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.
Highlights
Introduction72 The Open Atmospheric Science Journal, 2017, Volume 11 seismic observations [1 - 5] provided the general features of the fault rupture process, and various geodetic measurements including a radar technique clarified the spatial extent of the rupture zone [6 - 10]
The 2010 earthquake (Mw = 8.8) took place off the west coast of the Maule region in southwestern Chile (-35.909°N, -72.733°E, due to Universidad de Chile) on February 27, 2010, 06:34 UTC, as shown in Fig. (1a)
As described in the previous section, we calculated synthetic waveforms to be observed at each four International Monitoring System (IMS) stations, during two Chilean megathrust events, the 2010 Maule and 2014 Iquique earthquakes, respectively, incorporating their several probable source parameters, together with the standard atmospheric temperature structure up to a height of 220 km
Summary
72 The Open Atmospheric Science Journal, 2017, Volume 11 seismic observations [1 - 5] provided the general features of the fault rupture process, and various geodetic measurements including a radar technique clarified the spatial extent of the rupture zone [6 - 10]. These various measurements including GPS, InSAR, and near-field land-level changes clearly suggested that the rupture zone over the. 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
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