The theoretical and in situ investigations in recent years indicated that the dynamic change information of crustal stress can be obtained through the observation of bedrock temperature. In particular, the magnitude and spatial distribution characteristics of the co-seismic stress variation obtained based on the co-seismic temperature response of the Kangding M_S6.3 earthquake were consistent with the results obtained by seismology, which confirms the validity of the field analysis of the co-seismic stress variation by temperature observation. In the future, with the further improvement of temperature measurement technology, this method for detecting dynamic change in crustal stress through bedrock temperature is expected to bring new opportunities for earthquake science.
However, the stress changes caused by earthquakes are related to the distance from the measurement point to the source and decay rapidly with the increase of the distance, and they are also related to magnitude and decrease exponentially with magnitude. For example, the co-seismic temperature response observed in the Kangding M_S6.3 earthquake did not appear in the subsequent M_S5.8 earthquake. One key reason is that the detection of co-seismic stress changes in M_S5.8 earthquake requires a precision of temperature measurement system to be up to 0.01mK. But, the precision of the instruments used at that time was about 0.2mK, which could not detect temperature changes in the order of magnitude of 0.01mK. So, in order to make the above-mentioned method play a greater role in earthquake science, especially in detecting the stress variation information before a strong earthquake, it is urgent to develop a more accurate temperature measurement system.
In this paper, a new version of high-precision temperature measurement system is developed successfully, after considering a series of technical improvements such as constant current commutation driving and multiple Kalman digital filtering, based on the low temperature drift fixed value resistor and the temperature measuring resistor with a balanced bridge of four-wire temperature sensors. The new system has a designed temperature resolution of 0.003mK. According to in situ tests, the precision of temperature measurement reaches 0.03mK. In addition, field observations have confirmed the feasibility of the temperature measurement system. Based on the relation between stress change and temperature response, a dynamic stress change of the magnitude of 0.03MPa can be obtained, which implies that the observable range of thermal stress can be greatly improved with comparison to the previous version of 0.2MPa. It should be emphasized for earthquake research that co-seismic Coulomb stress is an importance parameter, whose magnitude focuses on a range of about 0.01~0.1MPa. Up to now, co-seismic Coulomb stress change cannot be measured directly(at least partially)because of limitation of detecting method. Since the ability of measuring dynamic stress by our system developed in this paper has reached to 0.03MPa, reaching the magnitude of the co-seismic Coulomb stress change, the potential application of the system is to explore the change of the co-seismic Coulomb stress. This is of great benefit to promote the development of ways of observing the dynamic changes in crustal stress through bedrock temperature.

Recent studies have confirmed that the bedrock temperature changes when the crustal stress changes, and the information of dynamic change in crustal stress can be obtained through the observation of bedrock temperature. Moreover, there are abundant fluids in the shallow crust, and the deformation of the crust will inevitably lead to the migration of fluids, which will change the bedrock temperature. The temperature change of bedrock is equivalent to the secondary fluid thermal effect caused by crustal stress change and may be an another indirect sensitive index of crustal stress dynamic change. The bedrock temperature data of Xianshuihe fault zones show that the variation of groundwater flow rate after the Kangding M_S6.4 earthquake is consistent with the zoning characteristics of co-seismic volumetric strain in the strike-slip earthquake, indicating that the variation of near-field fluid migration characteristics is probably related to the variation of co-seismic static stress change. Moreover, the response form of bedrock temperature to the dynamic change of crustal stress and its secondary fluid effect is not consistent, as the former shows step-rise characteristics, while the latter shows exponential variation. The observation of bedrock temperature itself can obtain the dynamic change information of crustal stress and the information of shallow crustal fluid migration. Compared with crustal stress change, the variation range of fluid secondary heat effect caused by stress change may be significantly magnified(approximately an order of magnitude), which is more conducive to capturing signals, and thus may even obtain precursory fluid change information.
On January 19, 2020, an M_S6.4 earthquake occurred in Jiashi, which happened in the bedrock temperature observation network. In particular, the Xike’er observation station is about 1.3 kilometers away from the epicenter, providing an opportunity to analyze bedrock temperature changes before and after the earthquake. The results showed that: 1)Obvious changes in bedrock temperature were found before and during the M_S6.4 earthquake. The appearance of co-seismic response means that these changes before the earthquake are related to the earthquake and may be precursory signals. 2)In terms of time, the bedrock temperature before the Jiashi earthquake first changed abnormally on the stable background, and the change reached the peak, and then fell back. When the earthquake was impending, there was a significant acceleration of the change, and the earthquake occurred after some time. The acceleration characteristics of change impending earthquake may be related to the meta-instability process of earthquakes. 3)Spatially, changes in temperature before the earthquake occurred in or near the seismogenic fault, and no obvious abnormal information was observed at the measurement points far away from the seismogenic fault, indicating that short-term and impending precursors are more likely the “near field” information; From the perspective of depth, the change in temperature before the earthquake was observed only at the local depth range. This implies that there is obvious uncertainty in the depth in precursor observation. Upon this, the ideal situation should be to carry out multi-depth joint observation, so as not to miss important precursor information. 4)Combining with the Kangding M_S6.3 earthquake on November 22, 2014, a comparative analysis is made. Similar to the Jiashi earthquake, the temperature at measurement points located in or nearby seismogenic fault of Kangding M_S6.3 earthquake shows significant changes. This means that change in the temperature before the Jiashi M_S6.4 earthquake is not an isolated case, and is a representative of universal phenomenon that occurs before strong earthquake. In a word, the change of bedrock temperature before and after the earthquake shows that the precursor information has the characteristics of near field, structural correlation and sensitive to stress change.

