A study of the aftershock sequence of the Tohoku, March 2011 (M=9.0) mainshock

Περίληψη

Japan has a long and interesting geologic history, since it is situated on the boundaries of major tectonic plates, continuously forming an arc system since the Permian due to subduction of the Pacific Ocean floor. The active margin of the floor is the cause of earthquakes that form a subducting zone, as it has been discovered by the great seismologist K. Wadati, extending to depths of 500 km. The purpose of this project is the understanding of the tectonic evolution of the Japanese arc system through studying the evolution of aftershock sequences. During the last decades, efforts have been made towards predicting where or when a large aftershock will occur since a seismic excitation has started. Most interesting results came from studying seismic sequences and more specifically from their time distribution, spatial distribution, time – space distribution and magnitude distribution. In this research a procedure is applied for estimating the strongest earthquake of a seismic sequence, taking published knowledge into consideration and new experience on time, space, time-space and magnitude distribution of non-strong
earthquakes of a seismic sequence. Data used concern a time interval of 10 years, from 2000 to 2010 in the Tohoku region that consists of the northeastern portion of Honshu, the largest island of Japan. In this region faults and volcanoes are considerably active in the last 10.000 years. Most earthquakes occur at depths less than 15 km (Zhao et al., 2000) and less frequently they occur beneath the land. This research was conducted in an attempt to understand how seismic sequences evolve, through main shock, foreshock and aftershock sequences and hoping in a better short-term and long-term prognosis of earthquakes.