It has been nearly 60 years since the destructive 1959 earthquake that shook Yellowstone National Park, but is it possible for its aftershocks to still be experienced decades after? According to a new study, over 3,000 small earthquakes in 2017 and 2018 were actually late aftershocks of the 1959 event.

1959 Hebgen Lake Earthquake

On Aug. 17, 1959, the Yellowstone National Park experienced a massive earthquake for about 30 seconds. The 7.2 magnitude earthquake, thereafter known as the Hebgen Lake earthquake and caused the deaths of 28 people, brought down the ground by 20 feet in some places, and caused groundwater to swell up and down in places as far as Hawaii.

Yellowstone National Park is no stranger to earthquakes, but from 2017 to 2018 there were over 3,000 small earthquakes recorded in the Maple Creek area. According to the researchers of a new study, while such events are quite common for the area, these ones were actually longer and had more events than normal. What’s more, they found that the small quakes might actually be connected to the 1959 earthquake.

3,000 Earthquakes

Researchers of a new study funded by the United States Geological Survey found that the over 3,000 small earthquakes recorded between June 2017 and March 2018 were actually, at least partly, aftershocks of the 1959 event.

The small quakes can be divided into two clusters: the northern and the southern cluster. The quakes in the northern cluster evidently fall along the same fault line that the 1959 quake did and are in fact also oriented in the same way. Furthermore, there were no signs that the quakes in the northern cluster were caused by the movement of magma or other fluids underground. This suggests that the quakes in this cluster were actually late aftershocks of the 1959 event.

On the other hand, while the quakes in the southern cluster also follow the same fault line, they were actually rotated by about 30 degrees and were shallower than the northern cluster. What this means is that while the northern and southern clusters did influence each other because they were so close together, they cannot be considered as one swarm.

Late Aftershocks

According to the authors of the study, such late aftershocks are not unheard of. In fact, they have also recorded in 2017 aftershocks for a 1983 Idaho earthquake. Furthermore, based on predictions, it initially appeared as though the Hebgen quake had deficits in aftershocks, but the expected number of aftershocks were met after determining that the 2017-2018 small quakes were, in fact, the “missing” aftershocks.

The researchers note that their study shows just how different earthquakes are from other natural disasters. When events such as floods or hurricanes pass, they are basically over, but when earthquakes happen, the aftershocks can be experienced for months or even years after.