Scientists from the California Institute of Technology (Caltech), U.S. and the Chinese Academy of Sciences in Wuhan, have developed a new method to derive the temperature of oceans via earthquake waves.
The ramifications of climate change have impacted Earth as the average temperature of the planet has increased and its glaciers are gradually melting. What is still relatively unrevealed is that around 95% of the total heat trapped in the planet due to the greenhouse effect is confined in the Earth's oceans. Therefore, it is of great importance to monitor and derive the temperature changes in the ocean waters.
The research provides a new tool through which those temperatures can be derived by manipulating the seismic waves produced below the oceanic crust. The findings of the study were recently published in Science Magazine.
When an earthquake occurs below an ocean, most of the generated energy is transmitted through the solid subsurface of the earth. Nevertheless, a small proportion propagates from the epicenter of the temblor into the water as sound waves. These sound waves travel and can be detected by monitoring stations in the same way as ground waves. However, they arrive later due to their reduced velocity and are interpreted as secondary events. Their amplitude is preserved and can be detected readily. "Interestingly, they are even 'louder' than the vibrations traveling deep in the solid Earth, which are more widely used by seismologists," Wenbo Wu, lead author of the study and a postdoctoral scholar in geophysics at Caltech, stated.
The correlation between these sound waves and the trapped heat in the ocean waters lies in the fact that their velocity is increased as the temperature of the water rises. Therefore, the sooner those waves are recorded by a seismograph station, the bigger the temperature of the water. Scientists explain that the difference is minor but measurable.
The new method is reliable and can be easily implemented with little cost since it utilizes existing equipment and facilities.
In order to have reference points, the team needed to collect data from regions that experienced consecutive earthquakes over a period of time to deduce any seismic wave velocities differences and thus detect heat trap patterns. As a case study, they used a seismometer installed in Sumatra since 2004 and recorded the temperature of the Indian Ocean every time an earthquake occurred.
The findings suggest that the Indian Ocean is indeed warming, a fact that has already been proved with conventional methods. What the new tool revealed is that the ocean is warming at a much greater rate (69% higher) than it was previously believed.
However, according to Jörn Callies, co-author of the study and an Assistant Professor of environmental science and engineering at Caltech, it is too early to deduce secure results since more data should be collected and interpreted.
The future purposes of the team is to take measures from seismic stations all over the world so they can identify the temperature changes patterns in all oceans.
A comprehensive video on the features of the new method was recently published and can be found below.
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