Response Of Earth Research Articles

The electrical conductivity and thermal profile of the Earth's mid‐mantle

Electrical conductivity in the Earth's mantle is sensitive to temperature and chemical environment. Recent laboratory measurements of electrical conductivity are combined with candidate mantle geotherms to produce synthetic electrical conductivity profiles. These profiles are used to forward model the Earth's geomagnetic response function C, results of which are compared with the observed globally averaged response function at periods of 3.5 days to 4 months. Candidate lower mantle geotherms, representing whole‐mantle and layered convection end‐members, are compared using published electrical conductivity measurements on alumina‐bearing and alumina‐free perovskite in the conductivity models. Comparison of the predicted response functions with the observed geomagnetic response of the Earth shows that a) if lower mantle alumina is incorporated into perovskite, then the lower mantle must be cool, and b) if the alumina is not incorporated in perovskite then the results are only consistent with a hot lower mantle. In addition, the maximum alumina content of lower mantle MgSiO3 perovskite is constrained at 4%.

A Method to Compensate Earth Filtering based on Wavelet Packet

The earth's filtering response to seismic wave propagation can be approximated by variable Q attenuation and is dispersive or minimum phase. A model to compensate earth filtering is developed based on the wavelet packet decomposition. According to the model, a new method to compensate earth filtering is presented. The step of the method is: firstly, decompose seismic wave into difference frequency band; then, according to the model of compensating earth filtering to find attenuation coefficients of every frequency component; thirdly, every wavelet packet decomposition coefficients are divided by attenuation coefficients, and finally reconstruct seismic wave from modified frequency component to compensate earth filtering.

Crustal deformation associated with glacial fluctuations in the eastern Chugach Mountains, Alaska

The changes of the solid Earth in south central Alaska in response to two major glacial fluctuations on different temporal and spatial scales have been estimated and we evaluated their influence on the stress state and ongoing tectonic deformation of the region. During the recent (1993–1995) Bering Glacier surge, a large transfer of ice from the Bagley Ice Field to the Bering Glacier terminus region occurred. We estimated the elastic displacement of the solid Earth due to ice mass redistribution from Global Positioning System (GPS) measurements at sites near the surging glacier. We can account for these displacements by transfer of an ice volume of about 14 km3 from the surge reservoir area to the terminus region. We examined the background seismicity (ML ≥ 2.5) before, during, and after the surge. We found that the occurrence of small earthquakes (ML ≤ 4.0) in the surge reservoir region increased during the surge time interval possibly in response to a decrease in ice mass. This suggests that a small decrease in the vertical stress, σ3, could be enough to modulate the occurrence of small, shallow earthquakes in this dominantly thrust fault setting. During this century the southern Alaska coastal glaciers have been undergoing an overall decrease in volume. Based on our compilation of changes in the extent and thickness of the coastal glaciers between the Malaspina and Bering, we calculated surface displacements due to the Earth's viscoelastic response to annual thinning and to the cumulative retreat over the last 100 years. The uplift of the region due to an average annual thinning rate of 1–6 m/yr in the ablation region is 1–12 mm/yr. For our reference model with a viscosity of 5×1019 Pa s for depths between ≈ 40 and 200 km the total viscoelastic response due to the retreat over the last century may be as much as a couple of meters within the coastal ablation zone near Icy Bay. The maximum decrease in σv between 0 and 10 km was ≈ 1.0 MPa, which is significant in relation to the stress drops in recent earthquakes (≈ 2 to 10 MPa) but small in relation to the estimated tectonic stress magnitude. Therefore the occurrence of an earthquake such as the St. Elias (1979, MS = 7.2) may have been advanced in time; however, most of the ongoing stress accumulation would be primarily due to tectonic forces.

Relative Importance of Near-, Intermediate- and Far-Field Displacement Terms in Layered Earth Synthetic Seismograms

Waveform modeling and moment tensor inversion commonly assume only the far-field response to the seismic source. However, for certain frequencies and distances the near- and intermediate-field terms of the Earth's response becomes important. We developed a criterion to estimate the relative importance of these terms for horizontally layered Earth models by comparing reflectivity synthetic seismograms, computed with just the far-field response (far-field terms only), with the complete response (all terms included). The frequency and range dependent differences of these two responses are quantified by measuring the difference between synthetics for regional and local earthquake scenarios, the 1992 Little Skull Mountain, Nevada ( M w 5.7) and 1997 Calico Hills, Nevada ( M w 4.0) earthquakes. For these crustal earthquakes, we found that the near-field term becomes important when the minimum frequency, f n (Hz) of the simulation at hypocentral distance r ( km ) is f n = γ cr -1 where a reasonable crustal velocity for c is 5.8 km/sec and γ is the fraction of a wavelength estimated in this study to be ≈ 0.6. The far-field response converges to the complete response for frequencies greater than f n. Manuscript received 30 September 1999.

