المؤلفون: Ali, Hashmat¹ (AUTHOR), Ahmed, Aarouj² (AUTHOR), Ahmed, Iftikhar¹ (AUTHOR), Jahangir, Adnan³ (AUTHOR), Azhar, Ehtsham⁴ (AUTHOR)

المصدر: Journal of Thermal Stresses. 2023, Vol. 46 Issue 10, p1022-1044. 23p.

مصطلحات موضوعية: *PLANE wavefronts, *ELASTIC wave propagation, *ELASTIC solids, *GEOPHYSICS, *REFLECTANCE

مستخلص: The present article is related to propagation and reflection of elastic wave through a nonlocal generalized thermo-diffusive semiconducting elastic solid. The non-local theory is employed to study the wave behavior. Three phase lag model with higher order fractional order derivative is incorporated to discuss heat propagation through the medium, in addition with two phase lags diffusion equation. The Helmholz vector rule is applied to decompose the system into longitudinal and transverse components. The frequency dispersion relation indicates the presence of four coupled longitudinal and one un-coupled shear vertical wave. The speed of the waves is plotted against angular frequency for local and nonlocal medium. The cutoff frequency of the waves is also depicted graphically. The longitudinal P-wave is taken to be an incident wave at the free surface of the solid to compute the reflection coefficients. The influences of fractional order and nonlocal parameters on amplitude ratios are also studied. The effect of these parameters is found to be significant. The results are proved in the context of energy conservation. The results obtained from the current investigation are very useful for scientists working on problems of geophysics and various fields of mechanics. [ABSTRACT FROM AUTHOR]

المؤلفون: Anne Etiko

مصطلحات موضوعية: Representation and Critique of DIKW Hierarchy, Management Science and Operations Research, Decision Sciences, Social Sciences, Study of Earthquake Precursor Phenomena, Geophysics, FOS Earth and related environmental sciences, Earth and Planetary Sciences, Physical Sciences, Rock Mechanics and Wave Propagation in Geomedia, Mechanics of Materials, Engineering, Mining Induced Seismicity, Resilience materials science, Critical infrastructure, Urbanization, Vulnerability computing, Environmental planning, Green infrastructure, Urban planning, Desk, Environmental resource management, Civil engineering, FOS Civil engineering, Computer science, Geography, Environmental science, Computer security, Physics, Economics

الوصف: Purpose: The main objective of this study was to explore urban geology and infrastructure resilience. Methodology: The study adopted a desktop research methodology. Desk research refers to secondary data or that which can be collected without fieldwork. Desk research is basically involved in collecting data from existing resources hence it is often considered a low cost technique as compared to field research, as the main cost is involved in executive's time, telephone charges and directories. Thus, the study relied on already published studies, reports and statistics. This secondary data was easily accessed through the online journals and library. Findings: The findings revealed that there exists a contextual and methodological gap relating to urban geology and infrastructure resilience. Preliminary empirical review revealed that urban geology and infrastructure resilience is essential in the face of rapid urbanization and increasing geological hazards. It emphasizes the vulnerability of urban ... : الغرض: كان الهدف الرئيسي من هذه الدراسة هو استكشاف الجيولوجيا الحضرية ومرونة البنية التحتية. المنهجية: اعتمدت الدراسة منهجية البحث المكتبي. يشير البحث المكتبي إلى البيانات الثانوية أو تلك التي يمكن جمعها دون العمل الميداني. يشارك البحث المكتبي بشكل أساسي في جمع البيانات من الموارد الحالية، وبالتالي غالبًا ما يُنظر إليه على أنه تقنية منخفضة التكلفة مقارنة بالبحث الميداني، حيث يتم تضمين التكلفة الرئيسية في وقت المسؤول التنفيذي ورسوم الهاتف والأدلة. وبالتالي، اعتمدت الدراسة على الدراسات والتقارير والإحصاءات المنشورة بالفعل. تم الوصول إلى هذه البيانات الثانوية بسهولة من خلال المجلات والمكتبة عبر الإنترنت. النتائج: كشفت النتائج عن وجود فجوة سياقية ومنهجية تتعلق بالجيولوجيا الحضرية ومرونة البنية التحتية. كشفت المراجعة التجريبية الأولية أن الجيولوجيا الحضرية ومرونة البنية التحتية ضرورية في مواجهة التحضر السريع والمخاطر الجيولوجية المتزايدة. ويؤكد على ضعف البنية التحتية الحضرية أمام المخاطر الجيولوجية، مثل الزلازل والانهيارات الأرضية، ويسلط الضوء على الحاجة إلى تحسين قوانين البناء وممارسات البناء وتصميم البنية ...

