Table of Content

20 June 2008, Volume 30 Issue 2

Previous Issue    Next Issue

Brief Report

SOME DESTRUCTION AND ITS SEISMIC INTENSITY IN MEIZOSEISMAL REGION OF WENCHUAN EARTHQUAKE WITH MAGNITUDE 8, SICHUAN, CHINA

YANG Zhu-en, DENG Zhi-hui, MA Wen-tao, SUN Qian, CHEN Gui-hua

2008, 30(2):  349-354. 

Asbtract ( )   PDF (4587KB) ( )  

Related Articles | Metrics

Some destructions in meizoseismal region of Wenchuan earthquake with magnitude 8,Sichuan,China are shown,and their seismic intensity is determined according to "The Chinese Seismic Intensity Scale".The type of earthquake-generating fault and some features of seismic destruction are discussed briefly.

SURFACE FRACTURES OF WENCHUAN EARTHQUAKE(M8.0) IN BEICHUAN AND YINGXIU

DENG Zhi-hui, YANG Zhu-en, CHEN Gui-hua, MA Wen-tao, SUN Qian

2008, 30(2):  355-358. 

Asbtract ( )   PDF (2017KB) ( )  

Related Articles | Metrics

After Wenchuan Earthquake(M8.0),surface fractures in Beichuan and Yingxiu were investigated.It was found that the earthquake deformation zone strikes in NE-SW.Earthquake fracture is characterized by thrust faulting with small amount of strike-slip movement.The compressional shortening is 3～4m in Beichuan and the left-lateral strike-slip displacement is 0.4～0.5m in Yingxiu.

RUPTURE OF THE M_S 8.0 WENCHUAN EARTHQUAKE

HE Hong-lin, SUN Zhao-min, WANG Shi-yuan, WANG Ji-qiang, DONG Shao-peng

2008, 30(2):  359-362. 

Asbtract ( )   PDF (2417KB) ( )  

Related Articles | Metrics

On the 12th of May,2008,a devastating M_S 8.0 earthquake struck Wenchuan County,Sichuan Province.The earthquake rupture extends about 200km,and the maximum co-seismic strike-slip displacement and vertical displacement are(4.8±0.2)m and(5±0.2)m,respectively.Only one fault plane(N32°E/NW∠76°)has been found on the southern section of the rupture.The high dip of the fault plane and high angle stria on the fault plane show that the fault is dominated by reverse motion,with a small amount of right-lateral strike-slip component in this segment.

THERMAL FIELD INDICATORS FOR IDENTIFYING ACTIVE FAULT AND ITS INSTABILITY FROM LABORATORY EXPERIMENTS

MA Jin, MA Shao-peng, LIU Pei-xun, LIU Li-qiang

2008, 30(2):  363-382. 

Asbtract ( )   PDF (10575KB) ( )  

Related Articles | Metrics

The relationship between the thermal field and strain field during deformation of fault is the physical basis to clarify whether satellite infrared information or the ground temperature field can be used to study fault activity.This study attempts to discuss these problems by laboratory experiments.A two-direction servo-control system was used to apply load on the samples with compressive and tensile en echelon faults.An infrared thermal image system and a contact-type thermometer recorded synchronously variations of the brightness temperature field of infrared radiation and temperature field during deformation of the rock specimens.A digital CCD camera and the digital speckle correlation method(DSCM)was used to collect and analyze images to obtain the evolution processes of displacement and strain fields.The experimental result shows as follows:1)the temperature is the highest of the jog area of the compressive en echelon faults,whereas that is the lowest of the extensional en echelon faults prior to failure of the jog area.The record by DSCM displays that the mean strain of the jog area is the largest for the compressive en echelon faults,while that is the smallest for the extensional en echelon faults.These mean that the temperature field has clear responses to the opposite stress states at the jog areas with two kinds of en echelon faults,and thus provides an indicator for determining whether the fault has slid;2)the en echelon faults experience two deformation stages from the stress building up and fault propagating in the jog area to the unstable sliding along the fault.Correspondingly,the mechanism of heating-up turns from strain heating into frictional heating.Three kinds of phenomena have been observed at the jog area and its vicinity during the stage of transformation.They are temperature drop,fast fluctuation of temperature,and pulses of temperature rising.Mechanism of these phenomena is discussed;3)these variations of thermal field at the jog area are followed by swift rise of temperature along the fault.The onset of temperature rise along fault occurs 2～3 seconds prior to its unstable slip.However,the temperature drop of the jog area happens about 20 seconds before the unstable slip of the fault and the appearance of temperature rising pulses is 10～20 seconds earlier than that of the fault slip.They are precursors to unstable slip of the fault.These experimental analyses demonstrate that observations and studies on the thermal variations at the sensitive portion of a fault comparing with other relevant data are of great importance for detecting precursors ahead of unstable slip of active faults.It is planned to design an observing project along a suitable fault.

