Estimation of the detailed structure of tsunami source based on survey results of submarine active aults

别府湾大分港Asamigawa断裂的海底岩心沉积物和地震剖面记录表明，该断裂是1596年keico - bungo地震的成因断裂之一。单通道高分辨率记录不仅显示了沉积层的地震偏移，还显示了1596年事件引起的海底雪崩。雪崩产生的沉积物有2-3米高，大约100米宽。这一观测结果似乎与Uryujima岛沉没的传说和历史上记载的高崎山山体滑坡一致。别府湾整个地区的地震有利记录显示，大部分地区有两个明显的反射层，即阿卡霍雅灰层（约6700年）和玉府灰层（约2500年）。发现阿卡霍雅火山灰显示的累积垂直偏移量与玉府火山灰成正比，表明各地震事件断层偏移分布的相似性。在相似度较高的基础上，对1596年Keicho-Bungo地震时的断层偏移量进行了估计，并建立了海啸震源模型，与简单的传统海啸震源模型相比，该模型显示出非常复杂的模式。为了比较，假设别府湾中央断层是1596年地震的唯一诱发断层，建立了一个简单的海啸震源模型。数值模拟结果表明，在两种震源模式下，南海岸遭受的海啸最大。然而，其他方向的辐射在这两种模式之间是非常不同的。这表明一个简单的传统震源模型可以预测海啸的一些主要特征，但不能预测细节。这表明海啸预报有一定的局限性；依赖于模拟海啸的精细特征的海啸测量可能是致命的。此外，本研究的结果表明，地震和海啸观测结果在估计断层非均质性方面存在一些分歧，可能是由于实际海底断层的复杂特征。少

Submarine cored sediments from the Asamigawa Fault in the Oita port, Beppu Bay, and the seismic profile records show that the fault is one of the causative faults of the 1596 Keicho-Bungo earthquake. The single-channel high-resolution records illustrate not only seismic offsets of sediment layers, but also submarine avalanche caused by the 1596 event. The mass of avalanche-derived sediment is 2-3m high and roughly 100m wide. The observation appears to be consistent with the legend of sunken Uryujima island and historically documented landslides of Takasakiyama mountain.The seismic profiting records in the entire area of Beppu Bay show two apparent reflecting layers in most parts, namely the Akahoya ash layer (about 6700 yrs B.P.) and Yufu ash layer (about 2500 yrs B.P). The observed cumulative vertical offsets shown by the Akahoya ash are found to be proportional to that of the Yufu ash, indicating the similarity of fault offset distribution for each seismic event. On the basis of the … More similarity, fault offsets at the time of the 1596 Keicho-Bungo earthquake is estimated and tsunami source model is constructed, which shows very complicated pattern, contrasting to much simpler conventional source models used for tsunami hazard estimate. For a comparison, a simple tsunami source model is also constructed by assuming the central Beppu Bay fault is the sole causative fault of the 1596 earthquake. Numerical simulation shows that the southern coast suffers the highest tsunami for the both source model. However, radiation in the other directions is very different between the two models. It suggests that a simple conventional source model may predict some major feature of tsunami, but not in details. This indicates a limit of tsunami forecast ; tsunami measure dependent on fine feature of simulated tsunami may be fatal. Furthermore, the result of this study suggests some disagreement in estimated fault heterogeneities between seismic and tsunami observations may be due to a complicated feature of actual submarine faults. Less