The origins of tremors and their relation to fault slip and impending earthquakes remain unclear. Laboratory studies on tremor‐like acoustic emission events generated during preslip may shed some light on the above issues. We conducted stick‐slip experiments and observed tremor‐like events and preslip in the laboratory. The results show the following. (1) The dominant frequency of tremor‐like events increases with accelerating preslip. (2) The evolution of tremor‐like events is spatiotemporally consistent with that of preslip. (3) Interactions between preslip and high‐frequency events indicate the formation of a positive feedback effect between the expansion of preslip and failure of asperities, which leads to stick‐slip instability. Thus, we propose that tremors may be caused by stress variations derived from asperity interactions along fault surfaces at dry conditions. The increasing dominant frequency of tremors may imply the accelerating preslip of an upcoming earthquake.

Principle on temperature response to the stress-strain variation is fundamental to the relationship between thermal radiation variation and stress-strain field. Current research indicates that temperature has a sensitive response to rock deformation under the condition of normal temperature background. However, the basic physical relationship between deformation and temperature variation is not clear and need to be investigated further. In this paper, principle on temperature response to stress-strain variation is studied in detail, based on thermodynamics, elastic strain theory, and experiments on both ideal material and rock. In the stage of elastic deformation, results indicate that: 1) temperature increment is positively correlated with volume strain variation. Temperature rises with hydrostatic pressure increase. In other words, temperature rises when the specimen is under the compressive state whereas temperature drops under the tensile state. 2) Pure shear deformation does not contribute to temperature variation. Namely, shape change of specimen does not produce temperature variation. However, there exist the relative tensile area and the compressive one in the specimen under the state of pure shear. Temperature drops within the relative tensile area while temperature rises within the compressive areas during the process of loading. stress-strain, temperature variation, volume strain, pure shear, sine-wave loadRecently, more and more thermal anomalies corresponding to earthquake and fault activity are investigated by using satellite remote sensing technology although many problems remain unsolved. Up to now, almost thermal infrared seismic precursors are found by rethinking of some phenomena, maybe related to seismic activity, after earthquake occurred. And it is lack of necessary analyses to physical mechanism on thermal infrared anomaly prior to earthquake, so that it does not judge the facticity and reliability of seismic precursor [1] . Relationship between thermal field and strain field during the process of fault deformation is the physical basis for applying the satellite infrared information or land surface temperature to analyze earthquake or fault activity. The temperature variation on rock deformation during the process of loading is studied through a series of experiments [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] , which lays the foundation for further work, but these experimental results are not in accordance with one another, some of which are conflicted with the classical physical principle. For instance, some researchers suppose that relationship between temperature variation and stress state is related with rock category, which temperature rises in some rocks, keeps stable in some rocks, and drops in some rocks, under compression state.There are two major reasons for the aforementioned discordant experimental results: 1) limitation of the experimental technology. The temperature variation during the deformation of rock is minimal. Therefore, the valid temperature signal...

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This study attempts to acquire information on tectonic activity in western China from land surface temperature (LST ) field data. On the basis of the established relationship between heat and strain, we analyzed the LST distribution in western China using the satellite data product MODIS/Terra. Our results show that: 1. There are departures from annual changes of LST in some areas, and that these changes are associated with the activity of some active tectonic zones. 2. When annual-change background values caused by climate factors are removed, the long-period component (LST LOW ) of temperature residual (DT ) of the LST is able to serve as an indicator for tectonic activity. We have found that a major earthquake can produce different effects on the LST fields of surrounding areas. These effects are characterized by both rises and drops in temperature. For example, there was a noteworthy temperature decline associated with the Sumatran M9 earthquake of 2004 in the Bayan Har-Songpan block of central Tibetan Plateau. 3. On the other hand, the LST field of a single area may respond differently to major shocks occurring in different areas in the regions surrounding China. For instance, the Kunlun M 8.1 event made the LST on the Longmen Mountains fault zone increase, whereas the Zaisan Lake M 7.9 quake of 2003, and the Sumatran M 9 event of 2004, caused decreases in the same area's LST. 4. The variations of land surface temperature (LST ) over time are different in different tectonic areas. These phenomena may provide clues for the study of tectonic deformation processes. On the basis of these phenomena, we use a combination of temperature data obtained at varied depths, regional seismicity and strain results obtained with GPS Geoscience Frontiers journal homepage: www.elsevier.com/locate/gsf Geoscience Frontiers (2010) 1, 57e67 measurements, to test the information related to tectonic activity derived from variations of the LST field, and discuss its implications to the creation of models of regional tectonic deformation. ª

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Field and experimental observations showed that preslip undergoes a transition from multiple to single preslip zones, which implies the existence of linkage of preslip zones before the fault instability. However, the observations of the linkage process, which is significant for understanding the mechanism of earthquake preparation, remains to be implemented due to the limitations of observation methods in previous studies. Detailed spatiotemporal evolutions of preslip were observed via a high-speed camera and a digital image correlation method in our experiments. The normalized length of preslip zones shows an increase trend while the normalized number of preslip zones (NN) shows an increase followed by a decrease trend, which indicate that the expansion of the preslip undergoes a transition from increase to linkage of the isolated preslip zones. The peak NN indicates the initiation of the linkage of preslip zones. Both the linkage of the preslip zones and the decrease in the normalized information entropy of fault displacement direction indicate the reduction of spatial complexity of preslip as the instability approaches. Furthermore, the influences of dynamic adjustment of stress along the fault and the interactions between the asperities and preslip on the spatial complexity of preslip were also observed and analyzed.

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