Table of Content

02 September 2004, Volume 26 Issue 3

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Brief Report

KINEMATICS OF PRESENT-DAY TECTONIC DEFORMATION OF THE TIBETAN PLATEAU AND ITS VICINITIES

ZHANG Pei-zhen, SHEN Zheng-kang, WANG Min, GAN Wei-jun

2004, 26(3):  367-377. 

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As the most prominent example of large scale continental deformation,Tibetan Plateau offers an ideal natural laboratory for quantifying such deformation and understanding the relevant dynamic processes. Global Positioning System (GPS) provides a powerful means to directly measure the kinematics of present day deformation. Our synthesis of GPS velocities from 553 stations in Tibetan Plateau and its margins quantitatively show that most of the relative India/Eurasia motion has been accommodated primarily by crustal shortening along the margins,strike slip and normal faulting in the plateau interior,and clockwise rotation around the eastern end of Himalayas. Taken 36～40mm/yr as total relative motion between India and Eurasia,the eastern Tibetan Plateau and its margins accommodates 85%～94% of the total motion,whereas western Tibet absorbs 70%～91% of total convergence and the rests are taken up by shortening across the Tianshan in the north. The NNE SSW shortening of the plateau interior is accommodated by conjugate strike slip faulting and orthogonal normal faulting,which do not require crustal thickening or thrust faulting. The eastward extrusion of Tibetan Plateau out of India's northward pass is carried out by roughly eastward flow of crustal material rather than by rigid block rotation. The flow of Tibetan crustal material rotates around the eastern Himalayan syntaxis,causing southeastward to southward and even southwestward velocities observed in southern and western Yunnan Province of China. To the east,the eastward flow of crustal material causes shortening across the eastern margin of the plateau and clockwise rotations of the region where resistance to such flow is weak. To the west,the westward motion of the western margin of the plateau is observed with only 4mm/yr slip rate. Components of velocity of Tibetan Plateau in both parallel and perpendicular directions to the relative motion between India and Eurasia can not be attributed to slips along a few faults either strike slip or thrust because of their distributed nature. Thus,the present day tectonics in the Tibetan Plateau is best described as deformation of a continuous medium,at least when averaged over distances of ～100km.

SURFICIAL SLIP DISTRIBUTION AND SEGMENTATION OF THE 426-km-LONG SURFACE RUPTURE OF THE 14 NOVEMBER,2001,M_S8.1 EARTHQUAKE ON THE EAST KUNLUN FAULT,NORTHERN TIBETAN PLATEAU,CHINA

CHEN Jie, CHEN Yu-kun, DING Guo-yu, WANG Zan-jun, TIAN Qin-jian, YIN Gong-ming, SHAN Xin-jian, WANG Zhi-cai

2004, 26(3):  378-392. 

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The 14 November,2001 M_S8.1 West Kunlun Pass Earthquake is the largest event associated with the longest surface rupture that has occurred in the Tibetan Plateau since 1951. We made 291 surficial left lateral slip measurements and 111 net vertical slip measurements along the main fault zone. The displacement on the main fault strand is dominated by left lateral strike slip of 2.7m in average,with vertical slip component of mostly less than 1m. The maximum left lateral slip is 6.4m,with as much as 5.1m of vertical slip component. Sinistral surficial slip is quite variable along the main strand of the rupture at distance scales ranging from a few tens of meters to a few hundreds of kilometers,with slip gradient ranging between 10^-1～10^-4. The slip variations over short length scales (tens of meters to a few kilometers) might be caused by variations in thickness of unconsolidated sediments,fault strike and slip of the previous earthquake,distributed non brittle deformation and secondary fractures,complexities in fault geometry,and perhaps by measurement error. Despite this short wavelength variability,there is fairly regular long wavelength (tens to hundreds of kilometers) behavior to the east of the Buka Daban Peak. One notable characteristic of slip distribution along the faults is that very large surficial slips (as large as 5～6 meters) were observed at 5～6 sites located at different surface rupture segments in asymmetry to their left lateral slip functions. Slip on each of these rupture segments diminishes away from the highest slip site to its terminations with different slip gradients. This asymmetric distribution of slips may indicate the propagation direction of the rupture along the faults. This long wavelength variation in slip might be influenced by fault geometry,while the segmentation of the surface rupture zone might play a key role. It should be pointed out that the surficial slip (at both short and long length scales) is only a near field slip measured in the field by using tape measure. Therefore,it should be considered as a minimum value,and may represent the real variations in the amount of brittle slip on visible fractures at the surface,but it potentially underestimates the actual slip produced by the earthquake and slip distribution over the whole surface rupture due to the difficulty in identifying distributed non brittle deformation. This calls for caution in discriminating between one or multiple discrete events and in estimating the size of past and future earthquakes by using displaced deposits in trenches or offset geomorphologic features along strike slip prehistoric fault ruptures.

