Table of Content

08 December 2005, Volume 27 Issue 4

Previous Issue    Next Issue

Brief Report

KINEMATIC MODELS OF FLUVIAL TERRACES OVER ACTIVE FAULT-RELATED FOLDS: CONSTRAINTS ON THE GROWTH MECHANISM AND KINEMATICS

CHEN Jie, Scharer K M, Burbank D W, WANG Chang-sheng

2005, 27(4):  513-529. 

Asbtract ( )   PDF (6116KB) ( )  

Related Articles | Metrics

Fluvial terraces,like growth strata,provide geomorphic markers that can record progressive deformation and mechanisms on underlying fault-related folds. Because terraces are generally preserved within the pre-growth strata,they record the deformation mechanism in the core of the fold. To explore the fold evolution and subsequent geometry of deformed terraces,we present ideal kinematic models for successively emplaced horizontal unconformities (terraces) across pre-growth strata in three types of growing fault-related fold. Three common mechanisms for fold growth are considered: hinge migration (Limb-lengthening),limb rotation,and a combination of the two. Both angular-hinge and curved-hinge zone migration are considered. Each model predicts distinct terrace architecture,fold scarps,and different angular relationships between the terraces and the pre-growth strata.Limb-lengthening fault-bend fold results in self-similar growth,marked by parallel pre-growth and terrace strath orientations across much of the fold,and steeply dipping asymmetric fold scarps along the fold's flanks.Limb-lengthening fault-propagation fold models result in self-similar growth parallel terraces,and step fold scarps in the back limb. Deformation by limb rotation detachment fold is marked by progressively less tilted terraces across the limbs and symmetric fold scarps along the fold's flanks.Migration of an angular hinge of detachment fold results in parallel,uplifted terraces in the core and steeply dipping symmetric fold scarps along the fold's flanks. When limb rotation and hinge migration are combined,the terrace architecture is consistent with the kinematics of each kink panel.The result of limb lengthening by migration of a curved hinge is dependent on the width of the curved hinge.If the hinge is wide and terrace abandonment is frequent compared to the migration rate,fanning terraces and fold scarps result. In additional,changes in base level have significant effects on the final terrace geometry. Uniform incision along the river profile results in an apparent uplift of the older terraces,while aggradation will cause older terraces to truncate into the less tilted,younger terraces.

QUATERNARY DETACHMENT FOLDING OF THE MINGYAOLE ANTICLINE,SOUTHWESTERN TIAN SHAN

CHEN Jie, Scharer K M, Burbank D W, Heermance R, WANG Chang-sheng,

2005, 27(4):  530-547. 

Asbtract ( )   PDF (7942KB) ( )  

Related Articles | Metrics

The preservation of multiple,clearly deformed Late Quaternary fluvial terraces and nearly continuous exposure of underlying Neogene sediments make the Mingyaole anticline detachment fold system particularly favorable for unraveling the geomorphic and structural history of underlying fold growth within the southwestern Chinese Tian Shan Foreland Basin. We mapped the Neogene structure and Pleistocene terrace surfaces along the south-flowing Kalanggouluke He within water gap across the anticline using 1∶50000 scale stereo air photographs and topographic maps. The anticline has steep (58°～70°) limbs and is box-like,characterized by broad north vergent core that rises above gently dipping outer flanks,suggestive of detachment folding. Since the growth strata are not sufficiently exposed to allow us to discern the kinematic style of fold growth,we profiled all sets of progressively deformed Pleistocene fluvial terraces plus the present rivers across the of the anticline using a laser ranging theodolite (total station) aiming to use the terrace flights as kinematic markers for the recent evolution of the folds. The terrace profiles are preserved across the steeply dipping cores and show several common features: (1) Where long profiles of terraces could be surveyed,the terraces show increased tilts with age. (2) The greatest tilts are preserved in the north limb towards the core of the fold. (3) Nearly all of the observed terrace heights are attributable to differential uplift. (4) The pre-growth strata and the terrace treads are discordant everywhere. (5) Part of the terraces are not folded across previously active axial surfaces that are now passive,and younger axial surfaces that remain active as evidenced by fold scarps. In combination with structural data,growth strata,and deformed terraces,we infer that the width of the Mingyale anticline is established early and is subsequently amplified throughout the history of the fold,but not in a purely self-similar style. Continued shortening is accommodated by vertical growth of the fold via a combination of limb rotation in the center and hinge migration on the flanks. Planar,rotated terraces indicate more recent folding is accommodated by block rotation of the limbs. In combination with paleomagnetic study and OSL dating,we infer the fold growth initiated ~1.6Ma and shortening rate and differential uplift rate decreased since then. Uplift is always greater than shortening which indicates limb rotation dominates.

