Vernon F. Cormier

University of Connecticut | UConn · Department of Physics

Stochastic tomography, made possible by dense deployments of seismic sensors, is used to identify phase changes in Earth's mantle that occur over depth intervals. This technique inverts spatial coherences of amplitudes and travel times of body waves to determine the depth and dependence of the spatial spectrum of seismic velocity. This spectrum is...

This chapter summarizes the properties of the geodynamo and the geomagnetic field it produces. It includes discussions of the physical ingredients necessary for planetary dynamos in general, the magnetic induction equation and its application to magnetic field generation by fluid motions in the outer core, the magnetic Reynolds number, the key dime...

Earth's gross stratification into a silicate mantle and denser, fluid, iron core are apparent from its bulk density, moment of inertia, and spatial and temporal variations of its magnetic field. The discovery of a solid inner core and the resolution of its structure at spatial scales as small as 10 km have primarily come from the observation and in...

We first review the composition of the core: primarily Fe, Ni, and the case for light elements. With the assumption that the entire outer core is convecting so that the geotherm lies along the adiabat, and with the inner core boundary temperature fixed at the Fe alloy melting temperature, we derive the core geotherm in terms of reasonably constrain...

We begin this chapter with a description of the physical environment of the outer core, focusing on its most distinctive attributes. We then characterize the outer core environment using dimensionless parameters defined in terms of the physical and chemical properties that govern its dynamics. Special emphasis is given to thermochemical buoyancy, t...

In this chapter, we present current theories on how the Earth and its core were formed, and how the core evolved between the time of formation and the present day. We begin by summarizing the enormous amounts of energy expended in Earth's formation. We briefly discuss the genesis of core-forming elements and the origin and early evolution of the so...

The physical properties and their lateral variation in 200–400 km thick regions surrounding Earth's core-mantle boundary and inner core boundary are important to the functioning and evolution of Earth's dynamo. The complexity of structure in the lowermost mantle rivals that near its tectonically active surface, but improvements in its imaging may a...

The solid inner core represents only 0.7% of our planet's total volume, and its surface area only 3.7% of Earth's surface area. Although its elastic structure is relatively poorly sampled by seismic body waves, it is of great interest to understanding the evolution of the core. Compositional convection in the outer core driven by inner core solidif...

Extending our knowledge of the structure and dynamics of planetary cores will require continuing advances in seismology, mineral physics, and geomagnetism. In seismology these include station coverage, instrumentation, routine incorporation of source-time functions, and use of the correlation wavefield and coherence. In mineral physics these includ...

The materials processes of solidification, deformation, and annealing, along with the geodynamics and material properties of the core Fe alloy, determine the inner core microstructure (including grain size) and texture. We first review solidification, including nucleation, translation, and the F layer. We then examine geodynamic sources of stress/s...

P ′ P ′ precursors have been used to detect discontinuities in the lower mantle of the Earth, but some seismic phases propagating along asymmetric ray paths or scattered waves could be misinterpreted as reflections from mantle discontinuities. By forward modeling in standard 1D Earth models, we demonstrate that the frequency content, slowness, and...

The relative contributions of scattering and viscoelastic attenuation to the apparent attenuation of seismic body waves are estimated from synthetic and observed S waves multiply reflected from Earth's surface and the core–mantle boundary. The synthetic seismograms include the effects of viscoelasticity and scattering from small-scale heterogeneity...

The relative contributions of scattering and viscoelastic attenuation to the apparent attenuation of seismic body waves are estimated from synthetic and observed S waves multiply reflected from Earth’s surface and the core-mantle boundary. The synthetic seismograms include the effects of viscoelasticity and scattering from small-scale heterogeneity...

Using envelopes of regional high frequency seismograms synthesized by an algorithm from 3-D radiative transport theory (RTT), we investigate tradeoffs between the velocity fluctuation parameter epsilon , the corner parameter "a" of the von Kármán heterogeneity spectrum, and intrinsic attenuation 1/Qint. In the frequency band 1 to 4 Hz and range 100...

Fluctuations in log-amplitude and travel time of teleseismic P waves recorded by the EarthScope USArray are used to invert for the heterogeneity spectrum of P-wave velocity in a 1000 km thick region of the upper mantle beneath the array. These fluctuations are used to form coherence functions. Best fits to joint transverse coherence functions requi...