STUDY ON THE QUATERNARY CHRONOSTRATIGRAPHIC SECTION IN TIANJIN AREA

CHEN Yu-kun, LI Zhen-hai, SHAO Yong-xin, WANG Zhi-sheng, GAO Wu-ping, YANG Xu-lian

2008, 30(2):  383-399. 

Asbtract ( )   PDF (3333KB) ( )  

Related Articles | Metrics

Based on the optical dating and paleomagnetic testing results,we make a chronostratigraphic research of Huanghua depression and Cangxian uplift which are two tectonic units of Tianjin area.In this paper,we establish a Quaternary stratigraphic section and make a new division of the Quaternary strata.The result shows that the two tectonic units have similar sedimentation histories,but many differences exist.On the one hand,both units have received transgression since the Quaternary and some marine strata formed to various extents,which indicates different transgression sedimentation histories between them;on the other hand,the Quaternary stratigraphic sequences of the two units are greatly different,indicating different sedimentation histories,and consequently,the type and thickness of sediments are obviously different,so they belong to different sedimentary units.The study also shows the depths of bottom interfaces of Holocene,upper Pleistocene and middle Pleistocene as 19m,45m and 103m,respectively in hole BZ1 in Huanghua depression and 13m,30m and 56m respectively in hole BZ2 and hole TN3 in Cangxian uplift.The depth of bottom interface of the Quaternary is about 162m,much smaller than the result of the previous Quaternary strata division.

STUDY OF PALEOEARTHQUAKES BY COMBINED TRENCH ON ZEMUHE FAULT AROUND DAQINGLIANGZI, XICHANG, SICHUAN

TIAN Qin-jian, REN Zhi-kun, ZHANG Jun-long

2008, 30(2):  400-411. 

Asbtract ( )   PDF (4163KB) ( )  

Related Articles | Metrics

There exist some uncertainties in dating paleoearthquakes.To improve the credibility of determination of the earthquakes,comprehensive analysis of movement patterns,sedimentary environment and micro-topography has been made to investigate the paleoseismic events along the Zemuhe active fault zone.Combined trenches were excavated near Daqingliangzi,which reveal three palaeoearthquakes with ages of 160a,3100a and 5500～8900a,respectively,and a recurrence interva1of about 3000 years.Sedimentary processes related to strike-slip fault type earthquakes are discussed and a sedimentary model is put forward for strike-slip fault on condition that bulges and reverse scarps were formed at hillside area.

Research paper

COMPARISON STUDY ON HOLOCENE PALEOSEISMIC ACTIVITIES AMONG MULTI-TRENCHES ALONG THE JIAOCHENG FAULT ZONE,SHANXI

XIE Xin-Sheng, JIANG Gui-Li, SUN Chang-Bin, YAN Cheng-Guo, FENG Xi-Yang

2008, 30(2):  412-430.  DOI: 古地震; 全新世; 探槽; 交城断裂带; 山西

Asbtract ( )   PDF (28039KB) ( )  

References | Related Articles | Metrics

The paleoseismic situation revealed by the trenches excavated at five locations along the Jiaocheng Fault zone is introduced in this paper.These five big trenches locate at the northern,central and southern segments of the Jiaocheng Fault zone.Two exploratory trenches were dug at the northern and central segments of the Jiaocheng Fault zone each,and one trench on the southern segment.The distances among these five trenches are 11～35km.Four trench sections where dislocated Holocene strata are exposed lie in