THE CHRONOLOGY OF THE FIRST HARD CLAY IN NINGBO REGION

YIN Gong-ming, WANG Xu-long, ZHOU Ben-gang, YE Jian-qing, LI Jian-ping,

2005, 27(4):  548-555. 

Asbtract ( )   PDF (2544KB) ( )  

Related Articles | Metrics

Several dark-green or yellow-brown layers with different thickness have been found in the late Quaternary strata in the area of the Changjiang River and Jiantangjiang River. They are very hard,called “hard clay”. The top hard clay layer is called the first hard clay. There are the marine sediments on the first hard clay. The boundary of Holocene has been discussed based on the first hard clay. The first hard clay is found in Ningbo region too. 19 samples from the first hard clay,the marine sediments on the first hard clay and the layer under the first hard clay,were dated using optical luminescence and 14 C dating method to provide age control of its development. According to our dating results,the age of the original material of the first hard clay is 45～55ka BP. The first hard clay is uncontinuously distributed,being eroded by the later stages transgression in some places,and unconformable with the upper marine sediments. The lower limit of the marine bed may not be simply delineated as the Holocene boundary. It is possible that the marine sediments occurred at the end of late Pleistocene.

STRATA DIVISION OF BURIED LATE QUATERNARY OF FUZHOU BASIN

ZHENG Rong-zhang, CHEN Gui-hua, XU Xi-wei, ZHU Jin-fang, HUANG Zong-lin, LI Jian-ping

2005, 27(4):  556-565. 

Asbtract ( )   PDF (3166KB) ( )  

Related Articles | Metrics

Fuzhou basin is tectonically located in the eastern part of South China fold system,within the Fuding-Yunxiao Fault depression area of East Fujian volcanic depression zone. Based on detailed logging,and combined with results of other researchers,the preliminary summarization on sedimentary characteristics of late Pleistocene of Fuzhou basin is done. The depositing of Fuzhou basin began from about 56.5ka BP,sediments comprise gravel,sand,clay and silt,showing a depositional sequence with the granularity becoming small from lower to upper,and a bigger variation of lithologic properties in horizontal direction. There are three silt layers in late Quaternary strata of Fuzhou basin. The first and second layers developed during the middle and late Holocene,the depositing time of them is about from 7.86ka BP to 3ka BP to 3.08ka BP and they are the results of “Changle Transgression”; the third developed during the late of late Pleistocene and the depositing time is about from 44ka BP to 20ka BP and it is the result of “Fuzhou Transgression”. The buried late Quaternary sediments in Fuzhou basin can be divided into upper Pleistocene series and Holocene series,which include four formations from old to new. They are Longhai formation(Q³_pl),Dongshan formation (Qhd),Changle formation (Qhc)and Jiantian formation (Qhj) respectively. The Longhai formation can be divided into three members,the sediments of the lower member are celadon,yellow gravel and moderate coarse sand; the middle member is of gray clay,silt,sand and gravel,or interbed of silty clay and fine sand; the upper member is of yellow moderate coarse sand. Dongshan formation comprises gray silty sand and clay. Changle formation can be divided into two parts,the lower part is of interbed of silt and flour sand; the upper is of gray and plumbeous silt or douke silt. The Jiantian formation comprises light gray,brown clay.

