84 Scientific American, December 2020GRAPHIC SCIENCE
Text by Mark Fischetti | Graphic by Shirley WuChristmas Day 2019New Year’s Day 2020Global High-Frequency Seismic NoiseLouderQuieterSunday Sunday Sunday Sunday Sunday SundaySeismic Noise Before and After Lockdowns
LouderQuieter
Global median loudness Uncertainty rangeDays before lockdown: 30 20 10 Lockdown Days after lockdown: 20 30 40Heilongjiang, ChinaChitwan, Nepal
Each line
is one
seismometer
stationMedian for all
172 locationsPostlockdown median amplitudePostlockdown median amplitudeChange in Amplitude by Location, Grouped by Population DensityHeilongjiang,
ChinaUrban
(more than 5,000)Suburban
(500 to 5,000)Rural
(fewer than 500)Urban
(more than 5,000)Suburban
(500 to 5,000)Rural
(fewer than 500)Prelockdown median amplitude for each sensor locationPrelockdown median amplitude for each sensor locationSeismic Noise by Population Density (people per square kilometer)Heilongjiang,
ChinaChitwan, Nepal Chitwan, NepalCOVID-19 Quiets the Earth
Seismic noise dropped worldwide as humans locked down
Earthquakes send strong tremors through the earth’s crust, recorded by seismometers planetwide. Human
bustle also creates an ongoing, high-frequency vibration—a background buzz—in the rock. After cities,
states and countries implemented lockdowns to try to slow the spread of COVID-19 this past spring, the
volume of human ground noise fell by up to 50 percent on average in various regions, as people stayed
home instead of taking cars, buses and trains to work and school and as businesses and industries cur-
tailed operations. The decline, evident for months, was recorded by seismometers as deep as 400 meters
underground. “We were surprised,” says seismologist Stephen Hicks of Imperial College London, “that
noise from daily human activity penetrated that far down.”Prepandemic Pattern
Ground vibrations created by human activity
sound like a steady buzz all week long, but
the volume drops during weekends and major
global holidays.
Lockdowns Kill the Buzz
The loudness of ground noise before lockdowns
were implemented was steady (left half of graph )
but quieted down after lockdowns began ( right ).
Lockdowns started at various times near different
seismometer stations; here the recordings are
shifted so the lockdown dates align at the center.Human Noise
Vertical graph lines
show the percent change in
power, or “loudness,” of ground
vibrations at a high frequency of
four to 14 hertz. This ambient clamor
was recorded at 172 locations
worldwide, from cities to prairies,
by seismometers at 0 to 400
meters belowground.Urban Calm
Ground vibrations generated by people in rural
regions (far left) quieted down after lockdowns
began, although the volume declined more in
sub urbia and even more in cities. The change
at individual seismometer stations varied
considerably, however; some sensors, for
example, are near universities or highways,
where noisy human activity plummeted.NOTE: Recordings at another 96 stations that
are remote or in places where lockdowns did
not occur showed little change.A steep drop may be from a seismometer
located inside a village school that closed,
for example; an odd rise might have occurred
if someone moved a sensor. SOURCE: “GLOBAL QUIETING OF HIGH-FREQUENCY SEISMIC NOISE DUE TO COVID-19 PANDEMIC
LOCKDOWN MEASURES,” BY THOMAS LECOCQ ET AL., INSCIENCE,VOL. 369; SEPTEMBER 11, 2020