An Explication of the Coriolis Effect

Inertia circle motion is a familiar concept demonstrating the behavior of a horizontally moving particle on the rotating earth in response to the Coriolis force. Three dynamical principles valid in nonrotating space are used to explain the principal properties of this motion without the need for solving differential equations. The motion is an oscillation about a central latitude selected by the particle's angular momentum, in which the restoring force is set by the relative magnitudes of the poleward attraction of gravity and the equatorward attraction of the centrifugal force as the particle oscillates about the central latitude.

Tectonic pattern of South America inferred from tidal gravity anomalies

The knowledge of several physical parameters that characterize a tectonic unit is important to evaluate its dynamic evolution and, therefore, its role in the continental evolution. Several methodologies have been used to measure the elastic properties of tectonic units using: seismic waves, the level of coherence between the wavelength pattern of the topography and gravity fields, borehole deformation rate, mineral fabric, etc. In this study, the Earth's dynamic elastic response to gravity tides is applied for measuring the lithosphere effective elastic thickness. This methodology proved to be a good alternative to the conventional coherence method. It was applied over the continent, taking into account the poor gravity coverage in South America and the restricted area of some tectonic units. Results are presented as lateral distribution of the effective elastic thickness in South America.

Implications of a non-adiabatic density gradient for the Earth's viscoelastic response to surface loading

SUMMARY The response of a viscoelastic Earth to the melting of the Late Pleistocene ice sheets has been the subject of a number of investigations employing PREM. In PREM, a non-adiabatic density gradient (NADG) exists in the upper mantle, and to understand the implications of this model it is thus important to examine the eVects of this NADG on the Earth’s response to surface loads. This paper is based on the assumption that the contribution to the depth dependence of the density that is not due to self-compression is due to compositional change. This contribution is referred to as ‘non-adiabatic’. We evaluate the eVects of a non-adiabatic density jump (NADJ) for the 670 km discontinuity and the NADG in the upper mantle by adopting a compressible earth model with both a compositional density gradient and a density jump. Numerical calculations based on these models indicate that the magnitude of the Earth’s response associated with the NADG is much smaller than that associated with the NADJ at 670 km depth. It is also confirmed that the higher modes associated with the NADJ and the NADG are much more sensitive to the existence of an elastic lithosphere than the fundamental modes associated with the density jumps at the surface and core‐mantle boundary.

CMT解と震源時間関数の迅速な自動決定とその結果の評価

Recent advances in broadband seismic observation enable us to analyze high quality waveform data just after the earthquake occurrence. An automated system for rapid determination of earthquake mechanisms for local events occurring beneath central Japan is developed with this point as background. When an earthquake occurs, its hypocentral parameters are determined automatically in several tens of seconds. In a case when an event occurring in a given area has a magnitude larger than a certain value, its source process is automatically analyzed by the use of a broadband waveform inversion technique. Considering the importance to shorten the computer process time to obtain the result, we calculate the Green's functions immediately after hypocentral parameters are calculated and when waveform data to be used in the inversion are being retrieved. The data of the Earth's response parameters, which are used in the calculation of the Green's functions, are stored on the hard disk so as to reduce the total lapse time. As a result, the CMT solution and source time function can be obtained in a few minutes after the earthquake occurrence. Inadequacy of theoretical waveform calculated by the 1-D Earth's model is corrected by introduction of station corrections to the observed arrival time and overparameterization to the source time function, where a number of double couple small sub-events are located in a certain time range. The CMT solution is represented by superimpose of moment tensors of small sub-events with very short duration. All the sub-events are assumed to occur at the same location (i. e., at the hypocenter) but to have different onset times. The source time function is also estimated from the temporal distribution of the sub-events. To evaluate the reliability of the results obtained from the present study, we compare them with the following two data sets: i) focal mechanism solutions determined by P first motion analysis, and ii) CMT solutions obtained from the other method for the same events. Our results are basically consistent with these two sets of mechanism solutions. However the agreement of the solutions is obviously better among the CMT solutions. Possible explanation for the difference between CMT and focal mechanism solutions is that the latter may be inaccurate because of insufficient push and pull first motion data, or that the total rupture may occur along the fault different from the initial rupture.

