An uptick in earthquake activity is being observed along the Oregon-Nevada border between Lakeview and Steens Mountain. For the 30 day period ending 12:00 PDT March 12, 29 earthquakes were located in this area. The vast majority have been too small to be felt by humans but a M3.5 earthquake was observed on March 9 with a M3.0 occurring on February 27. Earthquake activity focused on one area that is more frequent than background activity is often referred to as an earthquake swarm.
The Oregon-Nevada border region is incredibly remote for the Contiguous United States. While the M3.5 earthquake was large enough to be felt, only one person submitted a Did You Feel It report to the United States Geological Survey (USGS) – and that person was in the San Francisco Bay Area over 300 miles (500 km) away. The earthquake was not capable of being felt at that distance. Only about 300 people live with 30 miles (50 km) of the epicenter of the largest earthquake so far in this sequence.
The earthquakes have been rather shallow, generally less than 3 miles (5 km) deep though a few events have been a little deeper. Many of the earthquakes are listed in the USGS catalog as having a depth of 0.0 km. Dr. Kyren Bogolub, a seismologist at the Nevada Seismological Laboratory, reports that the depths of 0.0 km are “certainly not correct” but rather an artifact of sparce seismograph coverage in that region. Additionally, she says because of the lack of coverage “any single event depth should be taken with a grain of salt.”
Bogolub says “Basin and Range faulting [is] a safe bet” for being the cause of this earthquake swarm. The Basin and Range geologic province stretches from the Sierra Nevada of California and Nevada to the Wasatch Mountains in Utah, covering Nevada, the southeastern quarter of Oregon, and extending toward West Texas and parts of Northern Mexico. Here, the crust is stretching along the west-east axis creating fault blocks that tilt and form the repeated mountain-valley-mountain geography common in Nevada and other parts of the American West.
Earthquake swarms are common in geologically active regions. Pacific Northwest residents may be familiar with swarms at the Cascade volcanoes, such as recent ones around Mount St. Helens and Mount Hood. Volcanic activity, including some that might have been derived from the Yellowstone hotspot, has occurred in the past in Northwest Nevada and Southeast Oregon but the Smithsonian Global Volcanism Program does not list any known holocene eruptions near the swarm.
Non-volcanic earthquake swarms are common in the Great Basin. One was observed around Reno in 2008 and another that produced an M7.2 near Fallon in 1954. A few Pacific Northwest locations also experience small non-volcanic earthquake swarms, such as one around the Hanford Site in 2009-2010.
Earthquake swarms can be long-lasting. The 2009-2010 Hanford swarm produced over 2,000 small earthquakes over the course of a year. It’s impossible to predict when and where exactly earthquakes will strike, but seismologists are able to determine areas that have higher earthquake risk in general. This swarm appears to represent typical (albeit elevated) behavior for this part of Oregon and Nevada.
The featured image maps 30 days of earthquake activity ending 12:00 PDT March 12, 2024 between Lakeview and Steens Mountain via USGS. Thanks to Dr. Kyren Bogolub at the Nevada Seismological Laboratory in Reno for her valuable input.
