Microseismicity and Scarp Geometry of the Rattlesnake Ridge Landslide

Session: Recent Development in Ultra-Dense Seismic Arrays With Nodes and Distributed Acoustic Sensing (DAS) [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Atop an anticline in the Yakima Fold Belt of south-central Washington, a 3 million cubic meter translational landslide has been slowly moving toward Interstate 82 and nearby homes since October 2017. The initial acceleration of the slide mass raised concern over the stability of the ridge, resulting in road closures, mandatory evacuation of a nearby residential area and placement of physical barriers to block rockfall onto Interstate 82. Landslides pose obvious hazards to human life and property, yet seismic monitoring of landslides to characterize deformation of the landslide body is underutilized. We deployed 40 Fairfield three-component nodal seismometers around the landslide body for a four-month period in 2018 to record microseismicity generated by the landslide. The rockslide, comprised of Columbia River Basalt, accelerated for about six months from its onset, reaching a peak slip rate of ~74 cm/week, then gradually slowed down to half that rate by the end of 2018. Brittle failure of the landslide body generated repeating and non-repeating seismicity recorded by the array. The resulting dataset contains over 1 million small-magnitude earthquakes with dominant frequencies of 30-40 Hz, which we utilize to determine high-resolution earthquake locations. Over a year-and-a-half of continuous sliding has exposed the ~370-meter-long eastern bounding scarp, which appears to be the primary slip surface where these earthquakes occur. We also utilize terrestrial lidar to scan the ~20-meter-tall exposed portion of the scarp and compare its surface characteristics to earthquake locations. The exposure of the eastern bounding scarp presents a unique opportunity to study the influence of scarp geometry on the distribution and character of microseismicity.

Presenting Author: Tyler J. Newton

Authors