Extent In Depth Research Articles

Reconstruction of archaeological contexts through the integrated use of airborne LiDAR and geophysical survey: The case study of San Pietro Infine (Caserta, southern Italy)

San Pietro Infine (Caserta, southern Italy) is an archaeological area of significant historical interest as it is in the vicinity of the Roman site of Ad Flexum. Based on historical sources, the site would correspond to the junction of a road axis that, during the Roman colonization (3rd century BCE), was crossed by the Via Latina. At the intersection of these two roads, which coexisted for a time, a post station was built, most likely later replaced by an early medieval village near the religious building of S. Pietro, of which only the apse portion is preserved. However, the archaeological evidence is too scarce to allow a reliable historical reconstruction of the site and to direct any excavation work. In this paper, we present the integration of LiDAR and geophysical surveys with the aim of advancing the archaeological interpretation of the San Pietro Infine site over the-state-of-the-art while providing a cutting-edge example in archaeological investigation. In particular, LiDAR data analysis was addressed to recognize and characterize topographic micro-reliefs presumably correlated to buried archaeological structures, while subsurface geophysical prospecting, consisting of magnetic and electromagnetic surveys, was aimed at defining their possible location and extent in depth, due to the expected contrasts in the magnetic and electric properties between the targets (e.g., limestone materials, paving roads) and the host geological setting (mainly marshy deposits). The integrated study allowed us to identify a structure whose characteristics (i.e., location, shape and nature) could well match the hypothesized Ad Flexum junction. In addition, LiDAR micro-reliefs and geophysical anomalies individuate structures that, by location and extent, suggest the presence of a village developed around the religious building of San Pietro.

Impact of cross‐sectional orientation in one‐dimensional hydrodynamic modeling on flood inundation mapping

AbstractFlood management activities require development of flood maps that depict the spatial and temporal extent of floods with the help of hydrodynamic models. Two‐dimensional (2‐D) hydrodynamic models are frequently employed for flood inundation modeling and mapping with the help of high‐end computational resources and high‐resolution terrain information such as LiDAR (light detection and ranging) data. However, LiDAR data are either unavailable or not freely accessible in many parts of the world, especially in nations belonging to Global South. Hence, one‐dimensional (1‐D) models are still in practice owing to their lesser computational cost and data requirement. Nonetheless, the successful application of a 1‐D model depends mainly on the representation of the natural river and floodplain geometry, which is the primary input in the form of discrete cross‐sections. The assumed flow directions on floodplains while orienting the cross‐sections in 1‐D models induce some uncertainty in the model simulations. This study aims to evaluate the variability in the model simulations caused by the cross‐sectional orientations. Flood simulations were performed using a 1‐D hydrodynamic model for six different cross‐sectional realizations for three river reaches, having distinct morphological and topographical characteristics, and were compared with the simulations of a 2‐D hydrodynamic model and available reference inundation maps. The study suggests that the simulations of flood inundation extent and maximum flow depth variation are influenced by the cross‐sectional orientation on flood plains in river reaches characterized by broad flood plains with complex local topographical variations. In contrast, for reaches with relatively less wide and complex terrains, 1‐D models can generate robust simulations of flood inundation extent and spatial variation in maximum flood depth (R2 and NSE greater than 0.89) for high flood events.

Simultaneous magnetic field and field gradient mapping of hexagonal MnNiGa by quantitative magnetic force microscopy

Magnetic force microscopy (MFM) is a scanning microscopy technique that is commonly employed to probe the sample’s magnetostatic stray fields via their interaction with a magnetic probe tip. In this work, a quantitative, single-pass MFM technique is presented that maps one magnetic stray-field component and its spatial derivative at the same time. This technique uses a special cantilever design and a special high-aspect-ratio magnetic interaction tip that approximates a monopole-like moment. Experimental details, such as the control scheme, the sensor design, which enables simultaneous force and force gradient measurements, as well as the potential and limits of the monopole description of the tip moment are thoroughly discussed. To demonstrate the merit of this technique for studying complex magnetic samples it is applied to the examination of polycrystalline MnNiGa bulk samples. In these experiments, the focus lies on mapping and analyzing the stray-field distribution of individual bubble-like magnetization patterns in a centrosymmetric [001] MnNiGa phase. The experimental data is compared to calculated and simulated stray-field distributions of 3D magnetization textures, and, furthermore, bubble dimensions including diameters are evaluated. The results indicate that the magnetic bubbles have a significant spatial extent in depth and a buried bubble top base.

