GPS Derived Evolution of Strain Rate in Sichuan Region
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摘要: 为了研究汶川5·12地震事件对青藏高原东南缘及四川盆地的应力再分配作用及该区域现今的地震危险性，使用1997-2015年共计355个GPS站点观测资料获取了该区域1997-2008、2009-2011、2011-2013、2013-2015年共计4期独立的速度场，基于规则格网和张力样条插值方法计算了上述速度结果对应的面膨胀率、垂直轴旋转率及最大剪应变率.以2008年汶川Ms8.0级地震为主要节点，以芦山2013年Ms7.0级地震、康定2014年Ms6.3级地震为参考节点，分析了应变率场的时空演化过程及其与地震事件的潜在关联性.研究结果显示：随着汶川震后的时间推移，沿龙门山断裂的3种应变率分布均有减弱趋势，但至今仍未恢复至震前状态，说明该区域的震后回弹受下地壳黏弹性流变物质的弛豫影响较为显著；安宁河-则木河断裂及周边的面压缩率在汶川地震之后有增强趋势，该趋势可能与区域的地震危险性有所关联；安宁河-则木河断裂带及鲜水河断裂北段是未来一段时间该研究区域内应该持续关注的主要地震危险区.Abstract: To study the impact of the Wenchuan earthquake on the stress re-distribution and corresponding seismic potential of the southeastern Tibetan Plateau and Sichuan Basin, In this study, 355 GPS sites in the Sichuan region of the southeastern Tibetan Plateau were used to calculate 4 sets (1997-2008, 2009-2011, 2011-2013, and 2013-2015) of GPS velocity fields for the period 1997-2015. These velocity results were used to deduce the corresponding dilatation, vertical rotation, and maximum shear strain rates, based on regular grid and splined interpolation methods. Subsequently, taking the 2008 Ms8.0 Wenchuan earthquake as the primary reference point and the subsequent 2013 Ms7.0 Lushan and 2014 Ms6.3 Kangding earthquakes as secondary reference points, the spatial and temporal evolution of the aforementioned strain rates and their relationships with the seismic events were analyzed. The results indicate that all types of strain rates, both in space and time, taper off along the Longmen Shan Fault with the passage of time after the Wenchuan earthquake. However, they have not yet recovered to their pre-seismic status, which implies that post-seismic relaxation of the Wenchuan earthquake is now dominated by ductile flow in the lower crust. The dilatation strain rate of the area enclosed by the Anninghe and Zemuhe faults shows an increase after the Wenchuan earthquake. This reveals the seismic hazard faced by the region and further detailed studies are required here. The location of maximum vertical rotation strain rate seems to transfer from the southern segment of the Xianshuihe fault to the Anninghe and Zemuhe faults, and even further southward to the Xiaojiang fault. However, the magnitude of this transfer is so small that detailed further studies are required to ascertain whether this transfer is realistic and the implications it bears, if so. The maximum shear strain rate indicates that the Daliang Shan sub-block and the northern segment of the Xianshuihe fault are still regions with high level seismic risk, and these should be the focus of future studies.
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Key words:
- GPS /
- velocity field /
- strain rate /
- evolution /
- seismic risk
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图 2 不同时期GPS速度场获取的面膨胀率结果(×10-6 strain/yr)
Figure 2. Dilatation strain rate results calculated using GPS velocity fields of different periods(×10-6 strain/yr)
图 3 不同时期GPS资料获取的垂直轴旋转率结果对比(×10-6 strain/yr)
Figure 3. Vertical rotation rate results calculated using GPS velocity fields of different periods(×10-6 strain/yr)
图 4 不同时期GPS资料获取的最大剪应变率结果(×10-6 strain/yr)
Figure 4. Maximum shear strain rates of GPS velocity fields of different periods(×10-6 strain/yr)
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