Hee-Il Lee

An analysis of the infrasound signal from the Miyagi-Oki earthquake in Japan on 16 August 2005

Following the 16 August 2005 Miyagi-Oki earthquake in Japan, coherent atmospheric infrasonic waves were observed at regional distances (1200–1500 km) using three seismo-acoustic arrays on the Korean Peninsula. A source-location procedure was applied to the distinct long-duration infrasonic signals to construct earthquakegenerated infrasound source regions on the Japanese island arc. The results showed that the long-duration infrasonic signal was attributable to extensive seismic ground motions on land areas from the southwestern through to the northeastern part of the island arc as well as regions close to the earthquake epicenter. In many coherent infrasonic signals, an effect of seismic ground motions in sedimentary basins could be identified as a source of infrasound radiation from the large earthquake. These observations and interpretations were confirmed using predictions of possible infrasound arrival azimuth variation by converting real seismological data from the dense Japanese seismic network.

Seismic and infrasonic analysis of the 9 March 2014 fireball in South Korea

On the evening of 9 March 2014, a bright fireball was observed in many places in South Korea, the energy associated with the event was also recorded at local seismic and regional infrasound stations. Using impulsive seismic signals recorded at 19 stations, we calculated the possible extent of the sonic source of the fireball by assuming point- and line-source models, which might be physically linked to either a point-source explosion in the atmosphere or shock waves radiating from the fireball’s trail, respectively. By comparing the observed seismic arrival times with those predicted by both models, a line-source model resulted in better solution than a point-source model. It means that shock waves along the meteor’s high-speed passage through the atmosphere probably acted as the dominant source of the seismic signals. The parameters of the fireball’s sonic trajectory, after incorporating a realistic sound velocity model of the atmosphere, are estimated to be an azimuth arrival angle of 313.5° clockwise from the north and an elevation arrival angle of 44.5° above the Earth’s surface, with a time of 11:04:51 UTC at which the trajectory meets the Earth’s surface. The estimated ground impact point is about 2 km offset from locations where meteorites associated with the fireball were found. The line-source model also explained the large azimuthal deviation of infrasound waves observed at arrays in the vicinity of the trajectory. From the infrasound measurements, the kinetic local-source energy generating the sound was estimated to be approximately 0.8 tons TNT, based on semi-empirical relations for the point- and line-source models.

Acoustic surveillance of hazardous volcanic eruptions (ASHE) in Asia

The ASHE Ecuador (2004-2012) collaboration between Ecuador, Canada, and the United States demonstrated the capability to use real-time infrasound to provide low-latency volcanic eruption notifications to the Volcano Ash Advisory Center (VAAC) in Washington DC. The Atmospheric dynamics Research Infrastructure in Europe (ARISE, 2012-2018) supported by the European Commission fosters integrating innovative methods for remote detection and characterization of distant eruptive sources through collaborations with the VAAC Toulouse and the Comprehensive Nuclear-Test-Ban-Treaty Organization (CTBTO). The ASHE Asia project proposes an international collaboration between the Earth Observatory of Singapore, the VAAC Darwin, National Data Centers in Japan, Korea, and Palau, and will receive the support of ARISE, to provide improved early notification of potentially hazardous eruptions in Asia and the Western Pacific using a combination of established technologies and next-generation mobile sensing systems. The increas...

Seven years of infrasound monitoring of volcanic eruptions of Sakurajima

Korea Institute of Geoscience and Mineral Resources (KIGAM) is operating an dense infrasound array network which is comprised of eight seismo-acoustic array stations (BRDAR, YPDAR, KMPAR, CHNAR, YAGAR, KSGAR, ULDAR, and TJIAR) and we are continuously monitoring all the natural and artificial infrasonic events occurred in and around Korean peninsula with this network. Sakurajima volcano is one of the most active volcanoes in the world to the point where the Volcanic Ash Advisory Center in Tokyo issued 6,012 warnings over the past 7 years from 2009 to 2015. We have checked and analyzed all the infrasound signals possibly associated with the eruptions chronology of Sakurajima volcano based on the Tokyo VAA (Volcanic Ash Advisories) information, in order to know how daily, seasonal and yearly atmospheric changes affect the detection capability of each infrasound station. The result of preliminary analysis will be presented and how the geographical location of the infrasound network which is fan-shaped to the ...