scholarly journals Diffusion approximation with polarization and resonance effects for the modelling of seismic waves in strongly scattering small-scale media

2012 ◽  
Vol 192 (1) ◽  
pp. 326-345 ◽  
Author(s):  
Ludovic Margerin
Keyword(s):  
Diffusion Approximation ◽  
Seismic Waves ◽  
Small Scale ◽  
Resonance Effects

Time-Domain Simulation of Subsea Equipments Installation Using Hydrodynamic Derivatives

2020 ◽  
Author(s):  
Emerson M. de Andrade ◽  
Joel S. Sales ◽  
Antonio C. Fernandes ◽  
Mario L. Ribeiro ◽  
Pedro V. Teixeira
Keyword(s):  
Hydrodynamic Forces ◽  
Dynamic Responses ◽  
Elastic Behavior ◽  
Strong Interactions ◽  
Small Scale ◽  
Complex Geometries ◽  
Second Phase ◽  
Current Profile ◽  
Resonance Effects ◽  
Hydrodynamic Derivatives

Abstract The installation of a subsea equipment such as manifold needs careful planning and coordination. Studies on the behavior of the dynamic responses are crucial to guarantee safety. Some important factors in these operations include the current profile, waves characteristics, winches motions at topside, and the elastic behavior of the cable (due to resonance effects). Currently, most of the available commercial codes use simplified models for the hydrodynamic forces of submerged equipment. However, for cases with complex geometries and strong interactions with the environmental loads, those models fail to represent correctly the dynamics. In this paper we present an initial method and a hydrodynamic model to include terms that allow the modelling of complex behavior of submerged complex geometries by using hydrodynamic derivatives extracted from model tests. To verify the procedure, tests were performed both at a flume tank and at a towing tank. The model was implemented in a commercial code by using a Simplified Buoy model, to which a python procedure that calculated the hydrodynamic forces was attached. The study was divided into two phases: the first one consisted of the verification of the effectiveness of the external routine. This was done for a manifold in 1DOF and then in 6 DOF. In the second phase, the dynamic maneuvering model using Hydrodynamic Derivatives was implemented as an external routine and, using the output from dynamic excitation experiments at small scale with a manifold, kinematical behavior results were compared. Results showed good adherence, although some further investigations are still needed.

Surface topography effects on seismic ground motion and correlation with earthquake-induced landslide: An example of the JiuJiu peaks in 1999 Chi-Chi Taiwan earthquake

2020 ◽  
Author(s):  
Chun-Te Chen ◽  
Shiann-Jong Lee ◽  
Yu-Chang Chan
Keyword(s):  
Surface Topography ◽  
Seismic Response ◽  
Ground Motion ◽  
Seismic Waves ◽  
Velocity Structure ◽  
Seismic Hazard Assessment ◽  
Buffer Layers ◽  
Small Scale ◽  
Ground Shaking ◽  
Mesh Model

<p>The topography effect has been thriving investigated based on numerical modeling. It impacts the seismic ground shaking, usually amplifying the amplitude of shaking at top hills or ridges and de-amplifying at valleys. However, the correlation between the earthquake-induced landslide and the topographic amplification is relatively unexplored. To investigate the amplification of seismic response on the surface topography and the role in the Chi-Chi earthquake-induced landslide in the JiuJiu peaks area, we perform a 3D ground motion simulation in the JiuJiu peaks area of Taiwan based on the spectral element method. The Lidar-derived 20m resolution Digital Elevation Model (DEM) data was applied to build a mesh model with realistic terrain relief. To this end, in a steep topography area like the JiuJiu peaks, the designed thin buffer layers are applied to dampen the mesh distortion. The three doubling mesh layers near the surface accommodate a more excellent mesh model. Our results show the higher amplification of PGA on the tops and ridges of JiuJiu peaks than surrounding mountains, while the de-amplification mostly occurs near the valley and hillside. The relief topography could have a ±50% variation in PGA amplification for compression wave, and have much more variety in PGA amplification for shear wave, which could be in the range between -50% and +100%. We also demonstrate that the high percentages of the landslide distribution right after the large earthquake are located in the topographic amplified zone. The source frequency content interacts with the topographic feature, in general, small-scale topography amplifies the higher-frequency seismic waves. It is worthy of further investigating the interaction between the realistic topography and the velocity structure on how to impact the seismic response in the different frequency bands. We suggest that the topographic seismic amplification should be taking into account in seismic hazard assessment and landslide evaluation.</p>

Repeat well logging using earthquake wave amplitudes measured by distributed acoustic sensors

2020 ◽  
Vol 39 (7) ◽  
pp. 513-517
Author(s):  
Roman Pevzner ◽  
Boris Gurevich ◽  
Anastasia Pirogova ◽  
Konstantin Tertyshnikov ◽  
Stanislav Glubokovskikh
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Synthetic Data ◽  
Seismic Source ◽  
Small Scale ◽  
Acoustic Sensors ◽  
Linear Strain ◽  
Subsurface Characterization ◽  
Distributed Acoustic Sensing ◽  
Subsurface Monitoring

