海底冷泉的地震海洋学初探

海底冷泉活动在全球大陆边缘海域广泛分布.与传统利用高频声学方法探测海底冷泉羽状流不同,本文利用常规多道反射地震(地震海洋学)方法对海底边界附近水体进行成像,结合盆地流体逸散结构特征,圈定活动冷泉流体活动发育位置,分析其地震反射特征和流体活动特征.研究表明,活动冷泉流体渗漏、逸散活动在多道反射地震剖面上一般呈羽状、扫帚状和不规则状几何形态,内部反射杂乱,反射振幅偏弱,但也有振幅增强的情况出现,这可能是由于含有较多泥质和细粒颗粒物悬浮.所造成的.冷泉活动一般与盆地内部泥底辟、流体管道、断层和裂隙、气烟囱、海底麻坑和泥火山等流体逸散结构相关,反映了地层内部流体自深部向浅部运移,在海底渗漏、逸散形成了活动冷泉.但分析结果仍需要进一步实地观测和理论模拟等相关研究确认.

A preliminary study of submarine cold seeps applying Seismic Oceanography techniques

Submarine cold seeps are widely distributed in the continental margin seas around the world. As opposed to the earlier detections of cold seep plumes using a high frequency acoustic method, a conventional multichannel seismic reflection (Seismic Oceanography) method is applied in this study to image the water column near the seafloor. Along with ananalys of the fluid escape structures, the development position, seismic reflection characteristics, and features of the cold seeps have been described and discussed here.#br#Seismic reflection from the water column is very weak; therefore, seismic sections above and below the seafloor are processed in two different sequences as follows:(1) geometry definition, direct wave attenuation and amplitude recovery, highpass filter, common midpoint sorting, constant velocity (seawater sound velocity) stack, and post-stack FK filter in some sections; and (2) data quality control, amplitude recovery, 6~100 Hz bandpass filter, multiple attenuation, deconvolution, velocity analysis, normal moveout correlation, common midpoint stack, post-stack noise attenuation, 4~70 Hz bandpass filter, and FX migration. The processed sections are then assembled together along the seafloor after the color scale has been carefully adjusted.#br#The analysis shows that active cold seeps primarily present plume, broom, or irregular geometric shapes in the water column, with weak and chaotic seismic reflections. Sometimes the seismic reflection amplitude is enhanced, likely because of the suspended mud or particles in the water column. Cold seepage activities are usually associated with the fluid escape structures of mud diapirs, pipes, faults, fissures, gas chimneys, seabed pockmarks, and mud volcanoes, reflecting fluid migration from deep to shallow strata, seep or escape at the seafloor, and formation of wide-spread cold seep activities. All the results are derived from a comprehensive interpretation of the seismic sections of the water columns and strata; however, field studies, theoretical simulations, and experiments are required for further confirmation.