Earthquake Research in China Volume 27，Number 3，2013 A Brief Introduction to the Seismotectonic Map of Xinjiang and Its Neighborhood1 Shen Jun1，2) ，Bai Meixiang2) ，and Shi Guanglin2) 1) Institute of Disaster Prevention，Sanhe 065201，Hebei，China 2) Earthquake Administration of Xinjiang Uygur Autonomous Region，Urumqi 830011，China This paper briefly introduces the Seismotectonic Map of Xinjiang and its neighborhood in the scale of 1 ∶ 2500000． The map is amended，supplemented and expanded based of the newly compiled Seismotectonic Map of Xinjiang in scale 1∶ 1000000． The base map of this seismotectonic map is the geologic map of western China and its neighborhood compiled by Li Tingdong． The abundant new materials from related research，referential literatures and the analyses on remote sensing data were used in the compiling work． A database and relevant documents are built for nearly 300 active faults and 150 active folds． The basic information of the major active faults，especially those near the border areas in this map are introduced in this paper． Key words: Xinjiang and its neighborhood; Seismotectonic Map; Active fault In accordance with requirements of the special subject of the 973 Program “Characteristics of the Western Boundary of the Central Asia Big Triangle Seismotectonic Region and Strong Earthquakes ”， and the State special project for international cooperation on science and technology“the seismological，geological and geophysical conditions of large earthquake with M ＞ 8 in Central Asia”，on the basis of the seismotectonic map of Xinjiang ( Wu Chuanyong et al． ， 2009) in scale 1 ∶ 1000000 compiled by Institute of Natural Disaster Prevention of Xinjiang in 2007，and combined with relevant data from overseas，the 1 ∶ 2500000 seismotectonic map of Xinjiang and its surroundings is completed ( Fig． 1) ． The minimum distance from outside parts to the border is 200km in this map，and the scope of the map covers 32° ～ 51° north latitude，72° ～ 99° east longitude． Geological base map refers to the Geologic Map of Western China and Its Neighborhood (1∶ 2500000)( Li Tingdong et al． ， 2006) compiled by Li Tingdong et al． ，and on this basis further interpretation of satellite images is done． Meanwhile，abundant new materials from related research in this region are collected． By referring to referential literature，a database and documents for each seismic tectonics are set 1 Received: 2010-11-19; Revised: 2011-01-07． The Project was Funded by the State Special Project for International Cooperation on Science and Technology(2012DFR20440K02) and the 973 Program (2008CB4257) ． 412 Earthquake Research in China Fig. 1 The Seismotectonic Map of Xinjiang and Its Neighborhood up，including nearly 300 active faults and 150 active folds． Seismo-tectonics refers to geological structures where destructive earthquakes may occur， which are mainly major active faults that have been active since the Late Pleistocene，especially since the Holocene． The setismotectonic map manifests the active structures where destructive earthquakes once occurred or may take place in the future． Apart from active faults，the contents of the seismotectonic map also contain relevant information，such as strata，magma，geological structure，epicenter distribution of historical destructive earthquakes and surface rupture zone． Quaternary strata are subdivided down to series in this map． Pre-Quaternary strata are discriminated by Neogene，Paleogene，Mesozoic，Palaeozoic and Precambrian systems． Magmatic rocks only present acid，intermediate and mafic intrusive rocks． Classification of Quaternary volcanic rocks at different ages is done． A new-incorporation principle is adopted for classification 1 1 of strata． For example，N-Q p Northern India is classified as Q p Siwalik Group． In order to reflect active periods of active faults， Holocene active faults， Late Pleistocene active faults and Quaternary faults are distinguished． Meanwhile，the established fault natures are expressed: normal faults，reverse faults and strike-slip faults． Distribution of earthquakes with M ≥ 5. 