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At many of the largest glaciers and ice sheets on Earth, more than half of the annual ice loss occurs through iceberg calving into the ocean. Calving is also responsible for the most rapid ice mass changes, both directly (through the mechanical loss of ice at the terminus) and indirectly (through dynamic thinning of upstream ice initiated by terminus retreat). Yet, the mechanisms and factors that control calving are poorly understood. Recordings of glaciogenic seismic waves, known as "icequakes," produced during iceberg calving offer opportunities for insight that cannot be gleaned through other methods. In order to better understand iceberg calving and its links to calving icequakes, we conducted a 2-yr study of rapidly advancing Yahtse Glacier, site of one of the densest clusters of calving icequakes in southern Alaska. By synchronizing video of iceberg calving events with locally-recorded seismograms, we found that most icequake energy is produced after subaerial iceberg detachment from the glacier terminus, while the iceberg impacts and descends below the sea surface. Cavitation beneath the water surface generates the largest amplitude portions of icequakes-those that are detectable over several hundred km distances. Numerical simulations of these iceberg-sea surface interactions predict sources with durations that are consistent with the 1-5 Hz frequency content of calving icequakes. Oceanographic measurements in Icy Bay, where Yahtse Glacier terminates, reveal that warm water may melt most of the ice reaching the submarine terminus. During the summer, water with temperature > 10 °C flows from the Gulf of Alaska coast to within 2 km of Yahtse Glacier's terminus. We find that heat transport between 5 and 40 x 109 W can readily melt the submarine glacier terminus at a rate that matches the speed with which ice flows towards the glacier terminus (17 m d−1). Subaerial iceberg calving rates may be paced by submarine melt rates. To place our calving and submarine melt observations in a broader temporal context, we construct an empirical model of iceberg size using icequake properties and tune the model with over 800 visually-observed iceberg calving events. We find that iceberg calving is at its minimum during the winter, when seawater is cool and mixing of proglacial seawater by subglacial discharge is weak. Overlaying this long period cycle, we find significant daily to inter-annual variability and sensitivity of calving to tidal stage. These observations expand our appreciation for the ocean's important role in iceberg calving: at time scales ranging from the sub-second generation of icequakes, to the annual undercutting of the glacier terminus.
1. PURPOSE OF PRESENT BOOK During the period May 19-26, 2003 the NATO Advanced Research Workshop (ARW) “Mud volcanism, Geodynamics and Seismicity” was held in Baku. Participants coming from USA, Germany, France, Italy, Portugal, Russian Federation, Ukraine, Romania, Georgia, UK, Israel, Azerbaijan, Tunisia have discussed about different geodynamic features of mud volcanism and participated to field trips oriented to a better knowledge of mud volcanic features. The Meeting focused on many features of mud volcanism occurrence and related geodynamic topics. The purpose of present book is to collect contributions discussed during the Meeting and to fill a marked editorial gap on mud volcanism. Mud volcanism was to date described by local monographies or by articles published by scientific journals. In particular no books were published on topics able to highlight the link among mud volcanism, geodynamics and seismicity. Mud volcano of Nirano (Northern Italy). Engraving from Stoppani A. (1871), Corso di Geologia, Milan, Bernardoni G. and Brigola G. Publishers. 2. WHY MUD VOLCANOES ARE GEOLOGICALLY IMPORTANT ? Mud volcanoes have attracted the attention of earth scientists for many years. Due to their importance in hydrocarbon research, a consistent progress in the knowledge of mud volcanism took place in the past twenty years. Mud extrusion is a well-known phenomenon occurring in geological environments where fluid-rich, fine grained sediments ascend within a lithologic succession due to their buoyancy.
204 Pure app!. geophys. , P. Reasenberg demonstrated that in Cascadia earthquakes are four times more likely to be foreshocks than in California. Many speakers emphasized the regional differences in all earthquake parameters, and it was generally understood that basic models of the earthquake occurrence must be modified for regional application. The idea that the focal mechanisms of foreshocks may differ from that of background activity was advocated by Y. Chen and identified by M. Ohtake as possibly the thus far most neglected property of foreshocks, in efforts to identify them. S. Matsumura proposed that focal mechanism patterns of small earthquakes may differ character istically near locked fault segments into which fault creep is advancing. Considerable discussion was devoted to the status of the seismic gap hypothesis because M. Wyss argued that the occurrence of the M 7. 9, 1986, Andreanof Islands earthquake was a confirmation of Reid's rebound theory of earthquakes and thus of the time predictable version of the gap hypothesis, whereas Y. Kagan believed he could negate this view by presenting a list of nine earthquake pairs with M> 7. 4, moment centroid separation of less than 100 km, and time difference less than about 60% of the time he estimated it would take plate motions to restore the slip of the first event.
