Infrasonic stations are sparse at many volcanoes, especially those on remote islands and those with less frequent eruptions. When only a single infrasound station is available, the seismic–infrasonic cross-correlation method has been used to extract infrasound from wind noise. However, it does not work with intense seismicity and sometimes mistakes ground-to-atmosphere signals as infrasound. This paper proposes a complementary method to identify the seismic component and the infrasonic component using a single microphone and a seismometer. We applied the method to estimate the surface activity on Ioto Island. We focused on volcanic tremors during the phreatic eruption on April 11, 2013, and during an unconfirmed event on September 12, 2018. We used the spectral amplitude ratios of the vertical ground motion to the pressure oscillation and compared those for the tremors with those for known signals generated by volcano-tectonic earthquakes and airplanes flying over the station. We were able to identify the infrasound component in the part of the seismic tremor with the 2013 eruption. On the other hand, the tremor with the unconfirmed 2018 event was accompanied by no apparent infrasound. We interpreted the results that the infrasound with the 2013 event was excited by the vent opening or the ejection of ballistic rocks, and the 2018 event was not an explosive eruption either on the ground or in the shallow water. If there was any gas (and ash) emission, it might have occurred gently undersea. As the method uses the relative values of on-site records instead of the absolute values, it is available even if the instrument sensitivity and the station site effects are poorly calibrated.

中文翻译：

---

单站记录中次声和地震分量的识别：应用于日本 Ioto 岛的 2013 年和 2018 年事件

许多火山的次声波站很少，尤其是那些偏远岛屿和火山喷发频率较低的火山。当只有一个次声站可用时，地震-次声互相关方法已被用于从风噪声中提取次声。然而，它不适用于强烈的地震活动，有时会将地对大气信号误认为次声。本文提出了一种使用单个麦克风和地震仪识别地震分量和次声分量的互补方法。我们应用该方法来估计 Ioto 岛上的表面活动。我们专注于 2013 年 4 月 11 日潜水喷发期间和 2018 年 9 月 12 日未经证实的事件期间的火山震颤。我们使用垂直地面运动与压力振荡的频谱振幅比，并将震颤的频谱振幅比与火山构造地震和飞机飞越车站产生的已知信号的频谱振幅比进行比较。我们能够识别出 2013 年火山喷发的地震震颤部分中的次声成分。另一方面，未经证实的 2018 年地震引起的震颤没有明显的次声波。我们将结果解释为 2013 年事件的次声波是由通风口打开或弹道岩石的喷射激发的，而 2018 年事件不是地面或浅水区的爆炸性喷发。如果有任何气体（和灰烬）排放，它可能发生在海底。由于该方法使用现场记录的相对值而不是绝对值，