Seismic emission activity of Earth's crust in Northern Kanto, Japan

By using the semblance analysis of seismic noise prehistory of local earthquakes recorded by a dense seismic array, we reconstruct the image of distributed sources of weak seismic radiation beneath the Earth's surface. Array observations were carried out in the Nikko area, northern Kanto, Japan in 1993 by Joint Seismic Observation Team. The array consists of 195 three-component seismometers distributed along perpendicular profiles whose array diameters are 7 km. From the analysis of data, several active volumes in the upper crust were identified and new features of seismic emission discovered. A joint analysis of the coda and seismic noise shows that a mid-crustal magma body that was identified before by reflection analysis is both a scattering region and a source of seismic emission. Another large active volume is visible to the east of the array at depths of 2-15 km; it coincides with a known low-velocity and high-attenuation anomaly. This emission region corresponds to an area of large earthquakes. (C) 2000 Elsevier Science B.V. All rights reserved.