| Summary: | 博士 === 國立中正大學 === 地震研究所 === 105 === Seismic physical modeling (or physical modeling) is to make a scaled-down subsurface geological structure model in the laboratory and using the ultrasound to propagate through the model. According to the scale factor, ultrasonic transducers of appropriate frequency are selected, and the simulated seismic records are obtained by an ultrasonic system. This technique is used to study the seismic wave propagation and to test the correctness of the new seismic data processing method. Ultrasonic nondestructive testing (ultrasonic testing) is a non-invasive method, uses ultrasound to scan the object to detect any defect inside the object.
The development in seismic physical modeling technique is closely related to the development in ultrasonic testing technique. There are many similarities between them. This dissertation focuses on applying seismic physical modeling to two ultrasonic testing topics and two seismic wave propagation topics. In the first ultrasonic testing topic, I propose a simpler and cheaper ultrasonic array system incorporating the total focusing method (TFM). The resolution, signal-to-noise ratio (SNR) and array performance indicator (API) of this system are quantitatively evaluated. Its performance is compared with the sectorial scan and linear scan of a commercial phased array system. Study results show that both systems have similar resolution, however, based on performance indexes of the API and SNR, the TFM system is better than the phase array system.
The second ultrasonic testing topic is to apply the root-mean-square (RMS) velocity to synthetic aperture focusing technique (SAFT). When SAFT is applied to the object with a layered structure, since waves at the interface between different materials are refracted, the delay-and-sum in SAFT becomes quite complicated and time consuming. Using RMS velocity to compute approximated delays can effectively reduce the complexity of the algorithm and improve the imaging speed. Study results show this fast and simple algorithm without losing the resolution of the SAFT image.
For the seismic wave propagation topics, the first topic is to study the characteristics of the primary reflection and reverberation recorded by the multi-depth streamers. The study results show that the depth-arrival time relationships of the primary reflections and reverberations in the common-source vertical-array gather are linear but their depth-arrival time relationship slopes are different. The primary reflection slopes are the same for different common-source vertical-array offsets but the reverberation slopes increase with offsets.
The second topic of the seismic wave propagation is to study the traveltimes and conversion-point (CP) positions for P-SV wave propagation in a horizontal transversely isotropic (TI) medium. Using the non-hyperbolic moveout equations and Fermat's minimum-time principle to predict the traveltime results and comparing with physical modeling data show that Fermat's minimum-time principle is better than the non-hyperbolic moveout equations. However, the errors of the traveltimes predicted by the non-hyperbolic moveout equations are small. For the CP position, the difference of the CP position calculated by the Fermat's minimum-time principle and anisotropic CP equation is significant in the intermediate offsets. Physical modeling data shows that the Fermat's minimum-time principle is more accurate than the anisotropic CP equation.
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