scholarly journals VELOCITY MODEL OF THE UPPER MANTLE OF THE FLANKING PLATEAUS OF MID-OCEANIC RIDGES

2020 ◽  
Vol 16 (4) ◽  
pp. 19-31
Author(s):  
V.V. GORDIENKO ◽  
L.Ya. GORDIENKO
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Seismic Waves ◽  
Bottom Topography ◽  
Velocity Model ◽  
Transfer Scheme ◽  
Transition Zones ◽  
Velocity Section ◽  
Ocean Ridges ◽  
Using Data

A new element is included in the study of velocity sections of the upper mantle of regions of continents, oceans, and transition zones with different endogenous regimes (according to the advection-polymorphic hypothesis — APH). This is the flanking plateaus (FP) of the mid-ocean ridges (MOR). It is assumed that these regions underwent the process of oceanization in the Mesozoic along with other parts of the oceans. In the Neogene MORs were formed. Significant parts of the basins were engulfed in modern activation, including magmatism. Between these parts of the oceans, relatively narrow strips (200—300 km wide) have survived, which some authors refer to as flanking plateaus. They are located at the edges of the MOR. FP did not experience young activization. This is indicated by the features of the bottom topography, magnetic, gravitational and thermal fields, and a velocity section of the upper horizons of the mantle. An element of checking the nature of the FP can be the construction of a velocity section of the mantle beneath these regions. According to the APH, it should differ from the neighboring ones by the increased velocity of seismic waves in the upper about 200 km. The experimental data for such work turned out to be extremely small. It was possible to build only one travel-time, using data on the southern part of the Atlantic Ocean. Insignificant information was also attracted on the southern part of the East Pacific Rise and the Mid-Indian Ridge. The travel-time corresponds to the velocity section, which completely coincides with the forecast. The latter was calculated according to the heat and mass transfer scheme in the APH version and the thermal model of the mantle. The velocity section of the FP mantle does not contain indications of a partial melting layer. Consequently, there should be no manifestations of young magmatism in FP. Verification showed that in most of the studied fragments of MOR this is true.

scholarly journals Imaging the Mediterranean upper mantle by p- wave travel time tomography

1997 ◽  
Vol 40 (4) ◽  
Author(s):  
C. Piromallo ◽  
A. Morelli
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Three Dimensional ◽  
Velocity Model ◽  
Structural Heterogeneity ◽  
Linear Interpolation ◽  
P Wave ◽  
Travel Times ◽  
P Waves ◽  
Tectonic Lineament

Travel times of P-waves in the Euro-Mediterranean region show strong and consistent lateral variations, which can be associated to structural heterogeneity in the underlying crust and mantle. We analyze regional and tele- seismic data from the International Seismological Centre data base to construct a three-dimensional velocity model of the upper mantle. We parameterize the model by a 3D grid of nodes -with approximately 50 km spacing -with a linear interpolation law, which constitutes a three-dimensional continuous representation of P-wave velocity. We construct summary travel time residuals between pairs of cells of the Earth's surface, both inside our study area and -with a broader spacing -on the whole globe. We account for lower mantle heterogeneity outside the modeled region by using empirical corrections to teleseismic travel times. The tomo- graphic images show generai agreement with other seismological studies of this area, with apparently higher detail attained in some locations. The signature of past and present lithospheric subduction, connected to Euro- African convergence, is a prominent feature. Active subduction under the Tyrrhenian and Hellenic arcs is clearly imaged as high-velocity bodies spanning the whole upper mantle. A clear variation of the lithospheric structure beneath the Northem and Southern Apennines is observed, with the boundary running in correspon- dence of the Ortona-Roccamonfina tectonic lineament. The western section of the Alps appears to have better developed roots than the eastern, possibly reflecting à difference in past subduction of the Tethyan lithosphere and subsequent continental collision.

The identification and interpretation of upper mantle travel-time branches from measurements of dT/dΔ made on data recorded at the Yellowknife seismic array

1978 ◽  
Vol 15 (2) ◽  
pp. 227-236 ◽  
Author(s):  
A. Ram ◽  
R. F. Mereu ◽  
D. H. Weichert
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Body Wave ◽  
Processing Technique ◽  
The Body ◽  
Seismic Array ◽  
P Wave ◽  
Time Curve ◽  
Transition Zones ◽  
Short Period

There is broad agreement among various seismological studies that the upper mantle has two regions where very high positive velocity gradients or transition zones exist. In most cases, the presence of these zones implies that two major triplications are likely to exist in the body-wave travel-time curve for distances less than 30°. Because of the difficulties in observing and identifying later arrivals belonging to the various travel-time branches, the inversion of the seismic data is often very difficult. In this paper an adaptive processing technique was employed to examine the variations in slowness that occur along the first 36 s of the short-period P-wave trains recorded at the Yellowknife medium aperture seismic array. Over 100 earthquakes from the Alaska Peninsula and California regions were selected. From the California results we were able to clearly observe the 12–13 s/deg slowness branch as a later arrival out to distances as great as 26°. Other later arrival branches as well as cusps associated with the 400 and 650 km discontinuities were not well defined even though the cross-over point as determined from slowness measurements on first arrivals were clearly located. An inversion of the data showed that the '650 km' transition zone occurred at a much shallower depth west of the array compared to the corresponding region to the south.

