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 What is refraction seismology? The study of head waves using primarily first arrivals. What must be the conditions for a head wave to be generated? The velocity below an interface must be higher than above it. What happens when a velocity in a lower bed is less than the overlying bed? The result is referred to as a blind zone. What is snell's law? sinθc=V1/V2 how do you calculate h in a single interface? h=(1/2)V1t1/cosθc how do you calculate critical distance in a single interface? x'=2htanθc=2h[(V2/V1)^2-1]^(1/2) What is the typical velocity ranges for different lithologies? What is the effect of density on velocity of diagrams? p=aV^(1/4) a is .31 in m/s and .23 ft/s Rocks vary in density due to their porosity. They don't really vary in range too much with the exception of halite. What are common densities for different sedimentary rocks? What are common velocity values for different rock types? What are the effects of age, frequency and temperature? Velocity varies slightly with temperature, dispersion has little effect which is the change of velocity due to frequency, and age has little effect because of deformation due to different processes. What is the effect of interstitial fluid within a rock? Replacement of water by oil and gas changes the bulk density and elastic constants and therefore changes the seismic p-wave velocities vary greatly but sense it does not effect the shear wave velocity therefor s-wave value do not vary greatly. Using the two ratios one can find oil and gas within pores. What are surface waves and what are there properties? Surface waves are known as rayleigh waves or ground roll. The velocities range from 100 to 1000 m/s. The frequencies are lower and energy concentration is below 10 hz. Due to low velocity different geophones are affected at different times and are seen because they override strong reflections. What is resolution, what does it refer to and what are the different types of resolution? Resolution refers to the minimum separation between two features that two features can be distinguished. There is vertical resolution and horizontal resolution? What is vertical resolution? How far apart in space or time two interfaces must be to show as separate reflectors. What is horizontal resolution? How far apart two features involving a single interface must be separated to show separate features. What does the ability to distinguish features rely on? signal/noise ratio Whats the problem involving resolution in the real world? if seismic wavelets were extremely sharp, resolution would not be a problem, but real seismic wavelets involve a limited range of frequencies and hence have appreciable breadth. What is the ratio of deeper reflection lag relative to the more shallower. 2deltaz/gamma What is the rayleigh criterion and what is the equation? Resolution criteria that helps us see rayleigh waves. 2/3vu where vu is the upper frequency limit of a boxcar. What is tuning? When embedded in a medium of different properties is 1/4 wavelength in thickness the reflections interfere constructively causing a increase in amplitude. What is a thin bed? A thin bed is defined as a situation where the aggregate thickness of bed under consideration is less than gamma/4. When do you get a tuning amplitude maximum? V3=V1 not equal to V2 What is the horizontal resolution and the fresnel zone? The fresnel zone is often taken as limiting horizontal resolution on unmigrated seismic data. Horizontal resolution depends on signal/noise ratio, trace spacing, and three dimensional effects. What is migration in terms of seismic data? The collapse of fresnel zones. Ordinary migration collapses fresnel zones in the direction of the migration. What are attenuation mechanisms? Divergence cuasing time-dependent amplitude changes. Absortion is the wave energy being converted to heat. Partioning. Seismic amplitude decreases exponentially with time. What is one of the most important aspect of controlling data costs in reflection field methods? Avoiding delays due to some phases of operations having to wait on others to finish. What is the common methods for reflection field methods? common midpoint method. How are marine surveys different from land? Marine surveys acquire data fast and at hourly cost. Common facts the determine marine operation are shallow waters and obstructions that control acquisition. What corrections are made in reflection data? Elevation and weathering variations are corrected to prevent distortion or obscuring reflection data. Who acquires reflection data? geophysical contractors usually in direct relation with oil and gas clients or on speculative basis How does acquisition occur in the united states? It occurs in turnkey method, where data is paid per data unit opposed to a time basis. How are crews organized in reflection seismic? Supervisor(responsible for whole crew and often assisted by office manager), party manager(responsible for field operations and safety), surveyors (resposible for locating proper points), permit men, rodmen(help with measurements), observers(field layout and data aquistion), jug hustlers(lay out cables), and shooters(detonators). How are marine seismic groups laid out? Manager, chief observers, instrument engineer, three junior observers, two navigation engineers, chief mechanics, and three or more mechanics. What are seismic crews responsible for? Its operations and the impacts on the environment. Part of the International Association of Geophysical Contractors. What are the operations involved in land surveys? The program, permitting, laying out the line, field procedures What are the different types of field layouts? split-dip spreads, gapped split, end-on split, in-line split, broadside t, broadside L, and cross spreads. What is the common processing method in field processing data reduction? Vertical stacking which is combining records that were obtained without any major movement of sources or detectors and without any differential static or normal movement corrections made. What are some data reduction corrections? Elevation and weathering corrections which are based upon the elevation in which the geophones are located and the corrections based on weathering of different beds at depth. What are common integral transforms used in data processing of seismic data? Fourier transform and the laplace transform. Define Fourier Transforms A integral transform that transforms a fuction into a related function of different variables. This is