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Geophysics Images of June

By: , Posted on: June 25, 2015

Image from Temperatures, Heat, and Energy in the Mantle of the Earth article

earth heat map
Global heat flux of the Earth combining heat flux measurements on land and continental margins with a thermal model for the cooling of the oceanic lithosphere.

Temperatures, Heat, and Energy in the Mantle of the Earth

Today, we know that the Earth is not cooling by conduction only and that the convective motions that drive the oceanic plates are responsible for a large fraction of its heat loss. We also know that heat generated by the radioactive decay of U, Th, and K in silicate rocks accounts for a large fraction of the surface heat loss. It is fair to state, however, that the Earth’s heat engine works in ways that still elude us. In this context, it is worth remembering that we pursue two different goals in studies of mantle convection. One is to account for its present-day dynamics and for its role in shaping the Earth’s surface features. The other goal is to go back in time in order to evaluate how the rates of geologic processes have changed and to decipher processes that are no longer active today. Both goals require a thorough understanding of the Earth’s heat budget, but each relies on a different set of constraints. In this article we review both the constraints and the models pertaining to the global energy budget of the mantle.

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Image from Fault Interaction, Earthquake Stress Changes, and the Evolution of Seismicity article

dead sea
Topographic representations of the Dead Sea valleys (a) shows a Landsat Thematic Mapper image (band 2, red; 4, green; and 7, blue) draped overexaggerated digital elevation data (SRTM 3) to give a 3D effect. The vertical exaggeration is 25. The most prominent feature is the 11.5° change of valley strike occurring at the Dead Sea. While the valley is a clear feature, there are no clear normal faults marking the valley flanks (unlike Carmel Fault) such as in true rifts like Corinth or East Africa. (b) Shows a 3D image of the topography (SRTM3 data) colored by altitude. (c) Shows uplift and subsidence rates predicted by the model. Figure reproduced from Devès M, King GCP, Klinger Y, and Amotz A (2011) Localised and distributed deformation in the lithosphere: Modelling the Dead Sea region in 3 dimensions. Earth and Planetary Science Letters 308: 172. Figure reproduced from Devès M, King GCP, Klinger Y, and Amotz A (2011) Localised and distributed deformation in the lithosphere: Modelling the Dead Sea region in 3 dimensions. Earth and Planetary Science Letters 308: 172.

 

Fault Interaction, Earthquake Stress Changes, and the Evolution of Seismicity

This chapter focuses on advances in our understanding of the Earth’s lithosphere, over the last few decades – in particular, the way in which studies of earthquakes have added to our knowledge, by shedding light on how earthquakes interact one with another. There is a surprising lack of consensus about how the lithosphere behaves. We know that it is inhomogeneous at scales ranging from microns to tens or hundreds of kilometers, is porous, and is commonly anisotropic – remarks that apply with particular force to the continental lithosphere. Parts of the lithosphere are clearly brittle–elastic and generate earthquakes, but the greater part of the lithosphere is not seismogenic with a mechanical behavior that is poorly resolved. Even the brittle–elastic part behaves strangely when compared with the engineering materials that we normally come across. For example, before half the failure stress is reached in a laboratory sample, it has dilated dramatically. This effect has not been demonstrated to occur at large scales, a disappointment to earthquake prediction attempts in the 1960s and 1970s, but serves to remind us that the behavior of rocks at one scale may be a poor guide to their behavior at another. Commonly, rock sample studies may be only a metaphor for the behavior at larger scales.

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Image from Earthquake Hazard Mitigation: New Directions and Opportunities article

earthquake map
The global seismic hazard map developed by the Global Seismic Hazard Assessment Program (GSHAP) (Giardini, 1999). The map depicts peak ground acceleration (PGA) with a 10% probability of exceedance in 50 years, corresponding to a return interval of 475 years. The cooler colors represent lower hazard while the warmer colors are high hazard: White and green correspond to low hazard (0–0.08 m s− 2), yellow and light orange correspond to moderate hazard (0.08–0.24 m s− 2), darker orange corresponds to high hazard (0.24–0.40 m s− 2), and red and pink correspond to very high hazard (> 0.40 m s− 2).

 

Earthquake Hazard Mitigation: New Directions and Opportunities

Seismic hazard mitigation encompasses a suite of approaches to reduce the impact of earthquakes on our society. Since the development of earthquake seismology and earthquake engineering at the beginning of the twentieth century, the probability that any one person dies in an earthquake has been reduced by a factor of 3. This is at least in part a testament to the contributions of the field. Yet, the number of earthquake fatalities continues to grow. The likelihood of being killed in an earthquake has tracked population growth in some regions, and the dollar costs of earthquakes are escalating everywhere. In this chapter, we explore global seismic hazard, risk, and effective mitigation strategies to reduce them. Earthquake prediction, while often seen as a solution by the general public, does not represent a practical mitigation tool. In the category of long-term mitigation techniques, earthquake-resistant buildings have been most effective in the past. While design has largely been reactive to the successes and failures of the most recent earthquakes in the past, new simulation techniques for the earthquake process and the response of buildings now allow testing of future buildings in future earthquakes. Having successfully developed designs to prevent earthquake fatalities, the engineering community is now looking to reduce the economic impacts as well. Short-term mitigation involves rapid earthquake information systems. These systems have been developed over the last few decades to provide detailed information about earthquake shaking in the minutes following an event. Today, dense seismic networks with rapid telemetry and new approaches to hazard assessment are being integrated with the goal of supplying earthquake hazard information ever more rapidly, even before the ground shaking. Such warnings can be used to further reduce the impacts of earthquakes around the world.

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Treatise on Geophysics, Second Edition emphasizes developments and discoveries in the field since the first edition in 2007 and offers fundamental and state-of-the-art discussion of all aspects of geophysics. It features an entire new volume on Near Surface Geophysics that discusses the role of geophysics in the exploitation and conservation of natural resources and the assessment of degradation of natural systems by pollution. The editors and authors are leaders in their fields of expertise, the quality and coverage achieved by this group of editors and authors has insured that the Treatise is the definitive major reference work and textbook in geophysics. Topics are integrated into a coherent easy-to-use reference providing the ideal starting point for research. This title is essential for professionals, researchers, professors, and advanced undergraduate and graduate students in the fields of Geophysics and Earth system science.

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