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Thursday, April 9, 2020

April 09, 2020

 The fall in human din should allow seismologists to hear earthquakes more clearly. Photograph: Getty Images/iStockphoto

There’s a kind of hush all over the world as the reduction in human activity stops the Earth buzzing so much

The dramatic quietening of towns and cities in lockdown Britain has changed the way the Earth moves beneath our feet, scientists say.
Seismologists at the British Geological Survey have found that their sensors are twitching less now that human activity has been curtailed, leading to a drop in the anthropogenic din that vibrates through the planet.
The fall in the human hum that rings around the world means that, in theory at least, the scientists should be able to detect smaller earthquakes in the UK, and more distant tremors in Europe and in countries further afield than their equipment usually allows.
A wine store in Ridgecrest, California, after the largest earthquake for 20 years jolted an area from Sacramento to Las Vegas to Mexico. Photograph: Marcio José Sánchez/AP

“Seismometers measure ground vibrations and the vibrations we want to record are from earthquakes. But because they are so sensitive they pick up other sources too, including human activity, so road traffic, people walking past and nearby factories,” said Brian Baptie, a seismologist at BGS in Edinburgh. “All these things generate vibrations and those propagate through the Earth.”

Human-induced vibrations, known in the trade as “cultural noise”, spread through the planet differently to tremors from earthquakes and tend to die away a few miles from their origins. But seismometers placed near urban centres still pick up plenty of noise that makes it harder for scientists to analyse the more valuable seismic data.
The UK’s network of sensitive instruments picked up markedly fewer vibrations last week as the coronavirus lockdown took hold, the researchers found. “We had a look at the data from some of our seismic stations around the UK and we do see an effect,” said Baptie. At some sensors, cultural noise is running at five decibels lower than normal, about a quarter down on usual readings. Similar falls have been spotted by Belgian seismologists based in Brussels.
The BGS operates a national network of about 80 seismometers from Shetland to Jersey that provide a constant ear to the ground. The data are pored over by BGS scientists and fed into a global network that is used to monitor earthquakes anywhere on the planet. In contrast to low-frequency tremors, cultural noise vibrations are high-frequency waves, around one to 100Hz, that tend to travel through the surface layers of the Earth.
“In theory, this reduction in noise means we should be able to detect more earthquakes in the UK, in Europe and all around the world,” said Baptie. If so, it would shed light on the frequency of different magnitude earthquakes and, in the case of more distant tremors, how the seismic waves are affected by the Earth’s structure and the characteristics of the shifting faults that unleash them.
Researchers at the BGS now hope to check all their seismometers for the fall in human noise with the aim of producing a map that will reveal which areas of Britain have seen the most stark declines in the human hum. The hunt for smaller earthquakes may take longer than the lockdown holds, however. “We aren’t in a particularly active region,” said Baptie. “So we may not get anything in the short term.”