10:00 AM - 10:15 AM
[SSS13-05] Temporal occurrence pattern of repeated seismic waves observed at the seismic stations in the southeastern part of Kumakogen town, Ehime prefecture
Keywords:repeated seismic waves, limestone, mining
Obara (2021) detected repeated seismic waves with the duration of several seconds at Yanadani station of Hi-net (National Research Institute for Earth Science and Disaster Reliance, 2019) which is located at Kumakogen Town in Ehime prefecture. He suggested that these repeated seismic waves have some relation to mining of limestone because the detected seismic waves had similar characteristics to those from crust-stone blasting at the nearby limestone mine, Mt. Torigata. The fact that similar seismic waves were also detected at the seismic stations which are located near other limestone mines. On the other hand, Doi et al. (2015) is conducting seismic array observation at the landslide which is located between Mt. Torigata and Yanadani station. This seismic array provides us a chance to estimate hypocenters of the repeated seismic waves. In this study, using these seismic observation records, we estimated the hypocenters and temporal occurrence pattern of the repeated seismic waves.
First, utilizing travel times of the repeated seismic waves and crush-stone blasting, it was found that the hypocenters of the repeated seismic waves were estimated adjacent to Mt. Torigata. Also, the polarity of the repeated seismic waves showed opposite to that of crust-stone blasting at the station in the landslide.
Next, we estimated the appearing times of the repeated seismic waves by calculating cross-correlation function using the seismic waves at 18:16 on Jan 16, 2016 as a template. Continuous seismic waveform records from Nov 1, 2014 to Apr 30, 2016 were consulted. Setting a threshold as 0.7, there were both periods when more than 20 events were detected for an hour and those when no event was detected for an hour. Once a repeated seismic wave was detected, the detection tended to continue for eight hours. On the other hand, there are no events detected on most Sundays and around new year holidays. These facts suggested that the repeated seismic waves were derived from some activities related with limestone mining.
The website of the company which operates limestone mining at Mt. Torigata shows that the limestone crushed by blasting is thrown into the vertical shafts with the length several hundred meters and that it is got out from the shaft bottom for more crushing. We would like to discuss whether these activities can be sources for the repeated seismic waves by discussing their polarity observed at the landslide station.
Acknowledgment: We used the seismic waveform records obtained by Hi-net system.
First, utilizing travel times of the repeated seismic waves and crush-stone blasting, it was found that the hypocenters of the repeated seismic waves were estimated adjacent to Mt. Torigata. Also, the polarity of the repeated seismic waves showed opposite to that of crust-stone blasting at the station in the landslide.
Next, we estimated the appearing times of the repeated seismic waves by calculating cross-correlation function using the seismic waves at 18:16 on Jan 16, 2016 as a template. Continuous seismic waveform records from Nov 1, 2014 to Apr 30, 2016 were consulted. Setting a threshold as 0.7, there were both periods when more than 20 events were detected for an hour and those when no event was detected for an hour. Once a repeated seismic wave was detected, the detection tended to continue for eight hours. On the other hand, there are no events detected on most Sundays and around new year holidays. These facts suggested that the repeated seismic waves were derived from some activities related with limestone mining.
The website of the company which operates limestone mining at Mt. Torigata shows that the limestone crushed by blasting is thrown into the vertical shafts with the length several hundred meters and that it is got out from the shaft bottom for more crushing. We would like to discuss whether these activities can be sources for the repeated seismic waves by discussing their polarity observed at the landslide station.
Acknowledgment: We used the seismic waveform records obtained by Hi-net system.