Comprehensive evaluation of self-healing of concrete with different admixtures under laboratory and long-term outdoor expositions

This project presents the evaluation of the self-healing of fibre reinforced concretes containing various admixtures (crystalline admixture CA, expansive agent CSA, superabsorbent polymer SAP) and combinations. They were exposed to several laboratory conditions (water immersion, wet/dry cycles ambient air for 3 months, water flow for 1 week) and to a long-term outdoor exposure for 1 year. Self-healing capacity was assessed by water permeability measurements, mechanical recovery, visual observations and microscopic analyses on the same specimen. This paper presents the mechanical behaviour and microstructure of the healing products, and the correlations with the water permeability measures presented in previous research. The results showed that a high healing of cracks based on water permeability did not necessarily lead to a high mechanical recovery. The highest Strength Regains (109% in average) were obtained for specimens exposed outdoor that presented the lowest Healing Ratios (71% in average). The local density of the healing products may govern the Healing Ratio, while the type of healing products and their extent in the crack depth may control the Strength Regain. Finally, the SAP mix showed overall the best self-healing performance, regarding both durability and mechanical properties.

Light-based diagnostic methods for the in vivo assessment of initial caries lesions: Laser fluorescence, QLF and OCT.

To evaluate different light-based caries diagnostic methods for assessment of non-cavitated initial carious lesions on smooth surfaces. 39 participants were included. For each participant, three regions of interest (ROI) with ICDAS codes 0, 1 or 2 were defined. All ROIs (n = 117) were investigated/imaged with laser fluorescence (LF, DIAGNOdent 2095; KaVo dental GmbH), quantitative light-induced fluorescence (QLF; Biluminator 2+, Inspektor Research Systems B.V.) and spectral-domain optical coherence tomography (SD-OCT; Telesto II, Thorlabs GmbH). The values of LF, ΔF of QLF, and the lesion extent assessed by OCT were categorized. Frequency distribution of LF-/QLF- and OCT-scores was determined for each ICDAS code included. Inter- and intra-examiner reproducibility of QLF and OCT measurements were assessed by unweighted kappa coefficient (ĸ) and Wilcoxon test (α = 0.05). Compared with LF and QLF, OCT showed various manifestations of carious lesions for visually sound ROIs and a larger variation of caries extent in depth within the same ICDAS code groups. Intra-examiner reproducibility ranged between 0.49 and 1.00 for the QLF analysis and between 0.95 and 0.99 for the OCT analysis. Inter-examiner reproducibility ranged between 0.17 and 0.32 for the QLF analysis and between 0.65 and 0.79 for the OCT analysis. LF and QLF were insensitive to less pronounced smooth-surface lesions while OCT allowed differentiation based on the penetration depth of the carious lesions. This makes OCT a suitable method to complement conventional visual inspection in order to detect and assess (very) early lesions.

Optical coherence tomography to evaluate variance in the extent of carious lesions in depth.

Evaluation of variance in the extent of carious lesions in depth at smooth surfaces within the same ICDAS code group using optical coherence tomography (OCT) in vitro and in vivo. (1) Verification/validation of OCT to assess non-cavitated caries: 13 human molars with ICDAS code 2 at smooth surfaces were imaged using OCT and light microscopy. Regions of interest (ROI) were categorized according to the depth of carious lesions. Agreement between histology and OCT was determined by unweighted Cohen's Kappa and Wilcoxon test. (2) Assessment of 133 smooth surfaces using ICDAS and OCT in vitro, 49 surfaces in vivo. ROI were categorized according to the caries extent (ICDAS: codes 0-4, OCT: scoring based on lesion depth). A frequency distribution of the OCT scores for each ICDAS code was determined. (1) Histology and OCT agreed moderately (κ = 0.54, p ≤ 0.001) with no significant difference between both methods (p = 0.25). The lesions (76.9% (10 of 13)) _were equally scored. (2) In vitro, OCT revealed caries in 42% of ROI clinically assessed as sound. OCT detected dentin-caries in 40% of ROIs visually assessed as enamel-caries. In vivo, large differences between ICDAS and OCT were observed. Carious lesions of ICDAS codes 1 and 2 vary largely in their extent in depth.