RESEARCH ON EFFECTS OF CONTENTS OF RADIOACTIVE ELEMENTS ON GRANULARITY AND CLIMATE CHANGE——AN EXAMPLE OF SZK1 AND SZK2 DRILL HOLES STRATA IN FUZHOU BASIN

ZHENG Rong-zhang, XU Xi-wei, ZHU Jin-fang, HUANG Zong-lin, LI Jian-ping, JI Feng-ju,

2005, 27(4):  567-577. 

Asbtract ( )   PDF (2793KB) ( )  

Related Articles | Metrics

As a fault depression basin developed in the middle and late Quaternary,the Fuzhou basin consists of complicated deposit structures,including deposits of marine facies,terrestrial facies and marine and terrestrial alternating facies. The thick source alpha counter and flame-photometer are used to measure the content of radioactive elements (uranium,thorium and Potassium) of two drill holes (SZK1 and SZK2) strata in Fuzhou basin. Comparison of the content of radioactive elements with the result of spore-pollen analysis of one drill hole (SZK1) strata shows that the former changes with the variations of lithology and depositional environment. The content of radioactive elements in sediment is related to the scale of sediment granularity and lithology,being high in argillaceous sediments (e.g. silt and clay),low in sandy sediments and median in gravel strata. On the other hand,the contents of radioactive elements are relative to paleoenvironment,the warm and humid environment is propitious for high concentration of radioactive elements; while cool and dry climate is just the opposite.

THE RADIOCARBON AGES OF CHARCOAL AND THEIR IMPLICATION DERIVED FROM CIERGOU SITE ALONG THE HAIYUAN STRIKE-SLIP FAULT

YIN Jin-hui, CHEN Jie, ZHENG Yong-gang, ZHANG Ke-qi, LIU Yue-xia

2005, 27(4):  578-585. 

Asbtract ( )   PDF (2952KB) ( )  

Related Articles | Metrics

A trench across the Haiyuan active fault zone reveals many layers of charcoal with human bone,scruff,ceramic pieces or hearth ruin as well as three colluvial wedges in Ciergou paleoearhquake profile which is located on the northern margin of Tibet Plateau. It is important to distinguish these historical remnants as whether or not they are the product of earthquake. 12 radiocarbon dates and 6 post-IR OSL dates were determined from charcoal samples corresponding to human activity and sediments or burned clay samples around charcoal samples respectively. The ages of charcoal which mainly range from 1000 to 2400a BP were sharply younger than the age of strata. The age of living site inferred from charcoal with scruff,ceramic pieces,does not agree with timetable of the historical strong earthquake record. This evidence could indicate that the living site ruins is not the product of historical earthquake. The penultimate paleoearthquake prior to 1920 AD earthquake occurred in 21.8～14.5ka which was constrained by post-IR OSL dates. These dates would help to better understand the strong earthquake recurrence interval of the Haiyuan active fault zone.

OPTICALLY STIMULATED LUMINESCENCE DATING OF FLUVIAL DEPOSITS FROM THE MINGYAOLE ANTICLINE IN THE SOUTHWESTERN TIAN SHAN

WANG Chang-sheng, CHEN Jie, ZHANG Ke-qi

2005, 27(4):  586-598. 

Asbtract ( )   PDF (4623KB) ( )  

Related Articles | Metrics

Optical dating of fine-grained fluvial sediments remains a complex endeavour. Five fluvial sediments have been collected from the Kalanggouluke He,Mingyaole anticline,in the Southwestern Tian Shan. We employ both ‘Double-SAR' and ‘Double-SMAR' procedure in which aliquots are subjected to both infrared (λ=860nm) and blue (λ=470nm) stimulation and two sets of De determinations are produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively. There are significant differences between the equivalent doses for the IRSL and (post-IR) OSL measurements. We extracted fine-grained quartz via etching in fluorosilicic acid for sample LEDL03-87q,LEDL03-86q and LEDL04-54q. SMAR procedure (Wang et al.,2005) and SAR procedure were used to determine their equivalent dose (De). Our data indicate a significant IRSL De underestimate due to anomalous fading of the natural IRSL from feldspathic fine grains for all the samples. Caution should be taken when using the post-IR OSL De for fluvial sediments. BLSL De distribution analysis indicates that samples LEDL03-87q,LEDL03-86q and LEDL04-54q were partially bleached. We suggest using the minimum component of De to estimate their ages.

