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

碧浦湾大分港浅川断裂的海底取芯沉积物和地震剖面记录表明，该断裂是1596年Keicho-Bungo地震的发震断层之一。单通道高分辨率记录不仅显示了沉积层的地震偏移量，而且还显示了1596事件引起的海底雪崩。雪崩产生的沉积物高2-3米，宽约100米。这一观察结果似乎与乌柳岛沉没的传说和历史上记载的高崎山山体滑坡相一致。整个别浦湾地区的地震获利记录显示，大部分地区有两个明显的反射层，即Akahoya火山灰层(约6700年B.P.)。玉甫灰层(约2500年B.P.)。赤原火山灰观测到的累积垂直偏移量与玉甫灰的累积垂直偏移量成正比，表明各地震事件的断层偏移量分布具有相似性。在…的基础上与用于海啸危险性评估的简单得多的传统震源模型相比，该模型具有更多的相似性，估计了1596年Keicho-Bungo地震时的断层错距，并构建了海啸震源模型，其模式非常复杂。作为比较，假设别浦湾中央断层是1596年地震的唯一发震断层，还构建了一个简单的海啸震源模型。数值模拟结果表明，两源模式下南海岸的海啸强度最大。然而，在两种模型中，其他方向的辐射是非常不同的。它表明，一个简单的传统震源模型可以预测海啸的一些主要特征，但不是详细的。这表明海啸预报的极限；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，这项研究的结果表明，地震和海啸观测之间估计的断层非均质性存在一些不一致，这可能是由于实际海底断层的复杂特征所致。较少

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