FAULT ACTIVITIES OF LONGGAO PENINSULA IN FUQING COUNTY,FUJIAN PROVINCE

HUANG Qing-Qiu, FU Ping, YOU Hui-Chuan, CHEN Wen-Ban, SONG Yi-Cheng, XIE You-Quan

2008, 30(2):  431-442.  DOI: CNKI:SUN:DZDZ.0.2008-02-009

Asbtract ( )   PDF (3797KB) ( )  

References | Related Articles | Metrics

The paper discusses the characteristics of the fault activities since Quaternary and the relation between the seismicity and faults activities,basing on the analysis of Quaternary strata overlying the main faults of Longgao peninsula,shallow seismic exploration,distribution of geomorphic surfaces on both sides of the faults.The results show:1)The Zhonglou-Donghan Fault(F1),Sanshan Fault(F3)and Haikou-Jiangyin Fault(F4)are the middle Pleistocene active faults instead of the late Pleistocene active faults as

CRUST SHORTENING OF DALIANGSHAN TECTONIC ZONE IN CENOZOIC ERA AND ITS IMPLICATION

CHEN Chang-Yun, HE Hong-Lin

2008, 30(2):  443-453.  DOI: CNKI:SUN:DZDZ.0.2008-02-010

Asbtract ( )   PDF (3030KB) ( )  

References | Related Articles | Metrics

Daliangshan tectonic zone is the rhombic area east of the Anninghe and Zemuhe Fault zones,southeast of the Tibetan Plateau.The Daliangshan tectonic zone is enclosed by three tectonic units:the Bayan Har terrane in its northwest,the Yangzi platform in its southeast and the Longmen Mountain-Yanyuan nappe tectonic belt in the middle.The Daliangshan Fault zone is the most important fault zone in the Dalianshan tectonic zone.This fault zone,together with the Anninghe Fault zone and the Zemuhe Fault zone,make up

Brief Report

ACTIVITY OF THE LINTONG-CHANG AN FAULT IN LOESS TABLELANDS SINCE LATE PLEISTOCENE

LI Xiao-Ni, FENG Xi-Jie, DAI Wang-Jiang, SHI E-Qin, LIN Juan, LI Jin, HAN Heng-Yue

2008, 30(2):  454-463.  DOI: CNKI:SUN:DZDZ.0.2008-02-011

Asbtract ( )   PDF (33286KB) ( )  

References | Related Articles | Metrics

The late Pleistocene aeolian loess distributes widely in the loess tableland area.It has obvious features and is directly related with faulting.By the observation,measurement and dating to three typical sections at Xiaobaopo,Qiaogou and Zhongdicun,this paper obtained the activity parameters of the Lintong-Chang an Fault since the late Pleistocene and the age stratigraphic sequence of the tablelands of Bailuyuan,Shaolingyuan and Henglingyuan.Research results show that the Bailuyuan tableland has experienced

Research paper

PRELIMINARY RESEARCH ON THE RELATION BETWEEN ACTIVITIES OF HORGOS MUD VOLCANOES AND MID-STRONG EARTHQUAKES IN XINJIANG

GAO Xiao-Ji, WANG Hai-Chao, GAO Guo-Yang, GAO Ge, WANG Zhong-Dao, LIU Meng-Yong, SANG Li-Rong, YANG Xiao-Fang, GUO Wei-Yang, HU Qiu-Long

2008, 30(2):  464-472.  DOI: CNKI:SUN:DZDZ.0.2008-02-012

Asbtract ( )   PDF (1008KB) ( )  

References | Related Articles | Metrics

Based on the observation of Horgos mud volcanoes from 1991 to 2006,the article points out the relation between activities of those mud volcanoes and mid-strong earthquakes in Xinjiang,which can be used to predict occurrence time and magnitude of future earthquake to a certain extent,and advises extending the mud volcano observation for more meaningful data.Finally,the article lists three possible reasons why the activities of those mud volcanoes have a good correlation to mid-strong earthquakes.The first re

Brief Report

FEATURES OF MYLONITE AT CENTRAL SOUTHERN SECTION OF THE RED RIVER FAULT ZONE AND ESTIMATION OF ITS PRIMARY RHEOLOGICAL PARAMETERS

ZHANG Bing-liang, LIU Rui-xun, XIANG Hong-fa, CHU Quan-zhi, HUANG Xiong-nan, ZHENG Yong-gang

2008, 30(2):  473-483. 