GEOCHRONOLOGY SIGNIFICANCES OF THE POST-OROGENIC MAFIC-ULTRAMAFIC ROCKS IN HONGQILING AREA OF JILIN PROVINCE, NE CHINA

ZHANG Guang-liang, WU Fu-yuan

2005, 27(4):  600-608. 

Asbtract ( )   PDF (3088KB) ( )  

Related Articles | Metrics

Mafic-ultramafic complexes are widespread in Hongqiling area in central Jinlin Province,NE China. The Hongqiling complex comprises pyroxenite,olivine websterite,lherzolite,gabbro and leucogabbro. Based on the latest geochronological results,these intrusions yield a zircon U-Pb age of about 216Ma BP,which implicates they emplaced in late Triassic and the mafic-ultramafic complexes are post-orogenic in origin. These ages are coeval with the emplacement of A-type granites in the area,but slightly younger than syn-orogenic granitic magmatism. The composition of the parent magma during the equilibration of the cumulate olivine crystallizing is basaltic with high MgO,and it comes from depleted or juvenile lithospheric mantle according to the results of trace elements and Sr-Nd isotopes. Amount of crustal material contaminated the magmatic source,implying that mafic-ultramafic rocks originate from the mixing product of crust-and mantle-derived magma. So the magmatic source was contaminated by an amount of crustal material,and the subsequent crystal fractionation resulted in the Cu Ni mineralization. Dynamic analyses indicate that,after the collision of the North China Craton and Jiamuqi Massif,the lithospheric delamination during post-orogeny resulted in the upwelling of asthenosphere and the intruding of the mass of mantle-derived magma and the underplating of mantle-derived magma,which led to forming the primary mafic-ultramafic magma due to mantle-derived magma and partial melting of the lower crust. This result suggests that the mafic-ultramafic complexes belong to a typically important magmatic suite that evolved during post-orogenic processes,and they exposed as mafic-ultramafic dyke swarms that existed in the post-orogenic extension environment. It also implies the orogenic process finished ultimately in this regional geological setting. The widespread occurrence of mafic ultramafic complexes in the Xing'an Mongolian Orogenic Belt of NE China and in the Altay Tianshan Junggar Orogenic Belt of Northern Xinjiang indicates that mafic intrusions are an important magmatic suite that evolved during post-orogenic processes. Portions of this mafic magma could have underplated the lower crust,and served as the heat source for associated late-stage granitic magmas.

ACCURATE DATING AND TEST OF K-AR AND AR-AR METHODS

LI Da-ming, LI Qi, ZHENG De-wen

2005, 27(4):  609-614. 

Asbtract ( )   PDF (1786KB) ( )  

