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Tree ring correlation between prehistoric landslides and abrupt tectonic events in Seattle, washington
Summary
A prehistoric earthquake around 1000 years ago likely caused landslides in Lake Washington and a tsunami in Puget Sound. This seismic event also led to abrupt land subsidence in the Seattle region.
Area of Science:
- Geology
- Paleoseismology
- Quaternary Science
Background:
- Submerged trees on landslide deposits in Lake Washington provide geological evidence.
- Dating these deposits helps reconstruct past seismic events in the Seattle region.
Purpose of the Study:
- To determine the timing of the most recent landslides in Lake Washington.
- To investigate the potential link between these landslides and other seismic events in the Puget Sound area.
Main Methods:
- Radiocarbon dating of submerged trees from landslide deposits.
- Tree ring crossdating to precisely date tree mortality.
- Analysis of geological evidence for tsunami deposits and subsidence.
Main Results:
- Radiocarbon ages suggest simultaneous landslides in three Lake Washington areas approximately 1000 years ago.
- Tree ring analysis revealed that trees from a landslide deposit and a tsunami deposit died in the same season and year.
- Evidence points to a coincidence of lake landslides, a probable tsunami, and abrupt subsidence.
Conclusions:
- A strong prehistoric earthquake likely occurred in the Seattle region about 1000 years ago.
- This earthquake is implicated as the cause of the Lake Washington landslides and the Puget Sound tsunami.
- The findings provide crucial data for understanding seismic hazards in the Pacific Northwest.
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