The coda wave propagation path has received extensive attention as it is more sensitive to small changes in the medium than the direct wave. During the process of loading, the wave velocity, medium or source changes may cause the coda wave to change. The physical mechanism of change in the ultrasonic coda wave varies during different deformation stages. Meanwhile, there exist local damages in the rock sample during the deformation, and it will be accompanied by acoustic emission. Combining the ultrasonic coda wave and acoustic emission is beneficial to characterize the coda wave characteristics and damage degree of the sample at different deformation stages. In this paper, three kinds of rocks, including granodiorite, marble and sandstone with the sizes of 50mm×50mm×150mm, are used to carry out observations of ultrasonic coda wave and acoustic emission during the whole process of loading so as to study characteristics of the coda wave at different deformation stages. The major results are given below: 1)There is a good correspondence between the coda wave variation and the acoustic emission evolution process. When the acoustic emission frequency increases, the coda wave changes accordingly. In particular, the coda wave changes in the early stages of increased acoustic emission frequency, which indicates that the early damage information of rock can be obtained by analysis of the coda wave. 2)The physical mechanism of the coda wave change is different in different deformation stages. At the initial stage of loading, there are obvious scatterer changes in the coda wave change; then, in the linear elastic deformation stage, the wave velocity change is dominating; in the late-stage of loading, the scatterer change increases and coexists with the wave velocity change, the scatterer change effect is related with the rock micro-fracture degree, the rock will locally be damaged before rupturing, and the role of the scatterer will be enhanced. 3)With the increase of loading, the amplitude of increase of the wave velocity generally decreases gradually, which is basically consistent with the understanding obtained through the direct wave. The interference of acoustic emission can be eliminated because of the Kaiser effect when analyzing the coda wave. The consistency of the wave velocity change and stress loading and unloading is further verified. 4)The micro-fracture generated during rock deformation will change the physical mechanism of the coda wave change, and the scatterer effect will be significantly enhanced. At the same time, the acoustic emission waveform will cause interference to the ultrasonic coda wave. This means that attention needs to be paid when analyzing rock damage using only coda wave data. In short, the ultrasonic coda wave and acoustic emission can reflect the damage inside the rock, and the change mechanism of the coda wave in different deformation stages is different. The joint observation of the two can play a mutual verification role, which is conducive to improving the reliability of the observation results.

