Yellowstone earthquake activity remains at elevated levels since June 12

Yellowstone earthquake activity remains at elevated levels, compared with typical background activity, since June 12, 2017, when an energetic earthquake swarm started in the region. In total, 2 532 earthquakes were registered since then. However, there are potentially thousands of additional earthquakes visible on webicoders that cannot be located because they are too small or overlap another event. Earthquake sequences like the ones currently occurring are common and account for roughly 50% of the total seismicity in the Yellowstone region, the Yellowstone Volcano Observatory reported in their monthly update released September 1, 2017.

During August 2017, the University of Utah Seismograph Stations, responsible for the operation and analysis of the Yellowstone Seismic Network, reports 1029 earthquakes were located in the Yellowstone National Park (YNP) region. The largest event was a minor earthquake of M3.3 at 03:00 UTC on August 21 (August 20 at 21:00 MDT), located about 16 km (10 miles) north of West Yellowstone, MT, where the earthquake was reported felt. This earthquake is part of a continued energetic sequence in the same area that began on June 12. 

August seismicity in Yellowstone was marked by the ongoing earthquake activity approximately 10 km (6.2 miles) north of West Yellowstone, MT, where an energetic swarm added an additional 894 locatable earthquakes to the 475 in July and 1028 earthquakes in June. The swarm includes the largest event of the month on August 21 (magnitude 3.3).

Swarm activity for August consists of five earthquakes in the magnitude 3 range and 69 earthquakes in the magnitude 2 range. Including the events from the prior two monthly reports beginning on June 12, total swarm seismicity includes one earthquake of magnitude 4.4, 12 in the magnitude 3 range, and 181 earthquakes in the magnitude 2 range.

There are potentially thousands of additional earthquakes visible on the webicorders that cannot be located because they are too small or overlap another event, and they are not included in these numbers.

Additionally, August 2017 seismicity contained two separate small earthquake swarms:

1. A small series of 34 earthquakes occurred August 14 – 18. The largest earthquake in the series (M2.7) occurred at 14:04 UTC on August 14 (08:04 MDT), located 14.5 km (9 miles) north northeast of Old Faithful, WY.

2. A small series of 22 earthquakes occurred August 19 and 20. The largest earthquake in the series (M1.9) occurred at 04:04 UTC on August 20 (22:04 MDT on August 19) located 16 km (10 miles) south of West Thumb, WY.

"Earthquake sequences like these are common and account for roughly 50% of the total seismicity in the Yellowstone region. Yellowstone earthquake activity is currently at elevated levels compared with typical background activity," YVO concluded.

Ground deformation

Monitored locations within the Yellowstone Caldera show little change this month.

Uplift north of the caldera, centered near the Norris Geyser Basin, continues at a low rate (a few millimeters per month), similar to what has been occurring since late 2015. Current deformation patterns at Yellowstone remain within historical norms.

Featured image: Porkchop Geyser, Yellowstone National Park. Credit: USGS/YVO