Table of Content

30 December 2012, Volume 34 Issue 4

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Seismicity and earthquake mechanisms

A NEW UPSURGE IN GLOBAL SEISMICITY

DENG Qi-dong

2012, (4):  545-550.  DOI: 10.3969/j.issn.0253-4967.2012.04.001

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This paper studies the temporal and spatial distribution of global great earthquakes(M_W≥8.0)since 1900.We compare two periods of upsurges of great earthquakes occurring in the middle of last century and beginning of this century. The former took place between 1950 and 1965 when 13 great earthquakes(M_W≥8.0)occurred,including 3 events with moment magnitude greater than 9.0.The maximum magnitude in this period reached 9.6.The later period starts since the beginning of this century. In less than 12 years,15 great earthquakes have attacked the world with the largest magnitude of M_W 9.1.On the basis of comparison of these two upsurges of global earthquake activities,we postulate that the ongoing high level of earthquake activity may continue for another 5 years or so. Numerous great earthquakes(M_W≥8.0)and many large earthquakes(M_W 6～7)will occur globally in this 5 years. In addition,this paper also discusses the relationships between earthquake activities along the Sumatra segment of the Indian-Australia plate boundary and that in the Bayankala block in the middle of the Tibetan plateau as well as the plateau itself. The results indicate that Tibetan plateau,especially its middle and southern parts are the likely places for future earthquakes of magnitude over 7.

THE CHARACTERISTICS OF TIME SERIES OF STRONG EARTHQUAKES IN THE WORLD AND CHINA'S MAINLAND

SHAO Zhi-gang, MA Zong-jin, CAI Jin-an, REN Jin-wei, CHEN Hui-zhong, ZHANG Lang-ping

2012, (4):  551-565.  DOI: 10.3969/j.issn.0253-4967.2012.04.002

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Based on strong earthquake catalogue,this paper discussed the activity characteristics of time series of strong earthquakes in the world,western China mainland and its peripheral "big triangle" seismic region,as well as Chinese continent. According to the analysis of the periodic features of global seismicity of M≥8 strong events,we find that the global seismicity alternates between phases of decade scale of relatively strong and weak activities,and there are significant differences existing in the activity states of global great earthquakes before and after the 1960s. In addition,statistical analysis with Fisher method has revealed that the "big triangular seismic region" has experienced the process of M8 earthquake activity with a duration over a hundred years since 1800(quiescence stage-the transition stage before active-concentrated active stage-adjustment stage after concentrated activity-quiescence stage); further analysis shows the seismicity of the world and the "big triangular seismic region" possibly has a period of a hundred-year scale,and has a certain degree of the quasi-synchronization. The shallow earthquake activity of M_S≥7.0 in China continent is obviously controlled by the seismicity in the big triangular seismic region and by the larger spatial scaled global seismicity. In terms of the time series of these earthquakes,the seismicity shows a decadal or century-scale activity patterns. In the former 50 years of the last century,in the relatively active state of global M8.5 great earthquakes,the seismicity in the western part of China mainland and its adjacent "large triangular seismic region" was also active synchronously; however,the quasi-periodic feature of seismicity alternating between quiet and active periods of M≥7 earthquakes in China continent was not obvious. While in the latter 50 years of the last century,in the background of M8.5 seismic quiescence in global and M7 seismic quiescence in the big triangular seismic region,the characteristics of seismic quiescence and active alternating of M≥7 earthquakes in the mainland of China was obvious,the seismicity showed a better quasi-periodic feature of activity and quiescence alternatively in decade scale. Consequently,not only the temporal sequence of strong earthquakes present an activity feature of a ten-year period and nearly a century period in different time levels,but also the regional strong seismic activity in the China continent obviously is controlled by the strong seismicity of "big triangular seismic region",even by the global strong seismicity in larger spatial scale. This paper mainly uses the statistical methods to describe the characteristics of time series of strong earthquake activity in different regions,and analysis is focused on the temporal and spatial distribution of seismic activity,while,to gain an insight into the tectonic origin and geodynamic implication for these phenomena requires further in-depth study.

SEISMOGENIC STRUCTURE AND RUPTURE MECHANISM OF THE M_S 8.0 WENCHUAN EARTHQUAKE

ZHANG Pei-zhen, ZHU Shou-biao, ZHANG Zhu-qi, WANG Qing-liang

2012, (4):  566-575.  DOI: 10.3969/j.issn.0253-4967.2012.04.003

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A composite multiple seismogenic source model is presented to interpret the preparation and generation of the Wenchuan earthquake,based on the results of investigations on the coseismic surface rupture,aftershock distribution and crustal deformation of the Wenchuan earthquake and the studies on the tectonic deformation conducted before the earthquake. It is assumed that the differences in the structure and property of the lithosphere beneath the west Sichuan plateau,Longmen Shan and Sichuan Basin led to the differences in deformation behavior and stress accumulation between them,and their joint actions resulted in the high accumulation and abrupt release of stress in the Longmen Shan Fault zone,witch eventually generated the Wenchuan mega-earthquake. As a high-friction high-angle listric thrust,the Longmen Shan Fault zone is not liable to deformation(but high stress accumulation)to form "slip deficit zones" before earthquake,or to micro-rupturing to form "seismic gaps" before earthquake. When stress accumulated exceeded the strength of the Longmen Shan Fault zone,burst occurred,creating the huge earthquake. Coseismic deformation and energy release were concentrated mainly in the Longmen Shan Fault zone to offset the pre-earthquake "slip deficit" and "seismic gap".The high-angle listric thrust structure of the seismogenic fault of the Wenchuan earthquake played an important role in controlling the preparation and generation of the Wenchuan earthquake. The decrease of normal stress resulting from increased displacement rate on the fault plane was the major contributor to the rupture of the high-angle listric thrust fault.