Predictions of Antarctic crustal motions driven by present‐day ice sheet evolution and by isostatic memory of the Last Glacial Maximum

Detectable crustal motion and secular rate of change of solid‐surface gravity may be produced by the Earth's response to present‐day and past ice mass changes in Antarctica. Scenarios of present‐day ice mass balance, previously utilized to explore the global geodetic signatures of the Antarctic ice sheet, produce elastic crustal responses that are typically bounded by uplift rates ≤5 mm/yr, horizontal motion ≤1 mm/yr, and solid‐surface gravity change rates ≤1 μGal/yr. In a restricted locality, one scenario produces uplift rates slightly in excess of 10 mm/yr and correspondingly enhanced horizontal and gravity rates. In contrast, the viscoelastic response to ice mass changes occurring since Last Glacial Maximum (LGM) exceeds 5 mm/yr (uplift) over substantial portions of West Antarctica for a wide range of plausible choices of timing and magnitude of deglaciation and mantle viscosity. Similarly, viscoelastic gravity rate predictions exceed 1 μGal/yr (decrease) over large regions, confirming suggestions that a Global Positioning System (GPS) and absolute gravity‐based program of crustal monitoring in Antarctica could potentially detect postglacial rebound. A published revision to the CLIMAP model of the Antarctic ice sheet at LGM, herein called the D91 model, features a substantially altered West Antarctic ice sheet reconstruction. This revision predicts a spatial pattern of present‐day crustal motion and surface gravity change that diverges strikingly from CLIMAP‐based models. Peak D91 crustal rates, assuming deglaciation begins at 12 kyr and ends at 5 kyr, are around 16 mm/yr (uplift), 2 mm/yr (horizontal), and −2.5 μGal/yr (gravity). Tabulated crustal response predictions for selected Antarctic bedrock sites indicate critical localities in the interior of West Antarctica where expected responses are large and D91 predictions differ from CLIMAP‐based models by a factor of 2 or more. Observations of the postglacial rebound signal in Antarctica might help constrain Antarctic mass balance and contribution to sea level rise over the past 20,000 years.

Sea level higher than present 3500 years ago on the northern main Hawaiian Islands

Research Article| April 01, 1998 Sea level higher than present 3500 years ago on the northern main Hawaiian Islands Eric E. Grossman; Eric E. Grossman 1Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar Charles H. Fletcher, III Charles H. Fletcher, III 1Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar Author and Article Information Eric E. Grossman 1Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Honolulu, Hawaii 96822 Charles H. Fletcher, III 1Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Road, Honolulu, Hawaii 96822 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1998) 26 (4): 363–366. https://doi.org/10.1130/0091-7613(1998)026<0363:SLHTPY>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Eric E. Grossman, Charles H. Fletcher; Sea level higher than present 3500 years ago on the northern main Hawaiian Islands. Geology 1998;; 26 (4): 363–366. doi: https://doi.org/10.1130/0091-7613(1998)026<0363:SLHTPY>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract New data from an emerged coastal bench and associated fossil beach on Kapapa Island (Oahu), Hawaii, preserve a detailed history of middle to late Holocene sea level. These include 29 new calibrated radiocarbon ages and elevations indicating mean sea level reached a maximum position of 2.00 ± 0.35 m ca. 3500 yr B.P. These results correlate with additional evidence from Hawaii and other Pacific islands and provide constraints on Oahu's long-term uplift rate (0.03–0.07 mm/yr), previously based solely on Pleistocene age shorelines. Our sea-level reconstruction is consistent with geophysical model predictions of Earth's geoid response to the last deglaciation and with observations of increased Antarctic ice volume during the late Holocene. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Flexural rigidity of Fennoscandia inferred from the postglacial uplift

