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选取2016-01-21青海门源MS6.4强震发震区域周围200km范围的10个连续GPS观测站和74个流动GPS观测站资料,分析研究2016年门源MS6.4地震之前的区域地壳形变特征:1)基于10余年GPS资料的速度场计算结果表明,发震区域所处的祁连-海原断裂系具有显著高于周边区域的地壳应变率和地震矩累积率。在发震区域20km×20km范围内,最大和最小主应变率分别为21.5nanostrain/a(方向NW-SE,拉张)和-46.6nanostrain/a(方向NE-SW,挤压),地震矩累积率达17.4×10~(15) N·m/a。主应变挤压的主轴方向与本次地震的震源机制相一致。2)基于震前6a连续GPS观测站坐标变化时间序列的计算结果表明,自2010年以来,发震区域的面膨胀值随时间呈“非线性”不断变小的趋势,反映出发震区域一直处于应变的挤压缩减状态,但在震前的2~3个月,面膨胀与最大剪切应变均发生了一次明显的反向趋势变化。这些震前的地壳形变异常变化,或许反映了发震区应力-应变积累在接近临界破裂状态时的非线性调整。
The data of 10 continuous GPS stations and 74 mobile GPS stations in the 200 km range around the earthquake area of the MS6.4 strong earthquake in Qinghai Municipality from January 21 to January 2016 were selected to analyze and study the regional crust Deformation features: 1) The velocity field calculation based on more than 10 years of GPS data shows that the Qilian-Haiyuan fault system in the seismogenic area has significantly higher crustal strain rate and seismic moment accumulation rate than the surrounding area. In the range of 20km × 20km, the maximum and minimum principal strain rates are 21.5nanostrain / a (direction NW-SE, tension) and -46.6nanostrain / a (direction NE-SW, Rate of 17.4 × 10 ~ (15) N · m / a. The principal axis of the main strain extrusion is consistent with the focal mechanism of this earthquake. 2) Based on the time series of 6 consecutive GPS observational stations, the calculation results show that since 2010, the surface swell value of the seismogenic area shows a trend of “nonlinear ” decreasing with time, reflecting that the seismic area Has been in the squeeze of the state of strain reduction, but 2 to 3 months before the earthquake, surface expansion and maximum shear strain occurred a significant reverse trend. These anomalies of crustal deformation before the earthquake may reflect the non-linear adjustment of stress-strain accumulation in the seismogenic zone near the critical rupture.