关键词: 雁列断层, 温度场, 应变场, 热红外辐射温度场, 热场前兆模式, 数字散斑相关方法

Abstract: 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.

Key words: en echelon faults, temperature field, strain field, thermal radiation brightness temperature T_B, precursor pattern of thermal field, digital speckle correlation method