Asbtract ( )   PDF (12067KB) ( )  

Related Articles | Metrics

The Red River Fault zone is an inter-block tectonic deformation belt which has experienced long-term tectonic evolution.On the southwest of the fault zone,a suit of mylonites is exposed which was formed by ductile shear.In the study area,the mylonite exhibits many kinds of macroscopic deformation structures,such as planar lamination,linear lamination,and S-C fabric.Its microscopic deformation is characterized by mica fish,feldspar mortar,flaser and extension of feldspar and amphibole,and pressure shadow produced by mortar rotation.In particular,the quartz has experienced widespread deformation,resulting in wavy extinction,core-mantle structure,dynamic recrystallization,flaser and extension of single grain,and quartz fringe.The new quartz grain by recrystallization is well developed,of which the boundary has microscopic features of saw-toothed or embayed shape.These distinct features record the temperature-pressure conditions and rheological rates for deformation.Analysis of fractal dimension to the quartz grain shows that the boundary shapes of recrystallization grain of quartz have self-similarity,presenting a fractal feature,with values of fractal dimension 1.150～1.180,and deformation temperature about 500℃.The tectonic metamorphic condition is of high-greenschist facies and low-amphibole facies.It is estimated that the strain rate is probably less than 10^-8.4s^-1,and the paleo-stress for deformation is 42.0～58.0MPa based on grain size of recrystallization.

K-AR DATING ON THE TRACHYTES COMPOSING THE TIANCHI COMPOSITE CONE IN CHANGBAISHAN

SUN Chun-qiang, WEI Hai-quan, LIU Qiang, PAN Xiao-dong

2008, 30(2):  484-496. 

Asbtract ( )   PDF (2899KB) ( )  

Related Articles | Metrics

According to the field survey and K-Ar dating of the rock samples,the existing K-Ar ages and the new data are presented in this paper.It shows a different distribution feature of the trachytes from different stages on the north and northeast flank of the Tianchi volcano,and it is apparent that the ages of the trachytes on the north flank are newer than those on the northeast flank.It is inferred that the K-Ar age of the oldest trachytes composing the composite cone in the northeast flank of the Tianchi volcano is 0.38Ma BP,which is in the middle Pleistocene,and that the trachyte is the product of the third stage of the trachytic composite cone construction.No evidence of the first and second stages of eruption for the composite cone construction has been found on the northeast flank of the Tianchi volcano.At the meantime,new data from the cored samples provide new insight of a much earlier stage for the trachytic eruption beneath the Tianchi volcano.

ACTIVITY OF THE SOUTHWEST SEGMENT OF XIADIAN FAULT INVESTIGATED BY SEISMIC REFLECTION PROFILING

GAO Jing-hua, XU Ming-cai, RONG Li-xin, CHAI Ming-tao, WANG Guang-ke, WANG Xiao-jiang, LIU Guanjun

2008, 30(2):  497-504. 

Asbtract ( )   PDF (3976KB) ( )  

Related Articles | Metrics

Seismic method is a necessary exploration method for detecting active faults buried directly beneath major cities in deep coverage area.Different array length must be adopted for different detecting depth.The Xiadian Fault is a seismogenic fault and related to the 1679 Sanhe-Pinggu earthquake(M=8.0).The deep and moderate-deep structural characteristics of the fault are revealed from the deep and moderate-deep seismic profiles across the fault.To research the activity of the fault away from the earthquake region,moderate-shallow seismic reflection detection experiment was developed with the working parameters as 5m group interval,15m offset,10 folds,60 active receiving channels,single-ended spread shooting by Wacker source,and one point receiving by 40Hz geophones.Based on the results of moderate-shallow seismic detection,a shallow seismic profile was laid across the fault detected by moderate-shallow seismic profiling.The shallow seismic reflection detection experiment was developed by using 2m group interval and hammer source as well as other ways similar to the moderate-shallow seismic reflection.It shows by the results of moderate-shallow and shallow seismic detection that the Xiadian Fault is well imaged at the depth below 200m on the seismic profile of 5m group interval,but it is invisible at the depth above 200m on the profile.The fault on the seismic profile of 2m group interval is obvious,but the shallowest reflection(depth about 30m)on the profile is uninterrupted.It can be educed that the activity of Xiadian Fault weakens about 30km southwest of the epicenter of the 1679 M8.0 Sanhe-Pinggu earthquake.