A NEW ELECTROMAGNETIC TECHNIQUE FOR EARTHQUAKE MONITORING-CSELF AND THE FIRST OBSERVATIONAL NETWORK

ZHAO Guo-ze, WANG Li-feng, ZHAN Yan, TANG Ji, XIAO Qi-bin, CHEN Xiao-bin, WANG Ji-jun, CAI Jun-tao, WANG Xiao, YANG Jing

2012, (4):  576-585.  DOI: 10.3969/j.issn.0253-4967.2012.04.004

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Control Source Extremely Low Frequency(CSELF)electromagnetic technique is a new technique used in the earthquake monitoring. The signals transmitted by powerful generator propagate in "conductance" and cover the regions distant to thousands of kilometers. The signal frequency band contains the ELF and adjacent frequencies which were not used in earthquake monitoring by previous electric and magnetic observations and were understood for their sensitivity to the electromagnetic anomaly relative to events. The CSELF can monitor both the space electromagnetic fields and the sub-surface resistivity structures with their variations,which is favorable for four-dimensional monitoring. In the past experiments,the electromagnetic anomalies before shocks were measured twice. The experimental observation using observatory network-like stations shown that the data of artificial signals are quite stable and have high S/N ratio. A new observatory network with a certain scale is building for earthquake monitoring.

Active tectonics and seismotectonics

TECTONIC IMPLICATION OF CRUST AND UPPERMOST MANTLE P_n VELOCITY STRUCTURE OF EASTERN ASIA

ZHANG Guo-min, WANG Su-yun, WANG Hui

2012, (4):  586-596.  DOI: 10.3969/j.issn.0253-4967.2012.04.005

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In the paper,we use 296334 P_n rays from 27777 earthquakes recorded by 1354 seismic stations in the eastern Asia region,an area spanning from 15癗-60癗 and 60癊-145癊,to invert the P_n velocity structure of uppermost mantle and its lateral variations. We also discuss the tectonic implication of the lateral variation based on the P_n velocity structure. Inversion results show that the mean velocity of P_n is 8.03km/s in the eastern Asia region. The lateral variation spans from -0.42km/s to 0.41km/s. Two different tectonic regions can be identified according to distributions of P_n velocity and its lateral variation. In the region from the boundary of the Pacific plate to the east of 108癊,i.e.the eastern China,P_n velocity is relatively low. In the region located at west of 108癊,P_n velocity is high. The different distribution of P_n velocity is consistent to the regional geodynamic background. The dominant geodynamic effect is subduction of the Pacific plate in the eastern China and collision of the Indian Ocean plate in the western China. At the same time,P_n velocity is relatively low in active tectonic regions and high in the stable tectonic regions. The P_n velocity also shows negative correlation to the regional seismicity. The higher of the seismicity,the lower of the P_n velocity,and vice versa. The negative correlation indicates the relationship of lateral variation of P_n velocity and tectonic deformation with seismicity level. The region with low P_n velocity usually is a region with high tectonic deformation and intensive seismicity.

STRESS CHANGE OF SHANXI TECTONIC BELT RELATED TO THE 2001 M_S 8.1 KUNLUN EARTHQUAKE

WANG Kai-ying, MA Jin, DIAO Gui-ling, Yu. Rebetsky, WANG Xiao-shan, YAN Xiao-bin

2012, (4):  597-605.  DOI: 10.3969/j.issn.0253-4967.2012.04.006

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Shanxi tectonic belt is a historically earthquake-abundant area and the focal distribution of the majority of the strong earthquakes is controlled by the local north-south oriented structures on the tectonic belt. Using the cataclastic analysis method(CAM),we performed an inversion analysis on the stress state of focal mechanism solutions of earthquakes which happened on Shanxi tectonic belt from 1967 to 2010.Results show that spatial distributions of the maximum principal compressive stress axis of Shanxi tectonic belt have changed over time,with two different predominant directions,NW and NE,in different periods of time. When the maximum principal compressive stress axis is oriented in NE direction,the stress state is registered as horizontally shearing and horizontally extension on the north-south and southeast oriented local segments in turn. When the maximum principal compressive stress axis is oriented in NW direction,the stress state of north-south and northeast tectonic segments is primarily registered as horizontally shearing.