Highlight disparities contribute to perceived depth of shiny 3D surface

When a shiny surface is viewed binocularly, the specular highlights have different disparities than points on the surface. This study tested whether conflicting highlight disparities contribute to perception of surface shape when other shape cues are available. A recent study by Muryy et al (2013) found that perceived shape followed highlight disparities for mirrored surfaces, but not for surfaces with texture or shading. Is stereo information from highlights overridden by additional surface information, or is there still an influence on quantitative perceived shape? To test this, I varied the depth of specular highlights relative to a surface and measured the effect on perceived extent in depth. Subjects viewed stereo images of elliptical bumps with a flat frontal rim, with varied height and curvature, and estimated height of the bump. Surfaces had smooth shading with and without highlights, and highlights were either accurate or shifted in depth. Simulated illumination was a grid of light fixtures, which was translated and scaled to control the image position of highlights. Surfaces had either high contrast texture or very low contrast texture to vary the quality of surface disparity information. With high contrast texture, highlight disparities did not influence depth estimates. The presence of highlights produced an overall increase in perceived depth, but varying the depth of highlights had no effect. With low contrast texture, depth estimates were strongly influenced by highlight disparities. The presence of highlights improved accuracy, and varying the depth of highlights produced corresponding changes in depth estimates. The effect was the same whether the highlights were consistent or inconsistent with smooth shading. The results demonstrate that binocular highlights can influence perceived shape when other surface information is available but weak. This suggests that highlight disparities are perceptually integrated despite providing conflicting information Meeting abstract presented at VSS 2017

Along‐strike variations in the Himalayan orogenic wedge structure in Bhutan from ambient seismic noise tomography

AbstractThe geological units and tectonic structure exposed in the Bhutan Himalaya document significant regional variations, expressed primarily as tectonic windows and klippen. The along‐strike variations of these structures and their metamorphic grade are usually associated with the formation of local duplexes in the underlying tectonic units. To investigate these variations and their extent in depth, we image the isotropic shear‐wave velocity structure of the orogenic wedge by ambient noise tomography. Group velocities are extracted from cross correlations of ambient seismic noise, recorded by the temporary GANSSER network in Bhutan. The upper crustal structure beneath Bhutan is mapped down to 18 km depth by directly inverting Rayleigh‐wave group velocity measurements in the period range between 2 and 20 s with a ray tracing based inversion approach. Our results reveal several distinct high shear‐wave velocity anomalies ( km/s) and reflect the along‐strike variations in the upper crustal structure in relation to the alternating tectonic windows and klippen at the surface. In correlation with the surface geology in the northern part of Bhutan, we interpret shallow high shear‐wave velocity anomalies as quarzite‐dominated rocks or felsic migmatites with large intrusions of leucogranites. High‐velocity anomalies in the orogenic wedge in eastern and western Bhutan correlate with the local geometry of the Main Himalayan Thrust and provide evidence for the formation and depth extent of localized duplexes of quartzite dominated lithology in association with the formation of tectonic windows in the Bhutan Himalaya.

On the increase in thermal diffusivity caused by the perovskite to post-perovskite phase transition and its implications for mantle dynamics

The thermal diffusivity (κ) of perovskite and post-perovskite CaIrO3 has been measured, at elevated pressure and temperatures up to 600°C, using the X-radiographic Ångström method. At high temperatures we find that the thermal diffusivity of post-perovskite is slightly below twice that of isochemical perovskite over the temperature range investigated. Assuming a similar effect occurs in MgSiO3 post-perovskite, the effect of the contrasting thermal transport properties between perovskite and post-perovskite on mantle dynamics has been investigated using simple two-dimensional convection models. These show a reduction in extent and increase in depth of post-perovskite lenses, as well as increased core–mantle-boundary heat-flux, broader upwellings and more vigorous downwellings when compared to the reference, constant a, case.

The evolution of cranial form and function in theropod dinosaurs: insights from geometric morphometrics

Theropod dinosaurs, an iconic clade of fossil species including Tyrannosaurus and Velociraptor, developed a great diversity of body size, skull form and feeding habits over their 160+ million year evolutionary history. Here, we utilize geometric morphometrics to study broad patterns in theropod skull shape variation and compare the distribution of taxa in cranial morphospace (form) to both phylogeny and quantitative metrics of biting behaviour (function). We find that theropod skulls primarily differ in relative anteroposterior length and snout depth and to a lesser extent in orbit size and depth of the cheek region, and oviraptorosaurs deviate most strongly from the "typical" and ancestral theropod morphologies. Noncarnivorous taxa generally fall out in distinct regions of morphospace and exhibit greater overall disparity than carnivorous taxa, whereas large-bodied carnivores independently converge on the same region of morphospace. The distribution of taxa in morphospace is strongly correlated with phylogeny but only weakly correlated with functional biting behaviour. These results imply that phylogeny, not biting function, was the major determinant of theropod skull shape.

