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To investigate the manipulation of electromagnetic properties of two-dimensional materials, this effort characterizes charge transfer behavior of colloidal COF-5 (covalent organic framework) in the presence of various metal ions. A series of metal chloride compounds was introduced to COF-5 in solution and solid film phases and the interaction of the material with electromagnetic radiation was monitored across the visible region using electronic absorption spectroscopy. Notable changes were observed, quantified, and discussed for copper (II) chloride (CuCl2), chromium (III) chloride (CrCl3), and iron (III) chloride (FeCl3) with COF-5. Ligand-to-metal and metal-to-ligand charge transfer are explored as a possible mechanism for the observed electronic behaviors.
The Earth is continuously being deformed due to forces related to earthquakes, surface loads such as ice-sheets, the gravitational attraction to other planets, and many other phenomena. The relation between forces and the resulting style of deformation defines the rheology of a material. While the Earth behaves nearly like elastic rubber at short timescales from seconds to years, large parts of it can be treated as a liquid when studied over geologic timescales exceeding millennia. In this chapter we provide a detailed introduction to the various deformation styles of the Earth and their relevance to a wide range of processes, including the propagation of seismic waves, the deformation of the lithosphere near mountain ranges and subduction zones, and convective flow in the mantle.
This enduringly popular undergraduate textbook has been thoroughly reworked and updated, and now comprises twelve chapters covering the same breadth of topics as earlier editions, but in a substantially modernized fashion to facilitate classroom teaching. Covering both theoretical and applied aspects of geophysics, clear explanations of the physical principles are blended with step-by-step derivations of the key equations and over 400 explanatory figures to explain the internal structure and properties of the planet, including its petroleum and mineral resources. New topics include the latest data acquisition technologies, such as satellite geophysics, planetary landers, ocean bottom seismometers, and fibre optic methods, as well as recent research developments in ambient noise interferometry, seismic hazard analysis, rheology, and numerical modelling - all illustrated with examples from the scientific literature. Student-friendly features include separate text boxes with auxiliary explanations and advanced topics of interest; reading lists of foundational, alternative, or more detailed resources; end-of-chapter review questions and an increased number of quantitative exercises. Completely new to this edition is the addition of computational exercises in Python, designed to help students acquire important programming skills and develop a more profound understanding of geophysics.
Rocks contain a tiny proportion of magnetic minerals that make them weakly magnetic. Some are magnetized in the direction of the magnetic field in which they formed. By analyzing this direction, the position of a virtual geomagnetic pole (VGP) at the time the rock formed can be located. Connecting the VGP for rocks with different ages from the same continent gives a curve of apparent polar wander (APW), which results from the motion of the continent relative to the rotation axis. Comparing APW paths for different continents reveals a history of relative motions and allows the reconstruction of past supercontinents. The paleomagnetic field has reversed polarity numerous times in the geological past, leaving a record of geomagnetic polarity in the magnetizations of rocks. Polarity reversals cause oceanic magnetic anomalies, which are important for understanding plate tectonics and also form the basis of a geomagnetic polarity timescale for the past 230 Myr.
The geomagnetic field is generated by complex motions of electrically conducting liquid iron in the Earth’s outer core. It has been studied for centuries at observatories and for decades from orbiting satellites. Outside the Earth, the magnetic field deflects the solar wind, a stream of charged particles from the Sun, thereby shielding the planet from harmful radiation. Some radiation penetrates deep into the outer atmosphere, where it ionizes air molecules. These cause the aurora and also form spherical shells of ions encircling the Earth that produce their own magnetic fields. We have learned about the magnetic fields of the other planets from earth-bound observations and from space missions. The geomagnetic field provides an important tool for exploring the mineral wealth of our planet. We learn how to interpret the shapes of the magnetic anomalies of simple geometric bodies, including block models of oceanic magnetic anomalies.
The shape of the Earth is determined primarily by two forces. Gravitational attraction, directed toward the center of the planet, results in an almost spherical shape. The Earth’s rotation produces a centrifugal force away from the rotation axis that flattens the sphere to a rotational ellipsoid. Differences in internal mass distribution produce bumps and hollows in the ellipsoid, forming a smooth but uneven surface called the geoid. Gravity at any place acts in the vertical direction, which is everywhere perpendicular to the local geoid. We explain how the gravitational attractions of the Moon and Sun deform the Earth’s free surface, creating tides in the oceans and in the solid planet. The Earth’s ellipsoidal shape allows the gravitational attractions of other planets to modulate both its rotation and its orbit cyclically with periodicities of 21,000 to 405,000 years, which are correlated to long-term climatic changes.
