Obinna Ozioko PhD candidate
/
Obinna Ozioko PhD candidate
Temporal clustering of deep-seated landslides in the Puget Lowlands; a seismic trigger?
The Puget Lowlands of Washington State is about the most seismically active region in the Pacific Northwest. Paleoseismic records show ample evidence of prehistoric crustal and Cascadia megathrust earthquakes in the region with a temporal cluster of earthquakes in the crustal faults about 1000 years ago. Although multiple paleoseismic records exist for crustal and Cascadia megathrust earthquakes in the area, little is known about the temporal and spatial distribution of earthquake-triggered landslides. To address this, we conducted a comprehensive study applying surface roughness age dating techniques to over 600 landslides in the lower Puget Sound region to explore earthquake-triggered landslides' spatial and temporal patterns.
Preliminary results revealed compelling insights into the relationship between seismic activity and landslide occurrence. Approximately 20% of the dated landslides demonstrated ages corresponding to about 1000 years ago, aligning remarkably with the known ages of the crustal earthquakes in the Seattle, Tacoma, and Olympia faults, respectively. A second peak emerged from our analysis, indicating that about 15% of the total landslides fell within the age range of the last Cascadia subduction zone earthquake. This temporal coincidence suggests a strong link between seismic events and landslide occurrences during that period. This finding underscores the significance of seismic activity as a triggering or predisposing factor for landslides in the region. This study highlights that approximately 40% of the total landslides in the lower Puget Sound region may have been directly triggered by earthquakes or predisposed to previous seismic events. This substantial proportion indicates the inherent dangers of seismically induced landslides in the area and underscores the importance of understanding the complex interplay between seismic activity and slope stability.
