The series of earthquakes in Yellowstone National Park in the United States has become one of the longest in history. The earthquakes began on June 12 and continue to this day. Over the past three and a half months, about 2500 aftershocks have been recorded in the western part of the park. This value is close to the record when more than 3000 earthquakes occurred in three months.
The United States Geological Survey (USGS) monthly report on seismic activity in the park says 115 earthquakes were recorded in September. Of these, 78 were part of an ongoing swarm 10 kilometers north of West Yellowstone. The most powerful event in the swarm happened last month, with a magnitude of 2.3.
"Since the beginning of the swarm on June 12, there has been one earthquake of magnitude 4.4, 12 in the range of magnitude 3 and 185 in the range of magnitude 2," the service said in a statement.
Earthquake swarms account for about 50% of the seismic activity recorded in Yellowstone. A swarm is a series of earthquakes that occur over several weeks or months without a clear sequence - unlike traditional earthquakes, where there is a major event followed by a series of aftershocks.
One of the leading scientists at the Yellowstone Volcanic Observatory at the USGS, Mike Poland, notes that it is too early to talk about the end of the swarm, although seismic activity has dropped sharply since August.
According to him, the actual number of earthquakes that have taken place is difficult to establish, because earthquakes can occur simultaneously or be too weak to be recorded by the instruments. But there are ways to retrospectively search for these events, and, possibly, after checking it will turn out that there were many times more of them than were originally reported.
“This is the kind of work we will be doing in the coming months as we collect all the data we have and start analyzing it,” Poland says. - At the end of September, the University of Utah stations recorded 2,475 earthquakes in the swarm. In terms of its activity, the current swarm is close to the swarm of 1985, during which more than 3000 localized seismic events occurred within three months”.