利用卫星长波长地球物理位场对东亚地区深部结构的研究

Long-wavelength geopotential fields study of East Asia from satellite data

有研究表明从中国北部经黄海、朝鲜半岛、日本海至日本本州岛存在一个大型断裂带,被称为"北纬40°断裂带".为了验证该断裂带的存在性,本文通过GRACE和CHAMP卫星的位场数据中的大尺度区域重力和磁力异常来研究该区的大型构造特征.区域性研究范围为24°N～56°N,90°E～150°E,详细研究范围为32°N～42°N,122°E～132°E.2008年Taylor等利用CHAMP卫星2005年6月至12月收集的轨道数据,从测量数据中消除地核和外部产生磁场效应,经化磁极之后得到磁异常图,从中来追踪构造特征,并根据地质和地球物理资料建立了数学模型来进行解释.本文在此基础上,增加了GRACE卫星2003年10月份测量的重力异常场数据.实测差分位场数据利用高斯勒让德求积法转换为垂向重力异常值,通过减去最新地球重力场模型(EGM96)的场值来去除波长超过1100km的长波长异常,所得的重力异常数据和磁场数据进行比较.为了能从中得到研究区的共同构造特征,建立一个球面棱柱模型进行正演模拟、并进行重、磁异常场的波数相关性分析.研究发现在重、磁异常中均发现一个呈负相关的纬向构造特征,东亚地区"北纬40°断裂带"横穿了整个朝鲜半岛.

Kutina et al. proposed the existence of a large fracture zone extending from northern China across the Yellow sea, Korean peninsula, East Sea （a.k.a., Sea of Japan） and on to Honshu Island, Japan, which they called the ‘Forty-North Fracture Zone’. We investigated this proposed large tectonic feature from making large-scale regional gravity and magnetic anomaly maps by using GRACE and CHAMP satellite potential field data. The regional study area extended from 24° to 56° north latitude and 90°E to 150°E and the detailed area from 32°N to 42°N and 122°E to 132°E. Recently, Taylor et al. constructed the magnetic anomaly maps directly from CHAMP track data collected between June and December, 2005 after removing the core-generated and external fields from the measurements and then reduced these data to the pole to seek any tectonic features. They also produced a mathematical model using available geologic and geophysical information for their interpretation. In this study, we augmented a gravity anomaly field map from the GRACE data measured during a month of October, 2003. The measured potential differences data were converted to vertical gravity anomaly values using Gauss-Legendre quadrature method, and long wavelengths over 1100 km of the anomalies were removed by subtracting the latest EGM96 field to compare with the magnetic data. A curious latitudinal structure was found in both gravity and magnetic anomaly fields that showed an inverse correlation. A forward modeling was performed from using a spherical prism model and the wavenumber correlation analysis between these two anomaly fields was made to delineate the common features over the study area, and these results were discussed in relation to the existence of the ‘Forty-North Fracture Zone’ in the East Asian region.