A Characteristic Analysis of the Dynamic Evolution of Preseismic-Coseismic-Postseismic Interferometric Deformation Fields Associated with the M 7.9 Earthquake of Mani,Tibet in 1997

By using the D-InSAR technique,we have acquired the temporal-spatial evolution images of preseismic-cosesimci-postseismic interferometric deformation fields associated with the M 7.9 earthquake of Mani,Tibet on 8 November 1997.The analysis of these images reveals the relationships between the temporal-spatial evolution features of the interferometric deformation fields and locking, rupturing,and elastic restoring of the source rupture plane,which represent the processes of strain accumulation,strain release,and postseismic restoration.The result shows that 10 months prior to the Mani event,a left-lateral shear trend appeared in the seismic area,which was in accordance with the earthquake fault in nature.The quantity of local deformation on the north wall was slightly larger than that on the south wall,and the deformation distribution area of the north wall was relatively large.With the event impending,the deformation of the south wall varied increasingly,and the deformation center shifted eastward.Two and half monthd before the event,the west side of the fault was still locked while the east side began to slide,implying that the whole fault would rupture at any moment.These features can be regarded as short-term precursors to this earthquake.Within the period from 16 April 1996 to two and half months before the earthquake,the most remarkable deformation zones appeared in the north and south walls,which were parallel to and about 40 km apart from the fault,with accumulated local displacements of 344 mm and 251 mm on the north and south walls,respectively.The south wall was the active one with larger displacements.Five months after the earthquake,the distribution feature of interferometric fringes was just opposite to that prior to the event,expressing evident right-lateral shear.The recovered displacements are～179 mm on the north wall and～79 mm on the south wall,close to the east side of the fault.However,in the area of the south wall far from the fault there still existed a trend of sinistral motion.The deformation of the north wall was small but recovered fast in a larger area,while the active south wall began to recover from the east section of the fault toward the WSW.