العلاقة: https://dx.doi.org/10.60692/6te8c-v6150Test

الإتاحة: https://doi.org/10.60692/xrkhn-r7b7210.60692/6te8c-v6150Test

المؤلفون: Yu, Yao, Sandwell, David T, Gille, Sarah T, Boas, Ana Beatriz Villas

المصدر: GEOPHYSICAL JOURNAL INTERNATIONAL. 226(1)

مصطلحات موضوعية: Gravity anomalies and Earth structure, Satellite geodesy, Pacific Ocean, Wave propagation, Geology, Geophysics, Geomatic Engineering, Geochemistry & Geophysics

الوصف: SUMMARY The Ice, Cloud and land Elevation Satellite 2 (ICESat-2) laser altimetry mission, launched in September 2018, uses six parallel lidar tracks with very fine along-track resolution (15 m) to measure the topography of ice, land and ocean surfaces. Here we assess the ability of ICESat-2 ocean data to recover oceanographic signals ranging from surface gravity waves to the marine geoid. We focus on a region in the tropical Pacific and study photon height data in both the wavenumber and space domain. Results show that an ICESat-2 single track can recover the marine geoid at wavelengths >20 km which is similar to the best radar altimeter data. The wavelength and propagation direction of surface gravity waves are sometimes well resolved by using a combination of the strong and weak beams, which are separated by 90 m. We find higher than expected power in the 3–20 km wavelength band where geoid and ocean signals should be small. This artificial power is caused by the projection of 2-D surface waves with ∼300 m wavelengths into longer wavelengths (5–10 km) because of the 1-D sampling along the narrow ICESat-2 profile. Thus ICESat-2 will not provide major improvements to the geoid recovery in most of the ocean.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/18j4k8nzTest

المؤلفون: Paitz, Patrick, Lindner, Nadja, Edme, Pascal, Huguenin, Pierre, Hohl, Michael, Sovilla, Betty, Walter, Fabian, Fichtner, Andreas

المصدر: Journal of Geophysical Research. Earth Surface; May2023, Vol. 128 Issue 5, p1-18, 18p

مصطلحات موضوعية: AVALANCHES, GAUSSIAN mixture models, FIBER optic cables, INFRASTRUCTURE (Economics), STRAIN rate, GROUP velocity, ACOUSTIC wave propagation, SOUND waves

مصطلحات جغرافية: SWITZERLAND

مستخلص: Avalanches and other hazardous mass movements pose a danger to the population and critical infrastructure in alpine areas. Hence, understanding and continuously monitoring mass movements are crucial to mitigate their risk. We propose to use Distributed Acoustic Sensing (DAS) to measure strain rate along a fiber‐optic cable to characterize ground deformation induced by avalanches. We recorded 12 snow avalanches of various dimensions at the Vallée de la Sionne test site in Switzerland, utilizing existing fiber‐optic infrastructure and a DAS interrogation unit during the winter 2020/2021. By training a Bayesian Gaussian Mixture Model, we automatically characterize and classify avalanche‐induced ground deformations using physical properties extracted from the frequency‐wavenumber and frequency‐velocity domain of the DAS recordings. The resulting model can estimate the probability of avalanches in the DAS data and is able to differentiate between the avalanche‐generated seismic near‐field, the seismo‐acoustic far‐field, and the mass movement propagating on top of the fiber. By analyzing the mass‐movement propagation signals, we are able to identify group velocity packages within an avalanche that propagate faster than the phase velocity of the avalanche front, indicating complex internal structures. Importantly, we show that the seismo‐acoustic far‐field can be detected before the avalanche reaches the fiber‐optic array, highlighting DAS as a potential research and early warning tool for hazardous mass movements. Plain Language Summary: Avalanches and other hazardous mass movements pose a danger to the population and critical infrastructure in alpine areas. Therefore, it is important to be able to reliably measure and detect these hazardous events. We show a successful example to measure and characterize avalanches recorded with a Distributed Acoustic Sensing device that measures deformation along a fiber optic cable. We apply unsupervised machine learning to our avalanche recordings and are able to identify consistent properties between 12 avalanches. Ultimately, our results indicate that DAS might be a useful tool for detecting hazardous mass movements. Key Points: Distributed Acoustic Sensing measurements near the interface between avalanche and the subsurface reveal flow dynamicsStrain rate measurements of seismo‐acoustic waves are registered up to 30 s before avalanches reach the sensorsInternal group velocities larger than the propagation speed suggest the presence of complex internal structures [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Geophysical Research. Earth Surface is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Hell, Momme C, Gille, Sarah T, Cornuelle, Bruce D, Miller, Arthur J, Bromirski, Peter D, Crawford, Alex D

