intro In September of 1988, the Stanford Exploration Project (SEP) conducted a passive seismic experiment. In a remote area of the Stanford campus, 4056 geophones were set out in a two-dimensional array. Ambient seismic energy was recorded over an eighteen hour period. Several factors motivated us to perform such an experiment. First, the problem of observing and characterizing ambient seismic noise is an interesting one, particularly in a seismically active area such as this, where the San Andreas fault is only a few kilometers away. A two-dimensional receiver array allows us to determine the arrival direction of incident waves. A large number of channels offers the possibility to detect events weaker than those seen by isolated recorders. Second, we hypothesized that whatever energy is present in the earth, we might be able to image structures in the near surface by observing how ambient energy interacts with these structures. Ambient energy could scatter or ...
Beam steering of passive seismic data passive
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passive In this chapter, I present a technique that tries to improve upon the partial stacking results shown in the introduction, and give clearer pictures of where events present in the passive data are coming from. This technique is beam steering; semblance is computed as a function of plane wave arrival direction. The geometry of the problem is illustrated in Figure beam . Beam steering is applied here to the quarry blasts, and to the nighttime records where partial stacks showed evidence of near vertically incident events. beam 3in . Beam steering parameters. Beam steering parameters. Incident plane waves are characterized by azimuth angle and either the dip angle or apparent velocity. Beam steering procedure Aki and Richards (1980) show that the arrival time of a plane wave moving with apparent surface velocity and arriving from a direction specified by an azimuthal angle at the --th station of a seismic array is given by: ...
Correlation and scattering analysis of passive seismic data correlation
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corr In this chapter, I use two methods to attempt to image subsurface layers from passive data. The first is a correlation-based approach. My advisor Jon Claerbout hypothesized that the crosscorrelation of two seismic noise data traces should resemble what we would record from a shot at one trace location and a receiver at the other. This idea is illustrated in Figure corr . For each source-receiver offset, there is a certain arrival direction for incident plane waves that will follow the source-receiver raypath. If that incident plane wave is present, then that segment of the traveltime hyperbola will be present. corr width=6in . Illustration of crosscorrelation scheme. Illustration of crosscorrelation scheme. For each source-receiver separation, there is one plane wave angle of incidence that will follow the source-receiver raypath shown. If this incident plane wave is present, then, correlating traces recorded at the two locations should reveal a positive correlation at the corresponding ...
A drill-bit source experiment drillbit
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drillbit Several authors have used the drill bit as a seismic source. In one type of study SEG.1988.DEV2.7 , an accelerometer is placed on the drill string, giving an estimate of the signature of the drill bit source. Crosscorrelating this estimate with the data recorded by one or more geophones enhances drill-bit energy in the recorded traces and gives results whose quality is comparable to VSP data. A second study katz-80 located the drill-bit signal using an eight channel array, with no accelerometer on the drill string, for the purpose of guiding the drill bit during drilling. In a third study, Kostov Kostov.sepphd.63 obtained an estimate of the drill-bit source signature from 2-D seismic data. A 1-D array containing up to 90 geophones was used, and the drill-bit signal was separated from other noise sources by virtue of its spatial coherency. While Kostov was able to detect direct arrivals from the drill bit, the strongest noise sources seen ...
3-D Interpolation Applied to Passive Data
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interp Interpolation Jon Claerbout Claerbout.sep.73.401 developed a 2-D interpolation scheme based on a mono-planewave assumption. To fill in a gap between two traces, a spatial prediction method is used to determine the dip, and the missing traces are constructed by combining the two known traces from either end of the gap, with time shifts and weights appropriate to the estimated dip and the various distances. In three dimensions, the location of a trace to be filled in by interpolation will not always lie on a line drawn between some pair of input traces. Thus while it was sufficient in 2-D interpolation to find the apparent dip between two traces, in 3-D interpolation we need to find the true dip. A pair of traces is insufficient for finding the true 3-D dip. At least three traces must be used, since three points are required to define a plane. ...
Xtpanel - an interactive panel builder xtpanel
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xtpanel This appendix describes a program called xtpanel that I wrote, along with Dave Nichols, to facilitate user interaction with existing non-interactive software. It is used extensively at SEP to allow readers to interact with documents such as this thesis, recreating the figures with the ability to try out new parameters or look at alternative pieces of data. I have included a description of xtpanel here because I feel it is a useful component in moving toward the goal of reproducible research that may be of interest to readers of this thesis. The xtpanel program manages a set of interactive objects on the screen. These can either be specified on the command line or in a script file. The appendix contains the manual page for xtpanel, which describes the command line and script file syntax in more detail. The following types of objects are supported: messages ...