Recent Progress in Seafloor Earthquake Observations and Instruments in Japan

This paper reviews on recent progress in seafloor earthquake observations and instruments in Japan. Ocean bottom seismometers (OBS) have improved into a 24-bits digital OBS. Great strides were made in the 2000’s. The research of the earth’s interior from the ocean has been progressed rapidly by utilizing the data from the ocean borehole observatory and the broadband OBS array. Large scale array observations with the use of the long term OBS have imaged earthquake activities in a space-time domain in and around large asperities along Kuril Trench, Japan Trench, and Nankai Trough. A seafloor earthquake monitoring also has been evolving into a new generation for a two-dimensional dense network.