Related Articles | Metrics

The K-Ar and Ar-Ar dating methods are the developed methods and widely applied to various geosciences'fields. Study on the active tectonics,latter-day volcanoes and paleo-geomagnetism requires that the K-Ar and Ar-Ar methods should be developed towards the accurate dating and small time-scale. In recent years,geologists have paid much attention to dating the Tongchang volcano,Changbaishan volcano and Wadalianchi volcano in China and acquired many achievements. So it is practically significant to study and summarize the K-Ar and Ar-Ar methods and their test for accurate dating. The key to accurate dating is: (1) appropriate sample; (2) strict pretreatment; and (3) proper measurement. In detail,the appropriate sample is that the sample can stand for right geological meanings and it is examined to be fresh under microscope over rock slice. The pretreatment is a complex process and is very important. For example,the age of raw volcanic rock in eastern slop of Maanshan is 0.18?0.08Ma and 0.45?0.32Ma due to the effect of excess argon in crystal. However,by picking out the olivine and plagioclase crystal,the age is 0.025?0.004Ma,0.028?0.006Ma and 0.030?0.005Ma,showing a good consistency. The useful method to test the validity of the measurement process is the repeated measurement of standard sample and geologic specimen. At the same time,the difference between the repeatedly measured results should be less than the theoretic error. For example,the repeatedly measured results of the two samples from Maanshan are 0.028?0.006Ma and 0.030?0.005Ma,0.030?0.005Ma and 0.036?0.005Ma,and 0.046?0.004Ma and 0.050?0.003Ma,respectively. In addition,inter-lab comparison and inter-chronology comparison are valid methods,too. The result of K-Ar and Ar-Ar dating usually is the value which is measured one time from one sample. There are two factors,including sample and measurement,which affect the result. In order to improve the accuracy of measurement,the sampling and experiment process should be reasonable and stringent. In addition,it is necessary to test out the result by a series of methods,such as inter-chronology comparison,inter-lab comparison and geological feature.

LUMINESCENCE DATING OF FINE-GRAINED QUARTZ IN CHINESE LOESS-SIMPLIFIED MULTIPLE ALIQUOT REGENERATIVE-DOSE (MAR) PROTOCOL

WANG Xu-long, LU Yan-chou, LI Xiao-ni

2005, 27(4):  615-623. 

Asbtract ( )   PDF (2807KB) ( )  

Related Articles | Metrics

A Simplified Multiple Aliquot Regenerative-dose (MAR) protocol is introduced in this paper,in which after each natural and regenerative-dose OSL (L_i) measurements,the OSL response (T_i) to the test dose is used to monitor the sensitivity changes for multiple aliquots as Single-Aliquot Regenerative-dose (SAR) protocol does on single-aliquot. From the methodological aspects,Simplified MAR protocol can correct for the sensitivity changes,overcome the scattering of the experimental data in MAR measurement procedures and possibly avoid the buildup of OSL signals that happens in the SAR protocol; these lead to recover De values with high accuracy and precision. When comparing the OSL ages obtained in this way with the reference age of the M IS5/4 transition from the SPECMAP record,no apparent age underestimation occurred. On the basis of the methodology and validated by dating reference age samples,Simplified MAR protocol is a reliable and timesaving way for luminescence dating of fine-grained quartz in Chinese loess.

THE PERFORMANCE TEST OF QUANTULUA-1220 LIQUID SCINTILLATION COUNTER

ZHENG Yong-gang, YIN Jin-hui, LIU Yue-xia

2005, 27(4):  624-632. 

Asbtract ( )   PDF (2569KB) ( )  

Related Articles | Metrics

We use the Chinese Sucrose Standard and synthetical benzene as well as 13 paired-samples to assess the performance of a new Quantulua-1220 bought in July,2004. The results show that:1) when the background is below 0.5cpm and the fluctuation does not exceed 4‰ in the measuring surrounding,we infer the maximum datable age for this instrument would be up to almost 48ka; 2) The quench SQP(E) parameters of 261 radiocarbon samples vary from 700 to 758. The median is 735.522 and standard deviation is 9.150 57. The maximum age error caused by quenching factor is below 80a; 3) The t test results of 13 paired-samples indicate that the new Quantulua-1220 became stable after it ran for 10 months and the ages are indistinguishable in statistical test from ages supplied by other similar LSCs.

CALIBRATION OF DAYBREAK THICK SOURCE ALPHA COUN-TER AND PRELIMINARY STUDY OF INFLUENCING FACTORS

WANG Tong-li, CHEN Jie, YANG Chuan-cheng

2005, 27(4):  633-644. 