scholarly journals 12-Year Trends in Active School Transport across Four European Countries—Findings from the Health Behaviour in School-Aged Children (HBSC) Study

2021 ◽  
Vol 18 (4) ◽  
pp. 2118
Author(s):  
Ellen Haug ◽  
Otto Robert Frans Smith ◽  
Jens Bucksch ◽  
Catherina Brindley ◽  
Jan Pavelka ◽  
...  
Keyword(s):  
Czech Republic ◽  
Travel Time ◽  
Health Behaviour ◽  
Sociodemographic Factors ◽  
The Czech Republic ◽  
Family Affluence ◽  
School Aged Children ◽  
Recent Trends ◽  
Hbsc Study ◽  
Using Data

Active school transport (AST) is a source of daily physical activity uptake. However, AST seems to have decreased worldwide over recent decades. We aimed to examine recent trends in AST and associations with gender, age, family affluence, and time to school, using data from the Health Behaviour in School-Aged Children (HBSC) study collected in 2006, 2010, 2014, and 2018 in the Czech Republic, Norway, Scotland, and Wales. Data from 88,212 students (11, 13 and 15 years old) revealed stable patterns of AST from 2006 to 2018, apart from a decrease in the Czech Republic between 2006 and 2010. For survey waves combined, walking to and from school was most common in the Czech Republic (55%) and least common in Wales (30%). Cycling was only common in Norway (22%). AST differed by gender (Scotland and Wales), by age (Norway), and by family affluence (everywhere but Norway). In the Czech Republic, family affluence was associated with change over time in AST, and the effect of travel time on AST was stronger. The findings indicate that the decrease in AST could be levelling off in the countries considered here. Differential associations with sociodemographic factors and travel time should be considered in the development of strategies for AST.

Intensities and travel times of seismic rays in a sphere with a linear velocity function

1977 ◽  
Vol 67 (1) ◽  
pp. 33-42
Author(s):  
Mark E. Odegard ◽  
Gerard J. Fryer
Keyword(s):  
Velocity Profile ◽  
Travel Time ◽  
Upper Mantle ◽  
Intensity Ratio ◽  
Computation Time ◽  
Spherical Body ◽  
Travel Times ◽  
Velocity Function ◽  
Intensity Ratios ◽  
Distance Travel

Abstract Equations are presented which permit the calculation of distances, travel times and intensity ratios of seismic rays propagating through a spherical body with concentric layers having velocities which vary linearly with radius. In addition, a method is described which removes the infinite singularities in amplitude generated by second-order discontinuities in the velocity profile. Numerical calculations involving a reasonable upper mantle model show that the standard deviations of the errors for distance, travel time and intensity ratio are 0.0046°, 0.057 sec, and 0.04 dB, respectively. Computation time is short.

Reconnaissance seismic refraction-reflection surveys in northwestern New Mexico

1984 ◽  
Vol 74 (4) ◽  
pp. 1263-1274
Author(s):  
Lawrence H. Jaksha ◽  
David H. Evans
Keyword(s):  
New Mexico ◽  
Wave Velocity ◽  
Lower Crust ◽  
Seismic Waves ◽  
Seismic Refraction ◽  
Velocity Model ◽  
P Wave ◽  
Uppermost Mantle ◽  
P Wave Velocity ◽  
Crustal Thinning

Abstract A velocity model of the crust in northwestern New Mexico has been constructed from an interpretation of direct, refracted, and reflected seismic waves. The model suggests a sedimentary section about 3 km thick with an average P-wave velocity of 3.6 km/sec. The crystalline upper crust is 28 km thick and has a P-wave velocity of 6.1 km/sec. The lower crust below the Conrad discontinuity has an average P-wave velocity of about 7.0 km/sec and a thickness near 17 km. Some evidence suggests that velocity in both the upper and lower crust increases with depth. The P-wave velocity in the uppermost mantle is 7.95 ± 0.15 km/sec. The total crustal thickness near Farmington, New Mexico, is about 48 km (datum = 1.6 km above sea level), and there is evidence for crustal thinning to the southeast.

scholarly journals Using Data Mining to Analyze Dwell Time and Nonstop Running Time in Road-Based Mass Transit Systems

Proceedings ◽  
2018 ◽  
Vol 2 (19) ◽  
pp. 1217
Author(s):  
Teresa Cristóbal ◽  
Gabino Padrón ◽  
Alexis Quesada ◽  
Francisco Alayón ◽  
Gabriel de Blasio ◽  
...  
Keyword(s):  
Data Mining ◽  
Travel Time ◽  
Dwell Time ◽  
Mass Transit ◽  
Transit Systems ◽  
Running Time ◽  
Bus Stop ◽  
Transport Line ◽  
Using Data

Travel Time plays a key role in the quality of service in road-based mass transit systems. In this type of mass transit systems, travel time of a public transport line is the sum of the dwell time at each bus stop and the nonstop running time between pair of consecutives bus stops of the line. The aim of the methodology presented in this paper is to obtain the behavior patterns of these times. Knowing these patterns, it would be possible to reduce travel time or its variability to make more reliable travel time predictions. To achieve this goal, the methodology uses data related to check-in and check-out movements of the passengers and vehicles GPS positions, processing this data by Data Mining techniques. To illustrate the validity of the proposal, the results obtained in a case of use in presented.