Two-dimensional shear elasticity imaging using comb-push acoustic radiation force and algebraic direct inversion of the motion differential equation

Tissue mechanical properties can be obtained by algebraic direct inversion (ADI) of the shear-wave motion differential equation, which is insensitive to reflection and geometry of the pushing beam. Shear waves normally generated by a focused ultrasound pushing beam have limited spatial extent in depth and are transient in time, leading to noisy and unstable ADI results. A comb-shape acoustic radiation force distribution can generate shear waves with longer spatial extent and time duration, facilitating more robust ADI. For 400 μs, a linear array transducer simultaneously transmitted four unfocused pushing beams (12 on elements for each pushing beam, 8 off elements between beams) into a tissue-mimicking phantom (∼1.5 kPa) with a cylindrical inclusion (∼4 kPa). The ultrasound system (Verasonics Inc.) then immediately switched to flash imaging mode (frame rate = 2 kHz, spatial resolution = 0.31 mm) to measure shear-wave displacements in a 38 mm by 30 mm domain that was used for ADI. The reconstructed 2D shear elasticity map provides accurate shear elasticity estimates (background = 1.5 kPa with 7% variance; inclusion = 3.9 kPa with 15% variance) and excellent contrast between the background and inclusion.

Subsurface Zonal Flows

We study the zonal flow in solar subsurface layers, analyzing about six years of GONG++ high-resolution Doppler data with ring-diagram analysis. We focus on the variation of zonal flow with magnetic activity over a range of depths from the surface to about 16 Mm. There is a positive correlation between unsigned magnetic flux and zonal flow at most depths. We calculate the average zonal flow for a quiet- and an active-region subset defined as dense-pack locations with an unsigned magnetic flux less than 3.4 G and locations with greater than 65.0 G, respectively. The average zonal flow of active regions is about 4 m s−1 larger than the average flow of quiet regions. This difference increases slightly with increasing depth, which might be explained by a nonradial inclination of the flux tubes or a different extent in depth of different magnetic features. The difference shows no apparent pattern in time and latitude, which makes it unlikely that it is simply a manifestation of the torsional-oscillation pattern. As a byproduct, we find that the size of the North – South asymmetry of the rotation rate decreases during the same epoch.

The dynamical evolution and star formation history of the Small Magellanic Cloud: effects of interactions with the Galaxy and the Large Magellanic Cloud

In order to better understand the dynamical evolution and star formation history of the Magellanic system, realistic N-body simulations of the tidal distortion of the Small Magellanic Cloud (SMC) as a result of the Galaxy and the Large Magellanic Cloud have been carried out, taking into account gas dynamics and star formation processes explicitly. The best model succeeds in reproducing the observed structural, kinematic and star formation properties of the SMC, including other related tidal features in the Magellanic system, without resorting to the ram pressure model. The best-fitting simulation reproduced a gas stream with almost no stars and the observed H I gas fraction, for which the morphology and velocity field agree quite well with those of the Magellanic stream, a result of adopting an initial SMC model that has a compact stellar disc embedded in an extended gaseous disc. This implies that the existence of a purely gaseous Magellanic stream does not poses serious problems to a tidal model of formation. Also, in this best model, the central and south-east side (wing region) of the SMC contained an excess of young stars, as is observed. Comparison with a reference simulation of isolated evolution demonstrated that the acceleration of star formation activity in these regions may be a direct result of the last interaction between the Magellanic Clouds roughly 0.2 Gyr ago, which formed the inter-cloud region. The large extent in depth of the SMC implied by the spatial distribution of Cepheids, and the line-of-sight velocity pattern in H I around the SMC is also reproduced. Finally, the dependences of these results on the numerical parameters that specify the SMC mass model and interstellar gas processes are discussed.

