Single Horizontal Interface - any interface with a variation in acoustic impedance (velocity times density will produce a reflection

Travel - Time Equation - is a hyperbola rather than a straight line (depends on x^2 rather than x) so cannot use methods developed in refraction

Normal Move-Out (NMO) - is the amount of curvature in the x-t line. It is the actual travel time less the two-way vertical travel time. NMO decreases with velocity and depth to reflector. NMO increases with distance from the source.

Determining Depth and Velocity - x2-t2 Method - A plot of x^2 versus t^2 does plot on a straight line. The slope of the line is equal to the inverse of velocity squared. Depth to the interface can be determined from the velocity times the intercept time divided by two.

Dix Equation - introduces the concept of Vrms or weighted average velocity. An average velocity of a seismic wave traveling through more than one layer is a weighted average of the velocities of the layers. Thicker layers and slow layers have more of an influence. x^2-t^2 plots give Vrms for each interface. Interval velocities are determined by subtracting Vrms velocities. Once interval velocity is know, the thickness of each layer can be determined from the one way vertical travel time (the difference in intercept times divided by 2). Dix Equation assumes that ray paths are dominantly vertical thus maximum source-receiver distance should be equal to or less than the depth to the deepest interface.

xmin, and tmin - For a horizontal interface, the shortest travel time is t0 (the two way vertical travel time) at the seismic source (x0). The shortest travel time(tmin) is offset in the updip direction (xmin) for a dipping layer. The dip can be determined from the ratio of tmin and t0.

Averaging x2-t2 method velocities - The averages of arrival times from the updip and downdip geophones plot as a straight line on x^2-t^2 plot. The slope of the straight line is is equal to the inverse of velocity squared. Orthogonal distance to the interface can be determined from the velocity times the intercept time divided by two

Dip Move-Out (DMO) - The dip of a layer can also be determined using the difference in Normal move-out from two geophones on either side of the source. The dip angle is equal to arcsin of the velocity times the DMO divided by the distance between the geophones.

Optimum Window - offset and spacing between geophones such that all reflections of interest can be seen without interference from each other or slow moving direct or surface waves.

Multiples - occur when seismic energy bounces off an interface and returns to surface more than once. Short path multiples are usually not a problem because the arrival at almost the same time as the primary. Long path multiples also are usually not a problem because they lose so much additional energy (partitioning, absorption, and spherical spreading). When long path multiples have enough amplitude to be seen they can be distinguished from primary arrivals because they appear at approximately twice the time as a primary and have less normal moveout..

Diffractions - Diffractions also appear as noise on reflection records. They have larger NMO than true reflections and are symmetrical about the fault or other point of diffraction. Note that diffractions plot later in time than the true reflection and thus would be expected to have less NMO.

Resolution - both vertical and horizontal resolution are dependent on frequency of the seismic energy.

Split Spread - Geophones on either side of a shot. This simple procedure is used to determine dip and the optimum window.

Common Offset - Only one geophone is active for each shot and the offset between shot and geophone is the same. No normal Move-Out, common offset gives a true representation of subsurface geometry without additional processing. However, the geometry is slightly distorted. In common offset data, all arrivals (direct, refracted and reflected) plot as straight lines which complicates interpretation.

Common Depth Point (CDP) - Each point on the interface is sampled more than once with a different offset between source and geophone. This allows for recognition and elimination of NMO. Once NMO has been removed the traces can be gathered to enhance signal and elimination noise. Much more complicated acquisition and processing. This acquisition technique also provides Amplitude Versus Offset (AVO) information.

Static Corrections - raw data is corrected for variations in thickness and/or velocity of the uppermost layer. These corrections are made assuming vertical paths through the uppermost layer.

Correcting for Normal Move-Out - A variety of computer based techniques are used to identify and then remove NMO. Essentially, a computer tries a large number of guesses for the velocity and intercept time to determine which one best fits the observed NMO.

Migration - methods used to reposition reflections from steeply dipping layers or structures into their true positions.

Time and Depth sections - For structure/stratigraphic purposes, seismic sections are produced such that reflections are shown in their correct spatial orientation (travel time vertical and increasing downward). Where velocities are known, travel time can be converted into depths.