Standard Earth models assume a simple uniform inner core boundary (ICB) separating the liquid iron outer core from the solid iron inner core. Metallurgical and geodynamic experiments, however, predict lateral variations along this boundary originating from thermochemical and geodynamic instabilities during solidification. We search for evidence of...

Comprised of S waves trapped in the Earth's crust, the high-frequency (2-10 Hz) Lg wave is important to discriminating earthquakes from explosions by comparing its amplitude and waveform to those of Pg and Pn waves. Lateral variations in crustal structure, including variations in crustal thickness, intrinsic attenuation and scattering, affect the e...

Comprised of S waves trapped in Earth’s crust, the high frequency (2–10 Hz) Lg wave is important to discriminating earthquakes from explosions by comparing its amplitude and waveform to those of Pg and Pn waves. Lateral variations in crustal structure, including variations in crustal thickness, intrinsic attenuation, and scattering, affect the effi...

Radiative transport modeling can combine the effects of both large-scale (deterministic) and the small scale (statistical) structure on the coda envelopes of high frequency regional seismograms. We describe a computer code to implement radiative transport modeling that propagates packets of seismic body wave energy along ray paths through large-sca...

The solidification of the Earth's inner core shapes its texture and rheology, affecting the attenuation and scattering of seismic body waves transmitted through it. Applying attenuation tomography in a Bayesian framework to 398 high-quality PKIKP waveforms, we invert for the apparent Qp for the uppermost 400 km below the inner core boundary (ICB) a...

The existence of topography of the inner core boundary (ICB) can affect the amplitude, phase, and coda of body waves incident on the inner core. By applying pseudospectral and boundary element methods to synthesize compressional waves interacting with the ICB, these effects are predicted and compared with waveform observations in pre-critical, crit...

PKIIKP waves, reflected from the underside of the inner core boundary, are very sensitive to the S velocity in the uppermost 80 km of the inner core at antipodal distances, undergoing a phase change and a factor of 4 amplification as the distance approaches 180∘. Modeled PKIIKP waveforms are consistent with a near-zero shear modulus in the uppermos...

The complexity induced in seismic body waves by rapid or discontinuous spatial changes of elastic moduli and density can be efficiently modeled in radially symmetrical structure by a collection of closely related ray-, integral transform-, and modal-based solutions of the elastic equations of motion. These modeling techniques can be extended to inc...

The process of subduction provides continuous chemical and thermal heterogeneity to Earth’s mantle. How heterogeneity is stirred, stretched and distributed depends on the detail of mantle convection as well as chemical and physical properties of mantle materials. Seismic observations have revealed heterogeneities in Earth’s mantle at varying scales...

Seismic P velocity structure is determined for the upper 500 km of the inner core and lowermost 200 km of the outer core from differential travel times and amplitude ratios. Results confirm the existence of a globally uniform F region of reduced P velocity gradient in the lowermost outer core, consistent with iron enrichment near the boundary of a...

Geodynamic models of a convectively translating inner core have recently been proposed that would account for the seismically observed differences in isotropic velocity between the eastern and western hemispheres of the inner core. These models, however, have previously been thought to be incompatible with seismic observations of a 1.5% P wave velo...

Differential travel times and waveforms of PKIKP and PKiKP phases in the 129°–141° distance range, deconvolved for the effects of source time functions and average mantle attenuation operators, are inverted for velocity and attenuation in the uppermost 80 km of the inner core, and the velocity gradient and attenuation in the lowermost 200 km of the...

The outer core is one of the most dynamic divisions of our planet. However, despite undergoing vigorous convection, the outer core is not necessarily a uniform, homogeneous layer of the Earth. Accumulation of light element enriched iron at the top of the outer core, below the core-mantle boundary, may lead to the formation of a stably stratified la...

Lateral variations in the structure and crystallization of the inner core will likely be associated with lateral variations in the topography of its boundary. Depending on liquid fraction and the ratio of solid over liquid viscosity, the process of compaction of solids and expulsion of fluids at the solidifying boundary can be dynamically unstable,...

Hypotheses for the mechanisms of growth of Earth's inner core can be tested from observations of lateral variations of elastic and anelastic properties near the inner core boundary. Differential travel times of PKIKP-PKiKP and the apparent travel time of P waves diffracted around the inner core are consistent with the existence of a stably stratifi...