Based on the seismic data collected from regional permanent stations and 6 temporal stations, we analyzed the seismic activity from October 2008 to July 2011 in Rongchang area. On the basis of HypoDD relocated results, we used Match&Locate method to detect and located the micro-earthquakes. We obtained the focal mechanism solutions of some earthquakes with M_L ≥ 3.5 by using CAP method. Then we analyzed the temporal-spatial distribution of earthquakes and discussed the characteristics of micro-seismicity before the M_L5.1 earthquake occurring on September 10, 2010. We totally detected 3 354 micro-earthquake events, which are nearly 5 times of the earthquakes in the seismic catalog issued by China Earthquake Networks Center. The magnitude of the detected events is mostly from M_L-1 to 1, and the focal depth is from 2 to 4km. The magnitude-frequency analysis shows that the catalog completeness is obviously improved after adding the detected earthquakes, with the lowest magnitude decreasing from M_L1.0 to 0.3. The earthquakes hypocenters are mainly clustered along faults or buried faults and in a dominant depth range consistent with the depth of injection wells, and also show a tendency of lateral extension from injection wells. The focal mechanism solutions of 9 earthquakes of M_L ≥ 3.5 presented reverse faulting, as the same as the preexisting faults, indicating that earthquakes were surely related to reactivation of the faults. The strike, dip and rate of the causative faults separated in wide ranges, which indicates not only obvious changes in structure and strike of preexisting faults but also the effect of increasing pore pressure on the local stress field. Before the M_L5.1 earthquake on September 10 of 2010, seismicity firstly showed clustering in time and covered the most part of the seismogenic fault in space. Then an obvious seismic quiescence occurred and lasted about 3 months. The phenomenon is consistent with the mechanism of creep sliding and resistance-uniformization along the fault zone, suggested on the basis of laboratory experiments, and it may be one of patterns of sub-instability along fault zone. However, such explanation needs to be further confirmed.

Experimental and theoretical researches have confirmed that changes in crustal stress can be monitored by the in situ bedrock temperature. Monitoring stress by temperature requires the high-precision and multi-channel temperature measurement system. We have developed such a system, based on the several refinements. The key parameters on temperature measurement system mainly include:1)the accuracy is better than 1.0mK. At the 99.5%confidence level, the accuracy reaches 0.5mK. This system can be used to detect the change of magnitude of a few tenths to several MPa. The sampling period can be set, depending on remote control. The sampling period is usually set 5 or 15 minutes. 2)A system has up to 20 channels, and commonly uses for 8 or 12 channels. 3)This system has a significant performance in low power consumption. The power is supplied by lead-acid battery with 12 volt. It is at least 2 years that a lead-acid battery, with contents of 120Ah12V, can supply the power for a system with 8 channels. In conclusion, multichannel temperature measurement system with high precision and low power consumption is designed and realized. Specially, the performance in low power consumption is of great significance, which can greatly reduce the maintenance cost after the measurement station is constructed. This temperature measurement system provides a basic technology for monitoring changes in crustal stress with bedrock temperature.

Stick-slip of fault in laboratory accompanies change of temperature. Temperature change is not only concerned with sliding friction, but also with the stress state of the sample. In this article, we use infra-red thermal imaging system as wide-range observation means to study the temperature variation of different stages during the deformation of sample. The rock sample for the experiment is made of granodiorite from Fangshan County with a size of 300mm×300mm×50mm. It is cut obliquely at an angle of 45°, forming a planar fault. Two-direction servo-control system was used to apply load on the sample. The load in both directions was forced to 5MPa and maintained constant (5MPa) in the X direction, then the load in the Y direction was applied by a displacement rate of 0.5μm/s, 0.1μm/s and 0.05μm/s successively. The left and below lateral of the sample were fixed, and the right and top lateral of the sample were slidable when loaded. The experiment results show not only the temperature change from increase to decrease caused by conversion of stress accumulation to relaxation before and after the peak stress, but also opposite variation of temperature increase on fault and temperature decrease in rock during instability stage. Most important of all, we have found the temperature precursor identifying the position of instability through the temperature variation with time along the fault. It shows that rate of temperature increase of instability position keeps relative high value since the stage of strongly off-linear stage, and accelerates in stage of meta-instability. After separating the effect of friction and stress, we found that temperature increase occurs in the rock near the fault instead of on the fault, which means the mechanism of temperature increase is stress accumulation. Temperature of fault at the instability position does not increase, which means the position is locked. We speculate that the position of locked area on fault with high stress accumulation near the fault may be the future instability position. It is of significance of studying temperature variation during stick-slip to the monitoring of earthquake precursors. Heat caused by friction of earthquake needs long time to transfer to the surface and could not be detected as a precursor. While the stress of surface rock near the fault would change as the stress of interior rock changes, which could cause detectable temperature variations. The research purpose of this article is to find special change positions before instability. As the temperature variations are caused by stress and slip of fault, the results are also meaningful to analysis of stress and displacement data related to earthquake precursors.