المصدر: JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS. 125(4)

مصطلحات موضوعية: storms, wave propagation, sea ice, optimization, Ross Ice Shelf, surface winds, Geophysics, Oceanography, Physical Geography and Environmental Geoscience

الوصول الحر: https://escholarship.org/uc/item/68x5f09kTest

المؤلفون: Vasco, DW, Nihei, K

المصدر: Geophysical Journal International. 216(2)

مصطلحات موضوعية: Seismic tomography, Theoretical seismology, Wave propagation, Body waves, Computational seismology, Geophysics, Geology, Geomatic Engineering, Geochemistry & Geophysics

الوصف: We present a trajectory-based solution to the elastodynamic equation of motion that is valid across a wide range of seismic frequencies. That is, the derivation of the solution does not invoke a high-frequency assumption or require that the medium have smoothly varying properties. The approach, adopted from techniques used in quantum dynamics, produces a set of coupled ordinary differential equations for the trajectory, the slowness vector and the elastic wave amplitude along the ray path. The trajectories may be determined by a direct solution of the governing equations or derived as the by-product of a numerical wavefield simulation. Synthetic tests with interfaces and layers containing increasingly narrow transition zones indicate that the conventional high-frequency trajectories associated with the eikonal equation bend too sharply into high-velocity regions as the wavelength exceeds the transition zone width. Tests in a velocity model, based upon mapped structural surfaces from the Geysers geothermal field in California, indicate that discrepancies between high-frequency and broad-band trajectories can exceed several hundred metres at wavelengths of 1 Hz. An application to a crosswell tomographic imaging experiment demonstrates that the technique provides a basis for the seismic monitoring of fluid flow along narrow features such as fracture zones.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/69t2483mTest

المؤلفون: Vasco, DW, Nihei, KT

المصدر: Geophysical Journal International. 219(3)

مصطلحات موضوعية: Seismic anisotropy, Seismic tomography, Seismic wave propagation, Theoretical seismology, Geology, Geophysics, Geomatic Engineering, Geochemistry & Geophysics

الوصف: We derive equations describing the path and traveltime of a coherent elastic wave propagating in an anisotropic medium, generalizing expressions from conventional high-frequency asymptotic ray theory. The methodology is valid across a broad range of frequencies and allows for subwavelength variations in the material properties of the medium. The primary difference from current ray methods is the retention of a term that is neglected in the derivation of the eikonal equation. The additional term contains spatial derivatives of the properties of the medium and of the amplitude field, and its presence couples the equations governing the evolution of the amplitude and phase along the trajectory. The magnitude of this term provides a measure of the validity of expressions based upon high-frequency asymptotic methods, such as the eikonal equation, when modelling wave propagation dominated by a band of frequencies. In calculations involving a layer with gradational boundaries, we find that asymptotic estimates do deviate from those of our frequency-dependent approach when the width of the layer boundaries become sufficiently narrow. For example, for a layer with boundaries that vary over tens of meters, the term neglected by a high-frequency asymptotic approximation is significant for frequencies around 10 Hz. The visible differences in the paths of the rays that traverse the layer substantiate this conclusion. For a velocity model derived from an observed well log, the majority of the trajectories calculated using the extended approach, accounting for the frequency-dependence of the rays, are noticeably different from those produced by the eikonal equation. A suite of paths from a source to a specified receiver, calculated for a range of frequencies between 10 and 100 Hz, define a region of sensitivity to velocity variations and may be used for an augmented form of tomographic imaging.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/3wd1n3fzTest

المؤلفون: Vasco, DW, Nihei, Kurt

المصدر: Geophysical Journal International. 216(2)

مصطلحات موضوعية: Earth Sciences, Engineering, Geology, Geophysics, Seismic tomography, Theoretical seismology, Wave propagation, Body waves, Computational seismology, Geomatic Engineering, Geochemistry & Geophysics, Geomatic engineering