The Earth's response to glacial loading/unloading offers exceptional promise for the study of the physical properties of the lithosphere. In particular, tilting of paleoshorelines is very sensitive to the lithosphere rigidity. To determine the flexural rigidity, the isostatic response to deglaciation in Fennoscandia is modeled using an Earth model with a layered mantle viscosity overlain by an elastic lithosphere. The flexural rigidity and asthenosphere viscosity is allowed to vary to get a match between theoretical and observed present rate of uplift and tilting of paleoshorelines. Five different ice thickness models are used. For a relatively thin ice (2500 m in central areas) the resulting flexural rigidity is more or less uniform over Fennoscandia, with a value of 1023 N m (elastic thickness te ≈ 20 km). This is regarded as minimum for the flexural rigidity of central Fennoscandia. The pattern of the present rate of uplift and the tilts of the paleoshorelines of the area also sets an upper bound of the flexural rigidity, 2.5 × 1025 N m (te ≈ 110 km) in more central areas of Fennoscandia. The flexural rigidity at the western coast of Norway does not seem to exceed 1023 N m (te ≈ 50 km). The most likely glacier model gives a flexural rigidity of 1023 N m (te ≈ 20 km) at the Norwegian coast, increasing to above 1024 N m (te ≈ 50 km) in central parts of Fennoscandia.

Erosion of terrestrial planet atmosphere by surface motion after a large impact

The history of atmosphere accretion has a large significance in the evolution of the Earth and other planets. Here we present a quantitative analysis of the Earth's response to large impacts (in the 10 32–10 38 erg energy range), and the resulting atmosphere loss owing to the global radial surface motion. Our results show that it is possible to deplete the Earth's atmosphere via this mechanism in very large (lunar-sized, ∼ 10 38 erg) impacts.

Physical modeling of radiation belt response to geomagnetic storm: 2. On a 10 hour–10 day time scale

In order to reproduce the Earth's radiation belt response to geomagnetic storms on the 10 hours–10 days time scale we have developed a code, Salammbô 3D, (3D equivalent to two spatial dimensions, radial distance and latitude, and one dimension in energy) which solves the phase space diffusion equation. It is used to understand the dynamic conditions of the electron and proton radiation belt (from L = 1 to 7) after a geomagnetic storm, when distribution functions are averaged over the drift path. With such a model, which allows one to reproduce flux variations that occur over a time scale on the order of half a day, the outer belt electron dynamics can be characterized. Particles in the energy range 100 keV – 500 keV are diffuse throughout the belt. Particles with higher energies are “created” by acceleration of slower particles near the plasmapause location. The calculated shape of the fluxes in a L versus time grid for MeV electrons are in good agreement with CRRES particle data obtained during a typical event.

PREDICTIONS OF CRUSTAL DEFORMATION CAUSED BY CHANGING POLAR ICE ON A VISCOELASTIC EARTH

Changes in polar ice could cause vertical crustal motion of up to several mm yr-1 along the edge of the Greenland and Antarctic ice caps. Measurements of the uplift could help constrain the changing ice volumes. The problem is complicated by the Earth's visco-elastic response to past loading, including the Late Pleistocene deglaciation. A method is described for removing these visco-elastic effects, by using simultaneous measurements of vertical motion and surface gravity. A linear combination of these two measurement types can be formed which is relatively independent of visco-elastic effects, and which can be interpreted in terms of present-day fluctuations in ice.

Mantle Viscosity and Ice-Age Ice Sheet Topography

Ice-age paleotopography and mantle viscosity can both be inferred from observations of Earth's response to the most recent deglaciation event of the current ice age. This procedure requires iterative application of a theoretical model of the global process of glacial isostatic adjustment. Results demonstrate that the iterative inversion procedure converges to a paleotopography that is extremely close to that from the ICE-4G model. The accompanying mantle viscosity profile is furthermore shown to reconcile the requirements of aspherical geoid anomalies related to the mantle convection process, thus resolving a fundamental issue concerning mantle rheology. The combined model also explains postglacial sea level histories for the east coast of the United States.

Upper bounds on the energy dissipation in turbulent precession

Rigorous upper bounds on the viscous dissipation rate are identified for two commonly studied precessing fluid-filled configurations: an oblate spheroid and a long cylinder. The latter represents an interesting new application of the upper-bounding techniques developed by Howard and Busse. A novel ‘background’ method recently introduced by Doering &amp; Constantin is also used to deduce in both instances an upper bound which is independent of the fluid's viscosity and the forcing precession rate. Experimental data provide some evidence that the observed viscous dissipation rate mirrors this behaviour at sufficiently high precessional forcing. Implications are then discussed for the Earth's precessional response.

Analytic minimum information deconvolution and its application to ocean bottom seismometer data

Seismic refraction/wide angle reflection data for the study of the earth's crust generally lack resolution due to the low frequency wavelets from seismic sources. Standard deconvolution techniques to improve resolution of the data are limited by phase‐shifted waveforms such as supercritical reflections from the Moho as well as various refraction phases from the crust. We extended the minimum information deconvolution technique to the analytic formulation to deconvolve seismic data that contain phase‐shifted wavelets. When applied to a seismogram, analytic deconvolution yields the amplitude of the earth's impulse response function in the form of the signal envelope. An application example with ocean bottom seismometer data acquired along the Canadian continental margin of the Atlantic shows a remarkable improvement in resolution by compressing the wavelets effectively.