In order to study the complex strain field during the instability process of rapid deformation adjustment stage and the rock failure process in rock experiments, high-speed, high-resolution, multi-channel strain observation technology is applied to physical simulation experiment and developed as Multi-channel Dynamic Strain Observation System for monitoring the transient deformation field. The specially designed system has 96 channels with a sampling rate up to 3, 400 samples/s/ch, and a resolution of less than 1με(micro strain)and continuous recording. We found some important phenomena by observing the temporal and spatial variation during the fault instability process and crack propagation process. The experiment on three typical stick-slip models shows that the evolution of the unstable fault stick-slip process has a relatively stable feature characterized by three typical phases(precursory slip, rapid slip incorporated with high-frequency strain vibration and terminal adjustment). Each phase has its own characteristics of duration, strain rate, frequency, amplitude and energy. The experimental results on the three-dimensional fault propagation model show that the coalescence of the bridge area occurs at the last stage and is a rapid process. The crack initiation occurs at several points which combine each other randomly. There is a stable period existing between the full propagation and coalescence and sample failure, and the duration time is several tens milliseconds. Multi-channel dynamic strain observation system fills the band gap of strain observation in rock mechanics experiments and earthquake simulation experiments. High-density and high-precision strain data can be obtained by this system, which can further promote the studies on the transient strain field evolution and the temporal and spatial process of strain wave and provide technical support for understanding the process from a slowly progressive deformation releasing to the sudden instability.

The objective of this paper is to explore the current tectonic activity with satellite remote sensing thermal information by taking a case of the Wenchuan earthquake. Three items are accomplished as follows: 1)the process of evaluation of thermal field before and after Wenchuan earthquake is analyzed. The results indicate that there exist plenty of thermal information associated with the distribution of tectonics in the in-situ land surface temperature field, which is extracted from land surface temperature in which the effects of non-tectonic factors, such as topography, atmosphere and solar radiation are gotten rid of. 2)Combining with measurement of the shallow atmosphere temperature, the quantitative relationship between increment of land surface temperature and crustal stress-strain is preliminarily investigated. Results indicate that the increment generated by the crustal stress may obviously affect the shallow atmosphere temperature. Especially, the temperature-lowering zone has more reliability. There exist some temperature lowering zones along the boundaries of large geological blocks before and after Wenchuan earthquake, which reflects the relatively extensional movement (or stress relaxation) among these corresponding blocks. 3)Based on the co-seismic deformation, the comparative analysis is done between co-seismic deformation and thermal information. Results indicate that the tectonically adjusted area obtained from temperature field is largely accordant with that of co-seismic deformation. This shows that the variation of temperature along the boundaries of large geological blocks within the Tibet Plateau reflects the process of the adjustment of crustal deformation of the Tibet Plateau before and after Wenchuan earthquake. In summary, it is a possible approach to obtain the change of state of crustal stress by using the thermal method.

Earthquake is a form of tectonic activity, an earthquake contains a lot of information, its frequency range is very wide. So far, the main frequency range of seismic records is below 100Hz, and the ultrahigh frequency seismic information got less attention by researchers. However, high frequency microseismicity can provide important information on micro-activities of fault. This paper introduces a new 100kHz ultrahigh frequency seismometer and its first application on high frequency microseismicity observation. The telemeter has been applied in Dali, Yunnan. Several high frequency microearthquakes were recorded and the corresponding earthquake location and spectral analysis were done. The results show that high frequency microearthquakes caused by crustal movement do exist and can be recorded by our telemeter. The recorded microearthquakes are of magnitudes between M_W=-3.0 and M_W=-1.0, maximum hypocentral distance up to 4.87km, dominant frequency ranging from 100Hz to 300Hz, and maximum frequency as high as 800Hz. It is possible that the ultrahigh frequency microseismicity observation(UFMO) will become a new approach to the study on the tectonic movement.

