Tiago C.A. Oliveira toliveira(at)ua.pt
Physics Department & Centre of Environmental and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal,
Peter Nielsen pmlg.nielsen(at)gmail.com
Esberg N, Denmark
Ying-Tsong Lin, ytlin(at)whoi.edu
Applied Ocean Physics and Engineering Department, Woods Hole Oceanographic Institution, Woods Hole,
Massachusetts 02543, USA.
Noriyuki Kushida, noriyuki.kushida(at)ctbto.org
Comprehensive Nuclear-Test -Ban Treaty Organization, Vienna
International Center, 1400 Vienna, Austria
and
Sérgio M. Jesus sjesus(at)ualg.pt
LarSys, Universidade do Algarve, Campus de Gambelas, PT-8005-139 Faro, Portugal.
Comments: download file (pdf)
Ref.: Frontiers in Marine Science, 9:10090113, October 2022.
Abstract:
On 18 June 2020 and 4 March 2021, very energetic low-frequency underwater
T-wave signals (2 to 25 Hz) were recorded at the Comprehensive Nuclear-Test-Ban
Treaty (CTBT) International Monitoring System (IMS) hydrophone
stations in the Pacific Ocean (Stations HA11 and HA03) and the South Atlantic
Ocean (Station HA10). This work investigates the long-range (megameters)
propagation of these T-waves. Their sources were three powerful submarine
earthquakes in the Kermadec Trench and Islands, located at approximately
6000, 8800, and 15100 km from Stations HA11, HA03, and HA10, respectively.
Arrival time and back azimuth of the recorded T-waves were estimated using
the Progressive Multi-Channel Correlation algorithm installed on the CTBT
Organization (CTBTO) virtual Data Exploitation Centre (vDEC). Different arrivals
within the duration of the earthquake signals were identified, and their
correlations were also analyzed. The data analysis at HA03 and HA10
revealed intriguing T-wave propagation paths reflecting, refracting, or even
transmitting through continents, as well as T-wave excitation along a chain of
seamounts. The analysis also showed much higher transmission loss (TL) in the
propagation paths to HA11 than to HA03 and HA10. Moreover, strong
discrepancies between expected and measured back azimuths were
observed for HA11, and a three-dimensional (3D) parabolic equation model
was utilized to identify the cause of these differences. Numerical results
revealed the importance of 3D effects induced by the Kermadec Ridge, Fiji
archipelago, and Marshall Islands on T-wave propagation to HA11. This analysis
can guide future improvements in underwater event localization using the
CTBT-IMS hydroacoustic sensor network.