Table of Content

06 December 1995, Volume 17 Issue 4

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Brief Report

EFFECT OF DEHYDRATION OF MONTMORILLONITE ON CONSTITUTIVE BEHAVIOR OF FRICTION

Ma Shengli, Shimamoto Toshihiko

1995, 17(4):  289-304. 

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The velocity dependence of friction along fault zone with montmorillonite gouge at different temperatures has been studied on a biaxial friction rig at high temperature.The results show that the frictional strength of fault zone increases with increasing temperature,while the velecity dependence is rather complex. At room temperature and 100℃,the friction shows weak velocity weakening at slip rate below 1.4um/s,but velocity strengthening above 1.4 um/s.At 200℃,velocity strengthening is observed at all slip rates.At 300℃,the friction still shows velocity strengthening at slip rate above 1.4um/s,but changes into velocity weakening at slip rate below 1.4um/s. When temperatures are above 400℃,great velocity weakening is observed at all slip rates. The analysis indicates that the changes in frictional behav-ior are closely related with the dehydration and relevant change in deformation mode of fault gouge.

EXPERIMENTAL STUDY ON STICK-SLIP INSTABILITY AND EVOLUTION OF ITS PHYSICAL FIELDS

Deng Zhihui, Ma Shengli, Ma Jin, Liu Liqiang, Liu Tianchang, Ma Wentao, Zeng Zhengwen

1995, 17(4):  305-310. 

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Strain,displacement and AE waveform are observed along a fault in stick-slip experimentswith multi-channel digital sampling system.Some results are discussed in this paper:(1)Moststick-slip events and AE events took place at the same time.(2)There are pre-slip phenomenabefore some single events,No evident relationship between the fault displacement and magnitudeof AE events was found.(3)Inhomogenous spatial distribution of strain energy is an importantcondition for instable slip.Large events often take place in rapid energy change belts or low ener-gy region in high energy background,rather than in the highest energy area. This result can beapplied to outline of the seismic risk regions.(4)Exchange and mutual complement of strain en-ergy between source and adjacent regions are observed.The change of strain energy in source isalways contrary to that in adjacent regions.(5)There is an important difference between largeevents and small events,single events and multiple events.There are several times of energy ex-change before the large single events,and only an energy increase and hardening process beforethe small events or multiple events.

THE DOPPLER EFFECTS OF AE WAVEFORM IN ROCK FRICTION

Ma Wentao, Ma Jin, Ma Shengli, Lui Liquang

1995, 17(4):  311-317. 

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The waveform of AE(acoustic emission)events during rock friction has been studied.112large AE events through AE transducers attached along the faults have been recorded by a multi-channel digital recording system.The Doppler effects are evident by the waveforms of large AE events. For example,the firsthalf cycle of acoustic wave at AE transducers 1～3 is longer and at AE transducers 4～6 shorter.So it is shown that the displacement propagates in direction from AE transducer 1 to AE trans-ducer 3 with a dimension of 5.1 cm.The first phase(fore-excitation wave),source spreadingphase and stopping phase can be easily distinguished from the waveform of AE events.The ve-locity of fore-excitation wave and stopping phase is the same as P-wave. According to the break-ing phase recorded in different channels the breaking velocity of AE source increases from 0km/sto 2.62 km/s.It shows that the large AE events have an accelerating breaking process.The waveform of different events in a sequence of AE events changes with time,In earlystage the amplitude of fore-excitation wave is smaller and the difference in arrival time betweenfore-excitation wave and stopping phase is larger,the stopping phase is ambiguous and the break-ing velocity of AE source is low(1.6 km/s).Then the amplitude of fore-excitation wave increas-es gradually,the difference in arrival time between fore-excitation wave and the stopping phasebecomes smaller and the stopping phase is obvious.At the same time,the breaking velocity of AEsource reaches about 2.62 km/s.After that the first wave is overlapped by a large special phasewith higher frequency.This shows that the displacement process along a single fault is a complexprocess.