Researchers focus on Earth's response to hypervelocity impacts

Imagine witnessing the impact of a 10 km‐sized comet or asteroid onto a broad expanse of sea just off the Yucatan peninsula of Mexico. The bolide, a brilliant fireball traveling at speeds of 15 to 20 km/s, would melt about 20,000 km3 of rock and excavate a crater with a diameter of over 200 km within a few seconds, all due to the release of energy equivalent to 100 mega‐megatons of TNT. Now imagine, at a twelve order‐of‐magnitude smaller spatial scale, a perfectly ordered crystalline quartz lattice and the sudden compression felt by the constituent atoms within a matter of microseconds. The creation of lattice dislocations, electronic defects, shock lamellae, amorphization, and a myriad of other features characteristic of shock metamorphism, 65 million years later, is providing scientists with critical clues for unraveling the mysteries of the now famous Chicxulub impact structure.

Long‐period variations in gravity field caused by mantle anelasticity

A numerical perturbation approach is used to assess the effect of mantle anelasticity on the Earth's zonal response coefficient κ, the zonal geopotential coefficient J2, and the orbital node of geodetic satellites. The theoretical predictions are used to compare solutions of elastic ocean tide models and tides observed by geodetic satellites for Mf, Mm, Ssa, and Sa. The discrepancies between the satellite observed tides and the solution from Schwiderski and recent altimetric ocean tide models can be partly explained by the predicted effect of mantle anelasticity at Mf and Mm frequencies. Approximately 80% of the observed semiannual variation in δJ2 by geodetic satellites can be attributed to the tidal deformation from anelasticity and from the classical equilibrium ocean. The predicted κ for the 18.6‐year tide was computed for an Earth with an anelastic mantle and a nonequilibrium ocean. The range of the lower and upper bounds of κ for the 18.6‐year tide is from 0.345 to 0.377 in amplitude, and from −6° to 3° in phase, with preferred amplitude of 0.365 and phase of −0°.8.

Experimental petrology of upper mantle materials, processes and products

Experiments on rock materials and volatile components provide an array of phase equilibrium boundaries, giving the depth-temperature framework for the phase transitions experienced by rock masses as they move up or down within the Earth in response to the dynamic processes of mantle convection and plate tectonics. Sub-solidus phase transitions in mantle materials correlate well with upper mantle structure determined from seismic studies, but debate continues about whether there is a change in composition at some seismic boundaries. The interface at 650 km correlates with the transformation of most minerals into the perovskite structure, which may have significant effects on mantle dynamics. Recent research on mantle xenoliths has been concerned with extension of standard thermometers and barometers to higher pressures and their practical assessment, along with the development and refinement of new geothermobarometers. The experimental partial melting of mantle peridotite has been elucidated by detailed studies of model systems and new experimental techniques. Parameterization of the data makes prediction possible. The origin of MORBs involves a complex process of fractional fusion. Evidence from static olivine flotation experiments and shock wave compression experiments on molten komatiite indicates that the densities of mantle melts may exceed that of the residual rock at depths greater than 400 km, which would prohibit ascent of the magma. Recent investigations have identified many dense hydrous magnesian silicates (DHMS), stable through the upper mantle between ~ 300 and 650 km, and reaching the peridotite-volatile solidus curve through part of this interval. The near-solidus liquid composition in peridotite-CO 2-H 2O above ~ 2 GPa is carbonatitic (calcic dolomite), potentially a powerful agent for metasomatism. Experimental studies of trace element distributions between mantle minerals and carbonatitic liquids are beginning to permit quantification. Determination of the effect of reduced oxygen fugacity has introduced mantle scenarios with melting induced by redox changes There is indirect experimental evidence that the solidus may terminate at a critical end-point at depths of a few hundred kilometers. Recent experiments related to subduction of oceanic crust include measurements of liquid composition from the melting of H 2O-undersaturated peridotite, the vapour-absent melting of amphibolite, and partial melting of pelagic clays. Much H 2O is expelled during subduction, but the current estimates of low temperatures support the deep subduction and longterm storage in the mantles of both H 2O and CO 2.