EARTHQUAKES

A record of earthquake activity in Iowa.

EARTHQUAKES. Gigantic tremors of the Earth's crust capable of inflicting tremendous property damage. While not considered in prime earthquake territory, Dubuque had a minimum of two earthquakes beneath the city in 1938.

The first earthquake to affect this region came just ten years after the start of permanent settlement. Tremors were felt in eastern Iowa on January 4, 1843. The next occurred in 1858. On April 24, 1867, distinct vibrations detected in Dubuque caused people in many buildings to rush into the STREETS. Plaster fell from walls. Residents of one downtown building later said they believed the walls were sinking due to a defective foundation.

People living on the second and third stories of buildings were especially affected by tremors on October 20, 1870. Lasting several seconds, the earthquakes caused considerable fear, but did little property damage.

Dubuque residents were again shaken on November 15, 1877. Students in the Fifth Ward School clung to their desks in fear. Dishes rattled. The belief, however, was that this quake was not as strong as the one experienced seven years before.

The entire state felt an earthquake on September 26, 1891. Two shocks struck Dubuque. Fortunately little damage was observed.

One of the strongest earthquakes to strike Dubuque in the early twentieth century came in 1909. Factories were jarred to the extent that workmen fled outside for safety. Employees in the BANK AND INSURANCE BUILDING claimed the feeling was like a heavy object had been dropped down the elevator shaft to shake the building at its foundation. They too fled to the streets.

Tremors were again felt in Dubuque on January 2, 1912. Residents reported three distinct occurrences with again little property damage reported.

In 1961 LORAS COLLEGE constructed Iowa's first seismograph station on campus. In 1964 shock waves from the Good Friday Alaskan earthquake, which struck Alaska at 9:36 p.m., reached the Loras station at 9:43 p.m. The force of the shock waves caused considerable movement in the earth's crust in the Dubuque area for up to fifteen seconds and broke one of the seismographs.

Several geographic features of eastern Iowa suggest Dubuque could suffer significant damage from a major earthquake in the Midwest. A layer of stone called the Mississippi Arch would carry tremors along the MISSISSIPPI RIVER Valley. Layers of limestone containing caves, mines, and sinkholes could collapse. Mountain ranges and hot areas, which act to contain earthquakes and weaken them, are absent in this area.