Science of Tsunami Hazards (Nov 2020)
EVALUATION OF THE IMPACT OF MAJOR EARTHQUAKES ON EXCITING LONG PERIOD FREE-EARTH LITHOSPHERIC OSCILLATIONS, ATMOSPHERIC-IONOSPHERIC PERTRUBATIONS, AND FAR-FIELD TSUNAMI-LIKE WATER LEVEL FLUCTUATIONS
Abstract
The whole Earth resonates like a bell with normal modes of resonance at distinct frequencies. When extremely large earthquakes strike, the Earth’s free oscillations are excited. These excited, long period, enhanced earth oscillations have frequencies which have a tendency to resonate over long periods of time after a major earthquake. The Great Sumatra-Andaman Islands Earthquake of 26 December 2004 - the largest event in the last half century – was the first event in the Moment Magnitude (Mw 9) category to be recorded with modern digital instruments. The earthquake generated distinct stronger free oscillations of the Earth’s lithosphere. Also, further coupling of these oscillations reportedly resulted in distinct atmospheric as well as ionospheric perturbations of certain modalities and frequencies. The present paper examines whether the excited stronger "spheroidal normal modes" of free earth oscilations could have contributed as well to tsunami generation enhancement, and to the lasting and persistent tidal oscillations that were recorded in the Andaman Sea and elsewhere. The present review further examines the efficiency of coupling of excited stronger solid free earth oscillations with the ocean, and analyzes whether these could have contributed significantly to the destructiveness of the tsunami that was observed in the Indian Ocean, or to unusual far-field water level fluctuations recorded by tide gauges in the Pacific and Atlantic Oceans – which cannot be supported by calculated tsunami travel times. Additionally to the 2004 event, other major earthquakes, volcanic and meteorological events are similarly examined as to their possible excitation of free Earth oscillations or coupling with the sea surface and the atmosphere, to generate far-field, tsunami-like sea level fluctuations or meteotsunamis.