CO-SEISMIC SLIP DISTRIBUTION OF THE 2001 WEST OF KUNLUN MOUNTAIN PASS EARTHQUAKE INVERTED BY GPS AND LEVELING DATA

WAN Yong-ge, WANG Min, SHEN Zheng-kang, CHEN Jie, ZHANG Zu-sheng, WANG Qing-liang, GAN Wei-jun

2004, 26(3):  393-404. 

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The co-seismic displacement field of the 2001 west of Kunlun Mountain Pass earthquake is obtained through the analysis of GPS data measured before and after the earthquake and leveling data measured in 1979 and 2002. Adopting these data,constrained by detail surface rupture data measured after the earthquake,we inverted the co seismic slip distribution along the seismic fault. The result shows that the depth of rupture lower limit is 14.2～21km (with 70% confidence level),with 17km as the optimal value. The result also shows that left lateral strike slip of 2～3m exists in the area between the Sun Lake segment and the west end of the main rupture zone,although surface rupture is not observed there. This is consistent with the result of InSAR data analysis. The subsurface rupture of this earthquake is ended at the Sun Lake in the west,but it seems that left lateral slip of 1.5～ 2.0m still exists within the range of 30km to the east of the surface rupture zone. The vertical displacement inverted in this study shows that to the west of 93°E the southern side of the fault is elevated,while to the east of 93°E the northern side of the fault is elevated. The released seismic moment estimated by geodetic data and surface rupture surveying is 6.1×10²⁰ N·m,consistent with the result inverted by seismic wave records.

DUCTILE WEAKNESS-PLANE EFFECT OF PLASTIC-FLOW NETWORKS IN THE CONTINENTAL LITHOSPHERE

WANG Sheng-zu

2004, 26(3):  405-415. 

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Netlike plastic flow in the lower lithosphere,as visco plastic flow involving plastic flow network,controls tectonic deformation and dynamic processes within the continental plate. Plastic-flow network is composed of two conjugate sets of plastic flow belts (PFBs),which are ductile weakness planes (belts) resulted from shear localization,viscous friction heat production,and weakening of intra belt media in the visco-plastic flow field. The study indicates that,similar to brittle weakness planes (e g. faults,joints,etc.),the effect of ductile weakness planes on the yield strength of media is conditional,i.e. when the direction of stress is changed,sliding along the original weakness plane can occur only at the condition that the sliding angle θ is within the range of θ₁ ≤θ≤θ₂,showing the weakening of media; the relative decrease of yield strength of the ductile weakness plane can be expressed by the weakening level R,which is related to the lower limit of the sliding angle,θ₁,as shown by the equation R =sin2θ₁. In terms of the maximum conjugate angle of the "plastic flow/seismic" networks in central eastern Asia,it is estimated that the weakening level of plastic flow belts,R,is approximate to 0.81. Based on the recognition of ductile weakness plane effect,some problems,including the transition of tectonic belts from shear sliding to compressional folding,the inheritance and discarding of PFB,and the permissible change of stress direction,are discussed in this paper.

MULTI-CHANNEL MAXIMAL LIKELIHOOD DECONVOLUTION METHOD FOR ISOLATING 3-COMPONENT TELESEISMIC RECEIVER FUNCTION

LIU Qi-yuan, Rainer Kind

2004, 26(3):  416-425. 

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Up to now,all of the methods of isolating the receiver function from teleseismic P waves are based on the data recorded at a single station. However,the estimation of the receiver function based on the so called source equalization scheme will not be valid for broadband data,when a sharp discontinuity exists within the crust. The outlet for solving this problem is to avoid using the source equalization assumption. In this study,we propose a method for isolating the 3 component receiver function from multi channel seismic data based on multi channel maximal likelihood deconvolution princple. The source equalization scheme is avoided in our method,and this is valuable for improving the estimation of the receiver function in case of complex crustal structure. The numerical test by synthetics proves our method to be effective. Using this new method,we obtain the 3 component receiver functions at stations along the passive seismic profile across the Dabieshan orogenic belt from Daqipu (30°20′N,115°03′E) nearby Daye,Jiangxi Province to Cuilin(34°40′N,114°49′E)nearby Lankao,Henan Province. In comparison with the radial components of the receiver function from the data of a single station,it is indicated that the results given by both methods have un negligible differences.