The intrinsic attenuation of seismic waves in the earth has been found to be consistent with loss mechanisms that are thermally activated. The observed regional and frequency dependences of seismic Q agree with the expected lateral variations in a geotherm having a rapid temperature increase in the upper 400 km of the mantle, followed by a slower v...

The seismic velocity profile and its lateral variation just above and below the inner core boundary (ICB) are important factors constraining the fluid flow and the nature of compositional convection in the outer core that may drive the geodynamo. Studies of differential travel times, body wave amplitudes and waveforms, free oscillations and their s...

Combined sesimology, geodynamic, and geodynamo modeling can test several hypotheses for the mechanisms of growth of Earth's inner core exhibited by hemispherical lateral variations in its upper 600 km. Weak backscattered PKiKP in the equatorial eastern hemisphere can be made consistent with either a hypothesis of freezing or melting. In a melting h...

Earth’s core is thought to have formed from sinking metal diapirs that segregated at mid-mantle conditions. Consequently, the core and mantle may not be in chemical equilibrium. Recent experiments suggest that at the pressures and temperatures of the core, lower mantle oxides and silicates may have an increased solubility in iron. Geodynamic calcul...

Anomalous high frequency PKKPBC signals (displaying a large amount of energy around 2.5Hz), recorded globally for deep and intermediate depth earthquakes, are compared to PKKPAB signals. The attenuation difference t\textAB* - t\textBC* t_{\text{AB}}^{*} - t_{\text{BC}}^{*} is evaluated from spectral amplitudes in the range 96–111°, being approxim...

Seismic wave propagation through two-dimensional core-mantle boundary (CMB) ultralow-velocity zones (ULVZs) is modeled using a global pseudospectral algorithm. Seismograms are synthesized for several types of ULVZ models to investigate the effect of these structures on SKS and SPdKS phases. One-dimensional models and two-dimensional models with dif...

We investigate arrivals of seismic phases reflected from the core–mantle boundary (PcP waves) and those reflected from the inner-core boundary (PKiKP waves) at subcritical angles, with the goal of measuring their amplitude ratios. This adds invaluable data points required to study the density jump across the inner-core boundary (ICB). One nuclear e...

Recent studies find unusual high-frequency coda following the PKiKP phase, reflected from the inner core boundary. Seismic waves interacting with the uppermost 300 km of the inner core reveal this region to have strong lateral variations in elastic structure, anisotropy, attenuation, and scattering. The detailed spatial distribution of heterogeneit...

Recent theories for the pressure and temperature dependence of viscosity predict the lowermost liquid outer core (F region), near the solidifying inner core, to be in the state of a high, glass-like, viscosity. Seismic observations spanning the frequency band from 0.001 to 1 Hz can be made consistent with this hypothesis by assuming a Maxwell rheol...

New theories for the viscosity of metallic melts at core pressures and temperatures, together with observations of translational modes of oscillation of Earth's solid inner core, suggest a rapid increase in the dynamic viscosity near the bottom of the liquid outer core. If the viscosity of the lowermost outer core (F region) is sufficiently high, i...

The inner core boundary (ICB) of the earth is characterized by a discontinuous change in elastic properties between the liquid outer and solid inner core. In the ray theory approximation, a measure of the density contrast at the ICB is given by the amplitude ratio of P waves reflected from the core–mantle boundary (CMB; PcP waves) and the ICB (PKiK...

Lateral variation in the uppermost solid inner core has been documented in elastic anisotropy, attenuation, and scattering of high frequency body waves. Less well established are lateral variations in structure in the lowermost outer core (F region), on the liquid side of the solidifying boundary of the inner core (ICB). The assumption of lateral h...

Recent expansion of broadband seismic data have yielded a large number of new observations of PcP and PKiKP waves that reflect from the Earth's outer and inner core. Simultaneous observations of these waves are particularly important as they allow direct estimates of the density contrast at the inner core boundary, the quantity that has been a subj...

This report is drawn from the many presentations and discussions at the September 18-19, 2008 Workshop on a Long Range Science Plan for Seismology, held in Denver and attended by ~120 members of the seismological and geophysical research community. Financial support for the LRSPS Workshop was provided by the National Science Foundation. Logistical...

New theories for the viscosity of metallic melts at core pressures and temperatures, together with observations of translational modes of oscillation of the Earth's solid inner core, have suggested that the viscosity of Earth's liquid outer core may approach 1011 Pa-sec near the inner core boundary. If the viscosity of the lowermost 450 km of the o...

