【摘要】 乌鲁木齐地处天山中段.震源机制解研究表明,北天山中段区域主压应力方向为N10°E左右,且具有自西向东逐渐东偏的特点.在乌鲁木齐地区,由中强地震震源机制解反演的主压应力方向为N15°—20°E;由断层滑动资料反演的乌鲁木齐周边构造应力场的主压应力方向为N17°W—N2°E.上述两种资料反演的乌鲁木齐构造应力场主压应力方向与北天山中段比较接近.在乌鲁木齐市周围,由小震综合断层面解得到的主压应力方向为N40°—46°E,与区域主压应力方向具有20°—30°的偏转;而由钻孔应力测量的主压应力方向为N55°E,这与小震综合断层面解主压应力方向相比又向东偏转10°—15°,与区域的主压应力方向偏转达30°—40°.上述结果表明,在乌鲁木齐逆断层-褶皱构造的前缘隆起区存在张性作用,其主压应力方向与区域主压应力方向近垂直.而在乌鲁木齐开展的钻孔应力测量结果进一步表明,在NNE向主压应力的背景中,叠加了浅部与之近垂直的压应力场,致使浅部主压应力方向偏向ENE.这也可以解释为何乌鲁木齐市区ENE向的九家湾断层组表现为正断层性质.更多还原

【Abstract】 Urumqi city is located in central part of northern piedmont of Tianshan mountain.The mean direction of principal compressive stress in central section of northern Tianshan deduced from the focal mechanism solutions is around N10°E,with a clear feature of gradual change from west to east.In the region of Urumqi city,the direction derived from focal mechanism solutions of moderate-strong earthquakes is N15°—20°E.The principal stress direction found from fault striation inversion is N17°W—N2°E.The stress direction deduced from the above two data sets are basically in the variation range of the principal compressive stress in the central section of northern Tianshan.However,the stress direction inferred from composite fault-plane solutions of small earthquakes within 25 km of the Urumqi seismic station is N40°—46°E,which shows a deviation of 20°—30° from that of regional principal compressive stress.Nevertheless,the direction of maximum horizontal compressive stress measured in the boreholes in Urumqi city is around N55°E,which displays a further deviation of 10°—15°,and its deviation from that of regional stress field is up to 30°—40°.These phenomena indicate that a tension stress in the shallow layers in front part of the compressive fault-fold region has been superposed to the regional NNE--SSW trending compressive tectonic stress and makes the direction of local principal compressive stress turn to NEE--SWW.This is one of the causes why the normal faults,such as the Jiujiawan fault groups,were developed in Urumqi city.更多还原