Asbtract ( )   PDF (3449KB) ( )  

Related Articles | Metrics

It is very important to determine annual radiation dose in luminescence dating and electron spin resonance dating. The aim of this paper is to calibrate low background Daybreak 582 and 583 thick source alpha counter (TSAC) which is used extensively in OSL dating lab by comparison of different standard sources. Meanwhile we analyze the factors such as efficiency of ZnS scintillator,measurement time,and the loss of radon,grain size,moisture,colour of sample on alpha counting,and provide some suggestions for improvement of accuracy.

EFFECT OF LATERAL STRESS PERTURBATION ON FRICTIONAL BEHAVIOR: AN EXPERIMENTAL STUDY

CUI Yong-quan, MA Sheng-li, LIU Li-qiang

2005, 27(4):  645-652. 

Asbtract ( )   PDF (2256KB) ( )  

Related Articles | Metrics

The crustal movement shows obviously non-linear characteristics in time and space,and the tectonic deformation and related phenomena are undoubtedly affected by such non-linear mechanical process. Experimental study on frictional behavior under non-linear loading is helpful for understanding the effect of stress change on earthquake mechanism. In this paper,the frictional experiments on medium-scale granodiorite samples containing 45? precut surface have been conducted by using a servo-controlled biaxial rig,and the effect of lateral stress (σ₂) on friction has been studied. The experimental results indicate that the interval and stress drop of stick-slip events increase with increasing normal stress on sliding surface under constant loading velocity in the direction of maximum compression stress σ₁ and constant lateral stress σ₂.However,the relation is greatly changed when stress perturbation of sine wave with high frequency and small amplitude is added to σ₂. Stress drop and interval of stick-slip events are obviously scattered. In particular,the magnitude of stress drop may tremendously increase. Strain measurement indicates that the perturbation of lateral stress increases the heterogeneity of strain distribution and release along fault,and stick-slip events with large stress drop and that with small stress drop are corresponding to strain release along whole fault and that along parts of fault,respectively. Compared to the previous experiment result of stress perturbation in σ₁,the effect of perturbation in σ₂ on stick-slip is more obvious,meaning that change in normal stress may affect fault instability more greatly than change in shear stress. The experimental results imply that not only the effect of change in coseismic Coulomb stress on seismicity should be analyzed,but more attention should be paid to the possible effect of change in normal stress on fault when the fault interaction is considered.

DATA SERVICE SYSTEM FOR ACOUSTIC EMISSION EXPERIMENT IN LABORATORY

HU Xiao-yan, LIU Pei-xun, LIU Li-qiang, MA Sheng-li

2005, 27(4):  653-660. 

Asbtract ( )   PDF (2773KB) ( )  

Related Articles | Metrics

Acoustic emission (AE) technique is one of the important methods in rock mechanics and experimental seismology. Improving AE data acquiring and processing technology is a basic work in research of the features of AE during the process of rock deformation. Following the progress of the AE systems in State Key Laboratory of Earthquake Dynamics,more and more AE data were obtained with higher recording speed and higher resolution for every experiment. It is a challenge to store such growing data reasonably and deal with it efficiently up to now. Researchers who work in the stand-alone mode have to copy a lot of raw AE data files with different format from remote computer to local PC. Storage space and time are thus squandered away. In addition,every user has to rewrite some processing programs using his own language for the row data,as a result,human resource is wasted. The commercial data service systems are not designed for laboratory study. According to the special demands,AE data service system based on web is designed and realized in the laboratory. Experiment AE data and processing method can be accumulated with the system. On the AE data access interface which is independent of equipments,researchers can acquire and process data easily. The system enhances the frequency of data use and the efficiency of data processing because it allows more and more people to participate in processing and analyzing the AE data. The system not only satisfies the needs of researcher and programmer,but also overcomes the previous shortcoming in the operating mode of AE data management. The most important thing is that the resolvent of AE data service system can be extended and applied to other experiment data to improve work efficiency.