Recently,the strong earthquakes in China mainland occurred mainly around the Bayanhar block. It is important to monitor the information of ongoing crustal activity at the key tectonic positions. We have developed a set of wireless equipment for measuring the ground temperature in field,and have established a network of measurement of the ground temperature along Xianshuihe Fault. Some changes of temperature were observed before and after the Lushan earthquake on April 20,2013.First of all,an apparent and persistent change of the ground temperature in Kangding appeared,starting from January 31,2013.This temperature variation corresponded with the occurrence of the small earthquakes around the observation station. According to the relationship between the temperature and stress,the abrupt change of ground temperature is essentially the geological stress adjustment. From the viewpoint of geological structures,both Longmengshan Fault and Xianshuihe Fault are the boundary faults of the Bayanhar block,but located at different boundaries,so,Kangding in Xianshuihe Fault is tectonically related to Lushan in Longmengshan Fault. Thus,the temperature change described above would possibly be the precursor of the Lushuan earthquake.

Within almost five years,the 2008 Wenchuan M_S 8.0 and 2013 Lushan M_S 7.0 earthquakes ruptured the Longmenshan Fault zone successively. The characteristics of earthquakes and their development tendency on this fault zone have been a focus of subject of research. This article attempts to explore some features of seismic preparation process of the 2008 Wenchuan event from temporal-spatial evolution of earthquakes along the Longmenshan Fault zone during more than 40 years.(1)The spatial range of the earthquake preparation,or seismic nucleation,is much smaller than that of co-seismic rupturing. It indicates that the seismic source,probably consisting of some small asperities or barriers,prepared on a finite fault segment can be connected and expand into a large-scale rupture section along the fault when the fast instability occurs at the source.(2)Prior to the 2008 Wenchuan giant shock,its preparation area had experienced a dense distribution of small earthquakes for eight years or more,while no conspicuous slip and deformation were observed on the surface. This implies that the seismogenic fault segment of the Wenchuan event on the Longmenshan Fault was undergoing probably compressive deformation,accompanied with cataclastic process. When the cataclastic deformation of the great-shock source reached a critical state,fault instability occurred along the fault with rapid rupturing. (3)To further study the variations of the main-shock area prior to the event,this article analyzes the temporal-spatial processes of small earthquakes around the main shock since 2004 recorded by a special seismic network in the Zipingpu reservoir. The results indicate that the scope of the seismicity expanding along the fault took place along the fault in October 2005 and October 2006,respectively,in accordance with the time when the reservoir reached its high water level. Among them,the second expanding from October 2006 covered a relatively large area and with relatively big magnitudes,implying great importance for the study of the final instability process of the 2008 Wenchuan huge earthquake. Besides,this paper discusses the correlation of the rupturing process of the 2008 Wenchuan giant event with the geometry of the fault and the reason why the 2013 Lushan earthquake occurred many years after the Wenchuan event rather than immediately following this giant shock like usual big aftershocks. The research results are helpful for understanding of seismogenic processes of major earthquakes of the thrust type.

By using a newly developed distributed multi-channel transient signal acquisition system,the spatial distribution of arrival time and direction of the first motion of the acoustic emissions (AE) along the fault under near field conditions was well studied. With the high frequency strain recording system,the stress distributions along the fault were well characterized and the focal dislocation behavior during stick-slip was studied as well.The experiment was conducted in a biaxial servo-control loading system. Analysis shows that for each sudden stress drop event,the corresponding focal dislocation consists of a few smaller sub-dislocations and each sub-dislocation results in its own AE event and stress change. Besides,it can be proved that each sub-dislocation may correspond to multiple sources rather than point source,the evidences of which can be found in the heterogeneity of the spatial distribution of the first motion and the strain field along fault. Our study indicates that the multi-dislocation during stick-slip under near field conditions is very complicated. By the result of our study,it is more convenient to understand the complication of focal process. Besides,it could provide an evidence for the uncertainty of in-situ earthquake focus and the high contradiction rate of earthquake mechanism solutions.

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.

New software for acoustic emission location has been developed and the main functions,methods for location are introduced briefly.The tested location result with the software is presented also.The multi common Data Base interfaces are built in the software,so it is device-independent.Besides the three-dimension location,it can be employed for surface or linear location.In locating,the velocity of sample material will be an appointed constant or an unknown variable.There are two improvements in the algorithm.The first is that the least absolute deviation based on robust estimation is taken as objective function for location.The second is a simulated annealing method that is applied to search the global minimum of objective function in optimization procedure.The location accuracy of acoustic emission focus is much better with the software and it is a flexible tool for data processing.

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.

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.

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.

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.

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.

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.

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.

