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Geologic Effects of the 18 March 2020, Mw 5.7 Magna, Utah, Earthquake

Session: Intermountain West Earthquakes in the Spring of 2020 I

Type: Oral

Date: 4/20/2021

Presentation Time: 02:45 PM Pacific

Description: 

The March 18, 2020, M_w 5.7 Magna, Utah, earthquake was widely felt along the Wasatch Front urban corridor. Ground accelerations near the epicentral region under springtime hydrologic conditions indicated the potential to produce liquefaction features. Post-earthquake rapid reconnaissance around the Salt Lake Valley on the ground and from a sUAS (small unmanned aircraft system) documented liquefaction near the earthquake epicenter, along the Jordan River, and along the southeastern shoreline of Great Salt Lake. Additionally, the foothills of the Wasatch Range and Oquirrh Mountains were checked for fresh rockfall and urban landslide reactivation; one possible earthquake-induced rockfall was identified. Areas with documented liquefaction features typically have seasonal or year-long near-surface groundwater or standing water due to their proximity to Great Salt Lake and its tributaries. Liquefaction features included syneresis cracking and pooling near the epicenter, lateral spreading along the Jordan River, collapse features, and sand boils. Subaerial and subaqueous sand boils occurred in areas with roadway infrastructure and artificial fill on and near the shores of Great Salt Lake. Several of these features are known to be caused by fluctuating groundwater levels and their appearance after the Magna earthquake suggests they are related to earthquake ground motions. Observed damage to roadway infrastructure concentrated near the Great Salt Lake Marina State Park included tension cracks with vertical separation in asphalt concrete roadways and parking areas, as well as a fractured natural gas line on a maintenance building. Despite its moderate magnitude, the Magna earthquake caused over $70 million in public infrastructure damage and serves as a reminder of the critical importance of earthquake and geologic hazard research and preparedness in the Intermountain West.

Presenting Author: Emily J. Kleber

Student Presenter: No

Authors