FUYUN FAULT: LONG-TERM FAULTING BEHAVIOR UNDER LOW CRUSTAL STRAIN RATE

XU Xi-wei, SUN Xin-zhe, TAN Xi-bin, LI Kang, YU Gui-hua, Marie Etchebes, Yann Klinger, Paul Tapponnier, J. Van Der Woerd

2012, (4):  606-617.  DOI: 10.3969/j.issn.0253-4967.2012.04.007

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The Fuyun Fault is a typical right-lateral strike-slip fault in Altay region where the crustal strain rate is very low. Field observations and restoration of horizontal offsets from the 3D LiDAR data obtained from 3 sites along the Funyun Fault further confirm that the average coseismic right-lateral slip of the 1931 Fuyun earthquake is (6.3±1.2)m,and the slip distribution is unusually flat over its entire length of the Fuyun Fault. The maximum slip is only (6.7±0.5)m under the Karaxingar Range,near to the central part of the surface rupture zone other than 10m to 14m as reported before. Co-located larger offsets,interpreted as cumulative offsets,allow us to define at least 4 more events in addition to the most recent. The cumulative slip distribution of each event seems to follow a similar flat pattern,supporting a characteristic earthquake model interpretation for the 5 last events. Several successive offset landforms are dated at 2 sites by cosmogenic dating method (¹⁰Be)to constrain the long-term right-lateral slip rate of (0.76±0.24)mm/a. An average characteristic slip of 6.3m,a maximum slip of ～6.7m and a slip rate of (0.76±0.24)mm/a yield a recurrence interval of (9 700±3 300)a. Then,great earthquakes on the Fuyun Fault,a right-lateral strike-slip fault follow a characteristic slip behavior with a low long-term slip rate and long recurrence interval,which is a faulting response to the far-field strain resulting from the collision between the Indian and Eurasian plates.

FEATURES OF SEISMOGENIC STRUCTURES OF GREAT EARTHQUAKES IN THE BOHAI BAY BASIN AREA,NORTH CHINA

XU Jie, ZHOU Ben-gang, JI Feng-ju, GAO Zhan-wu, CHEN Guo-guang, SUN Jian-bao

2012, (4):  618-636.  DOI: 10.3969/j.issn.0253-4967.2012.04.008

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Seismogenic structure is the core of seismo-geology. The Bohai Bay Basin area in North China is highly active in terms of seismicity,where six earthquakes of M≥7.0 have occurred. After the 1966 M7.2 Xingtai event,some researchers suggested that the seismogenic structure of this earthquake was associated with the Cenozoic normal faults and the fault-depression basins the faults controls. In 1986,however,some authors proposed that this quake should be attributed to a high-angle fault beneath the basin.
The purpose of this paper is to give a systematic elucidation on seismogenetic structures in the Bohai Bay Basin area,North China,which are built on the geological studies in combination with exploration to deep structures in the seismic areas. The paper analyzes and compares the geometric features and structural attributes as well as their dynamic conditions of the Bohai Bay Basin in two evolution stages,i.e.the Eogene when the fault-depression formed and mid Miocene(12～10Ma)when the neotectonics developed. It emphasizes the distinct dynamic conditions in these two stages that formed different structural systems. In the stage of fault-depression,this area was subject to extension in NW-SE direction,which produced many gentle normal faults in the shallow subsurface that characterized the fault-bounded depression basins. While in the neotectonic stage,a set of conjugate fault system consisting of NE-trending right-lateral slip-strike faults and NW-directed left-lateral strike-slip faults were generated by the NEE to approximately EW-orientated horizontal compressional stresses. The structure of the first stage was pre-existing,while that of the second stage has both inheritance and variance to the first stage,i.e.superposition and reform,which accounts for the gestation and occurrence of the present-day major earthquakes in this area.

CHARACTERISTICS OF ACTIVE FAULTS BETWEEN THE NORTH SEGMENT OF THE NORTH-SOUTH SEISMIC BELT AND THE CENTRAL MONGOLIA

HUANG Xiong-nan, ZHANG Jia-sheng, LI Tian-bin, LIU Feng, FENG Jun

2012, (4):  637-658.  DOI: 10.3969/j.issn.0253-4967.2012.04.009

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The recent researches of active faults related to the north segment of the eastern boundary of GTSR(the great triangular seismotectonic region of Central Asia),including the north part of the North-South Seismic Belt and central Mongolia,are summarized based on their geological background and seismic activities at present. The north segment of the eastern boundary of the GTSR is composed by a series of terminal structures,lateral structures of large sinistral strike-slip faults,and transtensional graben fault systems between the large sinistral strike-slip faults. From south to north,the fault systems,which compose the north segment of the eastern boundary of GTSR,include: (1)Liupanshan arcuate fault zone, which is the eastern terminal compression structure of the Haiyuan Fault zone and Zhongwei-Tongxin Fault zone; (2)Zhuozishan-Helanshan Fault system, which is a transtensional graben fault systems between the Zhongwei-Tongxin Fault zone and the Yabulaishan-Bayanxiboshan Fault zone; (3)Langshan-Sertengshan piedmont fault system, which is the eastern relaxing structure of the Yabulaishan-Bayanxiboshan Fault zone; (4)Dalandzadgad Fault system, which is the eastern terminal compression structures of the Gobi-Tienshan Fault zone and Gobi-Altay Fault zone; (5)Mogod Faults system,the possible eastern terminal compressional structures of the North Hangay Fault zone; and (6)Hovsgol rift system, which is the extensional lateral structures of the Tunka Fault zone. The nature of the seismic structures of the north segment of the eastern boundary of the GTSR is the re-activation of the pre-existing faults that locate beside or on the terminations of giant strike-slip fault zones in the present regional stress field,controlled by the northward pushing of the Indian-Eurasia collision and local upper mantle material flow or significant anisotropies deep in the upper mantle.

