The readings show two wave signals, the first is the landslide at 17:37 UTC and a second is a slide that occurred at 17:41 UTC. There are no earthquakes or other local seismic events on the records around the time of the landslide. The seismic signals are of long period surface waves, with no clear high-frequency P or S phases that we would expect to see if a local earthquake occurred at the time of the event. The landslides generated elevated levels of local ground shaking for over an hour.
Seismic readings are from the University of Washington Pacific Northwest Seismic Network, operated in cooperation with the USGS.