主动源海底地震仪横波模型的自动搜索与非唯一性分析*

主动源海底地震仪探测在海底结构的研究中发挥着重要作用, 其中转换横波数据模拟为研究海底构造和物质属性提供了精确依据。本文针对现行转换横波模拟技术存在的步骤繁琐、难以确保最优解和无法进行非唯一性分析等问题进行研究, 提出了基于模型解空间和目标函数的模拟技术, 形成了主动源转换横波数据模拟的新方法, 该方法可借助计算机程序实现结构模拟的自动化。在南海西北陆缘的西沙地块OBS2013-3测线上对该方法进行验证, 分别利用单台PPS震相和全体台站的PSS震相走时数据进行模拟试验。结果表明, 本文的方法能够提供对于最优模型的快速、准确搜索和非唯一性范围的估计。这一方法有助于提高主动源海底地震仪转换横波数据模拟的效率, 并为结果的可靠性和稳定性提供更好的保障。

Automatic search and non-uniqueness analysis of shear wave models from active Ocean Bottom Seismometer data

Active Ocean Bottom Seismometer (OBS) prospecting is taking the leading role in illuminating submarine structures, among which converted shear wave modeling provides precise constrains on seismic structures and lithology. Due to the tedious procedures involved, difficulties in reaching optimal solution and insufficiency in non-uniqueness analysis in the present modeling method, we propose a new modeling method based on model solution space and objective function. Automatic modeling of converted shear waves can be realized using this new method with the aid of computer programming. This method is tested for its utilities in a realistic wide-angle OBS seismic profile, OBS2013-3, traversing the Xisha block, the northwestern South China Sea continental margin. PPS phases from a single station and PSS phases from all stations are employed in the case to model V_p/V_s ratios in sediments and the crust, respectively, where V_p is compressional wave velocity and V_s is shear wave velocity. Capacities of the new method to provide quick and accurate search for optimal models and estimates for modeling non-uniqueness are demonstrated. The new method is expected to promote the efficiency of converted shear wave modeling using OBS data and lay solid foundation for reliability and stability of modeling results.