关键词: 恩开断裂带, 活动断裂, 区域应力场

Abstract: Enkai fault zone is one of the important fault zones along the coast area of southeast China. The fault zone with the length of about 160km is mainly constituted by three approximately parallel NE faults (F₁ and F₂ incline to NW and F₃ incline to SE). In Tertiary the faults moved in a way of normal faulting. However, at the end of Tertiary or early Quaternary, the faults turned to be compressive ones by WNW-ESE strong horizontal force, resulting in compressive deformation along the whole fault zone. Probably because of weakening of the WNW-ESE compressive stress from middle Pleistocene and because of weakening tendency of compressive stress from the south to the north along the southeastern coast of China, compressive stress in the south segments of the fault zone is strong enough to make the faults move in a way of reverse faulting and form reverse faulting landform while compressive stress in the north segments of the fault zone is so weak compared to isostacy force as to make the fault blocks restart isostacy uplift, move in a way of normal faulting and form normal faulting landform. Because of the approximate equilibrium between isostacy and horizontal compressive force in the middle segments of the fault zone, the faults have kept relatively steady state, resulting in weak contrast landform. In about late Pleistocene, a series of NW faults in the fault zone came into being or reactivated. On one hand, these NW faults, due to small angle between their strike and main compressing stress axis, have relatively small friction stress on the fault surfaces so that they could be moved more easily and often offset NE faults, forming obstacles to the strike slip of NE faults. On the other hand, the movements of NW faults release some strain energy so that they weaken compressive stress on the NE fault surfaces. Both of them reduce the activity of NE faults.

Key words: Enkai fault zone, active fault, regional stress field