RESUMO
Atmospheric waves excited by strong surface explosions, both natural and anthropogenic, often disturb upper atmosphere. In this letter, we report an N-shaped pulse with period ~ 1.3 min propagating southward at ~ 0.8 km/s, observed as changes in ionospheric total electron content using continuous GNSS stations in Israel and Palestine, ~ 10 min after the August 4, 2020 chemical explosion in Beirut, Lebanon. The peak-to-peak amplitude of the disturbance reached ~ 2% of the background electrons, comparable to recently recorded volcanic explosions in the Japanese Islands. We also succeeded in reproducing the observed disturbances assuming acoustic waves propagating upward and their interaction with geomagnetic fields.
RESUMO
Day-scale Earth's free oscillation after large earthquakes has been detected by underground instruments such as strainmeters, gravimeters and seismometers, to investigate Earth's internal structure, geodynamics, and source properties of earthquakes. Here we show that Global Positioning System (GPS) can also detect the signals of the Earth's free oscillation. A dense GPS array in Japan (GEONET) recorded the surface deformation following the 2011 Tohoku megathrust earthquake. A simple array analysis over 300 stations reduces local noise in GPS time series. We find that the dense GPS array truly detected both spheroidal and toroidal fundamental modes in three-direction displacement. This new tool has a strong potential to investigate the free oscillations particularly in low-frequency bands.
