He tweeted a map of Houston, Texas, the worst affected area hit by flooding, which shows the phenomenon.
GPS data collected from stations around the city detected the area had been depressed under the weight of the extreme floods caused by Harvey.
Milliner replied to questions on Twitter to explain how it occurs.
The phenomenon, he said, is the result of sitting water caused by flooding rather than rain.
Although it is possible some of the subsidence around Houston is the result of soil compacting, some of the measurements were taken from stations situated on bedrock, which shows the Earth’s crust did give way.
In addition, it is possible the Earth’s crust around Houston will gradually spring back to its original position over time, but this is not certain.
The aftermath of Hurricane Harvey
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Hurricane Harvey made landfall in in the southern US at the end of August, killing more than 80 people and causing severe flooding, which displaced tens of thousands.
It is expected to be the costliest natural disaster in US history, surpassing the record set by Katrina in 2005.
Harvey is likely to wind up costing the economy around $190 billion (£140 billion), according to forecasting firm AccuWeather.
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