Brief communication "Seismic and acoustic-gravity signals from the source of the 2004 Indian Ocean Tsunami"

Abstract

Abstract. The great Sumatra-Andaman earthquake of 26 December 2004 caused seismic waves propagating through the solid Earth, tsunami waves propagating through the ocean and infrasound or acoustic-gravity waves propagating through the atmosphere. Since the infrasound wave travels faster than its associated tsunami, it is for warning purposes very intriguing to study the possibility of infrasound generation directly at the earthquake source. Garces et al. (2005) and Le emphasized that infrasound was generated by mountainous islands near the epicenter and by tsunami propagation along the continental shelf to the Bay of Bengal. Mikumo et al. (2008) concluded from the analysis of travel times and amplitudes of first arriving acoustic-gravity waves with periods of about 400-700 s that these waves are caused by coseismic motion of the sea surface mainly to the west of the Nicobar islands in the open seas. We reanalyzed the acoustic-gravity waves and corrected the first arrival times of Mikumo et al. (2008) by up to 20 min. We found the source of the first arriving acoustic-gravity wave about 300 km to the north of the US Geological Survey earthquake epicenter. This confirms the result of Mikumo et al. (2008) that sea level changes at the earthquake source cause long period acoustic-gravity waves, which indicate that a tsunami was generated. Therefore, a denser local network of infrasound stations may be helpful for tsunami warnings, not only for very large earthquakes.

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

“…It is to be mentioned here that similar observations of low-frequency atmospheric waves have been recorded after three megathrust events, since the 1964 Alaskan earthquake (Mw = 9.2) [16,17], the 2004 Sumatra-Andaman earthquake (Mw = 9.2) [18,19], and the 2011 great Off-Tohoku earthquake (Mw = 9.0) [20,21]. In the present article, we try to find the evidence of observations for low-frequency gravity waves propagating from each of the source regions of the above two great earthquakes through the atmosphere to some of these microbarograph stations.…”

“…For these possible reasons, we did not make further attempts to fit exactly the calculated amplitudes to their corresponding observations. We would like to mention here that these are the fourth and fifth megathrust earthquakes, from which lowfrequency atmospheric waves including gravity modes have been emitted, since the first, unusual observation after the 1964 Alaskan earthquake (Mw = 9.2) [16,17], the Sumatra-Andaman earthquake (Mw=9.2) [18,19], and the 2011 OffTohoku earthquake (Mw=9.0) [21].…”

Locating the Tohoku-Oki 2011 tsunami source using acoustic–gravity waves

“…This difference may result in a very useful tsunami warning time. Mikumo et al (2008) and Raveloson et al (2011) identified acoustic-gravity waves with periods of about 500 s caused by the great 2004 Sumatra-Andaman earthquake and used them to estimate the dislocation of the sea level in the source region.…”