Progresses of the researches and the causing mechanisms on the double seimic zones within the subduction zones around the pacific ocean
环太平洋俯冲带内双地震带及其成因机制研究进展

As our Planet's largest recycling system,subduction zone has become one of the most significant leading research aspects of earth science.Intermediate-deep earthquakes in some subduction zones,especially most of circum-Pacific subdution zones,occur in two distinct layers,forming two seismic zones with different focal mechanisms,separated vertically by an aseismic zone about 40 km thick.The discovery and simultaneous studies of double seismic zones greatly contribute to the further studies on stress regimes of subduction zones.Briefly introduced spatial location,morphology and stresses distribution of Double seismic zones within some subductions around the Pacific ocean.In addition to the two types of shallow Double seismic zones with depth range from 60 to 200 km,there are deeper(>325 km) Double seismic zones beneath Tonga and Izu-Bonin arcs.According to the morphology and thermodynamic conditions of Double seismic zones,several models including unbending,dehydration embrittlement and transformational faulting,have been proposed as possible causes for intermediate-deep earthquakes and Double seismic zones.Comparing with numerical modeling results,many researches considered serpentine dehydration and transformational faulting as the dominant causes for intermediate and deep Double seismic zones,respectively.However,there is no a uniform model,which can be accepted as a mechanism for both intermediate and deep double seismic zones.Although it is very questionable and disputable,the hypothesis that intermediate-deep events occur on pre-existing or fossil faults may be a intriguing and paradoxical feature of intermediate-deep double seismic zones.Furthermore,the combination of several factors,such as unbending and dehydration,perhaps contributes more or less to the complexity of the thermal and stress regimes within the subduction zone.