Object and space-based attentional selection in three-dimensional space

It has been previously demonstrated that visual attention has an extent in depth (3D space) as well as an extent in the fronto-parallel plane (2D space). Numerous experiments have also demonstrated that attention can be allocated to objects, and that “object-based” attention can overcome some of the costs associated with moving attention about in 2D space. In real visual environments, objects often have an extent in depth. Four experiments were conducted to examine the nature of object-based attention in 3D space. The experiments demonstrated large object-based attention benefits, as well as costs for switching attention in depth. However, the costs associated with switching attention in depth were eliminated with objects that had an extent in depth. Experiments 2-4 examined the interaction of spatial attention in 3D space and object-based attention. Evidence was found for the spread of spatial attention to objects. However, contrary to other work (Lavie & Driver, 1996), neither non-predictive exogenous spatial cues (Experiment 2) nor predictive exogenous spatial cues (Experiments 3 and 4) were able to eliminate object-based attention, suggesting that object-based attention can remain intact despite the allocation of attention spatially.

Coding of peripersonal space in inferior premotor cortex (area F4).

1. We studied the functional properties of neurons in the caudal part of inferior area 6 (area F4) in awake monkeys. In agreement with previous reports, we found that the large majority (87%) of neurons responded to sensory stimuli. The responsive neurons fell into three categories: somatosensory neurons (30%); visual neurons (14%); and bimodal, visual and somatosensory neurons (56%). Both somatosensory and bimodal neurons typically responded to light touch of the skin. Their RFs were located on the face, neck, trunk, and arms. Approaching objects were the most effective visual stimuli. Visual RFs were mostly located in the space near the monkey (peripersonal space). Typically they extended in the space adjacent to the tactile RFs. 2. The coordinate system in which visual RFs were coded was studied in 110 neurons. In 94 neurons the RF location was independent of eye position, remaining in the same position in the peripersonal space regardless of eye deviation. The RF location with respect to the monkey was not modified by changing monkey position in the recording room. In 10 neurons the RF's location followed the eye movements, remaining in the same retinal position (retinocentric RFs). For the remaining six neurons the RF organization was not clear. We will refer to F4 neurons with RF independent of eye position as somatocentered neurons. 3. In most somatocentered neurons (43 of 60 neurons) the background level of activity and the response to visual stimuli were not modified by changes in eye position, whereas they were modulated in the remaining 17. It is important to note that eye deviations were constantly accompanied by a synergic increase of the activity of the ipsilateral neck muscles. It is not clear, therefore, whether the modulation of neuron discharge depended on eye position or was a consequence of changes in neck muscle activity. 4. The effect of stimulus velocity (20-80 cm/s) on neuron response intensity and RF extent in depth was studied in 34 somatocentered neurons. The results showed that in most neurons the increase of stimulus velocity produced an expansion in depth of the RF. 5. We conclude that space is coded differently in areas that control somatic and eye movements. We suggest that space coding in different cortical areas depends on the computational necessity of the effectors they control.

Numerical simulations of the Magellanic system – I. Orbits of the Magellanic Clouds and the global gas distribution

The numerical model of the Galaxy and the Large and Small Magellanic Clouds devised by Murai & Fujimoto is employed, with revised values of various observational parameters, to reproduce the global gas distribution in the Magellanic system by a test-particle simulation. The Magellanic orbits that achieve the best reproduction of the Magellanic Stream and the inter-Cloud Bridge place the LMC and the SMC in a binary state for the past 15 Gyr, with a close encounter between the Magellanic Clouds occurring 0.2 Gyr ago at a minimum separation of 7 kpc. By performing a test-particle simulation with 20 000 particles representing the LMC and SMC discs, a detailed comparison can be made with observations of the structure of the Magellanic Clouds and inter-Cloud Bridge. In particular, the large extent in depth of the SMC, shell-like irregularities in the outer part of the LMC, and distinct gas masses in the inter-Cloud Bridge region are shown to result from the tidal interactions of the Magellanic system. The Magellanic Stream is modelled as a product of the tidal interaction of the Magellanic Clouds with the Galaxy, and some criticisms of the standard tidal model for the origin of the Magellanic Stream are addressed.

Trackability as a cue for potential obstacle identification and 3-D description

In many man-made environments, obstacles in the path of a mobile robot can be characterized asshallow, that is, they have relatively small extent in depth compared to the distance from the camera. We present a framework for segmenting shallow structures from their background over a sequence of images. Shallowness is first quantified asaffine describability. This is embedded in a tracking system within which hypothesized model structures undergo a cycle of prediction and model-matching. Structures emerge either as shallow or nonshallow based on theiraffine trackability. Two major contributions of this work are (i) aggregate object tracking based on 3-D motion and structure constraints in constrast with traditional primitive feature tracking based on image motion heuristics, and (ii) use of temporal behavior for object segmentation and 3-D reconstruction.