Antipodal seismic waves interacting with the inner core boundary (ICB) sample almost the entire surface of the ICB. Hence, models of antipodal observations of PKIKP, PKIIKP, and PKP-C diffracted waveforms can provide an estimate of the global average velocity and density discontinuities and their vertical gradients at the ICB. PKIIKP and PKP-C diff...

As a planet cools, an initially molten core gradually solidifies. Solidification occurs at shallow depths in the form of "snow", if the liquidus temperature gradient of the core composition is smaller than the adiabatic temperature gradient in the core. Experimental data on the melting behavior of iron-sulfur binary system suggest that the cores of...

The inner core boundary of the Earth is characterised by a discontinuous change in elastic properties between the outer and inner core. The size and nature of these discontinuities provides direct constraints on the age of the inner core and the energy needed to sustain Earth's magnetic field. In ray theory, a measure of the density ratio at the in...

Recent studies have confirmed the existence of scattering by a fabric of small-scale heterogeneities in the uppermost inner core. Seismic waves interacting with the uppermost 300 km of the inner core reveal this region to have strong lateral variations in elastic structure, anisotropy, attenuation, and scattering. The detailed spatial distribution...

1] We systematically searched for seismograms of waves diffracted around the inner core (PKP Cdiff) from all the temporary seismic arrays with data currently available at the IRIS DMC, as well as some permanent regional seismic arrays including F-NET in Japan and GRF in Germany, to assemble the largest high-quality PKP Cdiff database ever created....

The complexity induced in seismic body waves by rapid or discontinuous spatial changes of elastic moduli and density can be efficiently modeled in radially symmetric structure by a collection of closely related ray, integral transform, and modal-based solutions of the elastic equations of motion. These modeling techniques can be extended to include...

Precursors of P'P' around 80 degrees are very useful for studying discontinuities in the Earth, particularly the 410km and 660 km discontinuities. P'P' precursors from deeper discontinuities, however, can be contaminated by the PKPPcP (or PcPPKP) phase, which is strongest around the antipode and extends to 275 degrees according to geometric ray the...

Body waves interacting with the boundary of the solid inner core at narrow and wide angles of incidence provide independent constraints on a heterogeneous texture that may originate from the process of solidification. The equatorial, quasi-eastern hemisphere, of the uppermost 50–100 km of the inner core is characterized by a higher isotropic P wave...

Compact solutions for the scattering of plane elastic waves by spheres now exist that are valid for arbitrary levels of velocity and density perturbations and arbitrary ratios of wavelength/sphere radius. These solutions are easily incorporated into methods of seismogram synthesis that remain valid for the frequency dependence near caustics. Short-...

Because the computation of synthetic seismograms has become an invaluable tool for the study of the Earth, it is of major interest to know whether two different methods, the reflectivity method and the full wave theory, generate identical record sections when applied to the same body wave problem. The full wave theory employs approximations by assu...

Long-period multiple S and ScS phases observed in northern Europe were analysed to determine mantle attenuation in the 0.02 to 0.2 Hz range under the Eurasian shield. Two groups of events were used: deep Far-Eastern earthquakes and large earthquakes near the edges of the shield areas of Eurasia. The Q of the upper mantle under the Eurasian shield r...

P-wave seismograms at ranges less than 10 km are synthesized by asymptotic ray theory and by summation of Gaussian beams for point sources located in a low-velocity wedge surrounding a fault. The computations are performed using models of the wedge inferred from the analysis of reflection and refraction experiments across the San Andreas and Haywar...

SUMMARYA method for computing seismic wavefields in a high-frequency approximation is proposed based on the integration of the kinematic ray tracing equations and a new set of differential equations for the dynamic properties of the wavefront, which we call the vicinity ray tracing (VRT) equations. These equations are directly obtained from the Ham...

A large set of teleseismic body wave data covering a broad range in frequency was analysed to determine the frequency and depth dependence of Q for P- and S-waves under the northern shield areas of Eurasia. Based on numerous t* estimates for P- and S-waves covering the seismic band between 0.02 and 8 Hz, a Q model of the Eurasian shield was constru...

The results of short and intermediate period data analyses for the determination of a frequency dependent Q model of the mantle under the shield areas of Eurasia are presented. The spectra of short period P-waves from nuclear explosions in the 1-8 Hz frequency range give tp*∼ 0.15-0.2 s. Using recordings of Soviet nuclear explosions at NORSAR, P-wa...

