It’s no problem atoll
To show that this works, the researchers used a seismometer station on Diego Garcia, a small atoll in the Indian Ocean about 3,000 kilometers from Sumatra. The tectonic plate boundary there is incredibly active, so there’s no shortage of earthquakes to work with. Between 2004 and 2016, there were over 4,000 earthquakes of magnitude 3.0 or higher that occurred near the Nias Island area of Sumatra. The researchers carefully processed all of these events to find repeaters similar enough to do the temperature calculation. They found over 2,000 such pairs based on 900 earthquakes.
If this portion of the Indian Ocean were to warm 1° C, T-waves from those earthquakes would take 5.4 seconds longer to reach this seismometer. The observed changes are smaller than that but they are coherent—there’s both an annual cycle and a gradual warming trend that look similar to other, more traditional datasets.
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