Nobuo Arai

Infrasound signals detected by the observation system in Isumi, Japan

An infrasound observation system is installed in Isumi, Japan (35.3N, 140.3E) as the component of the International Monitoring System for CTBT. The observation system was deployed on November 2004. It comprises a six‐element array. Five elements of the array are deployed as a pentagon with sides approximately 1.2 km long. The sixth element is located within the pentagon‐shaped array. Until now, some interesting infrasound signals were observed. One of them was the infrasound wave produced by the large earthquake that occurred off the Pacific coast of North‐East Japan on 16 August 2005. The infrasound wave‐train, which had a spindle‐shaped envelope, was detected following the arrival of the seismic wave. The arrival direction of the infrasound wave, which had maximum amplitude, indicated the direction of the land area, which had maximum intensity. The time difference between the on‐set time of that infrasound wave and the origin‐time of the earthquake coincided with the travel time for propagation in the a...

Low-Frequency Atmospheric Gravity Waves from Vertical Tectonic Deformation During Two Recent Chilean Megathrust Events: the 2010 Maule (Mw8.8), and 2014 Iquique (Mw8.2) Earthquakes

RESEARCH ARTICLE Low-Frequency Atmospheric Gravity Waves from Vertical Tectonic Deformation During Two Recent Chilean Megathrust Events: the 2010 Maule (Mw8.8), and 2014 Iquique (Mw8.2) Earthquakes Takeshi Mikumo, Takuo Shibutani, Makiko Iwakuni and Nobuo Arai Kyoto University, Uji, Kyoto 611-0001, Japan, Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto 611-0001, Japan Japan Weather Association, Tokyo 170-6045, Japan Disaster Mitigation Research Center, Nagoya University, Nagoya 464-8601, Japan

Detection of snow avalanche locations using infrasound array data

Infrasound observation measures the energy radiated by a snow avalanche into the atmosphere and can be used to detect snow avalanches over large areas. Our research team has conducted infrasound observation in Tokamachi, Niigata Prefecture, Japan, during the last three winter seasons. First, between January and April 2013, we deployed an infrasound sensor in front of a selected slope, obtained visual observations using a web camera, and identified infrasound signals generated by snow avalanches. During the second season (2013-2014 winter), we deployed two infrasound sensors approximately 1 km apart and obtained the attenuation characteristics of infrasound signals. In the 2014-2015 winter season, we deployed three sensors spaced at 1-2 km in a triangular array and attempted automatic extraction of signals associated with snow avalanches from observed raw data using time-domain processing. For the extracted signals, the locations of snow avalanches were estimated with the cross-correlation method. Twelve e...