Algebraic reconstruction of a two‐dimensional velocity inhomogeneity in the High Hazles seam of Thoresby colliery

Geophysics ◽  
1981 ◽  
Vol 46 (3) ◽  
pp. 298-308 ◽  
Author(s):  
I. M. Mason
Keyword(s):  
Seismic Velocity ◽  
Seismic Survey ◽  
Two Dimensional ◽  
Arrival Times ◽  
Static Correction ◽  
General Line ◽  
Site Access ◽  
Distributed Faults ◽  
Wave Trains ◽  
Algebraic Reconstruction

A high proportion of faces started in mechanized coal mines run into underground faults. The faults take many forms, from the splitting of a seam through a hidden stress pattern caused by subsidence or folding, to a washout or a vertical throw. All faults reduce face output. A throw of only 1.5 m can lead to a face being abandoned. Faults of this order cannot be mapped reliably from the surface. They may be mapped in an underground seismic survey. Roadways of a mine may give access to fast refracting horizons above and below a coal seam. Waveguiding in the plane of the seam, if it occurs, simplifies migration of wave trains reflected from discrete faults. The reduction problem involved in a fault mapping is only two‐dimensional. Given guiding, whether leaky or not, it is possible to map distributed faults of low reflectivity by shooting in transmission across a panel of coal. Algebraic reconstruction techniques are used here to reduce first break times‐of‐flight through a 425 × 950 m rectangular block of coal into the profile of a velocity inhomogeneity. Input data are derived by static correction from hand‐picked arrival times. The reduction itself is effected using an algorithm which accommodates underground site access restrictions. In back projecting first break velocities, a truncated cosine is used to weight the relative contributions of rays passing at different distances from any given mapping point. The reconstructed velocity field suggests that the coal panel is bisected by a ridge of higher velocity. The suspicion of a ridge is reinforced by results of an aberration test based on a standard Huygens‐Kirchhoff migration. The ridge is found to follow the general line of a system of pillars left in place during the mining of a lower horizon. It is concluded that channel waves may be used to map subsidence into old workings underground. Coal seams apparently share, with other sedimentary rocks, the property of a pressure‐sensitive seismic velocity.

Computational Simulations of Dynamic Compaction of Dry Sand

2012 ◽  
Vol 598 ◽  
pp. 516-519
Author(s):  
Yu Qing Ding ◽  
Wen Hui Tang ◽  
Xian Wen Ran ◽  
Xin Xu
Keyword(s):  
Computational Analysis ◽  
Dynamic Compaction ◽  
Back Surface ◽  
Computational Results ◽  
Two Dimensional ◽  
Computational Simulations ◽  
Plate Impact ◽  
Arrival Times ◽  
Dry Sand ◽  
Impact Experiments

The computational analysis of plate impact experiments on dry sand utilizing the Mie- Grüneisen (MG) equation of state and the P-α compaction model were investigated in this study. A number of two dimensional axial symmetric computations were performed by using the hydrocode AUTODYN. The computational results were compared with the particle velocity on the back surface of the rear plate measured by the VISAR system and the first shock-wave arrival times detected by piezoelectric pins in the samples respectively. It was found that the P-α compaction model was more accurately reproduce the experimental data than the MG EOS.

Modelling of Lamb Waves Propagation in Orthotropic Plate

2020 ◽  
pp. 315-340
Author(s):  
Salah Nissabouri ◽  
Mhammed El Allami ◽  
El Hassan Boutyour
Keyword(s):  
Finite Element Method ◽  
Orthotropic Plate ◽  
Lamb Waves ◽  
Two Dimensional ◽  
Arrival Times ◽  
Localization Method ◽  
Waves Propagation ◽  
Signal Changes ◽  
2D Fft ◽  
Lamb Mode

