| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2000: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1999: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1998: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
I have investigated the characteristics and source mechanism of low frequency earthquakes in the inland area. The events are grouped into two categories ; the deep low-frequency earthquakes near Moho, and shallower low frequency earthquakes in the shallow crust. The earthquakes in the former group were recorded in the Shimokita Peninsula, and the events in the latter group were recorded near the Iwate volcano, both by the midband seismometers and continuous recording system.
In the Shimokita area, I confirmed the depth extent of the events by relocation. By examining the seismograms recorded by the midband sensors, I found the lack of significant signal lower than 1 Hz. The particle motion analysis suggests the repeated radiation of body waves from the source. The focal mechanisms are estimated as the tension crack for the initial phase and the single force for the phases of low-frequency, and large amplitude. This process is probable controlled by the movement of magma between the resovoirs.
In the Iwate volcano area, the low frequency earthquakes are accompanied by later phases with very large amplitude. From the semblance analysis and the particle motion analysis, the phase is interpreted as basin induced surface waves. However, the low frequency radiation from the source is essential to the basin induction. Since the earthquakes took place in the period when some magma bodies have moved upward beneath the volcano, I interpret the movement of crustal fluids derived from magma may play an important part to cause the low-frequency earthquakes.
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