Basic Characteristics of Active Tectonics of China

http://www.paper.edu.cn Vol. 46 No. 4 SCIENCE IN CHINA (Series D) April 2003 Basic characteristics of active tectonics of China DENG Qidong (邓起东), ZHANG Peizhen (张培震), RAN Yongkang (冉勇康), YANG Xiaoping (杨晓平), MIN Wei (闵伟) & CHU Quanzhi (楚全芝) Institute of Geology, China Seismological Bureau, Beijing 100029, China Correspondence should be addressed to Deng Qidong (email: [email protected]) Received November 14, 2002 Abstract During the last 20 years, studies on active tectonics in China have entered a new quantitative research stage and made a great progress. Summing up the quantitative results, a Map of Active Tectonics of China on the scale of 1︰4 million has been compiled. In the map all types of active tectonics and their kinematic parameters are reflected in possible detail, such as active faults, active folds, active basins, active blocks, volcanoes, and earthquakes. This paper summa- rizes the basic characteristics of active tectonics of China. The Himalaya Mountains and Taiwan Island are major plate boundaries where the slip rates are larger than 15 mm/a. Tectonic activity in the continental intraplate region is characterized by block motion. The crust and lithosphere in the region were dissected into blocks with different orders. Of them the Qinghai-Xizang (Tibet), Xin- jiang, and North China block regions exhibit the most recent tectonic activity. The kinematic characteristics of more than 200 active tectonic zones indicate that the intraplate tectonic activity represents a block motion at a limited low rate. Horizontal slip rate along the tectonic boundary belts between the blocks is generally less than 10 mm/a, and 10—15 mm/a in max imum, and hence it does not support the continental escape theory of high rate of slip. Keywords: active tectonics, fault block, fault block region, block motion, slip rate. Active tectonics is inferred to all the structures which have been active since the late Pleisto- cene, 100—120 ka B.P., are still active recently, and will be active in a certain time period in the future, such as active faults, active folds, active basins, active volcanoes, and the crustal-lithospheric blocks confined by them[1,2]. For the sake of earthquake disaster research and prevention, safety of engineering projects and urban facilities, and recent geodynamic research, active tectonics has been significantly studied since the second half of the last century. Especially during the last 20 years, the active tectonic studies in China entered a quantitative research stage and more than 2000 quantitative geometrical and kinematic data were obtained from more than 200 major active tectonic zones of the whole country[3— 15]. During the recent years, we have pre- liminarily assembled the quantitative data, compiled a Map of Active Tectonics of China on the scale of 1︰4 million, and finished the first draft of Outline of Active Tectonics of China. This paper firstly brings forth the recently compiled map and describes briefly the characteristics of active tectonics of China. 转载中国科技论文在线 http://www.paper.edu.cn No. 4 ACTIVE TECTONICS OF CHINA 357 1 The contents of the map of active tectonics of China (1︰4 million) The map is different from those compiled previously. It attempts to document all aspects of active structures in possible detail, such as active faults, active folds, active basins, active volcanoes, earthquakes, and active blocks (Plate Ⅰ). All late Quaternary (100—120 ka B.P. ) active faults shown in the map have sufficient geologic-geomorphic evidence and age dating. Their segmentation and slip rate are also shown in the map. The faults whose movements since 100— 120 ka B.P. are unknown or geologic-geomorphic evidence is insufficient are grouped into the faults activated since Quaternary. However, by more detailed work, some faults of this group may be identified as late Pleistocene active faults. Some of the active faults in the Qinghai-Xizang Pla- teau do not experience field investigation although their lineation from satellite image suggests late Pleistocene activity. These faults are shown as a special group in the map. Because this group of faults often cut the latest geomorphic surfaces, most of them should be considered to be active faults since the late Pleistocene. All structures in plain regions and sea areas are covered with Quaternary sediments and seawater, so they are grouped into buried structures. The latest activity for most of the buried structures is unknown, except few of them, so they are denoted as an indi- vidual group in the map. For the kinematic nature of the active faults, we use convenient conven- tional thrust, normal, and strike-slip faults to express their compressive, tensile, and shear charac- ters. The map also shows historical earthquake surface rupture zones and coseismic displacements. The paleoseismic surface rupture zones produced by paleoearthquakes are also reflected one by one in the map. Totally more than 800 active faults and more than 80 seismic rupture zones are given in the map. The map also shows about 400 slip rates along nearly 200 active faults and about 150 coseismic displacement parameters from more than 70 seismic surface rupture zones. The folds shown in the map are mostly the late Quaternary active folds from available data. But we studied only a part of them in detail. Conservatively, we show them as the Quaternary or late Quaternary active folds. 