| Budget Amount *help |
¥4,290,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥990,000)
Fiscal Year 2012: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2011: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
Fiscal Year 2010: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
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| Research Abstract |
The purpose of this research is estimation of eruption style variation establishing a new method relating to oscillation data and an internal state of a shallow part of a conduit. During the early period of volcanic activity at the Shinmoe-dake volcano in 2011, various kinds of activities, such as sub-Plinian eruptions, a magma effusion, and Vulcanian eruptions, occurred sequentially. We succeeded in obtaining multi-items data, such as broadband seismograms, tilt motions, and infrasonic signals, nearby the summit crater during these three different eruption styles. In the Vulcanian stage, almost all Vulcanian eruptions were preceded by trapezoidal inflations followed by various time sequences of tilt motions, which became increasingly more complicated throughout the frequent Vulcanian eruptions. In spite of the complicated time sequences of the preceding inflations, we have found clear linearity between the preceding duration versus elapsed time. These observations can be consistently explained based on the assumption that a Vulcanian eruption is induced by a catastrophic rupture of the strongest closed, solid magma frame in a conduit due to magma degassing overpressure, and the degassing from the magma declines exponentially with time. Switching between seismic-only harmonic tremor and seism-acoustic harmonic tremor has been reported during Shinmoe-dake eruptionactivity. Switching was simulated in a laboratory experiment. At lower fluid stiffness, a stable, open conduit was produced, and the harmonic signals generated within the experimental apparatus were efficiently transmitted into the atmosphere. We established a simple method to distinguish infrasonic signals from wind noise, demonstrating that it effectively detects not only main eruptions, but also minor activity generating weakinfrasound hardly visible in the wave traces.
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