中文摘要：

重力剖面金川—芦山—犍穿越芦山震区,近垂直于龙门山断裂带南段,长约300km,测点距平均2.5km,采用高精度绝对重力控制下的相对重力联测与同址GPS三维坐标测量,获得了沿剖面的自由空气异常和布格重力异常,并对布格重力异常进行了剩余密度相关成像和密度分层结构正反演研究.结果表明,芦山地震所在的龙门山断裂带南段存在垂直断裂走向的宽广的巨型重力梯级带,重力变化达252×10^-5 m·s^-2以上（龙泉山以西）,反映出四川盆地与松潘—甘孜地块地壳厚度陡变（约14.5km）性质;四川盆地与松潘—甘孜地块过渡区（龙门山断裂带与新津—成都—德阳断裂之间）存在（30～50）×10^-5 m·s^-2的剩余异常＂凹陷＂,可能与上地壳低密度体、山前剥蚀与松散堆积和推覆体前缘较为破碎有关;剩余密度相关成像显示地壳密度呈现分段性特征,在芦山地震位置出现高低密度变化;地壳呈现三层结构,四川盆地上、中、下地壳底界面平缓,反映其稳定阻挡作用,而松潘—甘孜块体上、中、下地壳底界面明显往盆地逐步抬升,反映出青藏高原往东的强烈挤压作用;松潘—甘孜块体往东推覆变形主要集中在上地壳范围内,推覆深度随离龙门山断裂带愈近而越浅.本文通过对密度分布及结构特征的研究,分析了芦山地震及龙门山地区地壳构造背景和当前活动性的深部动力环境特征.

英文摘要：

On April 20,2013,Lushan MS7.0earthquake occurred near the range-front fault of the southwest segment of Longmenshan fault zone（Dachuan-Shuangshi fault）.The focal depth of the earthquake was 13 km,and the epicenter was only 87 km away from the Wenchuanearthquake.There was no trace of surface rupture.The background of the deep tectonic dynamics and the difference with the Wenchuan earthquake were concerned.According to the gravity profile data of Jinchuan-Lushan-Qianwei which was across the southern segment of Longmenshan fault zone,we try to analyze the characteristics of gravity anomaly distribution,deep crustal formation and density structure along the profile,and then investigate the tectonic dynamics environment of the Lushan MS7.0earthquake.The profile was across the Lushan earthquake,nearly perpendicular to the south section of Longmenshan fault zone,about 300 km long,and the spacing between gravity stations was 2.5km.We obtained gravity observation value and the 3Dcoordinate（Longitude,latitude,altitude）by relative gravity surveying under the control of high precision absolute gravity and GNSS（global navigation satellite system）,respectively.And then we got free air gravity anomaly and Bouguer gravity anomaly along the profile.Through data processing using residual density image correlation algorithm and interactive inversion interpretation,we obtained results of residual density correlation imaging and density stratification structures.Gravity observation results showed that Bouguer gravity anomaly of the profile from northwest to southeast gradually increased.The maximum change of gravity anomaly reaches to252×10^-5 m·s^-2 in west of Longquanshan,and it was consistent with the giant gravitational gradient zone displayed in regional Bouguer gravity anomaly,which was parallel with Longmenshan fault zone.The gravity anomaly showed segmental feature.It was linear in the segment of JinchuanDawei-Baoxing, ＂depression＂ in the segment of Baoxing-Lushan-Ya′an-Hongya,which lies in between Yingxiu