Effects of the February 12,2014 M_S 7.3 Yutian Earthquake on Seismicity of the Northeastern Edge of Qinghai-Tibetan Block

First of all,using the GPS velocity field from campaign GPS measurements implemented by CMONC( C hina Crustal Movement Observation) a nd TEONC( C hina Tectonic Environment Observation Networks) u p to 2013, w e analyzed the background of regional crustal horizontal movement and deformation before the M S7. 3 Yutian,Xinjiang earthquake on February 12,2014. Then,by comparing this to the vertical movement from leveling measurements,we studied the crustal movement deformation and the state of strain accumulation on the northeastern edge of Qinghai-Tibetan block.Finally,we investigated the possible effects on the earthquake activity of the northeastern edge of Tibet from the M S7. 3 Yutian earthquake. The result indicates that,the M S7. 3Yutian earthquake occurred against the background of strong tectonic movement and intensive intracontinental crustal differential movement on the edges of tectonic blocks in western China,and also that it happened in the period of the strong tectonic stress field in Qinghai-Tibetan block and its edges. The sinistral strike-slip and stress transfer of the Yutian M S7. 3 earthquake may accelerate the rupture of fault segments with high strain accumulation at the northeastern edge of Qinghai-Tibetan block( especially in Qilian Mountain fault zone,and border area of Gansu,Qinghai and Sichuan provinces on the south of western Qinling).

Gravity evolution and earthquake activities of the northeastern edge of Qinghai-Xizang block

The relationship between temporal-spatial evolution of gravity and earthquake activity during 1992~2001 has been analyzed systematically by integrally adjusting the gravity observation data of the northeastern edge of Qinghai- Xizang (Qingzang) block. The result shows that the gravity observation data of the northeastern edge of Qingzang block obtained by using the uniform starting datum can completely reflect the precursory gravity information appearing during the seismogenic process. In the genesis stage of an earthquake, regional gravity anomaly appears in a large area, resulting in related local gravity anomaly. The dynamic image of gravity field can clearly reflect the orderly evolution and earthquake activity.

Effect of Kunlun Ms 8.1 earthquake on crustal deformation in northeastern edge region of Qinghal-Tibet plateau

Seismic fault parameters can be inversed with Okada model based on deformation data before and after earthquakes in focal region and its adjacent area. Co-seismic displacements can be simulated by using these parameters,and then regional velocity field obtained by deducting the co-seismic displacements from the observed displacements by GPS method. We processed and analyzed the data in the northeastern edge region of the Qinghai-Tibet plateau observed during 2001 -2003 in two steps： firstly, the displacements generated by Kunlun MsS. 1 earthquake of 2001 in this region was simulated, and secondly, deducted the co-seismic displacements from it and obtained the horizontal crustal velocity field. The results reveal ： 1 ） the effect of Kunlun Ms8.1 earthquake on crustal deformation in this region is significant; 2 ）the velocity field obtained with this method is better than the original GPS velocity field in reflecting the status of regional crustal movement and strain.

青藏高原东北缘、鄂尔多斯和华北唐山震区的地壳结构差异——深地震测深的结果

划分大陆活动地块的重要标志之一是它们在地壳结构间的差异。大陆不同地块具有不同的地壳结构特征。这些结构和构造上的不同反映了它们在地壳内部的变形特征和动力过程的差异。文中利用深地震宽角反射 /折射剖面的结果 ,讨论了青藏高原东北缘东昆仑巴颜喀拉地块、鄂尔多斯地块和华北地块唐山震区地壳结构的差异。它们分别是变形强烈的活动地块、内部变形小相对稳定的地块和现代发生过强震的活动地块。在地壳结构上它们之间的差别是明显的。这些差异表现在地壳的分层性质、上地壳和下地壳的结构、地壳结构的不均匀尺度、壳 /幔分界的性质、壳内低速层的分布、地壳界面、特别是莫霍面的构造形态等方面。

青藏块体东北缘重力场演化与地震活动

通过对青藏块体东北缘重力观测资料进行整体平差计算 ,系统分析了 1 992～ 2 0 0 1年重力场的时空动态演化特征及其与地震活动的关系 .结果表明 :利用统一起算基准获得的青藏块体东北缘重力观测资料 ,较完整地反映了青藏块体东北缘孕震过程中出现的流动重力前兆信息 .在地震孕育发生阶段 ,重力场出现较大范围的区域性重力异常 ,并产生与地震孕育发生有关的局部重力异常区 .重力场动态图象较清晰地反映了区域重力场的有序性演化与地震活动 .

汶川地震前后青藏高原东北缘重力场动态变化研究

通过对青藏高原东北缘重力观测资料进行整体平差计算,系统分析了该区重力场在汶川8.0级地震前后重力场的时空动态演化特征。研究结果表明,汶川地震的发生使青藏高原深部物质向北东运移,且部分通道受鄂尔多斯陆块的阻隔,青藏高原东北缘区域重力场出现大空间尺度的趋势性显著重力变化;汶川地震后,甘、宁、陕交界的六盘山断裂带与西秦岭北缘断裂带以及之间地区重力场出现显著的非均匀变化,该地区受汶川大地震的影响显著。

基于GPS观测的昆仑山8．1级地震微动态变形研究

借助板内块体的刚性运动、应变综合模型,利用青藏块体东北缘地区的GPS基准站连续观测数据,通过计算各测站累计差分位移得出该区域变形参数动态变化。结果表明,2001年昆仑山8.1级地震前后变形参数时间序列存在一致的变化趋势,同震变化明显的参量有东西向应变、最小主应变、面膨胀率与第二剪应变。该综合模型可以解释昆仑8.1级地震引起区域应变释放、调整的机制。研究还认为利用区域变形参数组合有可能识别出大震临震异常。

昆仑山8.1级地震对青藏高原东北缘地壳水平形变影响的讨论

为了从整体上(较大尺度)把握区域应变场的时—空变化势态,并对区域运动场的描述更加逼真,文中在整体无旋转的基础上使用了以提取低频应变信息为主的连续非线性应变模型。根据《中国地壳运动观测网络》位于青藏高原东北缘GPS测站所产生的复测资料(1999—2001—2004),以1999—2001年的运动为基本参考(阶段性形变背景),从2001、2004年两期资料中分离了2001年昆仑山8.1级地震对其产生的主要影响量,结果表明:①昆仑山8.1级地震对青藏高原东北缘产生了比较显著的影响,且位移与形变的方式与背景有很大的差异;②震后的位移分布更加有序,该区西北地区向西偏南向移动,东南地区向北移动;该区最大位移超过15mm;③地震对该区西北地区的影响是能量释放性的,对东南地区的影响是能量积累性的;④震前面应变以收缩为主,震后西北地区为面膨胀(越西越大),东南部为面收缩地区。从整体上看,昆仑山8.1级地震的发生对青藏高原东北缘地区地震活动具有"东增西减"的作用。