An international team of scientists reporting in Doklady Earth Sciences discovered that with an impending earthquake, the parameters of internal gravity waves (IGWs) can change several days before the seismic event. IGW is the fluctuation of air masses, which, in contrast to sound waves, and in addition to longitudinal, also has a transverse component. The discovery is expected to help develop better short-term earthquake forecast methods.
The authors of the new study used satellite data taken from earthquakes that occurred in several seismically active regions: in Uzbekistan on May 26, 2013; in Kyrgyzstan on January 8, 2007; and in Kazakhstan on January 28, 2013 and discovered that five days before the seismic disaster, in all three cases, the parameters of internal gravity waves (IGW) changed.
The researchers observed how the temperature of the middle atmosphere (the layer of the Earth's atmosphere, which includes the stratosphere and mesosphere) behaves over time. Then, the IGW wavelengths were determined. The maximum wavelengths were 14.2 km and 18.9 km, respectively. Moreover, it is known that IGWs with vertical wavelengths of more than 10 km can arise during periods of deep convective heating.
'This means that processes occur in the Earth's lithosphere, the development of which gives rise to convective instabilities in the lower atmosphere. They are the cause of IGW in seismically active regions. Internal gravity waves, once they reach mesosphere, can be destroyed.
When this happens, the IGW energy transforms into thermal motion, which affects the temperature,' explains Sergey Popel, Professor at the HSE Faculty of Physics and head of the IKI laboratory, one of the authors of the study.
Scientists determined that the wavelength begins to grow 4 – 5 days before the event, reaching its maximum value 2 days before the earthquake, and then dropping sharply the day before.
"Variations of the Parameters of Internal Gravity Waves in the Atmosphere of Central Asia before earthquakes" – V.V. Adushkin et al. – Doklady Earthquake Sciences – https://doi.org/10.1134/S1028334X19070201
Based on the data of experimental studies of wave disturbances in the Earth’s atmosphere before and after the earthquakes in Uzbekistan (May 26, 2013) and Kyrgyzstan (January 8, 2007), earlier unknown changes in the parameters of internal gravity waves are revealed. These changes were manifested during the period of five days before the earthquake and in certain cases can be used for short-term prediction of the time when seismic events are to occur.
Featured image credit: ADBC
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