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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Long-term variation of the shallow tremor sources at Aso Volcano from 1999 to 2003
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Long-term variation of the shallow tremor sources at Aso Volcano from 1999 to 2003

机译：1999年至2003年阿苏火山浅震源的长期变化

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In order to investigate the continuous volcanic tremor of Aso Volcano in Japan, we performed a series of temporary short-period seismic array observations near the Nakadake first crater (the active crater) during five years from 1999 to 2003. We deployed in all of the temporary observations a seismic array at the same location about 700 m west of the active crater, in order to investigate long-term changes in the tremor activity. In 1999 and 2003, another array was simultaneously deployed at a different location 700 m north of the crater to help locate the tremor sources. We developed a frequency domain semblance method and applied it to the waveform data of the frequency range where the continuous tremor is dominant (3-6 Hz). We measured arrival azimuths and slownesses of the continuous tremor signals as functions of frequency, which are then used to locate the epicenters of the tremor signals corresponding to the principal peaks of the power spectra.rnFor the observations in 1999 and 2002, the continuous tremor amplitudes are relatively small, and the slowness of the tremor signal observed at the west array takes a local minimum (0.5 to 0.6 s/km) near the frequency (～4.7 Hz for 1999 and ～4.8 Hz for 2002) which corresponds to the highest spectral peak. This implies that body waves dominate the tremor signals at the west array around the frequency. The tremor epicenters corresponding to 4.7 Hz for the observation in 1999 are located at the west rim of the currently active crater. While the surface crater activity of Aso remains low and the tremor activity is not clearly linked with the surface activity until early 2003, a close link between the tremor and crater activity appears in the middle of 2003, when a small phreatic eruption occurred a month before the array observation (July 10, 2003). Tremor signals of the observation in 2003 show a large spectral peak (4.2 Hz) where the slowness measured for the west array is very large (1.1 s/km), clearly suggesting that surface waves are dominant. The epicenter is again located at the western rim of the active crater. We interpret these observations as follows: in 1999 and 2002 when the surface activities of Aso were low, the continuous tremor excitation was deep and inactive. In the middle of 2003 when Aso Volcano became active with a series of phreatic eruptions a shallower tremor source was activated, possibly masking the deeper sources. This shallowing of the dominant tremor source could be due to the increase in the volcanic gas flow rate triggered by the phreatic eruptions.
机译：为了调查日本麻生火山的连续火山地震，我们在1999年至2003年的5年中在中岳第一个火山口（活动火山口）附近进行了一系列临时的短期地震阵列观测。临时观测活动环形山以西约700 m处同一位置的地震阵列，以调查地震活动的长期变化。在1999年和2003年，另一个阵列同时部署在火山口以北700 m的不同位置，以帮助定位震源。我们开发了一种频域相似度方法，并将其应用于连续震颤占主导地位（3-6 Hz）的频率范围的波形数据。我们测量了连续震颤信号的到达方位角和慢度作为频率的函数，然后将其用于定位与功率谱主峰相对应的震颤信号的震中.rn对于1999年和2002年的观测，连续震颤幅度相对较小，在西阵列观测到的震颤信号的慢度在对应于最高频谱的频率（1999年为〜4.7 Hz，2002年为〜4.8 Hz）附近取局部最小值（0.5至0.6 s / km）峰。这意味着体波在该频率附近的西阵列的​​震颤信号中占主导地位。 1999年观测到的与4.7 Hz相对应的震震中心位于当前活动火山口的西缘。尽管麻生太郎的表面火山口活动仍然很低，直到2003年初，震颤活动才与表面活动没有明显联系，但在2003年中期，震颤和火山口活动之间存在着密切的联系，当时一个小的潜水喷发发生在一个月前阵列观察（2003年7月10日）。 2003年观测到的震颤信号显示出一个大的光谱峰值（4.2 Hz），其中西阵列测得的慢度非常大（1.1 s / km），清楚地表明表面波是主要的。震中再次位于活动火山口的西边缘。我们将这些观察结果解释如下：在1999年和2002年，当Aso的表面活性较低时，连续的震颤激发很深且不活跃。 2003年年中，阿苏火山因一系列潜水爆发而活跃，一个较浅的震源被激活，可能掩盖了较深的震源。主导震源的变浅可能是由于潜水爆发引起的火山气体流量增加。

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