Sequences of Microearthquakes Near the Yamasaki Fault

Abstract

Data obtained by a long-running observation made by the Tottori Microearthquake Observatory reaveal separately distributed fractured regions where microearthquakes occur in clusters. Near the central part of the Yamasaki fault a linear configuration of such fractured regions parallel to the fault trace over ten kilometers at a depth of about 11km exists, whereas the depth of fractured regions around the eastern end of the fault is about 13km. Shallow-seated as well as deep-seated fractured regions are also confirmed. In terms of the multiple time-series which consist of separate sequential events at the respective fractured regions, the space-time distribution of earthquake events near the Yamasaki fault can be described explicitly. Adjacent regions within about 30km have nearly common active periods and successive migration of activity occurs around the regions. The life time of activity for each fractured region ranges from less than several months, a year or so, to more than several years. Magnitude distributions for the respective fractured regions also show a regional difference between around the central part of the Yamasaki fault and around the eastern end of the fault.