Electrical Structure and Fault Features of Crust and Upper Mantle beneath the Western Margin of the Qinghai-Tibet Plateau:Evidence from the Magnetotelluric Survey along Zhada-Quanshui Lake Profile

The magnetotelluric （MT） survey along the Zhada （札达）-Quanshui （泉水） Lake profile on the western margin of the Qinghai （青海）-Tibet plateau shows that the study area is divided into three tectonic provinces by the Yalung Tsangpo and Bangong （班公）-Nujiang （怒江） sutures. From south to north these are the Himalayan terrane, Gangdise terrane, and Qiangtang （羌塘） terrane. For the study area, there are widespread high-conductivity layers in the mid and lower crust, the top layers of which fluctuate intensively. The high-conductivity layer within the Gangdise terrane is deeper than those within the Qiangtang terrane and the Himalaya terrane, and the deepest high-conductivity layer is to the south of the Bangong-Nujiang suture. The top surface of the high-conductivity layer in the south of the Bangong-Nujiang suture is about 20 km lower than that in the north of it. The high-conductivity layer within the Gangdise terrane dips toward north and there are two high-conductivity layers within the crust of the southern Qiangtang terrane. In the upper crust along the profile, there are groups of lateral electrical gradient zones or distortion zones of different scales and occurrence indicating the distribution of faults and sutures along the profile. According to the electrical structure, the structural characteristics and space distribution of the Yalung Tsangpo suture, Bangong.Nujiang suture, and the major faults of Longmucuo （龙木错） and Geerzangbu are inferred.

Fault Characteristics in Longmen Mountain Thrust Belt, Western Sichuan Foreland Basin, China

Through field geological survey, the authors found that abundant thrust faults developed in the Longmen （龙门） Mountain thrust belt. These faults can be divided into thrust faults and strike-slip faults according to their formation mechanisms and characteristics. Furthermore, these faults can be graded into primary fault, secondary fault, third-level fault, and fourth-level fault according to their scale and role in the tectonic evolution of Longmen Mountain thrust belt. Each thrustfault is such as composed of several secondary faults, Qingchuan （青川）-Maowen （茂汶） fault zone is composed of Qiaozhuang （乔庄） fault, Qingxi （青溪） fault, Maowen fault, Ganyanggou （赶羊沟） fault, etc.. The Longmen Mountain thrust belt experienced early Indosinian movement, Anxian （安县） movement, Yanshan （燕山） movement, and Himalayan movement, and the faults formed gradually from north to south.

Analytical Method of Fault Characteristic and Non-unit Protection for HVDC Transmission Lines

An analytical method of fault characteristic for the HVDC system based on frequency response characteristics of boundary elements is presented here.The computational formulas of transfer function and input impedance are deduced using the distributed parameter model of HVDC transmission line,and the amplitude-to-frequency-characteristics of the transfer function and input impedance are analyzed.Based on the amplitude-to-frequency difference between internal and external faults,a non-unit protection method for VSC-HVDC transmission line is presented.Using the current ratio of high-to-low-frequency,this protection method can distinguish internal from external fault.The presented algorithm only uses local-end current,has high operation speed,and is easy to implement.Simulations on a±200 kV VSC-HVDC system are conducted to demonstrate the validity and feasibility of the developed protection method.