A DISCUSSION ON MECHANISM FOR SEISMIC QUIESCENCE BEFORE LARGE EARTHQUAKES BASED ON EXPERIMENTAL RESULTS OF ACOUSTIC EMISSION

MA Sheng-li, JIANG Hai-kun, HU Xiao-yan, BA Jing

2004, 26(3):  426-435. 

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This paper discusses the mechanism for seismic quiescence before large earthquakes based on experimental results of acoustic emission during rock deformation. Under the condition of biaxial compression and constant loading point velocity,samples simulating discontinuous faults,including compressional en-echelon faults,fault with macro-asperity,and model-Ⅲ shear fault,show relative quiescence of acoustic emission before slip instability,which is characterized by obvious decrease of occurrence rate and release of strain energy of acoustic emission events. The analysis indicates that the predominant deformation mode during this stage is creep sliding along fault zone,especially along the newborn fault segment in the discontinuous area,causing decrease of differential stress in the sample. The reason for occurrence of this stage is that a relatively uniform distribution of resistance along a fault zone is necessary for its slip instability,but uneven surface of newborn fault segment does not meet this condition,so the creep sliding is needed for resistance uniformization along the fault zone. Because there exist only very small asperities along the fault zone and the stress relaxation occurs in the whole sample during this stage,acoustic emission activity becomes weak. Based on the experimental results,it is suggested that the process of creep sliding and resistance-uniformization along fault zone is one possible mechanism for seismic quiescence before large earthquake.

THREE-STAGE FRACTURING MODEL FOR GRANITIC ROCKS UNDER TRIAXIAL COMPRESSION-ROLE OF MICROCRACK DENSITY AND STRESS RATE ON FAULT FORMATION

LEI Xing-lin, Takashi Satoh, Osamu Nishizawa

2004, 26(3):  436-449. 

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Based on the experimental results of two similar rocks having high/very low microcrack density under two extremely different loading conditions: fast constant stress rate (～6 MPa/m) loading and creep (at ～95% of the fracture strength) loading,the role of pre-existing microcracks and loading condition on the fracturing properties of granitic rocks was examined. The detailed spatio temporal distribution of acoustic emission (AE) events in these samples were monitored by the use of a high-speed multi-channel waveform recording system,which can record AE waveforms from 32 sensors mounted on the surface of tested sample without a major loss of events even for an event rate on the order of several thousand events per second. Event rate,b-value in magnitude-frequency relation,and hypocenter distribution of AE events characterize three typical long-term stages of microcracking activity during the fracturing process: primary,secondary and nucleation. Precursory anomalies on cracking activity such as event rate and b-value in the nucleation stage were observed. In general,a higher pre existing microcrack density or a lower loading stress-rate results in a longer nucleation stage,and therefore,increases the predictability of catastrophic failure event. Further,the physics of these stages is analyzed using the subcritical crack growth model for crack population of fractal size distribution based on the stress-aided corrosion theory.

FRICTIONAL STRENGTH AND RATE DEPENDENCE OF GABBRO GOUGE UNDER ELEVATED TEMPERATURE AND PRESSURE

HE Chang-rong, TAO Qing-feng, WANG Ze-li

2004, 26(3):  450-460. 

