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geology
Questions and Answers of
Geology
Describe the generalized Hilbert transform (GHT) after reading Luo et al., 2003.
Find out the meanings of the values in the earthquake phase data example shown in Figure 1.23.Figure 1.23 1981/04/01 02:05:14.60 L3.32 I 33.580 -116.822 7.1 B513877 29 130 0 0 POB VHZ 605 P IUO 15.16
Many data sorting procedures can be carried out by sorting the data headers. Why is this approach efficient? Can you give examples to illustrate your arguments?
Write a flow chart of the processing steps required to convert a seismic dataset in CSG arrangement into CMP arrangement, assuming that the data are in SEGY format. Try to write the processes and
Search the literature to find typical surface seismic survey geometry onshore and offshore, and the typical ranges of parameters such as source depths, receiver depths, source-to-receiver offsets,
Use your own words to define the concepts of: demultiplexing, time stack, matched filter, and walkaway RVSP.
If we have multi-component surface reflection data, can we use a hodogram to suppress ground rolls? How would you do it? What problems can you anticipate for your approach?
Prove or refute the statement that stacking of seismic traces has the effect of low-pass filtering.
Most semblance velocity analysis stacks all traces with equal weight. Should we apply variable weights as a function of offset and intersection time? Devise a way to conduct such a weighted semblance
The semblance velocities of multiple reflections are usually slower than the velocity of the primary reflection, as shown in Figure 2.8. Explain the reasons behind this observation.Figure 2.8 STEPOUT
Sketch the cross-correlation of two functions with equal time durations in Figure 2.13. you may first discretize the functions into short time series, and then use the formula of discrete
Compare and contrast the convolution and cross-correlation operations. It may be best to organize your answer by using a table listing the similarities and differences.
Cross-correlation is used to measure the similarity between two vectors \(\mathbf{u}=\left(u_{1}\right.\), \(\left.u_{2}, \ldots, u_{N}\right)\) and \(\mathbf{v}=\left(v_{1}, v_{2} \ldots,
Define white noise versus colored noise, and give several examples for each type of noise. Why is it usually more difficult to suppress colored noise than white noise?
Discuss the meanings of signals and noise in Figures 2.14a and 2.15a.Figures 2.14aFigures 2.15a T[s] 0 3 (a) 2 V2 Reflection 1 V1 V3 0 5 10 km
Find a couple of examples in the literature on noise suppression in seismic data processing using the \(\tau-p\) transform.
Discuss the advantages and limitations of using the concept of statics to correct for the near-surface effect on seismic data.
The sand dune curve shown in Figure 2.20b is a depth versus traveltime plot that can be obtained from an uphole or a check shot survey. Derive a 1D velocity function based on the depth versus
Search the literature to write a short description for: (1) refraction statics; (2) reflection statics; (3) trim statics. Which method is the most effective?
Find and discuss three applications of the law of decomposition and superposition from geophysics literature.
Conduct a modeling experiment to prove the Huygens principle by following the sketch by Isaac Newton in Figure 3.2.Figure 3.2 N P A e K
If we alter the amplitude of the \(20 \mathrm{~Hz}\) cosine wave in Figure 3.3a, will the pattern of the correlation function in Figure 3.3b change? Will the amplitude of the correlation
What happens to a function \(F(\omega)\) if you take two consecutive inverse Fourier transforms of it? What is the implication of the result?
Calculate the Fourier transform of \(f(t)=(4,-3,2,-1)\) using DFT formulation. Please show the resultant real part and imaginary part separately.
Using DFT to show the effect in the frequency domain of interlacing zeros into a time series \(x_{t}\). Here, interlacing zeros means turning an \(N\)-length \(x_{t}=\left\{x_{1}, x_{2}, x_{3},
Find three examples showing the benefits of the Fourier transform. How are the benefits realized? What are the assumptions? Are there any limitations or drawbacks?
When applying \(A G C\) to a seismic trace, will the phase spectrum be changed? Is it possible to alter amplitude without changing phase spectrum?
Figure 3.15 shows the power spectrum of a \(30 \mathrm{~Hz}\) Ricker wavelet denoted with the center frequency, the bandwidth, and the root-mean-square frequency. The two dashed lines are
Discuss wavelet transform in terms of what, why, and how. What are the main benefits and limitations of the method?
