Aftershocks from the deadly 1959 Hebgen Lake earthquake in Yellowstone National Park have been detected more than 60 years later, according to a study.
More than 3,000 small earthquakes which took place between June 2017 and March 2018 were found thought to emanate from the 7.2 magnitude quake.
On August 17th at 11.37pm that year, Yellowstone National Park shook violently for around 30 seconds causing a huge landslide and killing 28 people.
The shock was strong enough to drop the ground a full 20 feet (six metres) in some parts and caused groundwater to swell up in wells as far away as Hawaii.
Scroll down for video
Aftershocks from the Hebgen Lake earthquake that took place 60 years ago in Yellowstone National Park are still being detected, according to a study. Pictured here, a map of the Maple Creek swarm, made using data from the University of Utah Seismograph Stations
Since then, 3,345 quakes near Maple Creek were detected via seismograph stations and determined that they were late aftershocks from the 1959 earthquake.
Seismicity in the Yellowstone volcanic region dominantly consists of bursts of earthquakes, often referred to as ‘swarms’.
According to geoscientists from the University of Utah, previous swarms in 1985, 2008–2009, and 2010 were triggered by magmatic fluid flow.
But the burst of earthquakes that occurred in 2017–2018 differed.
They determined the accurate location for these earthquakes by measuring the ratio and speed and found the source region was where the 1959 quake took place.
Aftershocks usually occur near the mainshock.
The researchers said the tremors fell along the same fault line and were orientated in the same way as the Hebgen Lake earthquake.
The small quakes took place in Yellowstone National Park, outside of the Yellowstone volcano caldera.
Guanning Pang and Keith Koper, who both led the study, say that the phenomena of tremors taking place decades after the event isn’t unusual.
Plot of magnitude versus time in colour-matched subsets of earthquakes. The warm colours mark earthquakes in the northern cluster and the cool colours mark the earthquakes in the southern cluster
Geoscientists from the University of Utah detected the 3,345 quakes near Maple Creek via seismograph station detectors and determines that they were late aftershocks from the 1959 earthquake
‘These kinds of earthquakes in Yellowstone are very common,’ said Mr Koper, director of the University of Utah Seismograph Stations.
‘These swarms happen very frequently. This one was a little bit longer and had more events than normal.’
‘There are formulas to predict how many aftershocks you should see,’ he said.
For Hebgen Lake, there looked like a deficit in the number of aftershocks. Now that we’ve had these, it has evened things out back up to the original expectations.’
Together, the more than 3,000 small quakes of the Maple Creek swarm can be divided into two clusters.
The northern cluster consists of Hebgen Lake aftershocks.
The quakes fell along the same fault line, and were oriented the same way, as the Hebgen Lake event, the study claimed.
Furthermore, the team didn’t see signs that the northern cluster was caused by movement of magma and other fluids beneath the ground.
The southern cluster of the Maple Creek swarm seems to have a different origin.
Although the northern cluster was lined up with the Hebgen Lake fault, the southern cluster’s line up was rotated about 30 degrees and the quakes were about 0.6 miles (1 km) shallower than the northern cluster.
From this, the researchers concluded that although the shaking in the northern cluster influenced the southern cluster, the primary cause of the southern shaking was likely subsurface movement of magma.
‘Because they were so close, there was some feedback and influence between the two sections,’ Mr Koper said.
The results highlight how earthquakes are different than other natural hazards like floods, hurricanes or wildfires which are ‘over when they’re over’.
‘Earthquakes don’t happen as a single discrete event in time,’ he said.
The specter of aftershocks can continue for months, years or even, as Maple Creek shows, decades.
The study was published in Geophysical Research Letters.
THE HEGDEN LAKE EARTHQUAKE
The 1959 Hebgen Lake Earthquake measured a magnitude 7.2 on the Richter scale.
It happened at at 11:37 pm in and almost instantly, the shaking triggered a massive landslide that buried 19 people beneath 73 million metric tons of debris
It killed 28 people west of the park and caused measurable changes to Old Faithful Geyser, a cone geyser located in Yellowstone National Park in Wyoming and other hydrothermal features.
Yellowstone National Park hosts more than 10,000 hydrothermal features, and because they are part of a large, complex system of heat, water, rock and gas, they change over time.
The 1959 Hebgen Lake Earthquake measured a magnitude 7.2 on the Richter scale. It happened at at 11:37 pm in and almost instantly, the shaking triggered a massive landslide. Pictured, the ground and trees after the landslide
Sixty years after the earthquake, the scars remain in the area.
The local rock caused a massive dip into the canyon carved by the Madison River.
Because this foliation was shallowly dipping, it intersected the steep wall of the valley, creating a plane of weakness.
When the mighty force of the earthquake shook this weak juncture, the mountain broke and crumbled, and there was nowhere for the loose rock to go but down.
Within an instant, the mountain filled the valley, damming the Madison River. Behind the natural dam, Earthquake Lake was created, complete with forests of drowned trees.
