Focal Mechanism Solutions of the Tohoku-Oki Earthquake Sequence and Their Geodynamical Implications
详细信息
- 责任者：Yu Hongyu (School of Earth and Space Sciences ; Peking University ; Beijing 100871 ; China) ; Tao Kai
- 刊名：Chinese Journal of Geophysics
- 出版年：2013
- 卷期：56(8)
- 关键词：大震 ; great earthquakes ; 震源机制 ; focal mechanism ; 日本 ; Japan
- 页码：p.2655-2669
- 图表：7 illus., 38 refs.
- 分类号：0500
- issnNo：ISSN0001-5733
- isbnNo：CN11-2074/P
摘要
The stress state of Japan Sea region and its evolution are both concerned greatly by geoscientists.In this paper,we study Harvard CMT solutions of the March 11,2011 Tohoku-Oki Earthquake sequence from March 11th,2011 to March 15th,2012 by cluster analysis and find that they might be roughly sorted to four groups.The first group are low-angle thrust events,which are the same as the main shock and are mostly interplate events.The second group events are normal-fault earthquakes with principal extensional direction roughly pointing to E-W direction.Most of these earthquakes were located in the fore-arc uplift region of the Pacific plate,while some others occurred in the fore-arc accretionary wedge.The third group events are also normal-fault events mainly occurred in the fore-arc accretionary wedge though their principal extensional directions roughly parallel the Japan Trench.The forth group are reverse earthquakes with principal compressional directions roughly along N-S direction.We observe that Harvard CMT solutions of 2011 Tohoku-Oki earthquake sequence are obviously different from before.They show that Tohoku-Oki Earthquake sequence have released most of elastic energy in the main shock area.As a result,Pacific Plate and North America Plate have decoupled in the main rupture zone,which lowered the E-W compressional stress in Japan Sea and Northeastern China.However,Japan Sea Subduction Zone has not completely decoupled with North American Plate,even though the stress level in this region is lowered now.We claim that releasing of accumulated stress in the region of Japan Sea and Northeast China could lower the seismic hazard of roughly E-W direction compressive events,while tend to increase the activity of NNE-SSW strike-slip events as well as the volcanism,especially in Honshu.The characteristics of the Focal Mechanism Solutions of the Tohoku-Oki Earthquake Sequence remind us that stress state as well as evolution of Japan Sea might depend to some extent on coupling state between Pacific Plate and North American Plate.Long-lasting weak coupling might lead to re-opening of Japan Sea Basin because it will not only guarantee a relatively extensional environment,but also provide necessary water to deep depth.