Make a table to compare and contrast Fourier decomposition and wavelet decomposition.
Comment on the quality of the three filtering results shown in Figure 3.24. What are the signals and noises? What are the elements that high-quality signals should possess in such cases?Figure 3.24
Regularization of irregularly sampled data is a common need in geophysics. One may regularize data by first taking a forward Fourier transform of irregularly sampled data and then taking an inverse
Explain why a time series may lose its causality after a forward DFT plus an inverse DFT.
We may need to quantify the similarity between the original dataset and interpolated dataset. Explain how to quantify the similarity between digital data of two or higher dimensions. Please give your
Following Figure 4.6, make synthetic seismograms for a wedge model containing a low-velocity thin bed of decreasing thickness. Please demonstrate: (1) tuning; and (2) that the combined wavefield
Based on Figure 4.7, derive a relationship between the thickness of the thin layer in time domain and the spacing of the notches in the amplitude spectrum.Figure 4.7 G (a) Time (ms) Reflectivity 0 0
Make a table to compile the ranges of vertical resolution of various seismic imaging applications such as near-surface geophysics, petroleum exploration in onshore and offshore cases, crustal
Elaborate the reasons for preserving low-frequency components in seismic data acquisition and data processing.
Each geophone has its marked frequency. What is the position of the marked frequency on the geophone's amplitude spectrum? Is it the central frequency of the geophone? Search literature to find the
Explore the relationship between resolution and fidelity. Which one is easier to assess in the practice of seismic data processing? In practice, do the objectives of improving resolution and
A major objective of the work shown in Figures 4.14 and 4.15 is to probe the nature of the Moho discontinuity. Draw your own interpretation of the Moho based on these figures. What can you say about
In Figure 4.15, what kinds of signal can you identify from each imaging result? In your interpretation of each result, what may be missing and what may be misinterpreted? Is there anything extra to
For a seismic wave from a point source, its vertical resolution will be finer than its horizontal resolution. Does this mean that the resolution of reflection is finer than that of the direct wave of
Discuss the limitations of the checkerboard resolution test shown in Figure 4.17b. Will the test yield good results if the given dataset has good ray coverage but poor SNR? For such a dataset will
The two models shown in Figure 4.19 used different datasets to study the same area. If the two model results differ at a certain place, are these results wrong at that place? If the two models show
Search the literature to compile the \(Q\) values of common rocks into a table, including the physical conditions of the \(Q\) measurements or estimates.
Discuss factors that may cause error in the estimations of \(Q\) using the spectral ratio method.
A common notion states that \(Q\) is independent of frequency. In this case the spectral ratio will be linear, like the straight lines shown in the right panels of Figure 4.21. Discuss the validity
For an infinitesimal volume, informally show thatwhere φ is some (differentiable) property of the fluid. Hence informally deduce that D Dt Do (V) = pV : Dt (P1.1)
Show that the derivative of an integral is given byBy generalizing to three dimensions show that the material derivative of an integral of a fluid property is given bywhere the surface integral
(a) Suppose that a sealed, insulated container consists of two compartments, and that one of them is filled with an ideal gas and the other is a vacuum. The partition separating the compartments is
Why is there no diffusion term in the mass continuity equation? Suppose that a fluid contains a binary mixture of dry air and water vapour. Show that the change in mass of a parcel of air due to the
If it is momentum, not velocity, that responds when a force is applied (according to Newton’s second law), why is the momentum equation given by pDv/Dt -Vp and not D(pv)/Dt = -Vp. =
Using the observed value of molecular diffusion of heat in water, estimate how long it would take for a temperature anomaly to mix from the top of the ocean to the bottom, assuming that molecular
Show that viscosity will dissipate kinetic energy in a compressible fluid.
Show that it follows directly from the equation of state, P = RT/α, that the internal energy of an ideal gas is a function of temperature only.Solution: from (??) and p = RT/α, we haveBut,
Show that it follows directly from the equation of state P = RT/α, that for an ideal gas the heat capacity at constant volume, Cv, is, at most, a function of temperature.
(a) Carry through the derivation of the quasi-geostrophic system starting with the anelastic equations and obtain (5.65).(b) Carry through the derivation of the quasi-geostrophic system in pressure
In realistic calculations of the vertical propagation of Rossby waves one must take into account the vertical variation of density. Carry through the calculation leading to the Charney–Drazin
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