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As most earthquake focal depths are concentrated in the upper crust (e.g. Chen et al.,1983),previous studies on rate dependence of frictional strength have focused on granite that is typical in the upper crust (Lockner et al.,1986; Blanpied et al.,1995). However,recent reassessment of focal depth of many earthquakes revealed that some of them have been generated in the continental lower crust (Maggi et al.,2000). Moreover,teleseismic imaging of the structure across the San Andreas Fault also suggested the existence of deep fault that cuts through the crust (Zhu,2000). With this background,we need to pay more attention to intermediate and mafic rocks in the lower crust. Frictional resistance and the related rate-dependence of such rocks are critical to understand the mechanical behavior of deep faults that cut the lower crust. Specifically,this is crucial for answering two important questions,namely: 1) Is it likely for earthquake to nucleate in the continental lower crust? 2) How much stress can the lower crust support? We conducted experiments on frictional sliding of oven dried gabbro gouge at elevated temperatures with a triaxial testing system using gas as the pressure medium. A gabbro gouge layer of 1 mm thick (particle size of the gouge<76μm) was placed along an inclined saw-cut (35°to the loading axis) in a 20-mm-diameter cylinder sample to simulate a fault with gouge. Two series of experiments have been conducted with normal stresses of 200MPa and 300MPa,respectively,with temperatures up to 616℃. For both normal stresses,the rate-dependence of friction is either positive or approaching to neutral rate-dependence. With normal stress of 300MPa,the values of steady state rate dependence are positive in most of the temperature range but show a minimum around 315℃ (approaching to zero). Variation of rate dependence under normal stress of 200MPa is less pronounced. Based on theoretical analysis on slip nucleation (e.g. Dieterich,1992) and these experimental results,it is unlikely that unstable slip nucleates in larger scales under similar conditions as set in the experiments.

SHEAR STRUCTURE OF GABBRO GOUGE IN FRICTIONAL EXPERIMENTS AND ITS ORIGIN

WANG Ze-li, HE Chang-rong, TAO Qing-feng

2004, 26(3):  461-471. 

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Experiment on frictional sliding of simulated fault gouge is of great significance to the understanding of earthquake nucleation and natural shear zone structures. The present paper deals with deformational structure of simulated gabbro fault gouge and its origin,for the purpose of understanding fault activity in deep crust. The experiment also shows that various shear structures are well developed in the simulated fault gouge. Among them,the boundary shear,R₁ shear,Y shear and T gash are relatively well developed,but R₂,P and X shears are scarcely observed. R₁ shear has an angle of about 11°to the boundary surface,indicating the formation of a set of Coulomb fracture during the process of shear deformation. Observation of the thin sections shows that the density of R₁ shear increases with increasing normal stress,while under the same normal stress condition the density of R₁ shear increases with increasing temperature. Microstructural observations show that under temperature condition of 200℃the fault gouge is dominated by brittle deformation,involving grain crushing,cataclastic flow by shear comminution,and the banded alignment of dark colored minerals such as biotite and pyroxene along the shear plane. Between the temperature of about 200～400℃,preferred orientation of felsic minerals is gradually formed,defining mylonite like foliation. Above 500℃,the densely distributed R₁ shears occurr in the strongly deformed region,and they tend to coalesce with Y shears rather than to cut through the gouge layer,leading to the well development of Y shears. In these high temperature conditions,plagioclase begins to deform plastically,and the foliation defined by felsic minerals separates from that defined by dark-colored minerals,resulting in a typical S-C fabric.

THE EFFECT OF WATER ON BRITTLE-PLASTIC TRANSITION OF LOWER CRUSTAL MAFIC ROCKS

ZHOU Yong-sheng, HE Chang-rong, YANG Heng

2004, 26(3):  472-483. 

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Previous studies showed that the deformation of dry mafic lower crust is semi-brittle,which may locate in transition of semi-brittle slip to semi-brittle flow. Therefore,we perform tests on brittle-plastic transition of four kinds of dry and wet mafic rocks in order to comprehend the mechanical behavior of continental lower crust. The experimental confining pressure ranges between 450～500MPa,and strain rate is 1×10^-4s^-1. The results of experiments show that the samples of dry Jinan gabbro (sample C),dry Yanqin diabase (sample D) and wet Yanqin diabase (sample D) have experienced deformation regimes of faulting,cataclastic flow,semi-brittle flow and plastic flow under 300～900℃; and dry Panzhihua fine grained gabbro (sample A) and fine-to medium grained gabbro (sample B) have experienced deformation regimes of semi-brittle flow and plastic flow under 700～900℃. The temperature of brittle-ductile transition of dry gabbro is 100℃,higher than that of dry diabase. The temperature of brittle-plastic transition of all dry mafic samples is 700℃,but the microstructures of semi-brittle flow are variable. For example,grain-size reduction and preferred orientation of plagioclase and clinopyroxene occurred in deformed diabase,displaying the typical structures of protomylonite. However,this kind of microstructure did not appear in the deformed samples of gabbro. In contrast to the semi-brittle flow regime,the strength and microstructure of all dry mafic samples are basically the same in the plastic flow regime under higher temperature,when dislocation glide becomes the predominant deformation mechanism. The main effect of water on brittle-plastic transition of mafic rocks is embodied by both the change of strength and temperature of brittle-ductile transition and brittle-plastic transition. The strength of wet diabase is much lower than that of dry gabbro and diabase at the experimental condition. The temperature of both brittle-ductile transition and brittle-plastic transition of wet diabase is 100℃ lower than that of dry diabase,and 200℃ lower than that of dry gabbro. The temperature of transition from semi-brittle flow to plastic flow of wet samples is much lower than that of dry samples.