accomplished by multiplication of the original function with a kernel(a function of both sets of variables), then eliminate the first variables by taking the integral. What are the different types of fourier transforms? z-transforms and hilbert transforms What is the crucial factor regarding transforms? Theoretically no information is lost in transforming, so one can start with the waveform in the time domain, perform various operations, and then transform it back to the original with modifications equivalent to frequency-domain. What is fourier analysis and synthesis? Fourier analysis is transforming functions from time domain to frequency and synthesis is the inverse of this process. What is the function of fourier series? What is the Fourier Transform and inverse equation? What is the equation for a fourier transforms and the inverse? What is convolution? Convolution is the time-domain operation of replacing each element of an input function with an output function scaled according to the magnitude of the input element and then super imposing the outputs. What properties is convolution? It is commutative. What is the equation for convolution? What is the boxcar function? What is sampling? Sampling where we replace data in a analog-digital conversion. What is interoplating? It is used in many things such as time shifts. What is aliasing? Where one takes in account lost signal due to the sampling theorem What is correlation? The cross correlation function is a measurement of the similarity between two data sets. One data set is displaced by varying amounts relative to the other and corresponding values of the two sets are multiplied together and the products are summed to give the values of cross-correlation. How do we express cross correlation? What is normalized correlation? What is the method of least squared? How do you take a input, create a wave form, plot it f5 = input('input random noise frequency 4, e.g. 160: ') t = 0:sr:1; %This is the time sample space for the wave length ysignal= a1.*sin(2.*pi*f1*t); %single singal waveform Ysignal = fft(ysignal); Yrand = fft(yrand); Asignal = (Ysignal.*conj(Ysignal)); Anoise = (Yrand.*conj(Yrand)); SNR = ((Ysignal.*conj(Ysignal))/(Yrand.*conj(Yrand))) * ((Ysignal.*conj(Ysignal))/(Yrand.*conj(Yrand))) SNRdb = 20*log10(Asignal/Anoise) ampY = Y.*conj(Y); hertz = k*(1/(n*sr)); subplot (2,2,2) plot(hertz,ampY) What are the four fundamental waves? P-waves, S-wave, Rayleigh Waves, and Love waves What are the typical velocities associated with the different waves and their distinguishing properties? P-waves: 5.0-7.0 Propagation parallel to particle motion S-waves: 3.0-4.0 propagation is perpendicular to particle motion Rayleigh Waves: 2.0-4.5 propagation is retrograde to particle motion Love Waves:2.0-4.5 propagation is planar to particle motion Contrast deterministic with empirical approaches using gardner's relationship as an example? Deterministic and empirical approaches are two separate methods used to describe the value for any particular equation or situation. For instance on can take a trip to Dallas 180 miles away at 60 mph, and the empirical approach states D=vt and one should arrive in 3 hours. The determistic states there are factors such as traffic and construction that will change the actual value. Gardners equation is Kz^.23t yet the answer rarely meets this equation in actual measurements. What is young's modulus in terms of fluid incompressibility? sqrt("gamma+2mu"/ro) gamma + 2mu = K + 4/3mu = M What is the deterministic p-wave velocity equation as a fuction of density? sqrt((k+4/3mu)/(ro)) What is fermats principle? Fermats principle is the principle of least time that states a wave ray trace is going to take the least time to arrive. What is snells law for reflection? sin(theta1)/V1=sin(theta2)/V2 What is the reflection coefficient formula for normal incidence? R=(ro2v2-ro1v1)/(ro2v2+ro1v1) What is the equation for sperical divergence? I=I0(r0/r1)^-alpha(ro-r1) What is gardners equation which relates velocity to density in m/s? ro=aV^(1/4) a=.31 in m/s Why does the velocity of rocks increase with depth? Due to Porosity decrease because of an increase of density. Temp, age, and dispersion seem to have little effect on the velocity. What is the time-average equation? 1/v= porosity/vfinal = 1-porosity / Vn 2hcos(theta)/v = tavg what is the nyquist and what is its general formula? The nyquist is used to put a constraint on the analyzed waves. It is used to focus on frequencies that are important to the observations. The equation is 1/2*sr What is the fourier series equation? =A0 + Sigma an(cos(2*pi*f*t*n)) + bn(sin(2*pi*f*t*n))) f=frequency t=time n=sample rate what is the general equation for analyzing signal to noise? SNRdb= 20 log10 (sig/noise) SNR= [Asig/Anoise]^2 What is an example of an ornsby filter? Trap generator which uses high cut and high pass, and low cut and low pass to generate a trapezoid to convolve with the wave. What is the faust relationship equation? V=k(zT)^1/6 How do you get diagenetic porosity? sonic-density What do the zoeppritz equations give you? they give you amplitudes of reflected and transmitted waves with respect to incident wave amplitude. What are some important historical indicators of seismic in religion? The destruction of sodom and gomorrah in 1900 BC, the fall of jerico in 1400 BC, elijah at Mt. Horeb. Who is cheng heng? a mathmatician that first invented seismograph in 132 AD Who was choke? another chinese scientist that updated the seismoscope using columns of viscous liquid to help determine direction of tremors in 136 AD. Who was Baron Cauchy? french scientist in 1818 who first described wave propagation. who was SD Poisson? Scientist in 1812 that showed how P and S waves could be differentiated. Who was Robert Mallet? made artificial earthquakes using gun powder and tried to observe seismic waves using bowls of mercury. Who was Zoeppretz? Zoeppretz developed the reflection coefficient in 1907. Who was lord rayleigh? Found different theories of surface waves in 1911 along and Stoneley who developed more theories in 1924. Who was Reginald Fessend? Was first to concieve of using relfected waves in geology, motivated by the sinking of the titanic in 1912. Who was ludger mintrop? a german mine surveyor, who devised a method for detecting salt domes in 1914 using a seismograph. When was the first commercial discovery using seismic? 1924 Who was John Karcher? discovered seismic reflection in the means of finding big bertha for the United States government.