In this chapter, we model by Finite Element Method (FEM) the Lamb waves' propagation and their interactions with symmetric and asymmetric delamination in sandwich skin. Firstly, a theoretical model is established to obtain the equation of lamb modes propagation. Secondly, dispersion curves are plotted using Matlab program for the laminate [0]4. The simulations were then carried out using ABAQUS CAE by exciting the fundamental A0 Lamb mode in the frequency 300 kHz. The delamination was then estimated by analyzing the signal picked up at two sensors using two techniques: Two Dimensional Fast Fourier Transform (2D-FFT) to identify the propagating and converted modes, and Wavelet Transform (WT) to measure the arrival times. The results showed that the mode A0 is sensible to symmetric and asymmetric delamination. Besides, based on signal changes with the delamination edges, a localization method is proposed to estimate the position and the length of the delamination. In the last section, an experimental FEM verification is provided to validate the proposed method.

Map displays from an interactive interpretation

Geophysics ◽  
1986 ◽  
Vol 51 (10) ◽  
pp. 1999-2006 ◽  
Author(s):  
J. I. Denham ◽  
H. Roice Nelson
Keyword(s):  
Three Dimensional ◽  
Seismic Interpretation ◽  
Seismic Survey ◽  
Two Dimensional ◽  
Seismic Surveys ◽  
Mapping Techniques ◽  
Gippsland Basin

Map displays built during interactive seismic interpretation provide information not obtainable with traditional mapping techniques. Several map displays derived from the 1983 interactive interpretation of a Gippsland Basin three‐dimensional (3-D) seismic survey are presented below. Similar map display results have since been obtained with the interactive interpretation of two‐dimensional (2-D) seismic surveys. These types of mapping results are among the most important contributions of interactive interpretation procedures.

scholarly journals Short-term disturbance by a commercial two-dimensional seismic survey does not lead to long-term displacement of harbour porpoises

2013 ◽  
Vol 280 (1771) ◽  
pp. 20132001 ◽  
Author(s):  
Paul M. Thompson ◽  
Kate L. Brookes ◽  
Isla M. Graham ◽  
Tim R. Barton ◽  
Keith Needham ◽  
...  
Keyword(s):  
Sublethal Effects ◽  
Control Area ◽  
Seismic Survey ◽  
Two Dimensional ◽  
Survey Period ◽  
The North ◽  
Impact Area ◽  
The North Sea ◽  
Passive Acoustic ◽  
The Impact

Assessments of the impact of offshore energy developments are constrained because it is not known whether fine-scale behavioural responses to noise lead to broader-scale displacement of protected small cetaceans. We used passive acoustic monitoring and digital aerial surveys to study changes in the occurrence of harbour porpoises across a 2000 km 2 study area during a commercial two-dimensional seismic survey in the North Sea. Acoustic and visual data provided evidence of group responses to airgun noise from the 470 cu inch array over ranges of 5–10 km, at received peak-to-peak sound pressure levels of 165–172 dB re 1 µPa and sound exposure levels (SELs) of 145–151 dB re 1 µPa 2 s −1 . However, animals were typically detected again at affected sites within a few hours, and the level of response declined through the 10 day survey. Overall, acoustic detections decreased significantly during the survey period in the impact area compared with a control area, but this effect was small in relation to natural variation. These results demonstrate that prolonged seismic survey noise did not lead to broader-scale displacement into suboptimal or higher-risk habitats, and suggest that impact assessments should focus on sublethal effects resulting from changes in foraging performance of animals within affected sites.