Recent studies1 find unusual high-frequency coda following the PKiKP phase, reflected from the inner core boundary in the area of the Central Pacific and observed at teleseismic distances between 50 ° to 90 ° range. The majority of the observations of such codas were made at short-period teleseismic arrays in the USA, Eastern Asia and Australia. An...

Seismic wave propagation through two-dimensional core-mantle boundary (CMB) ultralow velocity zones (ULVZs) is modeled using a global pseudospectral algorithm. An isotropic velocity-stress formulation of the equations of motion and elastic equations is evaluated on a cylindrical staggered grid using Fourier spatial derivatives and finite difference...

Body waves interacting with the boundary of the solid inner core at narrow and wide angles of incidence provide independent constraints on a heterogeneous fabric that may originate from the process of solidification. The equatorial (35{°} to 60{°} N), quasi-eastern hemisphere, of the uppermost 50-100 km of the inner core is characterized by a highe...

Examining the velocity structure of the inner core-outer core boundary (ICB) is important for understanding the evolution and dynamics of the Earth's core. The velocity gradient can be linked to the density gradient at the base of the outer core, which gives us insight about the chemical composition and dynamics of the core. Seismic waves that diff...

Many characteristics of D'' layer may be attributed to the recently discovered MgSiO3 post-perovskite phase without chemical heterogeneities. They include a sharp discontinuity at the top of D'', regional variation in seismic anisotropy, and a steep Clapeyron slope. However, some features remain unexplained. The seismically inferred velocity jump i...

P'P' (PKPPKP) are P waves that travel from a hypocenter through the Earth's core, reflect from the free surface and travel back through the core to a recording station on the surface. Here we report the observations of hitherto unobserved near-podal P'P' waves (at epicentral distance <10°) and very prominent precursors preceding the main energy by...

Poor lateral coherence of seismic waves interacting with the lowermost mantle (D" region) may be consistent with either the effects of constructive and destructive interference of waves scattered from distributed heterogeneity in D" or the effects of topography on one or more discontinuities. Likewise the transverse isotropy inferred from S waves i...

Waveforms of the PKIKP seismic phase in the distance range 150o to 180o are analyzed for evidence of an inner-most inner core of the type proposed by Ishii and Dziewonski having an abrupt change in elastic anisotropy near radius 300 km. Seismograms synthesized in models having a discontinuity at 300 km radius in the inner core exhibit focused diffr...

Precursors to ScS and PcP seismic phases, often labeled as SdS or PdP, have been included in evidence for a sharp discontinuity in seismic velocities at depths between 100 and 300 km above the core-mantle boundary (the D"region). The poor lateral coherence of observed SdS and PdP may be consistent with either the effects of constructive interferenc...

P'P' (PKPPKP) are P waves that travel from a hypocenter through the Earth's core, reflect from the free surface and travel back through the core to a recording station on the surface. P'P' waves are sometimes accompanied by precursors, which were reported first in the 1960s as small-amplitude arrivals on seismograms at epicentral distances of about...

The structure of the uppermost 100 km of the inner core was examined from PKIKP and PKiKP waveforms in the distance range of 118o -140º. We found evidence of a low-velocity layer in the uppermost inner core in the equatorial region predominantly located between longitude 20o W to 140o E. In the latitudinal direction the anomaly is detectable from 3...

The effects of variations in crustal and basin thicknesses on the efficiency of Lg propagation in Central Asia are investigated by comparing the predictions of ray theoretical modeling of Lg as multiple, critically reflected, SmS rays with observations at the KNET, CNET, and ILPA arrays. Ray modeling predicts that strong spatial gradients in crusta...

Teleseismic wave fields occasionally exhibit rapid changes in travel times and waveforms over distances less than several great-circle degrees when observed at broadband arrays. These rapid changes in wave field suggest the existence of significant structural transitions occurring over scales of several hundred kilometers or less in the mid- and de...

Broadband (0.01 to 1 Hz), 3-component, seismograms are synthesized to 180\deg range by 2-D pseudospectral methods in several models having statistically described heterogeneity in the mantle. Considered models include gradient increases in RMS heterogeneity power in the lowermost (D'' region) of the mantle, and bi-modal models of D'' consisting of...

