Utah

Earthquake History

The following summary includes earthquakes centered in Utah with maximum intensity VII (Modified Mercalli Intensity scale) or greater.

Three distinct shocks rocked the Ogden area on July 18, 1894. Walls cracked (VI - VII) and dishes were shaken from tables. Many people were frightened during the violent motion. Another shock of similar intensity occurred on August 1, 1900, near Santaquin. An adobe house was split in two (VI - VII), and people were thrown from their beds. A chimney was damaged, dishes were broken, and some plaster fell at Goshen. There were additional reports that the deep shafts of a mine were shifted so that the cage could not be operated.

On November 13, 1901, a strong earthquake caused extensive damage from Parowan to Richfield. Brick buildings and many chimneys were damaged; some rockslides were reported near Beaver. Earth cracks with the ejection of water and sand were reported (VIII); in addition, some creeks increased their flow. The total felt area covered about 129,500 square kilometers. Intensity VI effects were observed over a 26,000 square kilometer area. Aftershocks continued for several weeks, the strongest of which was on November 14. Considerable damage resulted at Pine Valley, St. George, and Santa Clara from an earthquake on November 17, 1902. Chimneys were destroyed (VII) at Pine Valley and Santa Clara; additional damage occurred at Pinto and Toquerville. Reports were also received of a felt earthquake at Salt Lake City, 400 kilometers away; this may have been a distinct shock at about the same time.

A series of 30 to 60 earthquakes were reported in the vicinity of Garland and Tremonton between October and December 1909. Some of the shocks were strong enough to throw down chimneys (VII). Two tremors about 30 minutes apart were reported felt over a wide area of northwestern Utah on October 5, 1909. These reports probably are related to one event in the series. A May 22, 1910, earthquake damaged many chimneys (VII) at Salt Lake City and several old buildings. Two aftershocks of less intensity were felt.

The area around Ogden was strongly shaken on May 13, 1914. Windows were broken and chimneys thrown down (VII) at Ogden; near panic was reported at Central Junior High School. Dishes rattled and furniture moved at Farmington. The shock was felt from Collinston on the north to Riverton, south of Salt Lake City, an area covering about 20,700 square kilometers.

After several weeks of preliminary tremors, two strong earthquakes about 12 hours apart shook Elsinore, Monroe, and Richfield on September 29, 1921. The first shock, at 7:12 a.m., lasted 7 to 10 seconds and threw down scores of chimneys (VIII), tore plaster from ceilings, and fractured walls at Elsinore. In addition, gables of houses were thrown out and the foundation of a new school sank one foot, leaving gaps between the walls and the roof. Total damage was estimated at $100,000. Another shock of intensity VII occurred at 7:30 p.m. on the same day. On October 1, there was yet another strong tremor causing further damage at Elsinore. A number of brick and stone buildings were rendered uninhabitable by the 8:32 a.m. earthquake (VIII). The Monroe City Hall, built of rock, was severely damaged. Large rock falls were caused on both sides of the Sevier Valley. Warm springs were discolored for hours with iron oxides. Aftershocks continued until December 20, the most important being those on October 27, which were felt sharply at Richfield, and on November 1.

On March 12, 1934, at 8:06 a.m., an earthquake of intensity VIII originating near Kosmo, on the north shore of Great Salt Lake, affected an area of about 440,000 square kilometers, including much of northern Utah and parts of Idaho, Montana, Nevada, and Wyoming. This tremor, which measured magnitude 6.6, could have caused great damage in a densely populated area. Because of the sparse settlement in the region there was very little damage - mostly demolished chimneys and cracked walls in poorly constructed buildings. Two deaths, however, were attributed to the shock. The outstanding feature of the earthquake, related to the Hansel Valley fault, was the emission of large quantities of water from fissures and craterlets. Considerable faulting occurred in the epicentral region. Precise leveling revealed that areas sank to depths up to 390 millimeters. The onset of the shock was abrupt. There were no foreshocks, but aftershocks continued for 2 days; only one, at 11:20 a.m. on the same day, was outstanding (magnitude 6.0). There was moderate damage over a broad area, including Salt Lake City, where plaster fell. All chimneys fell in Kosmo and Monument; fissures, holes, cracks, and springs appeared in connection with a belt of fractures at least 8 kilometers long. The second shock was slightly less severe than the main tremor. Intensities for the aftershock are very unreliable because many observers tried to describe both earthquakes in a single report. Another strong aftershock (magnitude 5.5) affected an area of about 45,000 square kilometers in northern Utah and southern Idaho on May 6. It was reported to be strongest in Salt Lake City and Preston, Idaho, where the intensity reached VI.

Damages estimated at $1 million resulted from an August 30, 1962, shock in the East Valley fault zone. The magnitude 5.7 earthquake cause significant damage at Franklin, Lewiston, Logan, Preston, and Richmond. Cache County was designated a disaster region by the Small Business Administration. The greatest damage occurred at Richmond (VII) where at least nine houses were declared unsafe for occupancy, one church was damaged beyond repair, numerous houses lost walls, and 75 percent of the older brick chimneys fell. At Logan, principal building damage was cracked and twisted walls. Brick and timber fell through a church roof. At Lewiston, one brick wall fell and many chimneys were damaged. A sugar refinery near Lewiston sustained major damage when large pieces of cement coping fell, penetrating lower-level roofs. Four schools in Cache County were seriously damaged. The shock was felt over an area of approximately 168,000 square kilometers. Minor aftershocks, with slight additional damage, were reported through September 9.

On October 4, 1967, a magnitude 5.2 earthquake caused damage in the Marysvale area. Ceilings and walls cracked in numerous houses in Marysvale (VII). About 1 mile north of Marysvale, well water was badly muddied for 24 hours. At Koosharem, chimneys and plaster cracked. Chimneys were partially knocked down at Joseph. Rockslides were reported in the Joseph, Junction City, and Sevier area. The tremor was felt over 38,800 square kilometers of southern Utah and a few places in northern Arizona. Several aftershocks were felt.

Slight damage was reported at a number of northern Utah towns from a March 28, 1975, earthquake centered near the Idaho - Utah border. Ridgedale (VIII) and Malad City (VII), Idaho, sustained the most damage from this magnitude 6.1 shock. All of northern Utah felt the tremor; the 160,000 square kilometer felt area also include parts of Idaho, Nevada, Wyoming, and a few places in northwestern Colorado.

Abridged from Earthquake Information Bulletin, Volume 9, Number 4, July - August 1977, by Carl A. von Hake.