Geomorphological and Geological verification for documented paleo-seismic activity occurred in Nankai trough

该研究项目的主要目的是用地质学或地貌学的方法对历史文献中识别出的大地震进行验证。对位于海角以北约13公里的Muroto-Misaki至Meoto-Iwa沿线的全新世石灰岩进行了沉积学分析。这些石灰岩的海拔高度限制在9.2英寸以下。石灰岩的平均直径可达4.4分钟，厚度可达0.5英寸，主要由僵化的固着生物组成，包括环节动物、珊瑚、生物虫、结壳有孔虫、藤壶、非膝曲的珊瑚藻类，以及少量的软体动物和贝类藻类。针状水泥和均质水泥是次要成分。在珊瑚藻壳及其基质之间的半封闭空间中发现了针状胶结物。石灰岩的模式组成是用点造币技术确定的。根据生物成分可将全新世石灰岩划分为6种类型(I-VI型)。这些岩石类型的垂直分布与现代固着生物的垂直分布对比表明，I型石灰岩的顶部以典型珊瑚的产状为特征，大致对应于石灰岩形成时的平均低水位泉。两个地点I型灰岩最高产状的差异可能代表了近1000至1500年来总隆升的变化，导致了古北半球低水位泉以~10厘米/公里的速度明显向北下降。因此，全新世石灰岩是恢复该区过去地震活动的良好古水深仪。这项研究表明，温带碳酸盐沉积与热带碳酸盐沉积一样，是记录反复同震抬升和海平面上升的时间和规模等地质事件的良好记录器。

The main puipose of the research project is to verify huge earthquakes which were identified through historical documents in geological or geomoiphological method. Sedimentologic analyses were conducted on Holocene limestones that occur along the mast from Muroto-misaki to Meoto-iwa, located ~13km north of the cape. The limestones are limited to less than 9.2 in in elevation. The limestones are up to 4.4 min mean diameter, up to 0.5 in in thickness, and consist mainly of ossilized sessile organisms, including annelids, corals, biyozoans, encrusting foraminifers, barnacles, nongeniculate coralline algae, and, to a lesser extent, molluscs and peyssonneliacean algae. Acicular and equant cements are minor components. Acicular cements are found in semiclosed spaces between coralline algal crusts and their substrates. The modal composition of limestones was determined by a point-cointing technique. Based on the biotic composition, the Holocene limestones can be classified into six types(Types I to VI) A comparison of the vertical distribution of these rock types with that of modem sessile organisms indicates that the top of Type I limestone, which is characterized by the occurrence of hennatypic corals, corresponds approximately to the mean low water springs when the limestones formed. A difference in the highest occurrence of Type I limestone between two sites may represent the variation in the total amount of uplift over the last 1000 to 1500 years, which resulted in an apparent northward decline of palemnean low water springs at a rate of ~10cm/km. Therefore, the Holocene limestones are a good paleobathymeter to reconstruct past seismic activities in this area. This study shows thatwann temperate carbonate deposits are as excellent recorders of geologic events, such as the timing and scale of repeated coseismic uplifts and elevation of sea levels, as those in the tropics.