Seismicity of the 2014 Oso, WA Landslide

The banks of the Stillaguamish River near Oso, Washington have been known to landslide. In the last 50 years, 6 events were documented. On March 22nd, 2014 a catastrophic landslide occurred ~ 6.5 km from Oso causing 43 fatalities. The landslide traveled approximately 1.1 km covering a nearby highway, destroying several homes, and damming the Stillaguamish River. To investigate the slope failures a team of scientists analyzed short and long period signals from the landslide.

They found that the landslide was comprised of a series of multiple failures with two major collapses that occurred ~ 3min apart. The first event showed characteristic features of seismic signals generated by landslides, notably an emergent onset and lack of clear p and s waves. The second event was more impulsive with several discernible amplitude peaks.

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Shown above are the seismic signals from the 2 events filtered between 1-3 Hz and 3-10 Hz for (a&c) and (b&d), respectively. Figure from: Hilbert et al., 2014 (The entire report can also be found at that link.

The long period signals were used to invert for the forces acting at the source. Combined with remote sensing data they were able to estimate the volume of material displaced by the landslide. The first event displaced between 6.0e6 and 7.5e6 cubic meters of material. In total a volume of 7e6 and 10e6 cubic meters was mobilized during the landslide.

2 thoughts on “Seismicity of the 2014 Oso, WA Landslide

  1. Kerry Lynn Ryan Post author

    Thanks for sharing the documentary! Agreed, landslides can be very terrifying. This one is particular was incredibly devastating. The landslide was much more mobile than expected. Based upon the volume of material that slid, models predicted that the landslide would make it to the edge of the river. In reality, the landslide swept across the river covering ~ 1km by 1km area. Unconsolidated glacial lake sediments underlie the landslide slope and are very prone to collapse. The area also received increased rainfall preceding the event. The increase in precipitation combined with the sediment instability may explain why the landslide was more mobile than anticipated.

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