A generalized spatial-temporal model of rainfall based on a clustered point process

1995 ◽  
Vol 450 (1938) ◽  
pp. 163-175 ◽  
Keyword(s):  
Poisson Process ◽  
Point Process ◽  
Random Variable ◽  
Cell Types ◽  
Exponential Random Variable ◽  
Two Dimensional ◽  
Arrival Times ◽  
Hourly Rainfall ◽  
Temporal Model ◽  
Different Cell Types

The objective in this paper is to present and fit a relatively simple stochastic spatial-temporal model of rainfall in which the arrival times of rain cells occur in a clustered point process. In the x - y plane, rain cells are represented as discs; each disc having a random radius; the locations of the disc centres being given by a two-dimensional Poisson process. The intensity of each cell is a random variable that remains constant over the area of the disc and throughout the lifetime of the cell, the lifetime being an exponential random variable. The cells are randomly classified from 1 to n with different parameters for the different cell types, so that the random variables of an arbitrary cell, e. g. radius and intensity, are correlated. Multi-site second-order properties are derived and used to fit the model to hourly rainfall data taken from six sites in the Thames basin, UK.

scholarly journals On the use of earthquake multiplets to study fractures and the temporal evolution of an active volcano

1996 ◽  
Vol 39 (2) ◽  
Author(s):  
G. Poupinet ◽  
A. Ratdomopurbo ◽  
O. Coutant
Keyword(s):  
Seismic Velocity ◽  
Active Volcano ◽  
Temporal Changes ◽  
Time Interval ◽  
Velocity Change ◽  
P Waves ◽  
Merapi Volcano ◽  
Arrival Times ◽  
Cross Spectrum ◽  
Window Technique

Multiplets, i.e. events with similar waveforms, are common features on active volcanoes. The seismograms of multiplets are analyzed by cross-spectrum techniques: this procedure improves by a factor of about 10 the precision of differential P-arrival times and therefore the accuracy of the relative location of earthquakes. Long period events which cannot be located because of the impossibility to pick up P-waves on individual seismograms can be located with a precision of about 10 m. Such a precision permits fault planes to be mapped inside a volcanic edifice and the azimuth and strike of fractures to be defined. Seismograms of the two events (of a doublet) that occur on different dates are analyzed by the Cross Spectrum Moving Window technique (CSMW) for measuring the time delay between waves in the coda. The pattern of the delays in the coda is a function of the temporal changes of seismic velocity that occurred inside the volcano during the time interval that separates the two events of a doublet. We illustrate the potential of the doublet technique for detecting temporal changes inside a volcano by performing computations of synthetic seismograms. The case of a dyke injected inside the volcano is considered as well as that of the replenishment of a superficial magma chamber and of a general increase in velocity in the summit of the volcano. Data from Merapi volcano (Indonesia)illustrate a possible temporal velocity change inside the volcano several months before the 1992 eruption.

THREE-DIMENSIONAL DATA COLLECTION AND PROCESSING

1978 ◽  
Vol 18 (1) ◽  
pp. 116
Author(s):  
E. G. Selby
Keyword(s):  
Data Collection ◽  
Seismic Data ◽  
Signal To Noise Ratio ◽  
Three Dimensional ◽  
Depth Map ◽  
Seismic Survey ◽  
Seismic Exploration ◽  
Two Dimensional ◽  
Additional Advantage ◽  
Information Giving

There are many limitations in the ultimate accuracy of a conventional two dimensional seismic survey. One of the most important of these is that, in general, a prospect is not a two dimensional model but a three dimensional one. For a complete interpretation of a prospect area the final result should be a migrated time or depth map. With limited sampling (a seismic grid typically consists of loops with dimensions at least 1 km by 1 km) it is necessary to interpolate grid points to allow map migration and this method has inherent inaccuracies.The three dimensional seismic exploration technique is designed to provide a sufficiently close sampled grid of seismic traces, typically with a line and depth point spacing as close as 50-100 m, to allow the seismic data itself to be migrated three dimensionally. This allows the interpreter to work with migrated seismic sections and to contour directly the migrated map.Several techniques exist to allow practical and economic collection of seismic data to provide this close sampling. These techniques can be adapted to various terrain and cultural conditions.The main advantages of three dimensional data collection are correct imaging of the seismic information giving true vertical reflection time sections and improved signal-to-noise ratio due to the increased fold inherent in the three dimensional migration process. The additional advantage to the interpreter is that the data has a sampling which gives a line intersection at each depth point in the prospect.

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