UTC time | 1921-09-29 14:12:00 |
---|---|
USGS- ANSS | ComCat |
Local date | 29 September 1921 |
Local time | 07:12 a.m. MDT |
Magnitude | Mw6.3 |
Epicenter | 38°41′N 112°09′W / 38.68°N 112.15°W |
Areas affected | Utah |
Max. intensity | MMI VIII (Severe) |
Landslides | multiple |
Aftershocks | >35 |
Casualties | 2 injured |
The 1921 Sevier Valley earthquake was a series of three earthquakes. The primary quake was a magnitude Mw6.3 earthquake that occurred on Thursday, 29 September 1921 at approximately 7:12 AM MT in Elsinore, Utah, United States. The first aftershock occurred in the evening on the same day, and a second aftershock occurred two days later on 1 October. No people were killed in the quake or in the subsequent aftershocks.
The primary earthquake struck on Thursday 29 September 1921 at approximately 7:12 AM MT in Elsinore, Utah, United States, lasting for 7–10 seconds. [1] [2] [3] This quake was preceded by several weeks of smaller quakes. [3] A major aftershock occurred on the same day at approximately 7:30 PM MT, and a second major aftershock occurred on Saturday, 1 October at approximately 8:32 AM MT. [3]
The initial quake was a Mw6.3 and an intensity of VIII ("Severe"). [1] [3] [4] The official USGS report in their historical earthquakes list stated a magnitude of Mw5.2 and an intensity of VIII ("Severe"). [2] [5] [6] An official USGS report published in 1988 assigned the modified magnitude of Mw6.3. [3] It was felt in an area of between 2,500 square kilometers (970 sq mi) and 5,100 square kilometers (2,000 sq mi), which is considered a small area for a quake of this size. [2] [3] The farthest distance from the epicenter for the felt area was 25 miles (40 km). The quake lasted several seconds. [7]
The first major aftershock was a Mw5.7 and an intensity of VII ("Very Strong"). [3] The epicenter was at the same location as the initial quake, and the felt area was similar. [3] The second major aftershock was the same magnitude and intensity as the initial quake, was in the same location, and felt in a similarly sized area. [3] This quake was reported as "quick and short as the detonation of a cannon". [3] The quakes were felt as far north as Salina and as far south as Marysvale. [1]
Damage to chimneys and brick walls from the initial quake was "considerable". [3] Over US$100,000 in damage were caused (over US$1.44 million in 2020) by the primary quake. [8] [9]
The town of Elsinore, reported sunken foundations, damaged roofs from collapsing chimneys and brick walls, and brick, adobe, and stone buildings were significantly damaged. [4] More than half of the residences in the town were seriously damaged, a dozen were damaged enough to be condemned, and most residences received some cracking and plaster damage. [3] The newly built schoolhouse had walls collapse and a damaged roof, causing it to have to be rebuilt. [7] [8] Damage in Monroe included collapsed pipe trenches, cracked buildings, and the hot springs at the town turned "blood red" from iron oxide. [1] [3] Large boulders were dislodged and some landslides were reported in canyons near Monroe. [1]
The first major aftershock—in the evening on the same day—did further damage to structures, especially those already affected by the primary quake. [1] [3] Structures in Monroe received significantly more damage from this aftershock. [3] Damage was also reported in Richfield. [1]
On 1 October, the second major aftershock destroyed many of the damaged buildings, including a paint store in Elsinore. It also caused new damage to undamaged buildings, and caused previously-damaged buildings to be completely destroyed. [1] [3] More large boulders were dislodged and additional landslides were caused in various canyons near the affected towns. [1] Monroe was especially hard hit, with almost all chimneys being destroyed and many buildings being damaged beyond repair. [1] A man seated high on a bank of a river was thrown down to the edge of the river, the hot springs were discolored by iron oxide again, and the Monroe City Hall was "shattered". [3]
No people were killed in the quake, though at least two were injured by falling bricks or plaster. [3]