FAULT-ZONE STUDIES OF THE M9 TOHOKU-OKI, JAPAN EARTHQUAKE SEQUENCE

地震界面临的重大挑战之一是板块边界的滑动。多年来沿着俯冲带锁定所释放的能量尤其难以理解，因为它们发生在海洋最深处。但它们非常重要，因为大型俯冲带地震对人类构成了最大的自然灾害之一，要么是强烈的震动，要么是洪水(海啸)，或者两者兼而有之，例如最近的东北-冲之地震。人们对这些罕见事件的破裂性质知之甚少，特别是海啸引发的地震(TE)，海啸前几乎没有震动，比如1896年的三陆地震。记录良好的2011年东北冲地震揭示了这些问题的一些新的曙光，在这些问题上，深部的一般性板间事件似乎触发了罕见的TE事件。最近的报道表明，强震动来自深度30公里的破裂，震级较小(MW~8.5)，3D放大主要发生在较短的周期(2-10秒)或更高处，而洪水则是由靠近海沟(50米)的大位移(MW~9)引起的，以较长的周期(20秒)辐射为主。这些破裂类型的混合给这次地震的分析和建模带来了巨大的挑战，需要覆盖广泛时期的数据集。幸运的是，日本群岛的数据覆盖率非常高，为主震和多次余震提供了有史以来最好的一组观测。研究人员将使用高分辨率波形模拟来研究断裂带结构的变化，试图了解沿走向和作为深度函数的破裂性质的巨大变化。这项工作是一个伴随着东北-冲之地震序列的宽带反演而进行的技术开发计划。其基本目标是利用我们的半自动剪切粘贴(CAP)方法处理嵌入在3D结构中的这些事件的位置和震源参数，以获得区域数据(0至400公里)和远震距离的CAPT。联合反演将用于建立到阵列的最透明路径，以扩展主震和大前震和余震的宽带反演。

One of the grand challenges for the seismology community involves slippage along plate boundaries. Energy released from many years of locking along subduction zones is made particularly difficult to understand since they occur beneath the deepest portions of the oceans. But they are very important because large subduction zone earthquakes pose one of the greatest natural hazards to mankind, either by strong shaking, flooding (tsunami), or a combination of both, i.e., the recent Tohoku-Oki Earthquake. Rupture properties of these rare events are poorly understood, especially Tsunamigenic Earthquakes (TE) with little pre-tsunami shaking such as the 1896 Sanriku earthquake. The well recorded 2011 Tohoku-Oki earthquake sheds some new light on these issues where a generic interplate event at depth appears to have triggered a rare TE event. Recent reports indicate that the strong shaking came from rupture at depth 30km with relatively small magnitude (Mw~8.5) with 3D amplification occurring primarily at relatively short-periods (2-10 sec) and higher, whereas, the flooding was caused by the large displacement (Mw~9) close to the trench (50m) and was dominated by relatively long-period ( 20 sec) radiation. The mixture of these rupture styles presents significant challenges in the analysis and modeling of this earthquake and requires data sets covering a broad range of periods. Fortunately, the data coverage on the Japanese Islands is remarkable providing the best set of observations ever recorded for both the main event and the many aftershocks. The investigators will use high-resolution waveform modeling to investigate the variation in fault zone structure in an attempt to understand the great variation in rupture properties both along strike and as a function of depth.The work is a program of technique development along with broadband inversions of the Tohoku-Oki earthquake sequence. The basic aim is to address the locations and source parameters of these events embedded in a 3D structure, exploiting our semi-automated Cut-and-Paste (CAP) method for regional data (0 to 400 km) and CAPt at teleseismic distances. Joint inversions will be used to establish the most transparent paths to arrays for extending the broadband inversions of the main event and large foreshocks and aftershocks.