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Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Wave
-Equation Propagation as a Body-Wave Filter
(1) Spectraseis, Zurich, Switzerland.
Passive seismic data collected with broadband seismometers is usually under-sampled. The sampling problem makes it impossible to utilize multi-dimensional filtering techniques to isolate various propagation modes. We propose a chain of wave-equation imaging and simple signal processing in the image domain as an effective method to mitigate deleterious noise effects and improve the ability to extract body waves containing subsurface information.
We begin with the principles of time-reverse modeling: data are reversed in time and inserted into the model domain as source functions. In this domain, data are better sampled, and after sufficient propagation steps wave-front healing will allow events within the data to coalesce into approximately correct coherent wave fronts. At each time-step in the elastic propagation, the wave field can be filtered to remove unwanted energy. Also, the propagation itself will confine high ray parameter, undesirable, energy to the shallow section of the model domain due to evanescence in a v(z) medium. We also capitalize on being able to exactly separate the P- and S-wave components using simple vector operators. To accumulate a measure of body-wave
energy content as a function of surface coordinate, we sum the depth axis of the image after windowing away the contaminated shallow section.