Synthesized investigation of seismotectonic vertical processes in the forearc coastal area of the plate convergence zone

利用第四纪和地貌学技术，研究了地震构造隆升和非地震构造沉降的动力学组合模型，以了解太平洋板块与欧亚板块板块汇聚的构造过程。得到的结果如下：1。在MIS21 （ca.800ka）之后，至少在间冰期形成了9个海相阶地。平均抬升速率估计为0.2 ~ 0.4m/ka.2。在三陆海岸120公里长的北部海岸，至少可以在3到5米的高度上辨认出全新世的海洋阶地。出现年龄可能在7ka ~ 5ka之间。13个短钻和2个长钻的钻孔岩心资料显示了该区的构造历史：8ka ~ 7ka期间连续沉降速率为7 ~ 9mm/yr， 2.9ka前后可能出现幕式隆起，形成浅海地形，2.9ka后持续沉降速率大于1mm/yr。在过去50年里，五个港口的潮汐记录表明，三陆海岸正在不断下沉。沉降速率在2 ~ 11mm/yr之间，在靠近日本海沟的港口有增大的趋势。晚全新世至少有两次同震隆升事件，可能发生在7-5ka和3ka。这种地震情景假定其重现时间约为3000年，隆升超过10米。在100多公里长的海岸大隆起的极端同震事件中，板块辐合释放应力需要发生广泛的板块间断裂或板块边界的分支断裂。这种灾难性的断层可能与8级地震有关。

We investigated the dynamic combination model of seismotecotonic uplift and non-seismotectonic subsidence, in order to understand tectonic processes originated from the plate convergence between the Pacific Plate and the Eurasia Plate, using Quaternary and geomorphological techniques. The obtained results are as follows.1. A succession of nine marine terraces is recognized, which were formed at interglacial stages at least after MIS21 (ca.800ka). Average uplift rate is estimated to be 0.2 to 0.4m/ka.2. At least Holocene marine terrace is recognizable at the height in 3 to 5 meters along the 120km long, northern coast of the Sanriku Coast. The emergence age is probably between 7ka and 5ka.3. Boring core data of 13 short drilling and 2 long drilling show the tectonic history : successive subsidence in rate of 7-9mm/yr between 8ka and 7ka, a possible episodic uplift producing the emergence of shallow marine topography around 2.9ka, and continuous subsidence with the rate of more than 1mm/yr after 2.9ka.4. Tidal records in the past 50 years at the five ports indicate that the Sanriku Coast is continuously subsiding. The subsidence rate ranges in 2 to 11mm/yr and tend to increase at the port closer to the Japan Trench.5. At least two co-seismic uplift events are practically estimated in the late Holocene, which likely occurred at 7-5ka and 3ka. This seismic scenario prevides that the recurrence time is about 3000 years and the uplift exceeds 10 meters.6. The extreme coseismic event of large uplift along the more than 100km long coast requires the extensive interplate faulting or the branching faulting from the plate boundary for the stress release by plate convergence. Such catastrophic faulting is probably associated with the M8-class earthquakes.