Well-based technologies for seismic subsurface monitoring increasingly utilize fiber-optic cables installed in boreholes as distributed acoustic sensing (DAS) systems. A DAS cable allows measuring linear strain of the fiber and can serve as an array of densely spaced seismic receivers. The strain amplitudes recorded by the DAS cable depend on the near-well formation properties (the softer the medium, the larger the strain). Thus, these properties can be estimated by measuring relative variations of the amplitudes of seismic waves propagating along the well. An advantage of such an approach to subsurface characterization and monitoring is that no active seismic source is required. Passive sources such as earthquakes can be utilized. A synthetic data example demonstrates viability of the approach for monitoring of small-scale CO2 injection into an aquifer. Two field DAS data examples based on signal recordings from several distant earthquakes show that the relevant properties of the near-well formation can be estimated with an accuracy of approximately 5%.

2-D random media with ellipsoidal autocorrelation functions

Geophysics ◽  
1993 ◽  
Vol 58 (9) ◽  
pp. 1359-1372 ◽  
Author(s):  
L. T. Ikelle ◽  
S. K. Yung ◽  
F. Daube
Keyword(s):  
Aspect Ratio ◽  
Seismic Data ◽  
Random Media ◽  
Large Scale ◽  
Seismic Waves ◽  
Homogeneous Medium ◽  
Small Scale ◽  
Arrival Times ◽  
The Earth ◽  
Pulse Arrival

The integration of surface seismic data with borehole seismic data and well‐log data requires a model of the earth which can explain all these measurements. We have chosen a model that consists of large and small scale inhomogeneities: the large scale inhomogeneities are the mean characteristics of the earth while the small scale inhomogeneities are fluctuations from these mean values. In this paper, we consider a two‐dimensional (2-D) model where the large scale inhomogeneities are represented by a homogeneous medium and small scale inhomogeneities are randomly distributed inside the homogeneous medium. The random distribution is characterized by an ellipsoidal autocorrelation function in the medium properties. The ellipsoidal autocorrelation function allows the parameterization of small scale inhomogeneities by two independent autocorrelation lengths a and b in the horizontal and the vertical Cartesian directions, respectively. Thus we can describe media in which the inhomogeneities are isotropic (a = b), or elongated in a direction parallel to either of the two Cartesian directions (a > b, a < b), or even taken to infinite extent in either dimension (e.g., a = infinity, b = finite: a 1-D medium) by the appropriate choice of the autocorrelation lengths. We also examine the response of seismic waves to this form of inhomogeneity. To do this in an accurate way, we used the finite‐difference technique to simulate seismic waves. Special care is taken to minimize errors due to grid dispersion and grid anisotropy. The source‐receiver configuration consists of receivers distributed along a quarter of a circle centered at the source point, so that the angle between the source‐receiver direction and the vertical Cartesian direction varies from 0 to 90 degrees. Pulse broadening, coda, and anisotropy (transverse isotropy) due to small scale inhomogeneities are clearly apparent in the synthetic seismograms. These properties can be recast as functions of the aspect ratio [Formula: see text] of the medium, especially the anisotropy and coda. For media with zero aspect ratio (1-D media), the coda energy is dominant at large angles. The coda energy gradually becomes uniformly distributed with respect to angle as the aspect ratio increases to unity. Our numerical results also suggest that, for small values of aspect ratio, the anisotropic behavior (i.e., the variations of pulse arrival times with angle) of the 2-D random media is similar to that of a 1-D random medium. The arrival times agree with the effective medium theory. As the aspect ratio increases to unity, the variations of pulse arrival times with angle gradually become isotropic. To retain the anisotropic behavior beyond the geometrical critical angle, we have used a low‐frequency pulse with a nonzero dc component.

Large and small scale structures in the plasma sheet: A signature of chaotic motion and resonance effects

1991 ◽  
Vol 18 (8) ◽  
pp. 1603-1606 ◽  
Author(s):  
Maha Ashour-Abdalla ◽  
Jean Berchem ◽  
Jörg Büchner ◽  
Lev M. Zelenyi
Keyword(s):  
Plasma Sheet ◽  
Chaotic Motion ◽  
Small Scale ◽  
Resonance Effects ◽  
Scale Structures ◽  
Small Scale Structures

Identification and distribution of fractures in the Zhangjiatan shale of the Mesozoic Yanchang Formation in Ordos Basin

2017 ◽  
Vol 5 (2) ◽  
pp. SF167-SF176 ◽  
Author(s):  
Hui Shi ◽  
Xiaorong Luo ◽  
Hui Xu ◽  
Xiangzeng Wang ◽  
Lixia Zhang ◽  
...  
Keyword(s):  
Shale Gas ◽  
Seismic Waves ◽  
Ordos Basin ◽  
Super Resolution ◽  
Average Density ◽  
Gas Production ◽  
Small Scale ◽  
High Angle ◽  
Yanchang Formation ◽  
Angle Fractures

