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本研究利用1 243个架设于日本地面的GPS台站所取得的每日地表位移资料,来揭示2011年3月11日毁灭性的M9东北-近海地震前的地表位移。研究中用HHT(希尔伯特-黄)带通滤波扣除长期板块运动、短期噪音及与频率相关的变化的影响,所得的残余位移资料与东北-近海地震相关的震源机制参数进行比对。分析结果显示,由残余地表位移推断出的南向运动与东北-近海地震断层的走向一致,并且在震前第65天变得尤为明显。这项观测显示剪应力在东北-近海地震的潜伏期非常重要。在震前第47天,西向的地壳运动与最大水平压应力轴的角度一致,该向西运动范围涵盖了整个日本,并在距离震中75km的地方形成了一块受阻的区域(42°N,142°E)。本研究还将水平位移与从残余GPS资料得到的垂直位移结合构建全面的图像,用来判断俯冲带破坏性地震的地表形变。
In this study, daily surface displacement data obtained from 1 243 GPS stations on the ground in Japan were used to reveal the surface displacements before the devastating M9 northeast-offshore earthquake on March 11, 2011. In the study, HHT band-pass filtering was used to deduct the effects of long-term plate motion, short-term noise and frequency-related changes. The residual displacement data were compared with focal mechanism parameters related to NE-SE. The results of the analysis show that the southward movement deduced from the residual surface displacement coincides with the strike of the northeastern-offshore seismic fault and became especially evident on the 65th day before the earthquake. This observation shows that the shear stress in the northeast-offshore earthquake is very important. On the 47th day before the earthquake, the crustal movement in the west direction coincided with the axis of maximum horizontal compressive stress that covered the entire Japan and formed a blocked area (75 ° N) from the epicenter (42 ° N, 142 ° E). In this study, the horizontal displacement is combined with the vertical displacement obtained from residual GPS data to construct a comprehensive image to determine the surface deformation of the destructive earthquake in the subduction zone.