Practical Seismic Data Analysis

The discipline of subsurface seismic imaging, or mapping the subsurface using seismic waves, takes a remote sensing approach to probe the Earth's interior. It measures ground motion along the surface and in wellbores, then puts the recorded data through a series of data processing steps to produce seismic images of the Earth's interior in terms of variations in seismic velocity and density. The ground movements recorded by seismic sensors (such as geophones and seismometers onshore, or hydrophones and ocean bottom seismometers offshore) contain information on the media's response to the seismic wave energy that traverses them. Hence the first topic of this chapter is on seismic data and their acquisition, processing, and interpretation processes. Because nearly all modern seismic data are in digital form in order to be stored and analyzed in computers, we need to learn several important concepts about sampled time series such as sampling rate and aliasing; the latter is an artifact due to under-sampling. In exploration seismology, many useful and quantifiable properties of seismic data are called seismic attributes. Two of the most common seismic attributes are the amplitude and phase of seismic wiggles. They are introduced here together with relevant processing issues such as gain control, phase properties of wavelets, and the Hilbert transform, which enables many time-domain seismic attributes to be extracted. To process real seismic data, we also need to know the basic issues of data formats, the rules of storing seismic data in computers. To assure that the data processing works, we need to conduct many quality control checks. These two topics are discussed together because in practice some simple quality control measures need to be applied at the beginning stage of a processing project.