0 Volume 27，Number 3 413 during 1600 ～ 2008 A． D． ，earthquake and paleoearthquake deformation belts are shown in this map，and active faults and active folds are signified as major seismotectonic types． Active faults in this seismotectonic map and in the active fault database are divided into four types according to different research degrees． Type Ⅰ: Those on which large scale geological mapping is done or there are special works，and special scientific research and earthquake risk assessment have been launched，thus with higher certainty on their natures，scales，active ages and activity rates． Type Ⅱ: Active faults，which are proven by field research，but with less information or research work，thus only part of the activity parameters are determined． Type Ⅲ: Active faults，which are recognized by satellite images，aerial photographs and geological maps， but only their distributions are determined，while other parameters such as active ages and fault natures are still unknown; and Type Ⅳ: Buried active faults or inferred active faults in basins determined by relevant data． There are nearly 300 active faults in this map． In the Altay-western Mongolia region，there are mainly right and left-lateral conjugated strike-slip faults，and in the Tianshan Mountains，the reverse faults or reverse strike-slip faults are developed． The Qinghai-Tibetan Plateau is dominated by thrust nappe tectonics and large-scale strike-slip faults in general，and normal faults and grabens have developed in some parts． Thrust nappe tectonics are mainly distributed in Pamir-western Kunlun Mountains and the piedmont of the Tianshan Mountains． Strike-slip faults are different between the two sides of the Pamir arc． On the west side，the faults are left-lateral， and on the east side，they are right-lateral． Active faults of the Altai Mountains and Kunlun Mountains are mainly left-lateral reverse strike-slip faults． Some of these seismotectonic belts referred to in this map，such as the Qinghai-Tibetan Plateau，the Tianshan Mountains，and the Altai Mountains-western Mongolia-Sayan etc． ，are across the borders，thus，their systematic introduction by predecessors is insufficient． In this paper，a brief introduction of major seismotectionics in those three regions including the Himalaya-Pamir-western Kunlun Mountains， Western Tianshan Mountains and the Altai Mountains-Sayan is given based on new data achieved in the process of mapping． 1 WESTERN HIMALAYA-PAMIR-WESTERN KUNLUN MOUNTAINS This region includes the western Himalayan syntaxis on west side of the Qinghai-Tibetan Plateau and the Pamir arc structure． The former is mainly the major boundary fault ( MBT) in the piedmont of the Himalayas and the main central thrust structure ( MCT) in the Himalayas，the latter consisting of three arcuate fault zones ( Fig． 2) ． The major boundary fault of the Himalayas，also known as the major boundary thrust belt ( MBT)，is located in the suture zone between the Indian Plate and Kohistan-Yalu Tsangpo River Plate，which is a thrust nappe structure． The fault plane is pretty smooth，thus the fault line in the plane presents an arcuate shape tipping to the north． The upper Proterozoic-Lower Cambrian system，an overthrust above the Cretaceous system，is composed of 2 ～ 3 overthrust faults，which is 600km long． Mesozoic hornblende granite and gneissic granite at Zhangga，Sangri county in Tibet thrust to the north on top of the early Pleistocene conglomerate ( Li Xianggen，2003 ) ． Earthquakes with 7. 0≤M≤8. 0 occurred repeatedly at the south foot of the Himalaya Mountains． An M8. 0 earthquake took place in Kangna on April 4，1905，forming a 300km-long surface rupture zone． The main central thrust belt ( MCT) of the Himalayas is a major north-dipping low- angle ductile thrust fault in the Himalayan orogenic belt，and along this fault，a higher Himalayan tectonic zone which is composed of middle and high-grade metamorphic rock series thrust on top of lesser-Himalayan tectonic zone composed of low-grade metamorphic rock series． According to research by Nikonov (1977)，paleo-earthquakes took place during 7000 ～ 9000 a B． P． and ≥ 414 Earthquake Research in China 800 a B． P． The west flank of the Pamir arc，situated in Tajikistan and Afghanistan，is divided into three regions，namely，Southern Pamir，Middle Pamir and Northern Pamir． The Southern Pamir fault ( SPF)，also known as the Lushang-Pushata fault，is a trapezoidal fault protruding to the north． NNE-trending faults on both sides of the fault are chiefly dislocated in the Meso-upper Archaeozoic，and an EW-trending fault on the north side is dislocated in the Mesozoic，which is 400km long． Nikonov ( 1977 ) discovered that altogether four paleoearthquake events had occurred on this fault before 4000，2300 and 1000 ～ 1500a B． P． and after 1000 ～ 1500a． The Middle Pamir Fault ( MPF) is also an arcuate fault protruding to the north． Paleozoic or Mesozoic thrusts up on top of Paleogene，which is 600km long． Based on 14 C chronological data，Nikonov (1977) discovered paleoearthquakes which occurred around 2000 ～ 2500a B． P． The North Pamir fault ( NPF)，also known as the Derweze-Karakul fault，is also an arcuate fault protruding to the north，which is the boundary between the north Pamir fold system and Tajik basin，and the Paleozoic，Mesozoic，Palaeogene and Miocene series thrust up on top of Pliocene series，which is 1440km long． The fault on the west side is a NNE-trending，SE-dipping left-lateral strike-slip reverse fault，with dip angle of 15° ～ 80°，which is thousands