The temporal and spatial distributions of strong earthquakes in the past century in China's continent are analyzed in this paper. Both the temporal and spatial distributions of strong earthquakes display a clustering feature. The activity of strong earthquakes is undulate and clustered in the major region in certain period. Based on both temporal and spatial distributions of strong earthquakes in China's continent, a synthetic division of dynamic phases is carried out. The activities of strong earthquakes have approximately 13-year's periods in China's continent in the past century. In each period, most strong earthquakes cluster in a major region and a minor region, corresponding to a wave of energy release on the time axis. The major region and minor region are located on opposite sides of the Tibet Plateau. Quite a portion of strong earthquakes is developed in the original seismogenic area, but most events are developed outside the last major or minor regions. This may imply the fluctuation of energy accumulation in large-scale area. The division of active and quiescent periods of seismic activity is of benefit to understanding the undulation of energy release. However, both the length of active period and the intensity of energy vary with time, while within the active period the seismic activity is uneven. Comparatively, the division of dynamic phases is more advantageous to strong earthquake prediction.

In this paper, a 3-D visco-elastic finite element model is used to describe the long-term average movement of China's continent. The boundary conditions of the model are taken in reference to the average plate velocity obtained from geological information, as well as the subduction of the Philippines and Pacific Plates into the continent and the collision between the Indian Plate and China's continent. The results of GPS may reflect the contemporary movement of China's continent. The difference between the contemporary movement and the long-term average crustal movement can then be recognized by the comparison of the modeling result and the GPS result. The two kinds of results show much consistency and little difference. It indicates in one point that each short-term movement of the continent might be a small dynamic adjustment process near the long-term average state, and can be attributed to the continuous adjustment of the continental crust to reach an equilibrium state in response to the movements of the surrounding plates. The modeled stress field shows that the stress is higher in the western and southern parts and lower in the eastern and northern parts, consistent with the stress field obtained by the other studies. The subduction of the Pacific and Philippine plates has led to a complex effect on the eastern part of the continent. In Northeast and North China, the E-W-directed stress is dominated by compression due to the compression of the ocean plate and the obstacle of the block to the north. However, the S-N-directed stress becomes gradually to be extensional, as the S-N-directed displacement becomes greater from north to south. Because of the difference of motion rate between North China and South China, North China is subjected to extensional stress. This is consistent with the results of Shen et al. (2000) and DING Guo-yu (1986). In South China, the S-E-directed compressive stress is predominant, but alternating compressive and extensional stresses are predominant in the vicinity of the eastern boundary of the continent. Three cross sections are cut along the X-direction of the model to observe the stress and displacement on X-Z plane. In contrast to the compression of the Indian plate, the subduction of the ocean plates gives rise to the complicated distributions of stress and displacement on the profiles. Although the whole continent, and especially the western part of the continent, is dominated by compressive stress, alternating high, low and high stress regions may occur from west to east in the eastern part of the continent, and extensional stress may to different extent occur in the region from Huanghai sea to Taiwan. Because of the differences of the rheological properties of the media in various layers of the model, stress will gradually concentrate in the high viscocity layers of the model as time goes on. Due to the subduction of the ocean plates, small-scale high stress region with high stress gradient may occur at depth of the lithosphere beneath the eastern boundary of the continent. In addition, some convection circles may occur in the lithosphere beneath the eastern boundary of the continent, but the features of stresses in various quadrants are different due to the complexity of the crust and upper mantle. Further study is needed to test this conclusion. The modeling results in this paper indicate that the subduction of the Pacific and Philippine Plates into the continental lithosphere has very important effect on the orientation and features of the stress field in eastern China's continent. LI Zu-ning et al. (2002) proposed that the ignorance of the effects of the subduction of Pacific and Philippine plates is the main reason that causes the incompatibility of their modeling result to the results of GPS and seismic observations in China's continent. Obviously, a better understanding of the dynamic background of China's continent can be gained only by taking the effects of the Pacific and Philippine Plates into consideration.