THE CHARACTERISTICS OF THE LAOYACHEN FAULT IN ZHENGZHOU REVEALED BY SHALLOW SEISMIC DATA OF P WAVE AND S WAVE

LIU Bao-jin, ZHAO Cheng-bin, YIN Gong-ming, TIAN Qin-jian, LIU Yao-xing, FENG Shao-ying

2008, 30(2):  505-515. 

Asbtract ( )   PDF (6816KB) ( )  

Related Articles | Metrics

The investigation and study of fault activities are a basic work for urban earthquake prevention and disasters reduction.In order to find out the location,characteristics and activities of the Laoyachen Fault in Zhengzhou,the high-resolution shallow seismic P and S wave survey profiling across the Laoyachen Fault was carried out at the end of 2006,and different seismic sources along with combinations of diverse observation geometries with different parameters were used.The fine structures in different depths beneath the profile were obtained and the patterns as well as characteristics of the Laoyachen Fault were determined.The results show that the Laoyachen Fault,running in NW and dipping in NE,is a normal fault and its dip angle is about 60°～70°,which incises strata of Eocene,Permian,Carboniferous or Ordovician epoch and goes up to the top boundary of Eocene stratum at the 800～850m depth.There is no any reflector of offset stratum found in Q+N strata.The borehole geological sections across steep slopes of earth surface present that the layers inferred from reflected seismic wave groups of shallow seismic profile are well correspondent with boring geological layers.The borehole results reveal that the three reference laminas,i.e.the boundary between Malan loess and silt with clay soil at about 21m in depth,the calcareous gravel clay layer of 53.9m deep,and the calcareous silt layer of 61.9m deep,all have not depth variations at the two sides of surface steep slopes and are situated almost at the same ground surface elevations,which suggests that the steep slopes at the earth's surface should not result from the activities of Laoyachen Fault.In this study,through shallow seismic P wave and S wave exploration as well as combination of joint borehole geological sections,not only the location and characteristics of Laoyachen Fault was determined,but the geological and seismological evidences for the fault activity estimations were provided.

PRELIMINARY ANALYSES OF THE DEEP ELECTRICAL STRUCTURE AND DECOLLEMENT STRUCTURE IN NING'ER SEISMIC AREA-Ⅰ

WANG Xiao, ZHAO Guo-ze, TANG Ji, XIAO Qi-bin, CHEN Xiao-bin, WANG Ji-jun, CAI Jun-tao

2008, 30(2):  516-524. 

Asbtract ( )   PDF (3193KB) ( )  

Related Articles | Metrics

Magnetotelluric data have recently been obtained at 9 sites along a profile of about 8km long and orientated approximately E-W in the Ning'er earthquake area which lies in southwestern Yunnan province.From these data,the high-resolution apparent resistivity,impedance phase curves,skewnesses and regional strike were calculated by using the remote reference technique and robust data processing technique,and then analyzed.The 2-D inversion method NLCG was used for data interpretation.According to the 2-D electrical structure of Ning'er seismic area,there may be an extended fault because of an obvious different electrical structure between the left & right side of the site 12.On longitudinal distribution,the crust of this area can be divided into four electrical layers:1)Mesozoic and Cenozoic sediments,about 1km,2)Paleozoic sediment,about 5km,3)high conductive layers in crust,and 4)middle and lower crust.A high conductive layer exists in the crust of the area.Between the site 12 and 13,there might be a decollement structure on top of high conductive layer under them,because the buried depth of the layer is quite different between the left & right side of the site 12.Focal depth of the Ning'er earthquake is about 5km,the decollement structure presumed in this research lies in this layer,and its strike is NW,same as that of the major axis direction of the isoseismal curve of this earthquake.So we conclude that the decollement structure is the seismogenic structure.

A NEW ALGORITHM FOR THE CALCULATION OF AUXILIARY FIELD IN MT 2D FORWARD MODELING

MA Wei, CHEN Xiao-bin, ZHAO Guo-ze

2008, 30(2):  525-533. 

