Full interseismic locking of the Nankai and Japan‐west Kurile subduction zones: An analysis of uniform elastic strain accumulation in Japan constrained by permanent GPS
Full interseismic locking of the Nankai and Japan‐west Kurile subduction zones: An analysis of uniform elastic strain accumulation in Japan constrained by permanent GPS
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DOI：
10.1029/2000jb900060
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发表时间：
2000-06
影响因子：
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通讯作者：
S. Mazzotti;X. Pichon;P. Henry;S. Miyazaki
中科院分区：
文献类型：
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作者：
S. Mazzotti;X. Pichon;P. Henry;S. Miyazaki
我们分析了1995-1997年间在日本上空获得的永久性全球定位系统(GPS)数据，以估计由于太平洋和菲律宾海板块俯冲到日本岛屿下方而产生的地震孕育区的瞬时地震间耦合比。我们首先推导出表征日本南部和北部地壳形变的GPS应变速率场，并对其进行反演，以确定沿南开海槽中部和日本西部千岛海沟的有效俯冲速度。这些“参考自由”速度接近欧亚大陆板块运动模型所预测的速度。我们的结论是，欧亚参考框架对俯冲运动给予了很好的近似，并且在测量期间，两个俯冲带在测量期间都是完全锁定的。然后，我们测试耦合比是否在孕震带内表现出局部变化。为此，我们将俯冲界面划分为35公里×30公里的单元，以点源群为模型，并反演参考欧亚大陆的GPS速度场，以得出每个断层单元上的耦合比(介于0到1之间)。这三年的结果是一致的，证实了南开中部和日本西部千岛地震孕育带都是均匀完全锁定的。大多数耦合比接近于1，少数接近于0；中间值很少。去耦合区要么对应于1994年三陆-冲之间板间地震(日本海沟)的强烈震后余滑，要么对应于对锁定带实际下限的小幅高估。我们得出的结论是：在GPS数据和模型的分辨率范围内，(1)南开海沟和日本-西千岛海沟在这3年中不存在部分耦合；(2)以前对日本海沟和千岛海沟的地震分析得出的小地震耦合比可能表明，很大一部分弹性能量通过慢地震和震后余滑而悄悄消散；(3)打破这两个俯冲带的大地震和大地震观测到的不均匀同震滑动模式与均匀加载形成了巨大的反差。最后，我们讨论了日本岛屿长期变形框架内的非弹性残余变形。
We analyze permanent Global Positioning System (GPS) data obtained over Japan between 1995 and 1997 to estimate the instantaneous interseismic coupling ratio of the seismogenic zones due to the subduction of the Pacific and Philippine Sea plates below the Japanese islands. We first derive the GPS strain rate fields that characterize the crustal deformation of southern and northern Japan and invert them to determine the effective subduction velocity along the central Nankai trough on one side and the Japan-west Kurile trench on the other. These “reference free” velocities are close to those predicted by plate motion models with respect to Eurasia. We conclude that the Eurasian reference frame gives a good approximation to the subduction motion and that to first order, both subduction zones were fully locked during the period of measurements. We then test whether the coupling ratio shows local variations within the seismogenic zones. To do this, we divide the subduction interface into 35 km×30 km elements that we model by point source groups, and we invert the GPS velocity field referenced to Eurasia to derive the coupling ratio (between 0 and 1) on each fault element. The results are coherent over the 3 years and confirm that both the central Nankai and the Japan-west Kurile seismogenic zones are homogeneously fully locked. Most of the coupling ratios are close to 1 and a few are close to 0; intermediate values are rare. The zones of decoupling correspond either to strong postseismic afterslip associated with the 1994 Sanriku-Oki interplate earthquake (Japan trench) or to a small overestimation of the actual lower limit of the locked zone. We conclude that within the resolution of the GPS data and the model, (1) partial coupling did not exist during these 3 years along the Nankai and Japan-west Kurile trenches; (2) the small seismic coupling ratio previously derived from earthquakes analysis for the Japan and Kurile trenches may indicate that a significant part of the elastic energy is dissipated silently through slow earthquakes and postseismic afterslip; and (3) the heterogeneous coseismic slip pattern observed for the large and great earthquakes that rupture both subduction zones is in great contrast to the homogeneous loading. Finally, we discuss the nonelastic residual deformation within the frame of the long-term deformation of the Japanese islands.