Commuter Bicyclist Route Choice: Analysis Using a Stated Preference Survey

2003 ◽  
Vol 1828 (1) ◽  
pp. 107-115 ◽  
Author(s):  
Monique A. Stinson ◽  
Chandra R. Bhat
Keyword(s):  
Travel Time ◽  
Stated Preference ◽  
Empirical Models ◽  
Policy Implications ◽  
Facility Planning ◽  
Quality Factors ◽  
Stated Preference Survey ◽  
Factors Affecting ◽  
Choice Analysis ◽  
Using Data

The importance of factors affecting commuter bicyclists’ route choices was evaluated. Both route-level (e.g., travel time) and link-level (e.g., pavement quality) factors are examined. Empirical models are estimated using data from a stated preference survey conducted via the Internet. The models indicate that, for commuter bicyclists, travel time is the most important factor in choosing a route. Presence of a bicycle facility (especially a bike lane or separate path), the level of automobile traffic, pavement or riding surface quality, and presence of a bicycle facility on a bridge are also very important determinants. Furthermore, there are policy implications of these results for bicycle facility planning.

scholarly journals Measuring when Uber behaves as a substitute or complement to transit: An examination of travel-time differences in Toronto

2019 ◽  
Author(s):  
Mischa Young ◽  
Jeff Allen ◽  
Steven Farber
Keyword(s):  
Travel Time ◽  
Public Transportation ◽  
Ordinary Least Squares ◽  
Gap Filling ◽  
Service Levels ◽  
Transit Service ◽  
Logistic Regressions ◽  
Transit Agencies ◽  
Using Data ◽  
The City

Policymakers in cities worldwide are trying to determine how ride-hailing services affect the ridership of traditional forms of public transportation. The level of convenience and comfort that these services provide is bound to take riders away from transit, but by operating in areas, or at times, when transit is less frequent, they may also be filling a gap left vacant by transit operations. These contradictory effects reveal why we should not merely categorize all ride-hailing services as a substitute or supplement to transit, and demonstrate the need to examine ride-hailing trips individually. Using data from the 2016 Transportation Tomorrow Survey in Toronto, we investigate the differences in travel-times between observed ride-hailing trips and their fastest transit alternatives. Ordinary least squares and ordered logistic regressions are used to uncover the characteristics that influence travel-time differences. We find that ride-hailing trips contained within the City of Toronto, pursued during peak hours, or for shopping purposes, are more likely to have transit alternatives of similar duration. Also, we find differences in travel-time often to be caused by transfers and lengthy walk- and wait-times for transit. Our results further indicate that 31% of ride-hailing trips in our sample have transit alternatives of similar duration (≤ 15 minute difference). These are particularly damaging for transit agencies as they compete directly with services that fall within reasonable expectations of transit service levels. We also find that 27% of ride-hailing trips would take at least 30 minutes longer by transit, evidence for significant gap-filling opportunity of ride-hailing services. In light of these findings, we discuss recommendations for ride-hailing taxation structures.

scholarly journals Seismic anisotropy: an original tool to understand the geodynamic evolution of the Italian peninsula

1997 ◽  
Vol 40 (3) ◽  
Author(s):  
L. Margheriti ◽  
C. Nostro ◽  
A. Amato ◽  
M. Cocco
Keyword(s):  
Upper Mantle ◽  
Common Property ◽  
Seismic Waves ◽  
Seismic Anisotropy ◽  
Structural Features ◽  
Relative Strength ◽  
Plate Motion ◽  
Mantle Minerals ◽  
Anisotropic Bodies ◽  
Shallow Crust

Anisotropy is a common property of the Earth's crust and the upper mantle; it is related to the strain field of the medium and therefore to geodynamics. In this paper we describe the different possible origins of anisotropic behavior of the seismic waves and the seismological techniques used to define anisotropic bodies. In general it is found that the fast polarization direction is parallel to the absolute plate motion in cratonic areas, to the spreading direction near rifts or extensional zones, and to the main structural features in transpressive regimes. The delay times between fast and slow waves reflect the relative strength and penetration at depth of the deformation field. The correspondence between surface structural trends and anisotropy in the upper mantle, found in many regions of the world, strongly suggest that orogenic processes involve not only the shallow crust but the entire lithosphere. Recently in Italy both shear wave splitting analysis and Pn inversion were applied to define the trend of seismic anisotropy. Along the Northern Appeninic arc fast directions follow the strike of the arc (i.e., parallel to the strike of the Miocene-Pleistocene compressional features), whereas in the Tyrrhenian zone fast directions are about E-W SW-NE; parallel to the post-Miocene extension that is thought to have reoriented the mantle minerals fabric in the astenosphere.

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