5:15 PM - 7:15 PM
[MTT36-P05] Characteristics of seismic waves excited by snow avalanches – in case of Makunosawa in Niigata Prefecture –
Keywords:snow avalanche, seismometer
It has been reported that snow avalanches were detected by seismic network (Takeuchi et al., 2022; Kamiishi et al., 2022). It is essential to understand the characteristics of seismic waves excited by snow avalanches in order to utilize seismic network for auto-detection of snow avalanches. This study consulted the continuous seismic waveforms at Makunosawa in Niigata Prefecture recorded by Tohkamachi Experimental Station, Forestry and Forest Products Research Institute, detecting possible snow avalanche events according to the method of our past studies. Then, the characteristics of the detected waves such as durations and frequency components were compared with the meteorological conditions on the day when the events were detected.
The continuous seismic waveforms recorded at Makunosawa in Niigata Prefecture operated by Tohkamachi Experimental Station, Forestry and Forest Products Research Institute from 2016 to 2024 were used. The seismometer and the data logger were L-22D velocimeter with the natural frequency 2 Hz manufactured by MARK PRODUCTS Co. Ltd and LS8800 by Hakusan Kogyo Co. Ltd., respectively. The detection of possible snow avalanche events was conducted according to the method of our previous study (Doi et al., 2023): the geometric means of the spectral amplitudes of 5-12 Hz and 25-35 Hz are calculated from the velocity waveform in a 5-second window every second, and 1) the ratio of the geometric mean of the spectral amplitudes of the 5-12 Hz to those in the previous 30 seconds is larger than 2, and 2) the ratio of those of the 5-12 Hz to 25-35 Hz at that time is larger than 2. Adding the data in 2024 to those used in the previous research, 89 possible snow avalanche events were detected.
Next, the characteristics such as durations, temporal change in dominant frequency, and amplitudes were consulted for the detected events. Duration was determined as the maximum time length when a signal has larger amplitudes than the noise level in the running spectrum. As a result, while there were two events that had durations of longer than 40 seconds and four events around 30 seconds, the majority had around 15-20 seconds. Half of the events with longer durations took place on the days when the average daily temperature is below 0°C and the cumulative snowfall depth in the previous 3 days is 70 cm or more.
The continuous seismic waveforms recorded at Makunosawa in Niigata Prefecture operated by Tohkamachi Experimental Station, Forestry and Forest Products Research Institute from 2016 to 2024 were used. The seismometer and the data logger were L-22D velocimeter with the natural frequency 2 Hz manufactured by MARK PRODUCTS Co. Ltd and LS8800 by Hakusan Kogyo Co. Ltd., respectively. The detection of possible snow avalanche events was conducted according to the method of our previous study (Doi et al., 2023): the geometric means of the spectral amplitudes of 5-12 Hz and 25-35 Hz are calculated from the velocity waveform in a 5-second window every second, and 1) the ratio of the geometric mean of the spectral amplitudes of the 5-12 Hz to those in the previous 30 seconds is larger than 2, and 2) the ratio of those of the 5-12 Hz to 25-35 Hz at that time is larger than 2. Adding the data in 2024 to those used in the previous research, 89 possible snow avalanche events were detected.
Next, the characteristics such as durations, temporal change in dominant frequency, and amplitudes were consulted for the detected events. Duration was determined as the maximum time length when a signal has larger amplitudes than the noise level in the running spectrum. As a result, while there were two events that had durations of longer than 40 seconds and four events around 30 seconds, the majority had around 15-20 seconds. Half of the events with longer durations took place on the days when the average daily temperature is below 0°C and the cumulative snowfall depth in the previous 3 days is 70 cm or more.