48 of the active fold zones are shown in the map. Horizontal short- ening rates or the uprising rates are obtained for some of the folds. These quantitative data are also given in the map. The map shows more than 300 basins, which started to develop since the Quaternary and late Pleistocene. Because of limited data, we can give the isopach of Quaternary deposits in basins but could not show the isopach of the upper Pleistocene and Holocene sediments. The Quaternary volcanic activity is shown in a general way in the map due to limited studies. The map does not distinguish late Quaternary or recent volcanic activities, but an exposition of some volcanic activities is given when exact data are available. In order to reduce the load on the map, only M ≥ 6 earthquakes (more than 1100 in total) re- corded in China from 780 B.C. are shown in the map. Two orders of blocks were delineated, but only the code numbers of first-order blocks are shown in the map. The patterns of I and II order active block delineations are shown in fig. 1. 中国科技论文在线 http://www.paper.edu.cn 358 SCIENCE IN CHINA (Series D) Vol. 46 2 Active tectonic regionalization of China China is located at the southeastern corner of Eurasian Plate and is bounded by the Indian, the Pacific and the Philippine Sea plates. It represents a region with strong late Quaternary and recent tectonic activities. The late Quaternary and recent plate boundaries run through the Hima- layas and Taiwan Island, other regions of China are the plate interior. The plate boundaries are the most important active tectonic belts which are commonly recent active orogenic belts, strongly active seismic zones and volcanic zones. The plate interior is not really rigid. Particularly, the relative motion of intraplate blocks exists within continental interior. The differential motions form different active blocks and active tectonic zones. Zhang Wenyou had firstly suggested fault block tectonics as a geotectonic theory[16]. Since then many scientists pointed out that block motion is the main characteristics of neotectonic and recent tectonic movements[17— 21]. Deng Qidong and others had used active blocks of different orders, such as block region and block, in analysis of regional characteristics of active tectonics of China[17,20]. Ma Xingyuan and Ding Guoyu had suggested concepts of active subplates and tectonic blocks[18,19]. Zhang Peizhen et al. suggested recognition of active crustal blocks[21]. The es- sence of these suggestions is roughly consistent, as they considered that the continental plate interior is characterized by block motion, and the fault block movement is the most essential mode of tectonic activity in the plate interior. Active blocks are the geological units dissected and confined by the late Quaternary active tectonic belts, including active faults, active basins, and active folds. The tectonic activity of the same block is usually of relative unity and relatively stable in block interior. Strong activity occurs along block margins. Active blocks are of different orders. The large-scale block region is often an active structure of lithospheric or crustal scale. The first-order block I is often referred to as the fault block region, the second-order block II is the fault block, and the third-order block III is the block[1,2,17]. Their boundaries may be complex active tectonic zones, so they may be of certain width[21]. For example, the northern boundary (ANB) of Qing- hai-Xizang fault block region consists of the Altun fault zone, Hexi Corridor basin zone, and the Haiyuan fault zone. Its width is 50 to 100km. The eastern boundary (AEB) of the Qinghai-Xizang fault block region extends from Lanzhou area, passing through the Minshan and Longmenshan area, southward to Kunming area. Its width is as wide as 100 to 200 km. Boundaries(D1B) ar- round the Ordos block are 4 normal fault and graben zones, and their width is also several ten kilometers. With exception of Himalayas (PB1) and Taiwan (PB2) tectonic belts along the recent active plate boundaries, the continental plate interior of China can be divided into 6 active fault block regions, namely the Qinghai-Xizang (A), the Xinjiang (B), the Northeast China (C), the North China (D), the South China (E), and the South China Sea (F) active fault block regions.

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