EXPERIMENTAL STUDY ON THE PROPAGATION OF ACOUSTIC WAVES THROUGH PERIODICALLY LAYERED MEDIA

YANG Xiao-song, MA Jin, LIU Li-qiang

2004, 26(3):  484-491. 

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The propagation of acoustic waves through periodically layered media (PLM) is experimentally investigated for the purpose of determining how the velocities and waveforms depend on periodical structures and detection frequency. In our experiments the PLM were made of stacks of plastic and steel plates with different periodical spacing. The acoustic wave frequency used in our experiments was 240MHz. Velocities and waveforms were measured by Digitization Wave Meter with 12-bit resolution and 40MHz sampling rate. The results show that the velocity transition from the time averaged relation to the long-wave approximation (LWA) is related to the critical ratio of λ_i/d_i(i=1,2) (λ_i-the wavelength of wave going through medium i; d_i-the thickness of medium i in PLM) rather than to λ/d (the ratio of wavelength to the thickness of rhythmic layer). The LWA occurs when λ_i/d_i>5(i=1,2),and the velocities (V) approach to the Reuss bound (V^R),whereas the time averaged velocities hold when λ_i/d_i<4(i=1,2). We attribute the behavior of V→V^R to "softer shape" distribution of different rigid components in PLM. The waveforms are also frequency dependent. With larger thickness of rhythmic layer,the attenuation of the first arrival is low and the multiple waves reflected from interfaces can be observed. In the case of LWA,however,the transmitted waves tend to have relatively simple waveforms. This behavior implies that simple waveform does not always reflect simple medium structure through which the wave propagates. As λ_i/d_i～6 (i=1,2),the transmitted wave is obviously attenuated,and consequently it is equivalent to a shield layer for the wave. Therefore,the influences of medium structures on velocities and waveforms should be taken into account when interpreting deep structures and compositions based on seismic data. Tectonic nature of intracrustal low velocity zones is one of the hotly debated topics. An important implication of our experimental results is that PLM are potentially low velocity zones. If extremely reflective deep crust is caused by alternating layers,the relatively lower velocities observed in deep crust should probably be attributed to the rock properties that we wish to image,as well as to its structures,scales and detection frequencies.

INFRARED MEASUREMENT SYSTEM FOR ROCK DEFORMATION EXPERIMENT

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

2004, 26(3):  492-501. 

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The infrared signals produced during rock deformation are very faint and tiny,so that the measurements of them require excellent capabilities of detection system and strict working environment. The reliability of the results of infrared experiment,therefore,depends greatly on the reasonable technical specifications of infrared photodetector,high sensitivity recorder for temperature field and effectively controlled thermal background. All of the key parameters are discussed in detail in this paper based on laboratory infrared observation. The features for an infrared camera include spectral band,digitizing resolution,view field etc. For capturing the optimal infrared images,it is suggested that the spectral range should be 7～13μm,the observation range should be from 0.5m to infinity,and high-density focal plane array should be employed as far as possible. In order to confirm the temperature from infrared image,a surface temperature recorder with multi thermometers should be employed as an eyewitness working alongside the camera. A realistic experiment system has been developed based on the afore mentioned discussion. Aside from the traditional functions of infrared camera,the system is fitted with high-speed data transmission component. The infrared focal plane array has 320×240 pixels,and 25 frames of temperature field data are saved into the hard disk per second. Some steel beam bending and steel cylinder compressing experiments were made for testing the system. The tests have proved that the system is reliable and the data quality is improved greatly.

AN EXPERIMENT ON THE INFRARED RADIATION OF SURFICIAL ROCKS DURING DEFORMATION

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

2004, 26(3):  502-511. 