The Paradox of Drowned Reefs: A Caribbean Example Mapped Using SeaMARC II Side-Scan Sonar: ABSTRACT

Three models for the drowning of carbonate platforms and associated fringing coral reefs include (1) rapid submergence below the euphotic zone by tectonic subsidence and sea level rise; (2) excess nutrients in the water; and (3) burial by prograding marine siliclastic sediments. To examine these mechanisms on a regional scale, the authors mapped drowned barrier reef tracts around the active carbonate banks of the Nicaraguan Rise using SeaMARC II sidescan sonar, 3.5 KHz, and digital single channel reflection techniques. The reef tracts exhibited high sonar backscatter and were prominently displayed on sidescan images. Characteristic features of the reef tracts include (1) uneroded and slightly sinuous mounds that crop out on the sea floor and closely following bathymetric contours; (2) reef mounds that typically occur in stairstep sets of two to three terraces; (3) water depths at the crest of the reef mounds that range from 1,050 to 1,500 m; and (4) reef mounds that extend for 1,200 km around the base of the slope (depth 1,300 m) of an active carbonate platform in a moderately active, intraplate setting (Pedro Bank) and along the crest of a submerged fault block in a highly active, interplate setting (Bay Islands Ridge, ridge crestmore » depth at 1,600 m). Because these newly discovered reef tracts have not been dredged, their ages and compositions remain unknown. Based on the observed sea floor outcrop, regional extent, and approximate correlation in water depth of the reef tracts, mechanisms 1 and 2 appear to be the most likely drowning mechanisms.« less

Heat flow measurements under some lakes in the Superior Province of the Canadian Shield

Six heat flow values have been obtained from measurements made in the sediments of thermally-stable lakes in four major structural belts of northwestern Ontario. Each heat flow is the average of measurements from 3–6 neighbouring lakes. Corrections for the thermal history, lateral heat flow, sedimentation, and refraction effects have been applied. High heat flows which were measured in the Quetico gneiss superbelt (77 mW/m2) and on the Indian Lake intrusion in the Wabigoon superbelt (64 mW/m2) are related to above-average heat productivities at these locations, but the extent in depth of the sources is shown to be very different in the two cases. The consistency of the lake results with borehole measurements, on a heat flow – heat productivity plot, strongly suggests that the former are not perturbed by recent climatic variations.

Geomagnetic Deep Sounding and Upper Mantle Structure in the Western United States

Summary Magnetic field time variations were observed in September 1967, with a two-dimensional array of 42 three-component variometers between latitudes 36 and 43 N and longitudes 101 W and 116 W. Fourier analysis of a polar substorm and of a storm shows that the former has a smooth spectrum and the latter a complex spectrum with many maxima. Upper mantle conductivity structure can be seen qualitatively in the original variograms, but is far more sharply defined in maps of Fourier spectral component amplitudes and phases. A ridge of high conductivity runs at a depth no greater than 200 km under the Southern Rocky Mountains between the Great Plains and the Colorado Plateau, which marks a low-conductivity region within the Cordillera. A strong conductivity anomaly runs north-south along the Wasatch Front through central Utah, and indicates the presence of an upwelling of highly conductive material at depth no greater than 120 km along the edge of a step structure which brings the conductive mantle to shallower depth under the Basin and Range Province than under the Colorado Plateau. Long-period maps from the storm suggest a rise in the conductive mantle between the northsouth structures, from the Colorado Plateau southward to the Basin and Range. The daily variation shows the conductivity structures and indicates their great extent in depth. The geomagnetic deep sounding anomalies are found to be in excellent agreement with existing heat flow data, and this supports correlation of electrical conductivity with temperature. There is also good correlation with the available seismic velocity information for the upper mantle. 1. Introdaction Geophysical observations of several kinds indicate that the upper mantle of the Earth under North America is laterally inhomogeneous. Upper mantle seismic velocities of 8.0 km s-' or larger are characteristic of the eastern United States and the Great Plains Province, while velocities decrease to values of 7.9 km s-' or lower west of the Rocky Mountains (Herrin & Taggart 1962). A similar pattern is shown by travel-time anomalies of seismic waves at vertical incidence. P and S waves arrive early at stations in the eastern United States; late arrivals are predominant in the western United States (Cleary & Hales 1966; Doyle & Hales 1967; Hemn & Taggart 1968). As the differences between the P travel-time residuals and the gravity anomalies in the central and western U.S. cannot be explained by the Birch (1961) relation between velocity and density, Hales & Doyle (1967) suggested that tempera