THE IRON OXIDE CHANGES IN DRILLING CORES FROM THE TWO WALLS OF XIADIAN ACTIVE FAULT

YANG Xiao-ping, CAO Jing-hu, CHEN Xian-cheng

2012, (4):  659-671.  DOI: 10.3969/j.issn.0253-4967.2012.04.010

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Using the complete core drilling method,we completed two boreholes on both sides of Xiadian active fault on which an M8.0 earthquake occurred in 1679.From rock cores of the two boreholes,we collected ¹⁴C,OSL and TL samples and determined their depositional ages. According to the geochronological data,and in combination with the sedimentary features of the formation in borehole cores,the late Pleistocene strata in XD1 hole can be divided into four stratigraphic sections. And the late Pleistocene revealed by borehole XD6 can also be divided into four stratigraphic sections. Late Pleistocene can be juxtaposed in the two boreholes; the deposition times of corresponding stratigraphic sections are also consistent. We collected some samples from XD1(on the upthrown plate)at a 0.5 meters interval roughly,and from XD6(downthrown plate)at a 1.0 meters interval. In State Key Laboratory of Earthquake Dynamics,we determined the FeO content with potassium permanganate titration method,and the Fe₂O₃ content using phenanthroline spectrophotometry. Comparing the Fe²⁺/Fe³⁺ ratio in same borehole core,we can find that the Fe²⁺/Fe³⁺ ratio of gray-black sediment is greater than gray-yellow sediment in the same drilling,and gray-black sediment is in a strongly reducing environment. When the same sedimentary strata are gray-black sediments,Fe²⁺/Fe³⁺ ratio in the strata on the fault's downthrown plate is larger than that on the upthrown plate. The reducing environment for the deposits on the fault's downthrown plate is stronger than the upthrown plate.

INFLUENCE OF INTERFEROMETRIC BASELINE ON MEASUREMENTS OF SEISMIC DEFORMATION: A CASE STUDY ON THE 1997 MANI,TIBET M7.7 EARTHQUAKE

QU Chun-yan, SHAN Xin-jian, ZHANG Guo-hong, SONG Xiao-gang, ZHANG Gui-fang, LIU Yun-hua, GUO Li-min

2012, (4):  672-683.  DOI: 10.3969/j.issn.0253-4967.2012.04.011

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The interferometric baseline is a vital parameter in the InSAR technique,which determines the correlation between two repeat-pass images and imposes direct effect on the accuracy and reliability of the mapping result. If the baseline is not accurately estimated,the residual phases from the orbit and topography will be left in the expected phase of deformation leading to errors of the final result. In this work,we analyze the influences of the baseline on the reference phase and simulated topography phase,and present several methods of interferometric baseline estimation. Then we study the mapping process of the coseismic and post-seismic deformation of the 1997 Mani,Tibet M7.7 earthquake based on the 8-sence ERS2-SAR data and InSAR.Our attention is focused on comparison of interferograms under varied conditions for baseline estimations,such as rough orbit data,precise orbit data,frequency of interferometric fringes and control points on the ground. The result shows that when the baseline is estimated by rough orbit data,the yielded differential interferograms contain considerable phases of orbit residuals which make fringes dense and deformation enlarged. Thus we must use the precise orbit data for baseline estimation. Sometimes,however,the influence of the orbit cannot be removed completely even if we employ precise orbit data. In this case we should make further corrections,including removing superfluous fringes based on interferometric fringes frequency and baseline correction using the control points on the ground. With these improvements,the resultant coseismic displacement along the fault of the Mani earthquake is 4.5m. The post-seismic deformation by this event is concentrated in a narrow 10～20km-long zone around the fault. The accumulated fault slip 508 days after the main shock reaches at least 5.6m,which continues to grow with time. These analysis results are consistent with the field observations,meaning the improvement method presented in this paper is effective.

FORMATION OF ONE TYPE OF AN EN-ECHELON QUARTZ VEIN ARRAY AND ITS IMPLICATION

ZHANG Jin, LI Yan-feng, XIAO Wen-xia

2012, (4):  684-695.  DOI: 10.3969/j.issn.0253-4967.2012.04.012

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A set of en-echelon quartz veins in the Ordovician sandstone in the Noushoushan was analyzed. The quart veins in the Niushoushan show both characteristics of those formed at the tip of mode-I parent faults and the ones in the tip zone of mode-II faults,which means that they took place by different mechanism from those extensional veins. The bridges between the veins were deformed not only by bending but also by some extent of ductile deformation. And to those early fabrics such as faults,joints and bedding surfaces in the bridges,the buckling may take place. The early fabric in the rocks was one of the important factors which control the late development of the en-echelon veins. These results show that the development of these veins may be controlled by the R' shear zones at the fault-tip damage zone of a strike-slip fault(Mode-Ⅱ),instead of minor en-echelon ones formed at the tip of a mode-I parent fault. The wedge-type fault damage zone at the tip of a major strike-slip fault was bounded by R and P minor shear zones derived from the major fault,and in the wedge region antithetic and synthetic shear veins or fractures will take place. This type of deformation is pervasive at the termination of the strike-slip fault,and it is an important way for the propagation of faults.