We have developed and tested Source Specific Station Corrections (SSSCs) for Pn and Sn travel times at 30 International Monitoring System stations in East Asia, and for 127 other stations used for validation testing. We developed a 3D model of the P--wave velocity for East Asia (using 36 different 1D regions), and used 3D ray tracing in the aggrega...

We have completed a three-year consortium effort to improve the capability to locate seismic events based on data acquired by 30 International Monitoring System (IMS) stations in East Asia. We have developed and tested Source Specific Station Corrections (SSSCs) for Pn and Sn travel times at these 30 IMS stations (or suitable surrogates), and for 1...

Broadband velocity waveforms of PKIKP in the distance range 150-180° are inverted for a model of inner core attenuation due to forward scattering by a three-dimensional heterogeneous fabric. A mean velocity perturbation of 8.4 ± 1.8% and a scale length of heterogeneity of 9.8 ± 2.4 km are determined from 262 available PKIKP ray paths. The velocity...

Using reference source time functions, broadband velocity waveforms of PKIKP in the distance range 150–180° are inverted for a viscoelastic model of inner core attenuation. A mean Qα at 1 Hz of 307 ± 90 is determined from 345 available PKIKP ray paths. Both global and regional results find a depth-dependent attenuation in the deep inner core, with...

Broadband PKIKP waveforms in the distance range 150o-180o are inverted for both viscoelastic and scattering models of body wave attenuation in the inner core. Reference waveforms used in the inversion, which include a network averaged mantle attenuation operator, are constructed from source-time functions determined from P waves observed in the 30o...

Source-specific station corrections (SSSC's) to travel-time tables have been constructed for International Monitoring System (IMS) stations in Eastern Asia by ray tracing in three-dimensional earth structure. Two types of 3-D models have been tested: (1) a model consisting of 22 1-D velocity regions with lateral transition zones between regions and...

Seismograms are synthesized in two- and three-dimensional representations of a plume-like anomaly that has been tomographically imaged in the mantle beneath South Africa. Pseudospectral integration of the wave equation in two-dimensions and Gaussian beam superposition in three-dimensions are performed to constrain the shape, intensity, and lateral...

Three-dimensional models of the crust and mantle structure beneath Area 1 International Monitoring System stations in Eurasia are constructed for use with either asymptotic ray or numerical methods of waveform modeling. The models combine crustal and upper models of varying resolution specified on latitude and longitude grids having variable spacin...

Broadband PKIKP waveforms are modeled by convolving attenuation operators with reference source time functions, determined by inverting P-waves in the distance range 30o to 90o for far-field point source representations. The attenuation operators are parameterized to predict pulse shapes from either the effects of intrinsic anelasticity or scatteri...

Both deterministic and statistical heterogeneity has been resolved from seismic body waves in the lowermost mantle. Scattered PKIKP precursors can be explained by an increase in the vertical gradient of heterogeneity power in the lowermost 700 km of the mantle. Some statistical realizations of this type of model can generate an SdS phase between S...

Broadband SH and P wavefields are pseudospectrally modeled in three forms of the heterogeneity spectrum of the mantle, each having a transition in the power spectrum of heterogeneity in the lowermost mantle. With D” defined as a zone of increased heterogeneity, low and high pass filters of models of the heterogeneity spectrum demonstrate that the t...

Broadband SH and P wave fields are pseudospectrally modeled in three forms of the heterogeneity spectrum of the mantle, each having a transition in the power spectrum of heterogeneity in the lowermost mantle. With D" defined as a zone of increased heterogeneity, low-pass and high-pass filters of models of the heterogeneity spectrum demonstrate that...

The anisotropy of heterogeneity scale lengths in the lower mantle is investigated by modelling its effect on the high-frequency precursors of PKIKP scattered by the heterogeneities. Although models having either an isotropic or an anisotropic distribution of scale lengths can fit the observed coda shapes of short-period precursors, the frequency co...

Broadband velocity waveforms of PKIKP in the distance range 150° to 180° are inverted for inner core attenuation. A mean Qα of 244 is determined at 1 Hz from 8 polar and 9 equatorial paths. The scatter in measured Q−1 exceeds individual error estimates, suggesting significant variation in attenuation with path. These results are interpreted by (1)...

The efficiency of Lg propagation is predicted using known three-dimensional variations in large scale crustal structure with Lg modeled as a sum of SmS rays. The complexity of Lg coda is predicted assuming single scattering. Amplitude variations observed at Eurasian arrays agree with the predictions for the effects of known variations in crustal th...