The lithosphere – the thin outer shell of the Earth – is stronger than the underlying mantle. Geodynamic activity driven by heat in the planet’s interior has caused it to subdivide into a number of thin plates, several hundred to several thousand kilometers in horizontal extent. They are in constant motion at speeds of a few centimeters per year. The relative motion at plate margins where they adjoin results in tectonic activity, characterized by earthquakes and volcanism. We distinguish three types of margin – spreading centers, subduction zones, and transform faults – and describe the seismic, gravity, and magnetic data that characterize them. We explain how reconstructions of plate positions in the geological past are obtained and what they tell us about the planet’s geodynamic history.
Gravity measurements are made with a gravimeter at geodetically located places on land or on gyroscopically stabilized platforms in marine and airborne surveys. In airborne and satellite surveys, gravity gradiometers are used. We explain these instruments and how gravity data are reduced to the reference ellipsoid by correcting for the latitude and altitude of the measuring site and the attraction of surrounding topography. A residual gravity anomaly is due to subsurface structure. We distinguish two types of anomaly: free-air anomalies are not corrected for local rock densities, which are needed to define Bouguer anomalies. The interpretation of local anomalies is facilitated by modeling the gravitational attractions of simple geometric bodies. Regional gravity anomalies help us to understand the geological processes at mountain chains and plate boundaries. Isostasy is an important dynamic process, by which the excess mass of a mountain is compensated by a less dense subsurface structure. Vertical crustal movements occur when isostatic equilibrium is disturbed.
Just as air acts as the carrier of sound waves, the Earth supports the propagation of seismic waves, which are excited, for example, by earthquakes, eruptions and explosions. In human history, high-amplitude seismic waves and related events such as tsunamis have brought more destruction than any other natural phenomenon. However, seismic waves also transmit information about their source and about the medium through which they propagate. In this chapter, we introduce the basic elements of seismic wave propagation, starting with a description of different wave types that are distinguished by their propagation velocities, polarization directions, and the regions of the Earth’s interior through which they travel. We will learn how seismic waves interact with heterogeneities, i.e., how they reflect, refract, and convert into each other. This will allow us to decipher the wealth of information transmitted by these waves in order to construct images of the deep Earth’s interior.
Large earthquakes are among the most energetic phenomena observed on Earth, surpassing the biggest nuclear explosions by orders of magnitude. The family of earthquakes is very diverse. It includes natural events that occur within seconds along the boundaries of tectonic plates, slow earthquakes that last for days or weeks, swarms of thousands of little earthquakes beneath volcanoes, and clusters of earthquakes induced by industrial activity. Though individual earthquakes cannot be predicted with current methods, long-term seismic hazard can be estimated in order to inform building codes and to prepare the population. Seismic waves emitted by earthquakes travel through the Earth, thereby acquiring information about its internal structure. Seismic tomography based on earthquake recordings draws the image of a very dynamic planet, featuring cold lithospheric slabs that descend deep into the mantle, and narrow plumes that transport hot material toward the surface.
The Earth’s internal heat drives geodynamic processes. A primordial part results from cooling of the originally molten planet and part is produced by radioactivity. Temperatures inside the Earth are below the melting point in the crust, mantle, and inner core, but are above the melting point of liquid iron in the outer core. Heat is transported by conduction in the crust, mantle and inner core, and by vigorous convection in the outer core. Deformation of the solid mantle by viscous creep provides a mechanism for mantle convection. We examine the factors that control this process, which provides the power for plate tectonic motions at the surface. The heat flow on continents arises largely from radioactive decay in crustal rocks, but in the oceans results from cooling of lithospheric plates during sea-floor spreading. Plumes of hot mantle material are a possible magma source for volcanic hotspots.
The rocks and minerals that make up the Earth’s crust and mantle have variable electrical properties. This characteristic is made use of in important methods of surveying, to research the structure and properties of the interior. Natural and induced electrical currents conform to the underground pattern of electrical resistivity. We describe how this can be used to locate anomalous regions with mineral enrichment or that have environmental importance. Electromagnetic methods, employed on the ground and from the air, are particularly important in mineral exploration. Ground penetrating radar has become an important tool of environmental and archeological research. These methods are limited to the top several hundred meters of the crust, but magnetotelluric methods can probe deeper into the lithosphere and mantle. The high-frequency variations of the magnetic field induce currents in the solid Earth and in the oceans, delivering valuable information about the electrical conductivity in the upper mantle.