Asbtract ( )   PDF (1238KB) ( )  

Related Articles | Metrics

This paper focuses on the calculation of the auxiliary field-another important factor related the precision of MT 2D forward modeling.The purpose is to raise the precision of forward calculation and provide MT inversion with more sufficient supports.It suggests constructing a quadratic interpolation shape function in the surface grid for calculation of the auxiliary field,when employing the current available method of linear interpolation for calculating the principal field.In this work,the Direct Iteration Finite Element Algorithm(DIFE)is utilized to solve the calculations of interpolation nodes.This new algorithm is tested through model calculation.Comparing with the 2D forward modeling of the auxiliary field by the linear interpolation,the quadratic interpolation does not increase much amount of computation,but raises the precision of MD forward calculation.We also discussed the reason from theory,and on the basis of the result,the current design criterion for 2D forward grid has been improved.The element size can be enlarged to one skin effect depth.So the new algorithm has special meaning to the study of complex topography forward problem.We will further discuss this question and compare the results.Besides,the calculation of auxiliary field in 3D forward modeling is also very interesting.

STUDY ON THE RELATIONSHIP BETWEEN THE CHARACTERISTICS OF FOCAL DEPTH AND FAULTS IN URUMQI REGION, XINJIANG

LI Ying-zhen, GAO Guo-ying, GAO Ge, LI Zhi-hai

2008, 30(2):  534-543. 

Asbtract ( )   PDF (4194KB) ( )  

Related Articles | Metrics

We used the catalog of Earthquake Administration of Xinjiang and HYPODD to analyze the characteristics of focal depth and its tectonic significance in Urumqi region,Xinjiang.The results show that the focal depth in Urumqi region increases with the magnitude of earthquake and separates into three layers.For most earthquakes,the focal depth distributes from 1km to 35km,and the predominant depth is from 16km to 25km.The spatial distribution of the average focal depth is correlated with fault;for the earthquakes between the three groups of faults near the Urumqi city,the focal depth is the shallowest,ranging from 17km to 21km,while for the earthquakes occurring on the big and deep faults,the focal depth is deeper.The profile of focal depth in different parts of tectonics shows that most earthquakes didn't occur on the fault planes,but in the detachment layers below them.On the Xishan Fault,the focal depth extends from detachment layer to the fault plane,indicating the fault is in a weak motion state,being not completely blocked.In the regions extruded by Zhunger and Tien Shan,the focal depths extend to the ground surface.The distribution of focal depth is related with the complicated structure of lithosphere in Urumqi region,most earthquakes distribute above the low velocity body or between the low velocity body and high velocity body.

STUDIES ON STRATUM DENSITY CHANGES INVERSION IN XI'AN AREA WITH GENETIC FINITE ELEMENT METHOD

ZHU Gui-zhi, SHI Yao-lin, ZHU Yi-qing, WANG Qing-liang

2008, 30(2):  544-552. 

Asbtract ( )   PDF (2498KB) ( )  

Related Articles | Metrics

Gravity changes are the comprehensive reflection of density changes and deformation in Earth's medium.Gravity gradient changes reflect the change of gravity anomaly,with a resolution higher than the gravity anomaly changes.In this paper,using the gravity anomaly data during 1992—1994 and leveling data during 1988—1991,we compute the gravity anomaly caused by stratum density changes by eliminating Bouguer anomaly with Bouguer correction formula,then inverse the stratum density changes by using genetic finite element method.The gravity gradient changes are also computed in order to analyze the main contribution to the gravity change in the Xi'an area.The results show that the excessive extraction of confined groundwater has led to the confined water level drop,much water was lost and clay layer was compacted,and the resulting land subsidence is the main reason for gravity change.Densification of clay layer in most parts of the aquifer system can generate surplus stratum density,but for several local areas,such as Xiaozhai and Tielumiao areas,excessive extraction of ground water has lowered the groundwater level,resulting in water loss but not densification of clay layer.This is the major cause for some negative gravity changes.But we cannot rule out the contribution of possible activities of fissures in this area.

SOME DISCUSSIONS ON DETERMINATION OF THE LAST ACTIVE TIME OF FAULTS IN AREAS WITH QUATERNARY VOLCANIC ACTIVITY

XU Jian-dong, ZHOU Ben-gang, WEI Hai-quan, ZHAO Bo, PAN Bo, LUAN Peng

2008, 30(2):  553-561. 