EXPERIMENTAL STUDY AND NUMERICAL SIMULATION ON PHYSICAL FIELDS DURING THE DEFORMATION OF A 5癇END FAULT

Ma Jin, Ma Wentao, Ma Shengli, Deng Zhihui, Liu Liqiang, Liu Tianchang

1995, 17(4):  318-326. 

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The spatial and temporal evolutions of the physical fields during the deformation of a 5癰endfault are studied by experimental and numerical methods.It is shown that the AE events nearbend point occurred usually at the beginning time or the ending time in an AE event sequence.Even though their magnitude are small,they are very significant.During the deformation twofault segments on each side of the bend point become initiative,alternatively. The bend pointplays a role of valve during the displacement along a fault.

EXPERIMENTAL STUDY ON EVOLUTION OF PHYSICAL FIELD DURING DEFORMATION OF EN-ECHELON FAULTS(1)

Ma Shengli, Deng Zhihui, Ma Wentao, Liu Iiqiang, Liu Tianchang, Ma Jin, Zeng Zhengwen

1995, 17(4):  327-335. 

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The spatial and imporal evolution of acoustic emission, fault displacement and strain duringdeformation of compressional and extensional en-echelon faults has been studied experimentallyunder biaxial compression. The results show that two types of en-echelon faults have similar de-formation process,i.e. the deformation is predominated by fracturing and linking of jogs in thefirst stage and by sliding along faults in the second stage.However,in the compressional jog,high strain energy can be accumulated and intense release of strian and acoustic emission can beproduced,and the jog has a permanent resistance to the sliding of faults, But in the extensionaljog,rapid release of strain and strong acoustic emission event can not be produced,and the joghas almost no resistance to the sliding of faults in the second stage.The instability events causedby linkage of both jogs have obvious precursors,and the occurrence of precursors for instabilityoccured during the sliding depends on if there is strain transfer between different parts of faults.

EXPERIMENTAL STUDY ON EVOLUTION OF PHYSICAL FIELD DURING DEFORMATION OF EN-ECHELON FAULTS(2)

Ma Shengli, Liu Liqiang, Deng Zhihui, Liu Tianchang, Ma Wentao, Ma Jin, Zeng Zhengwen

1995, 17(4):  336-341. 

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The spatial and temporal evolution of acoustic emission, fault displacement and strain duringdeformation of complex en-echelon faults composed of compressional and extensional en-echelonfaults has been studied experimentally under biaxial compression.The results show that the deformation process and the evolution of physical field on complex en-echelon faults are not a simplecombination of that of two types of en-echelon faults,but contain interaction between them.Aninteresting phenomenon is that acoustic emission events with high energy occur mostly alongmain fault near extensional jog with lower stress level,not along fault near compressional jogwith higher stress level,but the time of such events is obviously controlled by the deformationprocess of compressional jog.

THE CHARACTERISTICS OF ACOUSTIC EMISSION IN EN ECHELON STRUCTURE

Ma Wentao, Ma Jin, Liu Liqiang, Ma Shengli, Liu Tiancang, Deng Zhihui

1995, 17(4):  342-348. 

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In this paper the difference in waves, frequences, and sources mechanism is analyzed by com-paring the characteristics of acoustic emissions in the rock bridge of tensile en echelon structurewith that in the rock bridge of compressive shear structure,or that on main fault so as to revealthe characteristics of acoustic emissions in en echelon structure,The result shows that acoustic e-missions in en echelon structure have several mechanisms. The acoustic emission in the rockbridge of tensile en echelon structure is of one single event,its amplitude of waveform is verysmall with short duration time and higher main frequency,and mechanism of acoustic emissionsbeing tensile. The acoustic emission in the rock bridge of compressive shear en echelon structureis also of single event with larger amplitude of waveform,short duration time and lower main fre-quency,and mechanism of acoustic emissions being compressive shear. But the acoustic emissionon main fault of en echelon structure is of multiple events with largest amplitude of waveform,longer duration time and lowest main frequency,and mechanism of acoustic emissions being com-pressive shear whose direction of fracture is opposite to that of that in the rock bridge of compres-sive shear.

CHARACTERISTICS AND EVOLUTION OF BACKGROUND STRAIN FIELD ON TYPICAL STRUCTURE MODELS

Liu Liqiang, Ma Jin, Ma Shengli

1995, 17(4):  349-356. 

