Mapping of asperities and estimation of spatiotemporal distribution of interplate slip

在这项研究中，我们一直致力于分析日本东北部太平洋下板块边界的锁滑细节，并了解板间地震的发生机制。主要研究内容有：1.重复地震分析；2.基于宽带地震波形资料的中、大震震源过程分析；3.GPS数据分析；4.数值模拟研究粗糙度特征。根据1.重复地震分析结果，通过识别北海道至日本东北太平洋板块边界各部分的重复地震，成功地估计了2003年东京地震破裂带周围板间滑动的时间变化。2.根据地震波形资料进行震源过程分析表明，2005年8月16日宫城7.2级地震的断裂区与断裂区…的东南部是重叠的。1978年宫城大地震的更多内容。因此，这意味着1978年地震位于北部和西部的凹凸体没有破裂；我们的研究指出了对这一地区进行持续仔细观察的重要性。此外，我们对20世纪30年代宫城7级地震的余震进行了重新分析，发现在20世纪30年代的宫城地震中，三个凸起可能分别滑动了三次。3.通过GPS分析，2005年宫城大地震后，我们探测到了向地震断裂区南侧扩展的余滑移。这一观测结果与地震波形反演分析的结果相吻合，北部和西部的凹凸体没有破裂。4.数值模拟分析结果表明，为了解释在靠近陆地的深部板块边界观测到的后滑移的传播速度，板块边界周围的孔压应非常大。另一方面，为了解释在靠近海沟的浅板边界观测到的后滑移的传播速度，不需要像上面的情况那样需要大的孔压。这些结果表明，由脱水反应引起的板块边界补水量的深度变化，或板块边界周围渗透系数的深度变化。如上所述，通过这项研究，我们取得了实质性的成果，加深了对板间地震孕育机制的认识。较少

In this research, we have been aiming to analyze details of lock and slip on the plate boundary under the Pacific Ocean in NE Japan and to understand the generation mechanism of interplate earthquakes. The main research contents are: 1. analysis of repeating earthquakes, 2. analysis of source process of medium ＆ large earthquakes based on broadband seismic waveform data, 3. GPS data analysis, 4. research on the property of asperities by using numerical simulation.According to the result of 1. analysis of repeating earthquakes, we successfully estimated the time variation of interplate slips around the rupture zone of the 2003 Tokachi-oki earthquake, by identifying the repeating earthquakes in all parts of the plate boundary under the Pacific Ocean from Hokkaido to NE Japan. As for the 2. analysis of source process based on seismic waveform data, we showed that the rupture area of Miyagi-oki earthquake (M7.2) on Aug. 16, 2005 is overlapped with the southeastern part of the rupture area … More of the 1978 Miyagi-oki earthquake. So, this means that the asperities of the 1978 earthquake located in the north and west part are left unruptured; our research pointed out the importance of continued and careful observation on this area. Moreover, we conducted reanalysis of aftershocks of Miyagi-oki earthquakes with magnitude >7 in 1930s, and found out that three asperities could have slipped separately, in three times, in the case of 1930s' Miyagi-oki earthquakes. With 3. GPS analysis, after 2005 Miyagi-oki earthquake, we detected the after slip which spread toward south of the rupture area of the event. This observation result corresponds with the result of seismic-waveform inversion analysis; the northern and western asperities are left unruptured. The result of 4. numerical simulation analysis shows that, in order to explain the propagation velocity of the after slip observed in the deep plate boundary close to land, pore pressure around the plate boundary should be extremely large. On the other hand, in order to explain the propagation velocity of the after slip observed in the shallow plate boundary close to the trench, large pore pressure is not necessary like in the case above. These results suggest the depth variation in the amount of water supplied to the plate boundary, which was caused by dehydration reaction, or the depth variation in coefficient of permeability around the plate boundary.As mentioned above, through this research, we have achieved substantial results to enhance understanding of the generation mechanism of interplate earthquakes. Less