Asbtract ( )   PDF (12985KB) ( )  

Related Articles | Metrics

Longgang volcano group is located in Huinan and Jingyu counties of Jilin Province,which occupies the middle segment of the Longgang mountain ranges.The volcanic activity in Quaternary,especially in the early Pleistocene,is very intensive,and as a result,over 2/3 of the total area is covered by Q_p¹(Xiaoyizishan Group)basalt sheet.The study area of this paper lies in the northeastern part of the Longgang volcano group,where some small-scaled faults are developed and their activity in the Quaternary Period is critical to the potential earthquake risk evaluation for the local engineering.In order to study the activities of these faults,a comprehensive project has been carried out by means of field investigation and application of ESR dating technique to determine the last active time of each fault.However,an inconsistent phenomenon was found in the study area,in which the age of fault gouge from ESR dating method is much younger that the age of Q_p¹ basalt sheet that covers both fault plane and fault deformed materials.We propose two facts that would be responsible for this contravention.Firstly,the extensive volcanic activity in the study area in Quaternary may produce a significant amount of heat regionally.For example,the temperature of the molten basalt lava is between 1050℃ and 1200℃,which is high enough to cause the effect of annealing and resetting of ESR signals.Consequently,such effect may result in the age of fault gouge with ESR dating method younger than the time when this heat event occurred.Secondly,after a fault is formed,chemical weathering will occur at the fault zone,which may result in dissolution on the grain surface of fault gouge.Such effect may significantly increase the amount of annual ESR dose and make the sample of weathered material younger than the un-weathered ones.Therefore,in this study area with extensively volcanic activity,the age from fault gouge dated with ESR method should be considered as the "upper limit age" of the last fault activity rather than the last time when the fault was active.Even though the "upper limit age" does not represent the age of the last activity of a fault,it is very useful in the practice of determining the capable fault for earthquake safety evaluation of large engineering sites.

STUDY ON THE RELATIONSHIP BETWEEN THE SATELLITE INFRARED BRIGHTNESS TEMPERATURE AND GROUND ELEVATION IN THE MAINLAND OF CHINA

MA Xiao-jing, DENG Zhi-hui, CHEN Mei-hua, ZU Jin-hua, WANG Yu

2008, 30(2):  562-572. 

Asbtract ( )   PDF (3329KB) ( )  

Related Articles | Metrics

The relationship between the satellite thermal infrared brightness temperature and ground elevation is very important information that can reflect the thermal state of earth surface.It is also one of the main factors which influence the analysis of satellite thermal infrared anomalies before earthquakes.Previous study is not enough and comprehensive and it needs a deep research.In this paper,the decreasing infrared brightness temperature per 100m increase of the ground elevation is defined as brightness temperature gradient.The mainland of China is divided into 6 regions for separate research:the Northwest,the Qinghai-Tibet,the Sichuan-Yunnan,the Northeast China,the North China and the South China.This paper selects remote sensing data at midnight in order to reduce the influence of solar radiation and preprocesses thermal infrared remote sensing images systematically including cloud and noise removing and so on.On the basis of filtering and processing the satellite thermal infrared remote sensing data,this paper analyses the relationship between the satellite infrared brightness temperature and ground elevation in the 6 regions with the method of regression analysis.Studying on the 6 regions separately,some abecedarian results are developed:1)the general trends of brightness temperature gradient are similar between different areas,but there are some differences in details;2)the brightness temperature gradient of the 6 regions are all less than the air temperature lapse rate(0.64℃/(100m))calculated on the basis of air temperature data,also less than 0.4℃/(100m),from 0.15℃/(100m)to 0.35℃/(100m)in most situations;3)except the Qinghai-Tibet area,the brightness temperature gradient of the other five regions is generally greater in summer than in winter.On the whole,the brightness temperature gradient increases from January to September,reaches the maximum around September,decreases subsequently and gets to the minimum around January.It is considered as the result of the effect of the cold air in winter,the absorption of the atmosphere to ground radiation and the diversity of different geographical environments are the key factors that influence the temporal and spatial variation of brightness temperature gradient.