The Mediterranean is one of the most studied regions of the world. In spite of this, a considerable spread of opinions exists about the geodynamic evolution and the present tectonic setting of this zone. The difficulty in recognizing the driving mechanisms of deformation is due to a large extent to the complex distribution in space and time of tectonic events, to the high number of parameters involved in this problem and to the scarce possibility of carrying out quantitative estimates of the deformation implied by the various geodynamic hypotheses. However, we think that a great deal of the present ambiguity could be removed if there were more frequent and open discussions among the scientists who are working on this problem. The meeting ofERICE was organized to provide an opportunity in this sense. In making this effort, we were prompted by the conviction that each step towards the understanding of the Mediterranean evolution is of basic importance both for its scientific consequences and for the possibleimplicationsfor society. It is well known, for instance, that the knowledge ofongoing tectonic processes in a given region and of their connection with seismic activity may lead to the recognition of middle long term precursors of strong earthquakes. The few cases of tentative earthquake prediction in the world occurred where information on large scale seismotectonic behavior was available. This led to identify the zones prone to dangerous shocks, where observations of short-term earthquake precursors were then concentrated.
The purpose of this book is to give a theoretical and practical introduction to seismic-while-drilling by using the drill-bit noise. This recent technology offers important products for geophysical control of drilling. It involves aspects typical of borehole seismics and of the drilling control surveying, hitherto the sole domain of mudlogging. For aspects related to the drill-bit source performance and borehole acoustics, the book attempts to provide a connection between experts working in geophysics and in drilling. There are different ways of thinking related to basic knowledge, operational procedures and precision in the observation of the physical quantities. The goal of the book is to help "build a bridge" between geophysicists involved in seismic while drilling - who may need to familiarize themselves with methods and procedures of drilling and drilling-rock mechanics - and drillers involved in geosteering and drilling of "smart wells" - who may have to familiarize themselves with seismic signals, wave resolution and radiation. For instance, an argument of common interest for drilling and seismic while drilling studies is the monitoring of the drill-string and bit vibrations. This volume contains a large number of real examples of SWD data analysis and applications.
The subjects refer to histories of ancient and modern use of seacoasts; possible macro-projects capable of massive changes in the coastlines of the Dead Sea, Red Sea and Persian Gulf caused by canal and massively scaled hydropower dam installations; relevant macro-projects for the Black Sea and Baltic Sea; possibilities of refreshment of the Aral Sea and Iran’s Lake Uremia with seawater or river freshwater importation macro-projects; potential rehabilitation of some vital arid zone regions now dominated by moving or movable surface granular materials using unique and unusual macro-projects; seawater flooding of land regions situated below present-day global sea-level; harnessing energy and obtaining freshwater from the world’s salt-laden ocean by modern industrial means; various macro-projects designed specifically for the protection (reduction of vulnerability) of particular Earth geographical regions.
Based on the graduate course in Earthquake Hydrology at Berkeley University, this text introduces the basic materials, provides a comprehensive overview of the field to interested readers and beginning researchers, and acts as a convenient reference point.
Accessibly written by a team of international authors, the Encyclopedia of Environmental Change provides a gateway to the complex facts, concepts, techniques, methodology and philosophy of environmental change. This three-volume set illustrates and examines topics within this dynamic and rapidly changing interdisciplinary field. The encyclopedia includes all of the following aspects of environmental change: Diverse evidence of environmental change, including climate change and changes on land and in the oceans Underlying natural and anthropogenic causes and mechanisms Wide-ranging local, regional and global impacts from the polar regions to the tropics Responses of geo-ecosystems and human-environmental systems in the face of past, present and future environmental change Approaches, methodologies and techniques used for reconstructing, dating, monitoring, modelling, projecting and predicting change Social, economic and political dimensions of environmental issues, environmental conservation and management and environmental policy Over 4,000 entries explore the following key themes and more: Conservation Demographic change Environmental management Environmental policy Environmental security Food security Glaciation Green Revolution Human impact on environment Industrialization Landuse change Military impacts on environment Mining and mining impacts Nuclear energy Pollution Renewable resources Solar energy Sustainability Tourism Trade Water resources Water security Wildlife conservation The comprehensive coverage of terminology includes layers of entries ranging from one-line definitions to short essays, making this an invaluable companion for any student of physical geography, environmental geography or environmental sciences.