Seismic imaging

Eruption forecasting Piton de la Foumaise Volcano Seismic imaging Seismic noise Volcano monitoring... 

Tapped-out oil and gas fields are full of drill holes that could leak the carbon dioxide. The stored gas might also seep into groundwater pools. But the North Sea project seems to be working well. Seismic images under the ocean floor show that a thick layer of clay capping the sandstone is sealing in the millions of tons of carbon dioxide injected. 

Bellefleur, G., de Kemp, E., Goutier, J., Allard, M. 2007. High-resolution 2D seismic imaging in the Noranda camp and implications for exploration. Exploration 2007, Toronto, Sept. 9 to 12, 2007. 

Improved magnetotelluric methods have detected deep conductors and shallow alteration zones in the search for deep unconformity-related deposits (Farqu-harson Craven 2008). Clay-rich, quartz-corroded quartz-arenite has relatively low resistivity, whereas quartz-rich silicified zones are characterized by high resistivity. Although expensive, 3D seismic has been used to image details of basement topology and more favourable areas for drilling. 

Raw data gathered from seismic surveys must be processed to compensate for and to remove a variety of distortions unwanted noises created by weathered near-surface rocks, normal time delays, and echoing by rebounding acoustic waves—to provide the clearest possible image of the strata below. Computers can restore these distortions in a fraction of the time that was formerly required to adjust the data painstakingly by hand. Advanced techniques not only permit presentations in three dimensions, but also in color, and to create contour maps and models of subterranean features. However, even with the use of sophisticated tools, there remains a large measure of uncertainty. History has shown repeatedly that a prospective area rejected by one petroleum firm has been accepted by another and proved to be successful. 

Bleistein Cohen Stockwell Mathematics of Multidimensional Seismic Imaging, Migration, and Inversion... 

Nevertheless, seismic tomography has been employed in efforts to image the roots of mantle plumes (VanDecar et al., 1995) and to determine whether or not they arise from deep-seated sources. An instructive example is the case of the Iceland hotspot, which tomographic images... 

Haslinger F., Thurber C., Mandernach M., and Okubo P. (2001) Tomographic image of P-velocity structure beneath Kilauea s east rift zone and South Flank seismic evidence for a deep magma body. Geophys. Res. Lett. 28, 375-378. 

Detrick R. S., Buhl P., Vera E., Mutter J., Orcutt J., Madsen J., and Brocher T. (1987) Multi-channel seismic imaging of a crustal magma chamber along the East Pacific Rise. Nature 326, 35-41. 

In the case of a layered model of the earth, one can use a simple technique of geometrical seismics, which is based on studying the geometry of rays of seismic wave propagation. In more complicated geological structures, comprehensive imaging and inversion methods must be used to analyze seismic data. In order to develop these methods, one should study carefully the physics of seismic waves. 

In the following chapters we will demonstrate that approximation (3.87) results in effective imaging schemes for different geophysical data interpretations, including gravity, electromagnetic and seismic migration. 

In the later sections of this book we will demonstrate that the same technique can be applied to electromagnetic and seismic wave field Inversion. In these areas of geophysics, migration serves as a useful practical tool for imaging geophysical data, because of the relative numerical simplicity and transparent physical interpretation of the results of electromagnetic and seismic migration. 

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