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Under loading force,certain strain image pattern appears in one of the typical models. The features of the strain image pattern will change during deformation. Study of the features andtheir changes is helpful to distinguish unstable precursors and predict trend of deformation. Astrain field can be divided into several areas.They have different behaviors and interact each other during deformation and instability.Aclosely integrated dynamic system is formed of them.Therefore,the temporal and spatial evolution processes should be monitored overall in order to obtain precursors and seek mechanism of instability.

DESIGN AND TRIAL-MANUFACTURE OF THE SYSTEM FOR MEASURING PHYSICAL FIELDS OF TECTONIC DEFORMATION IN LABORATORY

Liu Liqiang, Liu Tianchang

1995, 17(4):  357-362. 

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Setting up a system for measuring physical fields of tectonic deformation in laboratory is a valuable for study of earthquake prediction,improvement of the accuracy of physical prediction,and testing various methods for prediction.Therefore,a digital measurement system with multi-channel,high resolution,width energy scale and frequency band is designed and trial-manufac-tured.By using many kinds of sensors connected with the system,various physical fields can berecorded synchronously.

THE STAGES OF ANOMALIES BEFORE AN EARTHQUAKE AND THE CHARACTERISTICS OF THEIR SPATIAL DISTRIBUTION

Ma Jin, Ma Shengli, Liu Liqiang

1995, 17(4):  363-371. 

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The complication of tectonics in CHina gives us an advantage to find some anomalies near orfar from the coming earthquake.They may be alert to the occurrence of a strong earthquake.However the problems are:1)before some strong earthquakes there were no anomalies,2)insome cases no earthquake occurred after the anomalies,and 3)in some cases the place with obvi-ous anomalies did not correspond to the epicenter.Therefore,studying the stages of anomaliesand analysing the cause and spatial distribution may help us to elucidate the problems.The deformation process in a region may be divided into 4 stages:stage Ⅰ is before the yieldpoint,and stage Ⅱ is between the yield point and peak strength point.Stages Ⅰ and Ⅱ may berelated to the long-term to medium-term stages before earthquake。Stage Ⅲ is between strengthpoint and instable point and stage Ⅳ is after instable point.Stage Ⅲ may be related to the short-term to imminent stages before earthquake.The anomalies appearing in stages Ⅰ and Ⅱ may becaused by the change of driving force and the anomalies in stage Ⅲ may be caused by the propa-gation or weakening of the fault and smoothening of the fault surface.A numerical modelling has been made to study the spatial distribution of anomalies in eachstages. In order to reveal the distribution and its causes more clearly,the increment mean stressδσ_m and the increment maximum shear stress δτ_max are calculated. It is shown that the distributionof δτ_max in stages Ⅰ and Ⅱ is similar to the background stress field.The distribution of δσ_m instage Ⅱ is outstanding on the en-echelon jogs.the distribution of δτ_max and δσ_m display an eight-petaline pattern and a four-quadrant pattern,respectively,the propagation point is in the center ofthe pattern.The temporal process of the distribution of the increment stress field in an en-eche-lon fault system has also been studied.

A DISCUSSION ON THE DISTURBANT STRESS FIELD IN COMPLEX FAULT SYSTEM AND IDENTIFICATION OF SEISMOGENIC FAULT

Ma Jin, Liu Liqiang, Ma Shengli, Deng Zhihui

1995, 17(4):  372-382. 

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The anomalies are caused by the propagation or weakening of fault segments in short-termto imminent stages before an earthquake. The results of experiments and numerical simulationhave shown that the disturbant stress field accompanying by the short-term to imminant stage is afour-quadrant pattern for mean stress and an eight-petaline pattern for maximum shear stress.Inorder to judge the applicability of the mentioned patterns,a series of numerical models have beenstudied.It is found that no matter how complicated the fault system and the stress field are,thedisturbant stress field,basically,keeps the patterns,if the propagation or weakening has oc-curred along a fault.This result provides us a basis to distinguish the possibly coming instablefault.Meanwhile,the distortion of the disturbant stress field in complicated tectonic settingshould not be neglected.