MEAN GRAD METHOD (MGM) FOR DISTINGUISHING INFORMATION OF CURRENT TECTONIC ACTIVITY FROM THERMAL RADIATION FIELD OF LAND SURFACE

CHEN Shun-yun, MA Jin, LIU Pei-xun, LIU Li-qiang, CHEN Guo-qiang

2005, 27(4):  661-668. 

Asbtract ( )   PDF (14889KB) ( )  

Related Articles | Metrics

Compared with the strong noise background,intensity of efficient signal is very small when using thermal radiation to obtain the current tectonic activity. Increasing range of thermal radiation resulting from fault activity accords with dimension of inversion precision of thermal radiation of land surface,and information of fault activity is submerged by inversion error of thermal radiation of land surface. Besides,it is difficult to discriminate the information of fault activity when the data precision is high. This paper develops a new method,i.e. the Mean Grad Method (MGM),to solve the above-mentioned problems. First,we average the long-time data to gain a higher data precision at an expense of losing time information,then,distinguish the space distribution of the current tectonic activity from thermal radiation field of land surface by space grad of thermal radiation according to the difference between influence of atmosphere and tectonic activity on land surface. This method can offer some features on variation of current tectonic activity with time and space and is helpful for plotting out earthquake danger area.

DISCOVERY OF THE GREAT FAULT OF THE TANGSHAN EARTHQUAKE

QIU Ze-hua, MA Jin, LIU Guo-xi

2005, 27(4):  669-677. 

Asbtract ( )   PDF (4301KB) ( )  

Related Articles | Metrics

The twentieth century's deadliest M7.8 Tangshan,China earthquake killed more than 240,000 people because it took place beneath a city of dense population. Therefore a great amount of various phenomena relating to this seismic event have been observed and documented. It was accepted as the seismo-generic fault of the earthquake when an about 8km-long intermittent surface fissure zone passing through the city was located,although it has been puzzling researchers that the inferred fault does not seem to be great enough for such a strong earthquake. The right-lateral displacements about the fissure zone were acknowledged to represent the strike-slip of the fault. Consequently,studies with focus on this fissure zone have obstructed researchers from paying much attention to other discoveries beyond the city. For example,field surveys reported some large subsidence areas produced by the earthquake with remarkable boundary fissures but no special articles have been published on them. We began our investigations in order to locate the subsidence areas in aerial photographs that were taken immediately after the main shock and came up with the shocking discovery of a previously unknown great seismic fault of the earthquake. The newly revealed great fault is at least 90km and has a coseismic vertical dislocation of 3m at the surface. What is more,it possesses the characteristics of a normal listric fault. The great fault can be divided into two parts. The southwestern part is proved by field investigation,leveling data,aerial photography and geophysical exploration,while the existence of the northeastern part is exhibited with evidences in water-flow distribution and seismic reflection profile. Distribution of aftershocks and leveling deformation agree perfectly with the sense of this great fault.

AN OVERVIEW OF RADIOCARBON CALIBRATION

YIN Jin-hui, ZHENG Yong-gang, LIU Yue-xia

2005, 27(4):  678-688. 

Asbtract ( )   PDF (3302KB) ( )  

Related Articles | Metrics

This paper presents the importance of converting the radiocarbon date into calendar year in paleoearthquake study and summarizes the history of the calibration curve as well as the current progress back to 50ka BP. The calibration method and computer program were also mentioned.

OPTICAL STIMULATED LUMINESCENCE SAMPLING AND DATING OF BORING CORE IN URBAN ACTIVE FAULT EXPLORATION

WANG Ping, CHEN Jie, LU Yan-chou, LIU Jin-feng

2005, 27(4):  689-697. 