الوصف: We present a trajectory-based solution to the elastodynamic equation of motion that is valid across a wide range of seismic frequencies. That is, the derivation of the solution does not invoke a high-frequency assumption or require that the medium have smoothly varying properties. The approach, adopted from techniques used in quantum dynamics, produces a set of coupled ordinary differential equations for the trajectory, the slowness vector and the elastic wave amplitude along the ray path. The trajectories may be determined by a direct solution of the governing equations or derived as the by-product of a numerical wavefield simulation. Synthetic tests with interfaces and layers containing increasingly narrow transition zones indicate that the conventional high-frequency trajectories associated with the eikonal equation bend too sharply into high-velocity regions as the wavelength exceeds the transition zone width. Tests in a velocity model, based upon mapped structural surfaces from the Geysers geothermal field in California, indicate that discrepancies between high-frequency and broad-band trajectories can exceed several hundred metres at wavelengths of 1 Hz. An application to a crosswell tomographic imaging experiment demonstrates that the technique provides a basis for the seismic monitoring of fluid flow along narrow features such as fracture zones.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/69t2483mTest

المؤلفون: Pertuz, Tatiana, Malehmir, Alireza

مصطلحات موضوعية: Image processing, Seismic anisotropy, Wave propagation, Geophysics, Geofysik

الوصف: We studied the benefits of a nine-component (9C) seismic survey over a landslide-prone area in southwest of Sweden to retrieve ultrahigh-resolution shear wave reflection images of the subsurface as well as crucial information on physical properties of the sediments. A complete, 1 m shot and receiver spacing, multicomponent 2-D seismic profile was acquired using three-component microelectromechanical-system-based landstreamer receivers, and a 5-kg sledgehammer strike in vertical and horizontal orientations as three-component seismic source. Given the rich number of shear wave reflections observed on all the 9C data, the processing work focused on their retrievals. It revealed three distinct reflections, two of which associated with coarse-grained materials and one with an extremely undulating bedrock surface. Given the extremely slow shear wave velocities on the order of 60–100 m s−1, we obtained ultrahigh-resolution shear wave sections avoiding temporal and spatial aliasing. Imaging results suggest vertical-source and horizontal-radial receiver (V–HR), and horizontal-transverse source–receiver orientations (HT–HT) provided the most optimum images of the subsurface. A non-hyperbolic algorithm was applied to the normal-moveout corrections justified by the traveltime differences of the bedrock reflection in different shear wave sections. The improved images by incorporating the anisotropy term suggest that the data set reveals moderate shear wave anisotropy along some portions of the profile. The Vp/Vs ratio obtained by using bedrock reflection in P- and S-wave sections suggests values ranging 10–16, which implies high water content. Areas with lower Vp/Vs coincides with greater anisotropic parameters and this can indicate disturbed clays or presence of sensitive clays.

وصف الملف: application/pdf

العلاقة: Geophysical Journal International, 0956-540X, 2023, 235:3, s. 2094-2106; orcid:0000-0002-1234-0227; orcid:0000-0003-1241-2988; http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-516338Test; ISI:001093108000001

الإتاحة: https://doi.org/10.1093/gji/ggad346Test
http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-516338Test

المؤلفون: Diekmann, Leon, Vasconcelos, Ivan, Van Leeuwen, Tristan

المساهمون: Mathematical Modeling, Seismology, Experimental rock deformation, Sub Mathematical Modeling

مصطلحات موضوعية: Interferometry, Inverse theory, Theoretical seismology, Wave propagation, Waveform inversion, Geophysics, Geochemistry and Petrology

الوصف: Full waveform inversion and least-squares reverse time migration are the leading technologies for imaging with seismic waves. Both of them usually rely (in one way or another) on a single-scattering approximation, i.e. the Born approximation, to compute gradients and obtain an updated model. This approximation linearises the relation between modelled data and model by ignoring multiple scattering. We propose to use the Marchenko integral, an equation originating from inverse scattering theory, to obtain an alternative linear equation. Using the Marchenko method we can retrieve Green's functions, including all orders of scattering, for virtual sources anywhere within the volume of interest - without prior knowledge of the high-wavelength model variations that induce scattering. Plugging these estimated Green's functions into the Lippmann-Schwinger integral delivers a Marchenko-linearised relation between the full waveform data and the model. We present this new linearisation strategy and illustrate its advantages and disadvantages by comparing numerical results for different inversion kernels. Our new linearisation is exact, i.e. it does not exclude any orders of scattering, however, it relies on the quality of the Marchenko-derived Green's functions. These Marchenko-based Green's functions require an estimate of the first arrivals of the Green's functions - commonly obtained by modelling in a background medium. Although these first arrival estimates strongly bias our results for inaccurate background models, we find the Marchenko-linearisation to deliver overall slightly better inverted models than the single-scattering approximation.

وصف الملف: application/pdf

العلاقة: https://dspace.library.uu.nl/handle/1874/434362Test

الإتاحة: https://dspace.library.uu.nl/handle/1874/434362Test