EXPEKIMENTAL STUDY ON THE PREPARATION AND OCCURRENCE OF STRONG EARTHQUAKE

Wang Chunhua, Liao Suqiong

1995, 17(4):  383-389. 

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In this paper,the tectonic features for preparation of strong earthquakes in China are distin-guished into three types:pivotal,intersection and step area types after our laser holographic pho-to elasticity experiments.The characteristics of distribution of strain field and principal stress,shear stress under the effect of recent tectonic stress field are quantitatively analysed.The studyresult suggests a dynamic process for preparation of earthquake,mechanism of earthquake rec-currence and tectonic factors affecting earthquake magnitute for these three types of tectonic features.

BASIC CHARACTERISTICS OF ACTIVE FAULT ZONES IN SICHUAN PROVINCE

Tang Rongchang, Huang Zuzhi, Ma Senghao, Gong Yu, Zou Rongjun

1995, 17(4):  390-396. 

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From a large amount of available data in Sichuan Province,this paper deals with basic characteristics of active fault zones.The faulting is of zonal character,stronger in western and weak-er in eastern parts separated by NE-trending Longmenshan fault zone and NW-trending Xingjin-Mabian-Yanjing fault zone,The faulting is homogeneous in time,space,and strength and ofsegmentation character.Rupture cased by strong earthquake usually took place along the exisingfaults since later Pleistocene and Holocene.And displacement along the faults takes the form oftectonic pulsation as found in study of prehistoric earthquakes and instrumental records of seis-micity.

A PRELIMINARY STUDY ON RELATIVE MOTION OF ORDOS AND LONGXI BLOCKS DURING THE QUATERNARY PERIOD FROM PALEOMAGNETIC RECORD

Liu Aiguo, Lu Yanchou, Ding Guoyu

1995, 17(4):  397-404. 

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In this paper we describe our efforts to determine relative motion of different blocks duringthe Quaternary period by using paleomagnetic method. The Ordos and Longxi blocks,on whichLuochuan and Jiuzhoutai loess profiles lie respectively,are selected for the study.Luochuan andJiuzhoutai loess profiles are complete and comparable in age of loess-paleosol sequences;Samplesfor paleomagnetic measurement were collected from 4 loess layers of these two profiles:upperpart of L₁,bottom of L₁, bottom of L₅ and bottom of L₁₅.The age of these layers is 15 ka B.P.,85 ka B.P.,and 1.1Ma B.P.respectively.The Ordos block is considered to be motionless;The virtual geomagnetic pole(VGP)posi-tion of different periods was obtained from paleomagnetic measurements of each layer on Lu-ochuan profile and its location. Paleomagnetic declinations expected(D_ex)of Lanzhou were calcu-lated from VGP position and the location on Jiuzhoutai profile.There are differences between de-clination expected(D_ex)and declination observed(D_ob )in different periods. The differences are-0.7±5.2°,-1.8±2.4°,-4.1±3.8°and-9. 0±4.7°。It indicates that Longxi Block hasundergone clockwise rotation relative to the Ordos Block since 1.1 Ma B. P. The mean rotationrate is about 0.5′/ka.

ON THE STRUCTURAL FEATURES OF THE FRONTAL STEEP-DIP SHEAR ZONE OF THE GUANGNING DEEP-LEVEL NAPPE IN WESTERN GUANGDONG

Zhang Boyou, Zhao Zhenhua, Xia Bin, Shi Manquan, Yu Hongnian, Guo Lingzhi

1995, 17(4):  405-415. 

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Hetai gold-bearing ductile shear zone is a frontal steep-dip shear zone of Gunagning deep-level nappe structure in Western Guangdong,and is also a composite shear zone formed by thethrust shearing and subsequent dextral strike-slipping of Hetai shear zone. The characteristics ofdeformation and the microstructures of mylonites are also studied.In addition,the differentialstress and the strain rate of the deformation are estimated through study of the mylonites underpolarizing microscope and TEM.