Asbtract ( )   PDF (567KB) ( )  

Related Articles | Metrics

The reliability of ages from optically stimulated luminescence (OSL) dating of boring core has a stringent dependence on characteristic of samples,and on motheds of boring and sampling. When using a full core collected at boring,the uncertainty of estimation to equivalent dose at OSL dating is affected by some factors,such as mixture occurring in soft soil and sand,contamination due to mud penetrating into sample,the possible influence of heat from pressure and attrition on luminescence signals. In addition,a potential effect on dose rate of samples from boring cores should be emphasized,that is,the effect of change of water content and equilibrium of radioactivity. The basic conditions for sampling,protocols and methods of luminescence dating are important to for sampling correctly in the field. As general requirements for drilling in urban active fault exploration,this paper gives suggestions on sampling from boring core for OSL dating,and factors affecting results of measurement are also discussed.

DOSE DETERMINATION IN ESR DATING RESEARCH

LIN Min, JIA Li, DING Yan-qiu, CUI Ying, CHEN Ke-sheng, LI Hua-zhi, XIAO Zhen-hong, YIN Gong-ming

2005, 27(4):  698-705. 

Asbtract ( )   PDF (2685KB) ( )  

Related Articles | Metrics

In ESR dating,the age is given by the ratio of paleo-dose to annual dose. Generally,the paleo-dose is obtained by linear extrapolation in regeneration or additional irradiation method. Therefore,dose determination in manual irradiation becomes one of the important factors that effect reliability of the dating results. Usually,there are two ways to determine the dose of manual irradiation: one is called dose rate method,which calibrates the dose rate of the position by standard dosimeter before dating sample irradiation at the same position. Dose will be determined by the dose rate and irradiation time of the sample. In this method,Fricke dosimeter is usually used as standard dosimeter; the other is called concomitant method,which puts reference dosimeter together with the dating sample to the position before irradiation. They will be irradiated simultaneously and the dose will be given by the reference dosimeter. In this method,alanine dosimeter is generally used as the reference dosimeter. In the paper,these two methods are discussed. Two types of alanine dosimeter are used as reference dosimeters: one is pellet alanine dosimeter,the other is alanine film dosimeter. We use dose rate results that were calibrated one year ago to evaluate the current dose rates. Irradiation time is determined according to the nominal dose and the dose rate. However,the actual dose was determined by the alanine dosimeter that was irradiated with the dating sample together. Since it is not practical to calibrate the dose rate every time for every position before dating sample irradiation,the concomitant method that uses alanine dosimeter as reference to be irradiated with the dating sample together will be more practical and reliable compared with the dose rate method.

INVERSION OF SLIP RATES OF THE ZHUANGLANGHE FAULTS AND THE NORTHERN MARGINAL FAULT OF MAXIANSHAN BASED ON GPS MEASUREMENTS

ZHOU De-min, GAN Wei-jun, REN Jin-wei, Ni Guo-hui, NING Shu-zheng

2005, 27(4):  706-714. 

Asbtract ( )   PDF (4234KB) ( )  

Related Articles | Metrics

On the basis of geological data,the three-dimensional geometric model and the segmentation model of the spatial distribution of the Zhuanglanghe faults and the northern marginal fault of Maxianshan are firstly established; Then,with the constraints of slip rates of some studied thoroughly faults,the inferred GPS velocity from the project“Crustal Movement Observation Network of China”is simulated by using“Three-dimensional Deep-fault Dislocation Model”; Finally,the current sliding rates of some other faults are calculated with the inversion method. The results show that there is a rate of 1.4～3.0mm/a of thrust slip on the northern margin fault of Maxianshan,with a left-lateral slip rate of about 3.0mm/a on the middle of the faults,and that there is a thrust slip rate of 0.6～1.2mm/a on the Zhuanglanghe faults with unobvious left-lateral slip component. These results are in accordance with the geological results. The GPS station velocities predicted by the model are consistent with the observed velocities as a whole. It is therefore assumed that these results are all in the reasonable extent predicted before. For the faults with relatively low slip rates and on which the conventional geological methods are difficult to apply,e.g. the Zhuanglanghe faults and the Maxianshan fault,the inversion based on the GPS observations is an effective ancillary means.