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961.
962.
MAGNETOTELLURIC IMAGING OF MAGMA DISTRIBUTION BENEATH MA'ANLING AND LEIHULING VOLCANOES OF NORTHEASTERN HAINAN,CHINA 下载免费PDF全文
SUN Xiang-yu ZHAN Yan ZHAO Guo-ze ZHAO Ling-qiang DENG Yan HU Ya-xuan HU Jiu-chang XIANG Xiao-juan 《地震地质》1979,42(3):640-653
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 the Leihuling-Ma'anling volcanoes). Its resistivity value is less than several Ωm. This low resistive body is 40km long in WE direction and 30km wide in SN direction. Its burial depth is about 2km near the HNL1 profile and 6km near the NHNL1 profile. Its bottom reaches the depth of about 25~30km, which may be close to or through the Moho surface depth of 25~26km in this area. It is speculated that the magma eruption of Leihuling-Ma'anling volcanoes did not migrate vertically from its deep part to the surface. The high conductivity body C2 locates beneath Longquan. The buried depth of C2 tends to be shallower from north to south, but there is no exposed surface in the study area, nor is it connected with the shallow low-resistivity layer. It is speculated that the C2 may be a magmatic sac trapped in the crust, but may have nothing to do with the eruption of Ma'anling-Leihuling volcanoes. The recent volcanic magma in this area comes from the lower crust and upper mantle of the ocean area to the west of Hainan Island. As magma enters the upper and middle crust, it continues to move shallowly and eastward. In this process, it should be blocked by the high resistance structure on the east side of the Changliu-Xiangou Fault and then erupt around this fault, thus forming numerous craters in this area. After the repeated eruption, deep magma channels gradually closed and volcanic activity weakened. The magma in the mid-upper crust cooled consolidated gradually, but the speed was uneven in different areas, resulting in the channels having closed down gradually in some places, and some are in the process of closing. Our results show an uneven rise and fall depth of the low resistivity body in the middle and lower crust. There is no high conductivity body in the deep part of the Puqianwan-Fengjiawan seismic belt and the subsidence area in the northeastern Hainan, which rules out the possibility that the small earthquakes are related to deep magma systems. 相似文献
963.
松潘-阿坝地区深部电性特征 总被引:3,自引:0,他引:3
针对青藏高原东部特殊的“三角形”区域——松潘-阿坝地区,通过两条测线的MT资料分析和反演,对其深部电性特征进行了揭示,发现松潘-阿坝区中深层构造较为稳定,层状特点明显,地下电性横向变化小,具有稳定地块的特点.这里存在壳内低阻层,厚度近10~20km;深部(岩石圈地幔内部)的电性结构也有两种类型:高阻异常区和具有幔内低阻层的次高阻异常区,全区岩石圈厚度在120km左右,其四周由深断裂与邻区接触.该区深部电性特征不同于龙门山隆起的电性结构,也不同于西秦岭构造带,后者具有高阻基底,岩石圈厚度或更薄或加厚. 相似文献
964.
965.
覆盖区活动断裂探测往往需要选择合理的物探方法以确定断裂位置,高密度电法具有数据采集效率高、探测精度高等优点,已在覆盖区活动断裂探测中得到广泛应用。本文利用高密度电法在长白山玄武岩覆盖区进行断裂探测,对实测数据进行反演,分析了NE向鸭绿江断裂带抚松段西支断裂在松江河镇北东侧第二松花江畔的展布形态,同时,利用钻探对断裂探测结果加以验证。视电阻率剖面表明完整基岩主要呈现出高阻值,断裂破碎带由于含水丰富则呈现为低视电阻率异常值。而断层内较为破碎,且富含水,故在视电阻率剖面上呈现明显低阻异常,这些结果能够与钻孔揭露地层实物资料较好对应。钻孔的断层样品14C测年结果显示,西支断裂在松江河镇兴隆林场为晚更新世活动断裂。 相似文献
966.
Response evaluation of interconnected electrical substation equipment using real‐time hybrid simulation on multiple shaking tables 下载免费PDF全文
In an attempt to quantify the conductor cable effect on substation electrical equipment, real‐time hybrid simulation (RTHS) is conducted on interconnected equipment using two shaking tables. For this purpose, the existing RTHS system with advanced control capabilities at the Pacific Earthquake Engineering Research Center structural laboratory is enhanced to accommodate the simultaneous use of two shaking tables. An experimental parametric study is conducted to investigate the conductor cable effect using this system with a two‐table RTHS setup. Post insulators of disconnect switches, important components of substations that are usually tested with conventional methods for evaluating their seismic performance, are utilized as experimental substructures for realistic representation of the electrical equipment. Various global and local response parameters, including accelerations, forces, displacements, and strains, are considered to evaluate the effect of the tested conductor cable configuration for a wide range of support structure configurations, which are modeled in the computer as analytical substructures. The experimental parametric study results indicate that the conductor cable has a significant effect on the response of the interconnected equipment over the whole range of investigated support structures and needs to be explicitly considered for seismic testing of electrical equipment. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
967.
968.
Han Depin 《地球科学与环境学报》1997,(3)
推导了水平钻孔中电法测量煤层厚度的边界单元法的方法原理,对起伏煤层厚度的各种情况进行了正演模拟计算,结果表明该方法可行。 相似文献
969.
970.