THE STRUCTURAL STYLE AND TIMING OF UPLIFT OF THE AILAOSHAN-DIANCANG RANGE,WEST YUNNAN,CHINA

LI Bao-long, JI Jian-qing, LO Ching-hua, GONG Jun-feng, QING Jian-chun

2012, (4):  696-712.  DOI: 10.3969/j.issn.0253-4967.2012.04.013

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The uplift of West Yunnan plateau is one of the late Cenozoic great geological events in the Qinghai-Tibet Plateau tectonic domain,and the Ailaoshan-Diancangshan Range uplift is the key to understanding this tectonic process. In the former researches,many researchers mainly emphasized on the strike-slip movements and times of the Ailaoshan-Red River shear zone. The formation of Ailaoshan-Diancang Range has been widely considered to be the result of the strike-slip movements of the Ailaoshan-red River shear zone. Usually,the formation of geomorphic unit is the result of latest tectonic activity,for the time scale of topography-shaping process is much smaller than that of tectonic movement in the study of tectonic geomorphology. Based on the collection of detailed evidences,the structural style and timing of the uplift of Ailaoshan-Diancangshan Ranges are studied. Detailed evidences are as follows: First of all,the primary structural foliations in the study region have obvious distinctness. On the east side of the Ailaoshan-Diancang Ranges,steep-dipping structural foliation is developed,but on the west,bedding foliation is developed. In Ailaoshan,the dip direction transforms from northeast to southwest,and the dip decreases steadily. Second,the degree of deformation and metamorphism reduces gradually from northeast to southwest,producing different belts. From northeast to southwest,the metamorphic belts are,in turn,the high-amphibolite facies metamorphic granitic gneiss,the low-amphibolite facies and greenschist facies composite of schist,phyllite and slate,and the weakly deformed sedimentary rocks. Third,the fault facets developed on the northeast side of the Ailaoshan and the pseudotachylite discovered on the normal fault planes indicate that the eastern boundary of the ranges is a fast-moving tectonic boundary.⁴⁰Ar/³⁹Ar step-heating experiments were performed on biotite and K-feldspar extracted from granitic mylonite collected from the east side of Diancangshan near Xiaguan. The ⁴⁰Ar/³⁹Ar geochronological data suggest that Diancangshan experienced a fast cooling event at 3～4Ma BP.Therefore,we draw the conclusions that: The formation of the Ailaoshan-Diancang Range shows a tilted uplift structural style,with larger amplitude of uplift in the east and smaller in the west. The latest uplift of the Ailaoshan-Diancang Range is constrained to be in Pliocene,about 3～5Ma BP.

RESEARCH ON ACTIVE FAULT DATABASE CONSTRUCTION RELATED ISSUES

YU Gui-hua, DU Ke-ping, XU Xi-wei, WU Xi-yan, WANG Yin

2012, (4):  713-725.  DOI: 10.3969/j.issn.0253-4967.2012.04.014

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The goal of the exploration to active fault is to understand its activities,relative parameters,the spatial distribution characteristics and its deep structures. There're three major stages for active fault exploration,namely, preparation stage,exploration stage and analysis stage. The construction of the database for each of these stages has different focus.
Based on the review of other articles about the development of active Fault database from international sources,the paper introduces the construction of databases based on the Technological System of China Earthquake Active fault Exploration project. And along with the development and implementation of the projects such as ‘Seismic Risk Assessment of Active fault in Key Earthquake Monitoring Areas in China’,‘China Earthquake Active Fault Exploration’, so on,database templates corresponding to each of the stages of active fault exploration are worked out according to the design idea,architecture and implementation of ArcGIS-based active fault database and the work procedure for active fault exploration. The main functions of the bulk storage software and data quality monitoring software developed for the construction of the database are introduced.
Due to the numerous data and the extensive sources as well as the complexity of the data acquisition during the building of database,there are chances to have either manual or systemic errors,and moreover,the data quality might be impacted,resulting in a database failing to represent the real activities of the active faults. On the other hand,the data stored in the database lacks consistency and integrity,thus,the database is ineffective and opposite to the original intention of its construction. The paper analyzes the main data sources used to establish the active fault database and the causes for generating low quality data,and discusses the advantages for building the active fault database simultaneously along with the implementation of active fault exploration.

ASSESS THE RESERVOIR-INDUCED SEISMIC HAZARD IN THE HUBEI SECTION OF THE THREE GORGES RESERVOIR USING GRAY CLUSTERING METHOD