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The correlation between deformation and temperature is tested in detail on five rock types commonly observed on the Earth's surface. It is proven by both experimental and theoretical analysis that during the elastic deformation stage,the temperature of the rock is directly proportional to the loading force. According to the first and second laws of thermodynamics and Maxwells equation,the following relation can be deduced: σ-σ₀=-(cσρ)/α ln [T/T₀] or T/T₀= exp [-α/cσρ(σ-σ₀)] where σ is stress,T is temperature in Kelvin scale,α is modulus of heat strain,c σ is heat capacity and ρ is density. The results of the experiment are consistent with that of classic thermodynamics. Under Earth's surface condition,i.e. ordinary temperature and pressure,the maximum temperature increment of the sample elastically deformed in an open system is around 0.2K,and the normal rate of temperature rise is approximately 3mK/MPa. At the moment of fracturing,the temperature increment of the samples is much greater than that during elastic deformation,ranging from a couple degrees to more than ten degrees. The temperature increments caused by the elastic deformation of rocks are so minute that not only will they have any effect on climate,but cannot be identified by satellite infrared detectors. Therefore,new methods have to be explored for distilling faint information from infrared images,while the other thermo anomalies aside from elastic deformation should be carefully reviewed.

A SIMPLE METHOD FOR MEASURING EMISSIVITY OF ROCK AND ITS SIGNIFICANCE

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

2004, 26(3):  512-518. 

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The calculation of land surface temperature from thermal radiation requires the emissivity value of rock. However,there are lots of rocks in the Earth,and even the rocks of the same type may have obviously different emissivity. Recent methods for measuring the emissivity of rock are relatively complex,and most of them depend excessively on environmental condition. Therefore,when plenty of emissivity data are needed,it is necessary to develop a simple method of measurement. In fact,emissivity is a constant at room temperature,and the radiation of instrument itself and environment can enjoin the inversion as an unknown quantity. Then emissivity can be obtained by least square method through measuring the radiation of rock in a series of temperature and radiation conditions. On the basis of this method,the emissivities of 16 rock samples were measured. The square error of the results keeps in about 0.01,mostly less than 0.01,and the correlation coefficient of all linear fits is larger than 0.99.

HEAT PENETRABILITY INDEX (HPI) METHOD FOR DISTILLING SUBSURFACE THERMAL INFORMATION FROM SATELLITE INFRARED IMAGES

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

2004, 26(3):  519-527. 

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After a series of complicated modifications the surface temperature of the Earth can be measured. Usually this surface temperature is referred to as land surface temperature. The heat effect that engenders this temperature variation may come from the climate and subsurface heat sources. Among them,the subsurface heat sources are of particular importance to earthquake and active fault studies. Unfortunately,the heat effect of climate is much larger than that of the subsurface heat sources so that it may conceal the information of subsurface thermal activity. Heat Penetrability Index (HPI) method is proposed in this paper for measuring subsurface thermal activity. The first assumption for HPI method is that the sun is heating the land surface synchronously. The second is the horizontal variation of heat exchange rates of rocks on top of subsurface heat sources. Provided that the rocks are heated,then the variation of surface temperature can be observed. According to the afore mentioned concepts and thermodynamics,the HPI can be deduced through correlation analysis as expressed by: where u and v represent surface temperature in two different areas,n is the sample number in the scanning window and D is the Heat Penetrability Index. When subsurface heating event takes place,D will go up,and vice versa. Some examples from experiment and satellite infrared image analysis are presented to test the effectiveness of HPI method.

NORMAL ANNUAL VARIATION FIELD OF LAND SURFACE BRIGHTNESS TEMPERATURE IN CHINA

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

2004, 26(3):  528-538. 

