Abstract: The triaxial compression experiments of dry Zoukoudian granodiorite at temperature up to 700℃ and confining pressure up to 7 kb with solid confining media,the microscopic observations to the tested specimens,and the theoretical analyses indicate that both shear fracture and frictional sliding have a similar pregnancy process and generation mechanism.The pregnancy process of major shear fracture in a specimen can be divided into three stages: (1) microfracturing with plastic deformation of soft mineral grains; (2) appearance and propagation of macroscopic shear fracture and formation of rock bridges between them; (3) failure of rock bridges and final occurance of the major shear fracture running obliquely through the specimen.Fracturing-through shear strength is a special kind of frictional strength,which characterizes the friction behavior of the nei sliding surface in the originally intact rock specimen.Both shear fracture and frictional sliding can be classified into two types: the gradual and sudden one.Sudden frictional sliding is the stick-slip along pre-existing fault while sudden shear fracture is the "first stick-slip" of intact rock.The confining pressure condition neccessary for the "first stick-slip" and the closely subsequent one is basically the same,which is about 5 kb or higher at the room temperature and increases with temperature.However,it is possible to induce stick-slip under confining pressure far less than 5 kb for pre-existing flat faults which have undergone a quite long sliding distance or a certain change in the orientation of stress field.The upper temperature limit of stick-slip is about 300-350℃ and the lower confining pressure limit of stick-slip is less than 1 kb for dry Zoukoudian granodiorite.In consideration of little possibility for strong earthquakes caused by shear fracture of intact rock owing to the increase of crustal temperature with depth,the principal shock-generation mode for most of strong shallow earthquakes may be the stick-slip along pre-existing faults.