Based on the analyses of the density of energy released by strong earthquakes in East Asia, the contemporary dynamics of continental deformation is studied. The west China and its vicinity including North China can be considered as the Continental Meizoseismal Region of China. The deformation and stress fields in China and its vicinity are studied by modeling the long-term squeezing of the Indian subcontinent in term of 3-dimensional layered visco-elastic finite element method. The regime of energy distribution in this region is basically similar to the model with Indian's indentation, but has some differences. The super shear zones on both sides of the Tibet Plateau proposed by Dewey et al. (1990) are essentially the deformation twist belts: the stress is concentrated in both belts as compared with that inside and outside the plateau, in spite of a slight difference of stress orientations from the elastic homogeneous model. The vectors of crust motion in east China are leaning towards the east, and the vectors in the east and northeast parts of the Tibet Plateau are significantly different from those in their vicinity. There are three arcuate belts with high seismic energy densities in the eastern Tibet Plateau: Chayu arc in the southeast, Kangding arc in the northeast and Haiyuan arc in the north-northeast. The meisoseismal region in China is developed by three combined dynamic processes: (1) The long-distance squeezing of the Indian subcontinent results in the gradual extending of the deformation starting from both corners of the plateau and ending in the collision zone, which then causes the formation of the deformation twist belts on both sides of the plateau. The thick crust of the Tibet Plateau provides the medium condition for elastic energy accumulation. The creep of the lower crust at higher temperature leads to the concentration of stress in the upper elastic layer. (2) The large-scale eastward motion of the eastern Asia has given rise to the change of the squeezing direction of Indian Plate in the northern Tibet from north-northeast to northeast, and the turning of both the deformation twist belts from north-northeast-trending to northeast-trending. (3) The inhomogeneous extrusion within the Tibet Plateau promotes the formation of three arcuate belts on the eastern side of the Tibet Plateau.

According to the researches of strong earthquake distribution in China's continent and its vicinity, many researchers proposed that the strong earthquake activities in China and its neighboring areas may concentrate mainly in a certain seismic region during a certain time period. Hong Han-jing(1997)suggested that the seismic activities in China and its surrounding areas in the past century can be divided into several micro dynamic periods, and in different periods there should be a relatively stable region of seismicity. Moreover, in different periods the features of strong earthquake distributions are different in space and the main seismic regions may migrate for a long distance. In the research of this large-scale seimogenic model, the transfer of stress in various layers of the lithosphere has attracted more and more attention of most researchers. The dynamic analy~ses demonstrate that it is difficult to explain the long distance migration of the main seismic regions in the micro dynamic periods by considering only the brittle layer of the crust. Therefore, the layered rheological structures of the whole lithosphere and the process of stress accumulation must be taken into consideration. The layered structure of the lithosphere has been given in many previous studies, and the rupture in brittle layer of the crust was proved to initiate at deeper layer of greater strength and propagate to the shallow layer of lower strength. Kusznir & Bott(1977)have introduced a simplified model of two layers visco elastic lithosphere, which comprises an upper layer with higher viscosity coefficient and a lower layer with lower coefficient. As a boundary condition, they applied uniform horizontal boundary stress at one side of the model and maintain the other side to be fixed. The simulation proved that after the application of stress at one side of the model the stress relaxes in lower part of the model and concentrates in the upper part as a function of loading time. However, there are various kinds of boundary conditions in the nature, and the movement of Plate boundaries is a dynamic process. Sometime plates move at a certain rate(such as the squeezing rate of the Indian Plate), but do not maintain a constant force on the adjacent plate. In this case, the stress on the boundaries of the plate is not a constant stress, but within a certain time scale and precision scale the velocity can be considered as a constant velocity. We modify, therefore, the boundary condition of the lithospheric model of Kusznir & Bott to constant velocity boundary condition, and give the analytical resolution. It is proved that if the thickness of high viscosity coefficient layer, the Young's modulus and viscosity coefficients of each layer are given, then the rate of stress accumulation in the high viscosity coefficient layer increase with increasing thickness of the high viscosity coefficient layer. According to the result, under the same boundary condition, if the accumulation of stress for one layer homogenous model needs 950 years, then for two layers visco elastic model(with the ratio of the two layers of 1/100 and the viscosities of 10¹⁸ Pa·s and 10²² Pa·s, respectively), it needs only 38 years. Obviously, the accumulation time of stress is significantly shortened. The above discussions prove that the low viscosity coefficient layer plays an important role in the transfer and concentration of stress in different media. This result may provide a new insight into the understanding of the short term geological problems. In a word, by analyzing the transfer condition of stress in lithosphere and the dynamic boundary conditions surrounding the continent, we suggest that under the effect of dynamic boundary conditions, the accumulation time of stress in lithosphere can be shortened significantly.