A Quake on the Great Plains

Earthquakes are rare phenomena for the Great Plains, more common in places along the edges of tectonic plates, like on California’s San Andreas Fault, instead of their far interior. But earthquakes can still happen, as experienced by Sioux Falls in 1938.

During the Great Depression of the 1930s, the city of Sioux Falls had to learn to live through economic hardship as South Dakota experienced an outmigration of people. As agriculture and industries worked towards economic stabilization, another disaster struck. On October 11, 1938, at 3:37 a.m., an unexpected earthquake struck Sioux Falls.

The earthquake registered a magnitude of 4.1 on the Richter scale and affected about 3,000 square miles of Sioux Falls and the surrounding region. Albeit mild by global standards, the earthquake rattled the windows of residents and the Sioux Falls police received about fifty calls by concerned citizens as mentioned in a government report. Although no structural damage occurred due to this earthquake, the event did challenge the notion held by many South Dakotans that the Great Plains was a region of geological stability. According to an Argus Leader newspaper article from October 19, 2003, this was the only earthquake ever recorded in the county. The newspaper also mentioned a historical marker being dedicated to the earthquake near its epicenter which was reported to be near the Northern Links Golf Course. The earthquake’s cause was a phenomenon known as “isostatic rebound." As described by geologist Leah H. Joseph from the University of Michigan, isostatic rebound was seismic activity that occurs “when a load is imposed on or removed from the lithosphere.” In plain terms, isostatic rebound refers to the slow and gradual lifting of the Earth’s crust due to glaciers that were compressed during the Ice Age retreating and causing the Earth’s crust to rebound.

The 1938 earthquake was documented through local newspapers and through scientific institutions. Journalists in the aforementioned Argus Leader reported on the reaction of local residents and sought to describe the earthquake intricately. The accounts of local newspapers seized the details about the civic impact of the event such as confusion, bewilderment, and even curiosity. Concurrently, the U.S. Geological Survey recorded the seismographic data. In addition, physical records about the quake have also been preserved by the State of South Dakota and some are present in Siouxland Heritage Museums.

Despite its modest scale, the 1938 Sioux Falls earthquake stands out because the occurrence of such tremors is considered to be atypical in the Great Plains. Far from the reach of the tectonic plates that generate the bulk of the world’s seismic activity, South Dakota is a place that is regarded as a safe, geologically silent place where everything is expected to stay still. Therefore, the 1938 Sioux Falls earthquake serves as a reminder that sometimes even the most stout and secure landscapes can move and leave an impact on its inhabitants and history.

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