MA Wen-tao, XU Xi-wei, YU Gui-hua, YUAN Jing-li, XU Chang-peng, LIN Rong

2012, (4):  726-738.  DOI: 10.3969/j.issn.0253-4967.2012.04.015

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In this paper,a statistical analysis is made using the gray clustering method on the earthquake inducing factors,such as dam height,storage capacity,regional stress state,fault activity,lithology medium conditions and seismic activity background,based on a database of reservoir-induced earthquakes,which includes 150 reservoir-induced earthquake cases and 532 large reservoirs data. Corresponding earthquake occurrence ratios are obtained and used as predictors for reservoir-induced earthquakes. According to the six quake-inducing factors,assessment is made on the maximum magnitude of reservoir-induced earthquake for the Three Gorges Reservoir dam area,the bayou of Xiangxi stream and the cross-river section of the Xiannushan Fault zone,the west Xietan,Badong,and on both banks of Shenlong stream. The results show that the upper-limit of magnitude at dam area is less than magnitude 3,that at the bayou of Xiangxi stream and the cross-river section of Xiannushan Fault zone is between magnitude 4～5,that at west of Xietan is less than magnitude 3,and that at the northern bank of badong and on both banks of the Shenlong stream is between magnitude 3～4.The results have been validated by the actual reservoir-induced seismicity after the impoundment of the Three Gorges Reservoir, with the M_L 2 earthquake at Xiaoxikou 4 km far away from the dam of the Three Gorges Reservoir on February 6, 2009, the M_S 4.1 earthquake at the bayou of Xiangxi stream and the cross-river section of the Xiannushan Fault zone on November 22,2008, the M_S 2.6 earthquake at the west Xietan on August 22, 2009, and the M_L 3.5 earthquake at the bank of Shenlong stream on December 14,2009.

Volcanic hazards and mechanisms

A PRELIMINARY STUDY OF THE ORIGIN ABOUT THE YELLOW MATERIAL AT CHANGBAISHAN TIANCHI VOLCANO

YIN Gong-ming, FAN Qi-cheng

2012, (4):  739-742.  DOI: 10.3969/j.issn.0253-4967.2012.04.016

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The Changbaishan Tianchi volcano is one of the most famous volcanoes in China. It erupted many times in the Holocene time. The top of this volcano is regionally covered by some yellow material (pyroclastics), the origin of which has been under debating since its discovery. Based on the information provided by the eruption of Mount St Helens of USA on May 18th, 1980, in conjunction with the chemical composition and distribution characteristics of the yellow materials, we estimated that it resulted from hot water metasomatism during the Millennium eruption, rather than a separate product of an individual volcanic event.

LAVA FLOW STYLES IN DAYINGSHAN,MAANSHAN AND HEIKONGSHAN IN TENGCHONG VOLCANIC FIELD

ZHAO Yong-wei, FAN Qi-cheng, LI Ni, LIU Gui, ZHANG Liu-yi

2012, (4):  743-754.  DOI: 10.3969/j.issn.0253-4967.2012.04.017

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Based on detailed field investigation,three lava flow styles are identified in the Dayingshan,Maanshan and Heikongshan in the volcanic field of Tengchong: pipe flow,inflated flow and laminar flow. Lava flows of Dayingshan are characterized by pipe flow. Heat lost gradually increased from the core to the edge of the flow pipe,resulting in lava consolidating gradually from the surface to the core. Lava of Maanshan is dominated by plane pahoehoe inflated by aa. The lava,in high temperature,was inflated into the lava tunnel as liquid-gas mixing phase,which generated aa. Heikongshan is featured by typical aa lava flow in the proximal phase and middle phase from the vent. The high-temperature plastic lava carried breccias on its top when advancing in a state of laminar flow,forming typical aa lava flow sections with breccias on the top and bottom and dense lava in the middle. In the distal phase,the lava flow formed numerous strip-shaped uplifts of breccias.

GEOMORPHIC CHARACTERISTICS AND FAULT RESTRICTION IN THE TENGCHONG VOLCANIC REGION——-INTERPRETATION BASED ON DEM AND TM DATA

ZHANG Liu-yi, LI Ni, ZHAO Yong-wei, CAO Yuan-yuan, GONG Li-wen

2012, (4):  755-767.  DOI: 10.3969/j.issn.0253-4967.2012.04.018

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Based on WorldView-2 high-resolution satellite image and ASTER GDEM(V1)digital elevation model(DEM)data,the authors studied geomorphological characteristics of the Tengchong volcanic region by means of remote-sensing interpretation,topography-elevation analysis,surficial-slope analysis and terrain-section analysis,with ArcGis and Global Mapper. According to the results of the study,the Tengchong volcanic region has several kinds of geomorphic units which possess corresponding interpretation keys in satellite image,and the latest typical volcanic geomorphic unit can be divided into four categories. Topography-elevation and surficial-slope analysis show that there is obvious difference in surface relief of geomorphic units in the horizontal direction and the geomorphic surface can be vertically divided into four classes. Geographically,the terrain elevation of the basin is higher in west and centre than in east,north and south,which associates with the original landform,tectonic evolution and volcano-magmatic activities. The NS-trending tectonic belts in the study zone controlled the eruption and distribution of the volcanoes. Early pyroclastic volcanoes,such as Daliuchong and Xiaoliuchong,had strong eruption power and shaped towering mountains which cover the middle part of the basin,while the lava-type volcanoes,such as Heikongshan,Dakongshan and Maanshan,with a decreased eruption power,erupted mainly in the form of overflowing lava. On the whole,the structure and evolution of the basin directly controlled and restricted the volcanic activities. At the meantime,the volcanic process transformed the geographic and geomorphic conditions of the basin and shaped the modern volcanic landscape features.