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For extracting the information about fault activity and seismicity from thermal infrared radiation,two crucial problems should be taken into consideration: 1) Aerosphere exists between solid earth and the satellite based sensor,and thus influences the infrared energy of land radiation when it passes through the aerosphere to arrive at the sensors. Moreover,the atmosphere itself is involved in thermal radiation,too. Therefore,to extract the geophysical information from thermal radiation,we have to begin with the estimation of atmospheric influence; 2) for identifying the anomalies induced by fault activity in thermal radiation,we should be able to distinguish the normal radiation from anomalous radiation,as anomaly can only be identified in reference with normality. This paper discusses these problems from the following aspects: 1) define the concepts of land surface brightness temperature (LSBT) and its annual variation field. LSBT would be an important physical concept in extracting the geophysical information from thermal radiation. LSBT should be assigned to the category of radiation energy of land surface,rather than the traditional "temperature" concept. Once the emissivity is known,the temperature can easily be calculated according to Planck law; 2) introduce the split window method for calculating the LSBT and the influence of atmosphere. The calculation shows that the influence of atmosphere on brightness temperature received by satellite based sensor is about ?10K; 3) the annual variation field of LSBT in China is extracted from the LSBT data by using the wavelet and split-window methods; the data used in this study come from the observations of NOAA/AVHRR from 1981 to 2001. The results of this study may provide a basis for further analyzing the anomaly field of thermal radiation.

AN ATTEMPT TO OBSERVE GAS RELEASING PHENOMENA OF THE EARTH BY USING SATELLITE THERMAL INFRARED TECHNIQUE

QU Chun-yan, MA Jin, SHAN Xin-jian

2004, 26(3):  539-547. 

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Some researchers believe that satellite thermal infrared anomaly before earthquake is related to gas releasing of the earth. Accordingly,whether the gas releasing phenomena can be observed by satellite thermal infrared remote sensing becomes a key problem. In this paper,two sites where gas releasing phenomena of the Earth occurred assuredly were selected for the study of this key problem. One is the Kaixian County where high pressure and high concentration gas blow-out event of the No.16 oil well took place,and the other is around the epicenter of the west of Kunlunshan Pass M_S8.1 earthquake where gas releasing has been observed to continuously occur along the Kunlunshan Fault even one year after the earthquake. The characteristic features of satellite thermal infrared images before and after gas releasing process have been analyzed,and the thermal infrared anomaly related to gas releasing or gas blow-out has been identified. Furthermore,the feasibility to observe gas releasing phenomena by satellite thermal infrared was discussed. The result shows that the gases blew out from the oil well and the fire from ignited gases are distinctly reflected on satellite thermal infrared images,but the gas releasing phenomena along the Kunlunshan Fault after the M_S8.1 earthquake are poorly displayed on thermal infrared image,so that the infrared thermal anomaly related to gas releasing along this fault is difficult to be recognized by visual interpretation. The comparison of brightness temperature,however,has revealed that the brightness temperature in the gas releasing sites along the fault is higher than that of the surrounding areas either before or after the earthquake.

DISCUSSION ON THE ANOMALOUS INCREASE OF GROUND TEMPERATURE ALONG THE SEISMOGENIC FAULT BEFORE THE KUNLUNSHAN M_S 8.1 EARTHQUAKE IN 2001

GUO Wei-ying, SHAN Xin-jian, MA Jin

2004, 26(3):  548-556. 

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The Kunlunshan M_S 8.1 earthquake of Nov.14,2001 is the biggest seismic event in China's continent in the past five decades. For this event,some researchers have developed an analysis method of brightness temperature difference inside and outside the Eastern Kunlun Fault,and have drawn an important conclusion. They found that before the earthquake (beginning from Oct.2001),the brightness temperature along the seismogenic fault became higher than that outside the fault,and affirmed that this phenomenon was the impending precursor of the 2001 Kunlunshan M_S 8.1 earthquake. However,our comparison study on the IR images of 2001 with those of 1999 has revealed that the same phenomenon has occurred also in 1999,in which no earthquake has been recorded. The Eastern Kunlun Fault is interpreted and analyzed by using NOAA thermal infrared (IR) remote sensing images combining with numerical processing of IR brightness temperature. The comparison of IR images in seismically quiet period of 1999 with those before and after the Kunlunshan M_S 8.1 earthquake in 2001 has indicated that seasonal meteorological factor greatly affects the change of IR images along seismogenic fault. In early winter,the IR brightness temperature along the fault is equal or even higher than that outside the fault. Moreover,the comparison between brightness temperature along the Eastern Kunlun Fault and along the Altyn Tagh Fault has also revealed that during the transitional period between autumn and winter,the disturbance of meteorological factors on ground surface are significantly greater than the IR of ground object itself. We suggest,therefore,that the anomalous increase of ground temperature before the occurrence of the M_S 8.1 Kunlunshan earthquake on Nov.14,2001 incorporated natural phenomenon of seasonal change,while the identification of anomaly related to earthquake needs a further study.