THE TORSIONAL SEISMIC RESPONSE ANALYSIS OF THE END-BEARING PILE FOUNDATION

Liu Zongxian, Li Yuting, Jia Xiangyu, Fu Wenbin

1995, 17(4):  416-418. 

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A STUDY ON THE RECENT ACTIVITY ALONG THE SOUTHERN SEGMENT OF WUCHUAN-SIHUI FAULT ZONE

Zhang Hunan, Ji Fengju, Li Ziquan, Chen Weiguang, Liu Mingda, Li Jianping

1995, 17(4):  419-426. 

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Based on the tectonic-geomorphic features,comparison of Quaternary system with isochron-ic geomorphic surface on both sides of the fault as well as the micro-and macro-structural indica-tions of the fault trace,the activity since late Pleistocene along the southern segment ofWuchuan-Sihui fault zone is discussed.It is suggested that this segment of the fault is relativelystable during this period.

RECENT MOVEMENT PATTERN ALONG THE ZEMUHE FAULT AND DEFORMATION INDICATORS FOR ITS IDENTIFICATION

Zhang Chongli, Ren Jinwei

1995, 17(4):  427-431. 

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The recent movement along the Zemuhe fault and deformation markers for its qualitativeidentification are discussed in the paper.Our investigation shows that the recent movement alongthe fault is characterized by clear segmentation and the fault has been bisected into southern andnorthern segments bounded at Daqing site. The northern segment shows mainly stick-slip move-ment and the southern segment shows creep movement.The spatial distribution of vertical dis-placement rate is evidently different on the fault segments and hence can be used as indicators foridentifying the recent movement pattern on the fault.The relative displacement rate is also an in-dicator for identifying the recent movement pattern along the fault.

PRELEMINARY DISCUSSION ON THE GEOLOGICAL ENVIRONMENT OF SEISMIC GAP IN SONGXIAN BASIN AND ITS PERIPHERY,WESTERN HENAN

Han Derun, Su Yizhi, Sheng Xiaoqing

1995, 17(4):  432-438. 

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In this paper,the characteritics of Meso-Cenozcic Songxian faul basin in western Henan arestudied after a tentative analysis of tectonic pattern,fault development,and fault activity.It issuggested that there are some features in the basin and its periphery,such as small-scale faults,lower neotectonic movement,no graben,horst and fault-block movement confined by second-order faults in the basin.The seismic gap,therefore,is formed as the basin is cut by deep faultsalong the basin boundary.

MOHR CIRCLES AND MAGNETOTELLURIC IMPEDANCE TENSOR INVARIANT ANALYSIS

Jin Guangwen, Sun Jie, Jiang Zhao

1995, 17(4):  439-445. 

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Mohr circles and their application to Magnetotelluric(MT)impedance tensor analysis aredescribed in this paper,It iS illustrated that the rotational invariants of MT impedance tensors,having the advantages of providing variety of MT in a formation and stability,are frequently usedin MT data interpretation,Mohr circle,connecting the different forms of invariant impedancetensors,becomes an important graphic dignostic tool in studying MT impedance tensor properties.With the help of this powerful tool,some MT parameters,such as structural dimensional-ty,skewness,anisotropy,can be expressed visually and simply in the circle diagrams which giveimportant information for studying both vertical and lateral variation of the conductivity structures.

SEISMIC VELOCITY IMAGE OF MOHO DISCONTINUITY BENEATH WEIHE FAULT DEPRESSION ANO ITS ADJACENT AREAS

Yuan Zhixiang, Xue Guangying, Ding Yunyu, Wang Caiyun

1995, 17(4):  446-452. 

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In this paper,using travel time data of head waves from natural earthquake and industrialexplosion recorded by local seismic network in Shaanxi Province and adjacent areas,the velocitvimage of Moho discontinuity beneath Weihe fault depression and adjacent areas is obtained bymeans of seismic tomographic technique.Then the relationship between the lateral velocity het-erogeneity and geological structures and seismicity is discussed.

THE NORTHERN PART OF THE NORTH CHINA PLATFORM AS A CANDIDATE REGION FOR THE CHINESE CONTINENTAL SCIENTIFIC DRILLING

1995, 17(4):  453-458. 

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