천부 퇴적구조 분석을 위한 chirp 반응 신호의 속성분석

Abstract

A subbottom layer is composed of different types of sediments or the exposed rock, etc. It represents the different physical properties, depending on facies. Its physical properties and geological characteristic may be useful in the interpretation of geophysical data. Chirp SBP has been widely used to study a subbottom layer classification based on acoustic characteristics analysis. Generally, Chirp SBP provide the seismic data of the envelope type without polarity and phase information. Therefore, Envelope signal is limited to expressing subbottom sediments that represent the various physical properties because it ignores polarity and phase information. In this study, we analyzed attribute results of chirp signal response for a shallow subbottom sedimentary structure. We generated a FM pulse according to the frequency bandwidth, the sampling interval, the window function and composed numerical model using P-wave velocity, density, attenuation coefficient, thickness of transitional layer and roughness standard deviation. We conducted Chirp SBP modeling and derived a chirp raw data. We conducted attributes analysis using a chirp signal response obtained after a matched filter process on the acquired chirp raw data. We confirmed the envelope signal of the corresponding layer and lower layer don’t appear for the coarse sediment, subbottom gas, transitional layer. But, when various attribute methods such as instantaneous frequency and bandwidth were applied to the chirp signal response, the corresponding layer and lower layer could be confirmed. In the field survey, it is considered that the subbottom sediment structure should be analyzed by comparing the results of applying attribute methods such as the instantaneous frequency and bandwidth to the chirp signal response in the area where the corresponding layer and lower layer of envelope signal don’t appear.