MINERAL CHEMISTRY OF LAMELLA OLIVINE AND ITS IMPLICATIONS FOR MANTLE RHEOLOGY

SUI Jian-li, FAN Qi-cheng, LI Ni, ZHAO Yong-wei, DU Xing-xing

2012, (4):  768-781.  DOI: 10.3969/j.issn.0253-4967.2012.04.019

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Olivine creep dominates the major characteristics of mantle rheology. Such ductile deformation affects not only mineral microstructures but also microchemistry of olivines. However,very few works focus on mineral chemistry of these dislocation-rich olivines,because the dislocation structure is too small to be analyzed by electron microprobe. And even these few works led to controversial interpretations on chemical mechanisms of the phenomena,such as exsolution of Fe-Mg olivine,Cottrell cloud and fluid erosion. Here we report two cases of lamellea(in scales of 1μm and over 100μm seperately)olivines in mantle xenoliths from the Halaha River and Chaoer River area,Central Great Xing'an Range. Results of EMP analysis indicate that the lamellae is Fe rich olivine. In response to the arguments against the hypothesis of exsolution and erosion,we discuss the behavior and mechanism of Cottrell cloud in olivine.

Earthquake emergency response and integrated disaster reduction

ADVANCES IN EARTHQUAKE EMERGENCY DISASTER SERVICE

NIE Gao-zhong, AN Ji-wen, DENG Yan

2012, (4):  782-791.  DOI: 10.3969/j.issn.0253-4967.2012.04.020

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The concept of earthquake emergency response was put forward in the 1960s and 1970s abroad,and was formally established in the early 1990s in China. Up to now,considerable progress has been made in earthquake emergency response in China,and at present,it faces a good chance of developing rapidly and catching up with the international advanced level.
Earthquake emergency response is a paramilitary action in which the key point is to make scientific and rational decisions and put them into action in the shortest possible time,which highlights the urgency and necessity of disaster information services.
Earthquake emergency disaster service is oriented to the decision-makers and their supporters,and also to the broad masses of the people of either affected or non-affected from all sectors of society,and even from abroad. Its contents include quick acquisition of disaster data,rapid extraction of disaster information,and disaster situation reporting and releasing and so on.
China's earthquake emergency disaster service is faced with urgent needs from various parties,yet it has a long distance to reach the advanced level abroad in terms of mechanisms and technical approaches,and cannot meet the needs of earthquake emergency response. The main reason is that the disaster service mechanism needs to be improved, including the overall flow of disaster service,the disaster reporting and decision-making supporting,and the classified and graded disaster releasing; the utilization rate of high- and new-technology in the disaster service,especially in the quick acquisition of disaster data is very low; the ability of rapid processing of data and information is relatively weak,and also the related basic research is lagging. To solve the problems,it is suggested to strengthen the construction and optimization of the overall framework of the earthquake emergency disaster service, and also to promote the integrated management of the central authority on it,to strengthen the integrated application of the high-and new-technology to the disaster service and to promote the research and development of new technologies and new equipment of emergency relief.

RESEARCH ON ASIAN CATASTROPHE GRADE CLASSIFICATION

LI Zhi-qiang, XU Jing-hai, LI Xiao-li

2012, (4):  792-804.  DOI: 10.3969/j.issn.0253-4967.2012.04.021

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The hazard grade assessment,which simply and clearly reveals how big the damage is,is an important part of emergency response and rescue work after disaster. Upon collection and sorting out of the data on Asian natural disasters occurring between 1900 and 2011,this paper studies the method of classifying those disasters. After discussing the definition of catastrophe and that of earthquake-affected population and exploring the basis on which catastrophe could be classified,this paper comes up with a formula,in which the logarithms of three factors,death toll,direct economic loss and quake-affected population,are summed up. Then,Asian catastrophes are classified by the formula. The calculation based on the formula shows that the results of 54 of all the disasters are above 10.0,102 above 9.0 and 178 above 8.0.After repeated comparison with data from several other disaster databases,it is concluded that the result achieved by the formula of the disaster which is generally considered as a catastrophe,is above 8.0.Therefore,a disaster with a result above 8.0 is defined as a catastrophe. The formula mentioned above in this paper is simple and convenient,and is suitable for making a comparison of the damage caused by the disasters of different types in different regions in Asia.

DISTRIBUTION AND FORMATION OF EARTHQUAKE-INDUCED SECONDARY GEOLOGICAL DISASTERS IN CHINA

ZHANG Ye-cheng, ZHANG Li-hai, ZHAO Xiao-qing

2012, (4):  805-809.  DOI: 10.3969/j.issn.0253-4967.2012.04.022

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The earthquake secondary geological disasters refer to the geological disasters induced by earthquake,including mainly landslide,collapse,and also ground caving in and soil liquefaction,etc. The earthquake secondary geological disasters not only aggravate the earthquake losses,but also bring on difficulties in disaster relief and post-quake reconstruction. More than 20 provinces(municipalities and autonomous regions)in China have been subject to earthquake secondary geological disasters but with various degrees in different regions. The areas of Shaanxi,Gansu,Ningxia,Sichuan,Chongqing,Yunnan and Tibet in the central part of Chinese continent are the most seriously affected,forming a NNE-trending high danger zone. The geologic and geomorphic conditions for generating earthquake secondary disasters are basically the same with that of general geological disasters,but the trigger factor for the former is earthquake. Secondary geological disasters are likely to happen in areas of M≥5.0 and seismic intensity ≥Ⅵ,and the higher the earthquake magnitude and intensity,the more serious the secondary geological disasters. The damage caused by earthquake secondary geological disasters is similar compared with other geological disasters,but the chance of occurrence of the former is smaller.

