3:30 PM - 3:45 PM
[HDS10-07] Infrasound magnitude: Ultra-rapid tsunami size estimation from one-point atmospheric pressure observations
Keywords:tsunami early warning, infrasound, atmospheric Lamb waves, tsunami magnitude
Atmospheric Lamb waves excited by tsunamis
Large tsunamis are known to excite atmospheric Lamb waves (long-period atmospheric waves propagating at the speed of sound along the earth's surface) (e.g. Arai et al 2011; Mikumo et al 2008). Based on numerical calculations and analytical discussions of compressible atmospheric disturbances excited by tsunamis, Nakajima (e.g., JpGU 2017), showed that the amplitude of this Lamb wave is directly proportional to the wave height of the tsunami and that this amplitude is insensitive to the rise time of the fault motion. Imada and Nakajima (JpGU 2024) and others have argued that this property is useful to solve the inverse problem of the initial wave height of a tsunami from land-based atmospheric pressure observations.
Relationship between Lamb wave energy and tsunami energy
Using the relationship between the amplitude of the Lamb wave and the tsunami wave height, the relationship between the energy of the Lamb wave excited by the tsunami and the energy of the tsunami is directly related. Since the propagation speed of a ram wave (about 300 m/s) is usually faster than that of a tsunami (200 m/s even in the open ocean), if the amplitude of the ram wave can be determined from barometric observations, energy of tsunami can be estimated before its arrives.
Ultra-Rapid Tsunami Early Warning by Single Point Observation
Assuming the location and shape of the tsunami wave source area, and making some further simplifications, it is possible to estimate the magnitude of a tsunami from a single point of atmospheric pressure observation. We can thus define a formula of “infrasound tsunami magnitude". We will apply this method to several distant and near-surface earthquakes, including the 2011 off the east coast of East Japan and the 2004 off Sumatra, to verify its usefulness, and discuss its potential for ultra-rapid tsunami early warning, especially in areas such as the coast along the Sea of Japan where seafloor pressure gauges are not deployed.
Large tsunamis are known to excite atmospheric Lamb waves (long-period atmospheric waves propagating at the speed of sound along the earth's surface) (e.g. Arai et al 2011; Mikumo et al 2008). Based on numerical calculations and analytical discussions of compressible atmospheric disturbances excited by tsunamis, Nakajima (e.g., JpGU 2017), showed that the amplitude of this Lamb wave is directly proportional to the wave height of the tsunami and that this amplitude is insensitive to the rise time of the fault motion. Imada and Nakajima (JpGU 2024) and others have argued that this property is useful to solve the inverse problem of the initial wave height of a tsunami from land-based atmospheric pressure observations.
Relationship between Lamb wave energy and tsunami energy
Using the relationship between the amplitude of the Lamb wave and the tsunami wave height, the relationship between the energy of the Lamb wave excited by the tsunami and the energy of the tsunami is directly related. Since the propagation speed of a ram wave (about 300 m/s) is usually faster than that of a tsunami (200 m/s even in the open ocean), if the amplitude of the ram wave can be determined from barometric observations, energy of tsunami can be estimated before its arrives.
Ultra-Rapid Tsunami Early Warning by Single Point Observation
Assuming the location and shape of the tsunami wave source area, and making some further simplifications, it is possible to estimate the magnitude of a tsunami from a single point of atmospheric pressure observation. We can thus define a formula of “infrasound tsunami magnitude". We will apply this method to several distant and near-surface earthquakes, including the 2011 off the east coast of East Japan and the 2004 off Sumatra, to verify its usefulness, and discuss its potential for ultra-rapid tsunami early warning, especially in areas such as the coast along the Sea of Japan where seafloor pressure gauges are not deployed.