Low-Frequency Atmospheric Gravity Waves from Vertical Tectonic Deformation During Two Recent Chilean Megathrust Events: the 2010 Maule (Mw8.8), and 2014 Iquique (Mw8.2) Earthquakes

Abstract

Background: Low-frequency atmospheric waves with gravity modes were recorded within 6.5 hours and 4.7 hours after two recent Chilean megathrust events, the 2010 Maule (Mw = 8.8), and 2014 Iquique (Mw = 8.2) earthquakes, respectively, at several microbarograph stations of the International Monitoring System (IMS) in South America and its surrounding regions. Method: Their apparent phase velocity up to the epicentral distances of 7,404 km and 6,481 km was found to be around 319 m/s and 337 m/s, respectively for the gravity modes after the two earthquakes. We tried to construct synthetic waveforms to be recorded at some of these microbarograph stations, incorporating various seismic source characteristics of the two earthquakes, and also a standard sound velocity structure up to a height of 220 km above the ground surface. The comparison appears to show some agreement between the observed and synthetic waveforms at least for the first 22 min for appropriate combinations of these source parameters. Results: The results indicate that the observed atmospheric gravity waves at the initial stage appear to have actually been excited at the source region of these megathrust earthquakes. Conclusion: The average rise time of vertical tectonic movement at the source region, which is estimated to be from the observed gravity waves, appears to be in the range between 2 and 3 min.