RESEARCH ON SIMULATION TEST OF RAINFALL-INDUCED LANDSLIDE AND SEISMIC LANDSLIDE

WANG Wei-feng, GENG Yun, WANG Qing-zhen, SHAN Xin-jian, CHEN Xiao-li

2012, (4):  810-819.  DOI: 10.3969/j.issn.0253-4967.2012.04.023

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In order to study the genetic mechanism of the geohazards induced by rainfall-induced landslide and seismic landslide,the influence of the factors such as the texture of the slope,shape of the slope,vibration intensity,critical rainfall amount,on the slope failure is discussed,and the main models and processes of the slope failure under rainfall and earthquake are investigated,by the means of taking on-site simulation test for rainfall-induced landslide and seismic landslide. For rainfall-induced landslide,the critical rainfall amounts are determined for slopes of different angles. It is found that the critical rainfall amount and the slope angle follow logarithmic distribution. For seismic landslide,the slope failure extent is proportional to the angle of the slope,duration of vibration and the vibration intensity. The relation between landslide slope gradient and earthquake failure time is analyzed according to experimental data. It has been found by statistical analysis of landslides induced by the Wenchuan earthquake that the possibility of occurrence of landslide is greater in the slope with gradient greater than 30 degrees when the earthquake magnitude is above 4.The results of simulation experiment substantially meet the actual situation.

STUDY ON THE CHANGES OF VULNERABILITY AND LOSS RISK OF BUILDINGS FROM SEISMIC DISASTER IN THE PROCESS OF URBANIZATION——A CASE STUDY OF TANGSHAN AREA

QI Wen-hua, SU Gui-wu, ZHANG Su-ling, LIU Xin-sheng, WEI Ben-yong, SUN Lei

2012, (4):  820-834.  DOI: 10.3969/j.issn.0253-4967.2012.04.024

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Based on our previous researches and taking the year 1976,1995,2002 and 2009 as the representative reference time periods,the temporal and spatial changes of vulnerabilities and loss risks of building groups from seismic disaster of the Tangshan area in the last more than thirty years have been analyzed mainly through high-resolution remote sensing-based method and scenario earthquake analytical method. The main achievements are concluded as follows: 1)The total construction area of all buildings increased four times over the period from 1976 to 2009; the increased area is distributed mainly in the western part of the study area; and the structure vulnerability of buildings reduced gradually.2)Under the earthquake scenarios of intensity Ⅵ～Ⅺ,both damaged building areas and direct economic losses increased significantly,and with the increase of intensity,the increments of both were more remarkable,but the area ratios of buildings were gradually reduced.3)Under the earthquake scenarios of low intensity and high intensity,the loss risks differed greatly. Under the low intensity,because of the increased number of brick-concrete and reinforced concrete buildings which have better anti-seismic performance,the damage ratio,damage area growth and damage degree all reduced significantly. So, buildings with good anti-seismic performance can reduce effectively the loss risk from earthquake of low intensity. Under the high intensity,however,more such buildings were damaged. In a sense,the loss risks increased. 4)If the 1976 Tangshan earthquake had occurred in 2009,the damage areas and economic losses of buildings would be six times and twenty-eight times more than that of 1976,respectively.

DESCRIPTIVE STATISTICAL FEATURES OF EARTHQUAKE DISASTER AWARENESS OF THE ELEMENTARY SCHOOL STUDENTS IN YUSHU AREA, QINGHAI PROVINCE, CHINA

WU Huan-jie, SU Gui-wu, WEI Ben-yong, TIAN Qing, LIU Feng-gui

2012, (4):  835-849.  DOI: 10.3969/j.issn.0253-4967.2012.04.025

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By taking the M_S7.1 earthquake occurring in Yushu area,Qinghai Province on April 14th,2010 as an example,the descriptive statistical features and their educational implications of the earthquake disaster awareness(EDA) in elementary school students in Yushu area were analyzed preliminarily through questionnaire survey method. The main conclusions are as follows: (1)The EDA level of the targeted students in this area is very low. Firstly,the vast majority of them do not know what the earthquake origin is,can not identify earthquake rumors,and do not know that only the government department that has the authority to release earthquake prediction. In addition,most of them do not know how to escape from dangers quickly and safely when an earthquake happens. The surveyed data show the knowing rates of each of the specific attention-required items during the earthquake emergency are all less than 50%.All of these facts prove strongly that it is very important to intensify ceaselessly the earthquake disaster education in that area.(2)The desire of most elementary school students to learn more knowledge and skills of earthquake disaster reduction has increased after the earthquake. Therefore,it is more important to improve the publicity and education on earthquake prevention and disaster reduction in the study area.(3)The main ways of getting the earthquake knowledge and the earthquake disaster coping skills are the classroom targeted education and publicity in school. The role of religious figures,government and popular science books in publicity and education of the knowledge and disaster-coping skill of the earthquake has no significant difference,which are also the important information sources of earthquake knowledge for most elementary school students. However,the effects of radio,television,newspapers,mobile phones and the internet on publicity of earthquake knowledge are very limited,which is different with that from the investigation of other areas. Therefore,it is more necessary to strengthen the publicity of earthquake knowledge by reinforcing the school education and bringing into better play the roles of the government and the monastery.