance be the case in the northern Barbados subduction zone, a setting that similar to the North Sumatra subduction zone has been shown to have a porous, overpressured décollement and predécollement consisting of material that contains elevated amounts of hydrous amorphous silica. Thus, this thesis raises the possibility that subduction zones with a shallow seismogenic zone may be more common than predicted by the seismogenic zone model. This inference implies that earthquake and tsunami hazards could be highly underestimated at some subduction zone settings.
Author: Beth Shaw Publisher: Springer Science & Business Media ISBN: 3642208037 Category : History Languages : en Pages : 178
Book Description
This work examines what was responsible for a tsunami that destroyed settlements in the Mediterranean in 365 AD. It details how western Crete was lifted out of the sea by up to 10 meters in a massive earthquake, which occurred on a previously unknown fault.
Author: Garry D. Karner Publisher: Columbia University Press ISBN: 0231501897 Category : Science Languages : en Pages : 367
Book Description
Traditionally, investigations of the rheology and deformation of the lithosphere (the rigid or mechanically strong outer layer of the Earth, which contains the crust and the uppermost part of the mantle) have taken place at one scale in the laboratory and at an entirely different scale in the field. Laboratory experiments are generally restricted to centimeter-sized samples and day- or year-length times, while geological processes occur over tens to hundreds of kilometers and millions of years. The application of laboratory results to geological systems necessitates extensive extrapolation in both temporal and spatial scales, as well as a detailed understanding of the dominant physical mechanisms. The development of an understanding of large-scale processes requires an integrated approach. This book explores the current cutting-edge interdisciplinary research in lithospheric rheology and provides a broad summary of the rheology and deformation of the continental lithosphere in both extensional and compressional settings. Individual chapters explore contemporary research resulting from laboratory, observational, and theoretical experiments.
Author: Timothy H. Dixon
Author: Timothy H. Dixon
Author: Jeanne Sauber
Author: Harold Kuehn
Author: Katja Stanislowski
Author: Geological Survey (U.S.)
Author: Renata Dmowska
Author: J. R. Rice
Author: Eric L. Geist
Author: Beth Shaw
Author: Garry D. Karner