琼东北马鞍岭-雷虎岭火山区深部岩浆系统大地电磁三维探测  

MAGNETOTELLURIC IMAGING OF MAGMA DISTRIBUTION BENEATH MA’ANLING AND LEIHULING VOLCANOES OF NORTHEASTERN HAINAN,CHINA

作　　者：孙翔宇[1] 詹艳[1] 赵国泽[1] 赵凌强 邓琰[1] 胡亚轩[2] 胡久常[3] 向小娟[3] SUN Xiang-yu;ZHAN Yan;ZHAO Guo-ze;ZHAO Ling-qiang;DENG Yan;HU Ya-xuan;HU Jiu-chang;XIANG Xiao-juan(State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;The Second Monitoring and Application Center,China Earthquake Administration,Xi′an 710043,China;Hainan Earthquake Agency,China Earthquake Administration,Haikou 570203,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [2]中国地震局第二监测中心,西安710043 [3]海南省地震局,海口570203

出　　处：《地震地质》2020年第3期640-653,共14页Seismology and Geology

基　　金：中国地震局地质研究所基本科研业务专项(IGCEA1608,IGCEA1706);国家自然科学基金(41372345)共同资助。

摘　　要：海南琼东北地区是中国新生代以来火山活动最强烈、持续时间最长的地区之一,历史上曾发生1605年琼山7.5级大地震。最新的水准、形变测量以及In SAR资料揭示在琼山7.5级大地震震中以南的地区存在1条SN向展布的沉陷区,沿该区小地震活动频发,即铺前湾—冯家湾小地震密集条带,有研究推测该小地震密集条带与深部岩浆系统的发育有关。为了进一步探测研究琼东北火山区火山岩浆系统的深部结构、地下介质属性、小地震活动和形变变化与火山深部岩浆系统分布的深层关系,2017年初在琼东北地区以雷虎岭-马鞍岭火山区为中心针对2条剖面开展了大地电磁探测,使用相位张量分解技术对其电性结构进行分析,并使用大地电磁三维反演技术获得了沿剖面的三维深部电性结构图像。探测结果进一步确定了琼东北火山区下方的介质属性和低阻体的赋存范围,并发现琼东北地区的电性结构存在明显的东西差异,电阻率值东高西低。此外,在琼东北地区地壳中存在2个低阻体,分别为海南岛西北部澄迈县区域(即雷虎岭和马鞍岭火山口西侧)下方中地壳碗状向W倾斜的低阻体和龙泉下方的低阻体;而在海南岛东北部的铺前湾—冯家湾小地震密集条带与地面沉陷区的深部并没有低阻介质赋存,排除了小地震是由于壳内火山岩浆活动引起的可能。The northeastern Hainan Province is one of the areas subjected to the strongest,most frequent and longest-lasting volcanic activities in China since the Cenozoic era.Under the influence of magma and fault activities,northeastern Hainan Island has experienced many moderate and strong earthquakes in history.The Qiongshan M7.5 earthquake occurred in this region in 1605.The deformation measurement and InSAR data found a subsidence area in the south of the Qiongshan M7.5 earthquake.Small earthquakes frequently occur in this area.It has been inferred by some studies on this subsidence area,namely the Puqianwan-Fengjiawan seismic belt,that the subsidence and frequent seismic activity are related to the development of deep magma systems.Magnetotelluric methods are very sensitive to subsurface fluid,different temperature conditions,and resistivity property of the medium in the molten state.With the development of magnetotelluric three-dimensional inversion technique,using dense array magnetotelluric data in three-dimensional inversion can image the medium resistivity occurrence state and position in the volcanic area.To study the deep structure of the magma system and its relationship with seismic activity,we conducted MT observations on two profiles that cross Leihuling and Ma’anling volcanoes.Phase tensor decomposition was used to analyze the electrical structure.This paper investigates the two MT profiles using three-dimensional electromagnetic imaging technology and obtains the electrical structure of the two profiles.The result reveals the media properties and high conductivity bodies’occurrence range beneath the volcanic area in the northeastern Hainan.There are obvious differences in the electrical structure of the northeastern Hainan.The resistivity values are high in the east and low in the west.In addition,there are two high conductivity bodies in the northeast of Hainan.The high conductivity body C1 inclines to the west and locates beneath the Chengmai County area in the northwestern Hainan Island(west of t

关 键 词：马鞍岭-雷虎岭火山区 大地电磁三维成像 电阻率结构 小地震密集条带 

分 类 号：P319[天文地球—固体地球物理学]