2:30 PM - 2:45 PM
[MTT43-04] A prompt report of multiple-site infrasound observation by the nation-wide infrasound observation consortium for M 7.3 Fukushima offshore earthquake on Feb. 13, 2021
Keywords:Infrasound, Earthquake, Lamb waves, Consortium, Multiple-site observation, Tsunami Magnitude
Nation-wide infrasound observation consortium was established in 2019 mainly for obtaining dense collaboration when any events are rarely or occasionally happened, and rapid understanding is required. Nowadays, we have almost 100 infrasound monitoring sites in Japan to detect natural geophysical events that would make disaster level affection into the human society or as a reference sensor for another type of sensing. Members of the consortium can provide some datasets on request, but there are many types of infrasound sensors whose detectable frequency range and sensitivity is different from each other.
At 23:07 JST on Feb. 13, 2021, Fukushima Offshore M 7.3 earthquake occurred, and severe vibration made more than 100 persons injured and destructed some traffic facility, buildings, etc. in and around Fukushima pref., however no apparent tsunami was observed afterward. At Ishinomaki port, slight sea level change of 20 cm was reported. There seems to be severe vibration without tsunami was because of 60 km depth of the earthquake epicenter. For this case, there is weak affection on the bottom of the ocean thus it does not make large amplitude vertical ground motion on the ocean bottom.
On the other hand, Tohoku Offshore M 9.0 earthquake occurred on Mar. 11, 2021 brought out severe tsunami disaster. At that time, an infrasound sensor located at Mizuzawa, Oshu-city, Iwate pref. recorded huge amplitude vibration signal due to severe vertical ground motion, but followed by large scale overpressure signal of 20 Pa amplitude with a period of 24 minutes. This long period signal is considered as the Lamb waves coming from the ocean surface change above the epicenter (Arai et al., 2011).
This time, the huge amplitude vibration signals due to severe vertical ground motion were also observed by multiple infrasound sensors, simultaneously, but there is no followed signal of long-period large-scale overpressure waves. We tried to estimate the infrasound tsunami magnitude for those cases and will discuss the recorded signals in comparison with the other cases as well as possibilities of dense infrasound observation for disaster mitigation.
At 23:07 JST on Feb. 13, 2021, Fukushima Offshore M 7.3 earthquake occurred, and severe vibration made more than 100 persons injured and destructed some traffic facility, buildings, etc. in and around Fukushima pref., however no apparent tsunami was observed afterward. At Ishinomaki port, slight sea level change of 20 cm was reported. There seems to be severe vibration without tsunami was because of 60 km depth of the earthquake epicenter. For this case, there is weak affection on the bottom of the ocean thus it does not make large amplitude vertical ground motion on the ocean bottom.
On the other hand, Tohoku Offshore M 9.0 earthquake occurred on Mar. 11, 2021 brought out severe tsunami disaster. At that time, an infrasound sensor located at Mizuzawa, Oshu-city, Iwate pref. recorded huge amplitude vibration signal due to severe vertical ground motion, but followed by large scale overpressure signal of 20 Pa amplitude with a period of 24 minutes. This long period signal is considered as the Lamb waves coming from the ocean surface change above the epicenter (Arai et al., 2011).
This time, the huge amplitude vibration signals due to severe vertical ground motion were also observed by multiple infrasound sensors, simultaneously, but there is no followed signal of long-period large-scale overpressure waves. We tried to estimate the infrasound tsunami magnitude for those cases and will discuss the recorded signals in comparison with the other cases as well as possibilities of dense infrasound observation for disaster mitigation.