The natural fractures in mud or shale directly affect the quality and efficiency of shale gas reservoirs, and fracture identification and prediction play an important role in drilling shale gas wells and making plans for reservoir stimulation. We adopted ant tracking technology for 3D poststack reflective seismic waves to identify the size and distribution of high-angle structural fractures in the Zhangjiatan shale of the Yanchang Formation in the Ordos Basin, which is a typical continental shale. The parameters for ant tracking fractures are extracted from the investigation on outcrop, cores, and image logs. The prestack seismic diffractive wave imaging technique for the super-resolution identification of mid- and small-scale breakpoints can be used as the constraint conditions for ant tracking. The identified result of high-angle fractures was validated by the image logging and drilling gas logging results. The geologic and logging data indicate that the Zhangjiatan shale is mainly characterized by high-angle fractures and a smaller number of low-angle fractures. The fractures mainly trend in the near east–west direction, followed by the near north–south direction, and a small amount of fractures in the north–northeast and northwest–west directions. The average density of structural fractures is relatively low, but the cemented rate is only 15.7%, and most structural fractures maintain an open state. The identified and predicted structural fractures are mainly distributed in the southeast of well LP180 and south of well LP179. The higher gas shows from actual well drilling in shale directly correspond to the density and intensity of high-angle fractures rather than the matrix gas abundance in shale, which indicates that the sweet spot of gas production in shale is clearly controlled by structural fractures.

scholarly journals Characterizing seismic scattering in 3D heterogeneous Earth by a single parameter

2020 ◽  
Author(s):  
Jagdish Chandra Vyas ◽  
Martin Galis ◽  
Paul Martin Mai
Keyword(s):  
Standard Deviation ◽  
Correlation Length ◽  
Hurst Exponent ◽  
Seismic Waves ◽  
The Other ◽  
Small Scale ◽  
Seismic Scattering ◽  
Von Karman ◽  
Velocity Variations ◽  
Von Kármán

&lt;p&gt;We analyze the power spectral density (PSD) of von Karman autocorrelation function (ACF) to derive a theoretical parameter which characterizes the scattering of seismic wavefield due to random heterogeneities in 3D Earth structure. We then verify our analytical findings by performing ground-motion simulations. We characterize scattering using root-mean-square (RMS) fluctuations of normalized seismic wave speed, which represents wavefield scattering due to random heterogeneities in 3D Earth under the diffraction condition. The isotropic von Karman ACF is parameterized by correlation length a, standard deviation &amp;#963;, and Hurst exponent H. To compute the RMS value, we simplify the von Karman PSD for three regimes: k&amp;#183;a &amp;#8811; 1 (&amp;#955; &amp;#8810; a), k&amp;#183;a &amp;#8776; 1 (&amp;#955; &amp;#8776; a) and k&amp;#183;a &amp;#8810; 1 (&amp;#955; &amp;#8811; a), where &amp;#955; is wavelength and k wavenumber of the seismic waves. The analysis of the RMS values reveals that 1) scattering is proportional to the standard deviation &amp;#963; of small-scale velocity variations in all three regimes, 2) scattering is inversely proportional to the correlation length in the k&amp;#183;a &amp;#8811; 1 regime, but directly proportional to the correlation length in the other two regimes, 3) a small Hurst exponent H for the k&amp;#183;a &amp;#8811; 1 regime leads to scattering controlled solely by the standard deviation of small-scale velocity variations (for the other two regimes, it leads to weaker scattering). The seismic scattering effectively vanishes for H approaching zero. Our theoretical findings are purely physics based and are furthermore verified by 3D high resolution numerical simulations. Hence, we developed solid physics-based understanding of 3D seismic scattering due to random heterogeneities in the Earth which will be helpful for future modeling studies.&lt;/p&gt;

Leaky mode: A mechanism of horizontal seismic attenuation in a gas-hydrate-bearing sediment

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. E159-E163 ◽  
Author(s):  
Sebastian R. Zanoth ◽  
Erik H. Saenger ◽  
Oliver S. Krüger ◽  
Serge A. Shapiro
Keyword(s):  
Gas Hydrate ◽  
Seismic Waves ◽  
Seismic Attenuation ◽  
Leaky Mode ◽  
Small Scale ◽  
Low Velocity ◽  
Scattering Loss ◽  
Typical Situation ◽  
Intrinsic And Scattering Attenuation ◽  
Attenuation Mechanism

The leaky mode is a possible attenuation mechanism of seismic waves propagating along lamination in gas-hydrate-bearing sediment layers. This horizontal propagation attenuation mechanism occurs when a high-velocity layer is embedded in a low-velocity zone. This is a typical situation for gas hydrate occurrences. To quantify this attenuation mechanism, a 2D digital rock model based on the crosswell data of the Mallik 2002 Gas Hydrate Production Research Well Program is used. For simplicity, our elastic simulations exclude attenuation mechanisms like scattering loss or intrinsic absorption. We demonstrate that the leaky mode is a significant horizontal attenuation mechanism that cannot be neglected. The effective attenuation of gas-hydrate-bearing sediments is a combination of intrinsic and scattering attenuation by small-scale heterogeneties and the leaky mode.

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