Futurity] Large earthquakes can cause underwater landslides thousands of miles away, weeks or months after the quake occurs, new research suggests.
Researchers analyzing data from ocean bottom seismometers off the
Washington-Oregon coast tied a series of underwater landslides on the
Cascadia Subduction Zone, 80 to 161 kilometers (50 to 100 miles) off the
Pacific Northwest coast, to a 2012 magnitude-8.6 earthquake in the
Indian Ocean—more than 13,500 kilometers (8,390 miles) away. These
underwater landslides occurred intermittently for nearly four months
after the April earthquake.
Previous research has shown earthquakes can trigger additional
earthquakes on other faults across the globe, but the new study shows
earthquakes can also initiate submarine landslides far away from the
“The basic assumption…is that these marine landslides are generated
by the local earthquakes,” says Paul Johnson, an oceanographer at the
University of Washington and lead author of the new study. “But what our
paper said is, ‘No, you can generate them from earthquakes anywhere on
The new findings could complicate sediment records used to estimate
earthquake risk. If underwater landslides could be triggered by
earthquakes far away, not just ones close by, scientists may have to
consider whether a local or a distant earthquake generated the deposits
before using them to date local events and estimate earthquake risk,
according to the study’s authors.
The submarine landslides observed in the study are smaller and more
localized than widespread landslides generated by a great earthquake
directly on the Cascadia margin itself, but these underwater landslides
generated by distant earthquakes may still be capable of generating
local tsunamis and damaging underwater communications cables, according
to the study authors.
The discovery that the Cascadia landslides were caused by a distant earthquake was an accident, Johnson says.
Scientists had placed ocean bottom seismometers off the
Washington-Oregon coast to detect tiny earthquakes, and also to measure
ocean temperature and pressure at the same locations. When Johnson found
out about the seismometers at a scientific meeting, he decided to
analyze the data the instruments had collected to see if he could detect
evidence of thermal processes affecting seafloor temperatures, such as
methane hydrate formation.
Johnson and his team combined the seafloor temperature data with
pressure and seismometer data and video stills of sediment-covered
instruments from 2011-2015. Small variations in temperature occurred for
several months, followed by large spikes in temperature over a period
of two to 10 days. Read More