球体位错理论在2011年日本强震中的应用研究

利用球体位错理论计算了2011年日本强震产生的远场同震位移与应变，并利用GPS远场数据修正了该强震的总地震矩。结果表明：1）利用球体位错理论计算得到的理论水平位移场显示，垂直于发震断层的广大区域同震位移较大，位移矢量总体都指向震中地区，震中距约5 000千米的地方亦产生了3 mm以上的同震水平位移。理论位移与远场GPS观测结果具有良好的一致性；2）比较两个独立断层模型对应的理论同震位移场发现，震源西部地区远场位移总体上只有1%～4%的微小差异，而东部广大海域的差异则达到同震信号的6%～15%，震中周围差异更大。该差异表明，相对于震源仅局域覆盖的日本本土GPS观测数据对2011年日本强震的断层滑动分布模型的约束能力有限；3）依据中国及邻区的远场GPS同震观测数据修正2011年日本强震的总地震矩，把该地震释放的总能量约束在(3.24～4.96)×10 ²² Nm，相应的矩震级为Mw8.97～9.10；4）2011年日本强震在华北地区产生的同震应变与该区的长期应力变化背景场大体相反，表明该强震使华北地区的地壳产生了松弛效应。

APPLICATION OF SPHERICAL DISLOCATION THEORY TO 2011 TOHOKU OKI EARTHQUAKE,JAPAN

This paper presents several applications of spherical dislocation theory to the 2011 Tohoku Oki earthquake. 1) We first calculate the coseismic horizontal displacements of the great earthquake using spherical dislocation theory. Our results show that as follows.a) The coseismic displacements are relatively bigger at areas perpendicular to the fault plane; b)most of the horizontal displacements point to the epicenter; c)as far as 5 000 kilometers from the epicenter the coseismic horizontal displacements reach up to 3 mm; d)in total, our theoretical predictions agree very well with the observations detected by GPS in far field. 2) Comparing with the theoretical displacements themselves, the discrepancies between two sets far field displacements, which are deduced from two independent fault models, are about 1%-4% west to the epicenter but about 6%-15% east to the epicenter. The misfits near the epicenter are much bigger than those of far field. Such discrepancies indicate the limited constraint capability of the dense GPS data on Japan Islands to the fault model of the 2011 Tohoku Oki earthquake, because of GPS stations’ ill distribution relative to the epicenter. 3)We constraint the total seismic moment of the 2011 Tohoku Oki earthquake within (3.24-4.96)×10 ²² Nm using the far field GPS data.The corresponding moment magnitude is about Mw8.97-9.10. 4) At last, the coseismic strains caused by the 2011 Tohoku Oki earthquake are roughly crosscurrent with the background of stress change fields at North China. As indicate that the crustal blocks at North China are relaxed as a whole due to the great earthquake.