P wave attenuation structure beneath the Kanto district and surrounding area, Japan

Abstract

Spectral ratios of teleseismic P waves for 15 deep (>200 km) earthquakes recorded at 146 High-Sensitivity Seismographic Network stations in the Kanto district and its surrounding area, eastern Japan, were inverted for attenuation parameter \( t_P^{ * } \). The dataset consisted of good-quality vertical-component seismograms, whose P phases were handpicked. The P wave spectral ratios with high signal-to-noise ratios were calculated up to 1 Hz for all the station pairs, linear regressed, and then inverted for \( t_P^{ * } \) using the technique of least squares . The result showed that the active volcanic areas were clearly characterized by high \( t_P^{ * } \). In contrast, \( t_P^{ * } \) varied in the nonvolcanic areas. The present result on the \( t_P^{ * } \) distribution was roughly consistent with the shallow part (<30 km) of an attenuation structure, which has been previously obtained based on 3-D tomography by using records of high-frequency (around 5 Hz) P waves from local earthquakes. This suggested that the present method of \( t_P^{ * } \) estimation is valid. The advantage and possible application to other areas were also discussed.