Using Coastal, Lacustrine Vibracore Data to Constrain Prehistoric Tsunami Events and Rupture Recurrence Intervals Along the Cascadia Subduction Zone, Floras Lake, Oregon
Abstract
Although the geologic record of rupture on the Cascadia megathrust has been documented at numerous coastal and offshore sites, many questions remain on how earthquakes and tsunamis have varied in magnitude, extent, and recurrence. Because coastal lakes may contain the most complete onshore record of tsunamis and earthquakes, we identified Floras Lake on the southern coast of Oregon as an ideal location for the purpose of this study. We present new data from 38 vibracores collected from Floras Lake. These data will initially be used to answer three questions: (1) Are tsunamis or large storms the source of sand layers observed in lake muds? (2) Besides sandy deposits, what are the other sedimentological indicators of tsunami inundation and earthquake shaking? (3) What was the frequency of tsunami inundation and/or earthquake disturbance in Floras Lake over the last 7,000 years? X-Ray Computed Tomographic (CT) scanning, high resolution line scan photography, detailed core sedimentological descriptions were used to describe the different sediment facies observed and to correlate event layers between cores. Preliminary grainsize analyses of a sandy event bed indicates fining upward sequences that are indicative of deposition from a tsunami. Diatom analyses indicate that Floras Lake typically contains freshwater species and that marine diatom assemblages are observed following the deposition of tsunami deposits. Plant macrofossils were sampled for 14Cdating and tsunami deposit ages were estimated using Bayesian age models. Preliminary results indicate that at least 7 sandy tsunami deposits from the last 7,000 years are preserved in Floras Lake. Future work will involve correlating facies along transects in Floras Lake and comparing the age of event deposits of nearby onshore and offshore earthquake and tsunami records.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNH43F0996N
- Keywords:
-
- 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS;
- 4333 Disaster risk analysis and assessment;
- NATURAL HAZARDS;
- 4341 Early warning systems;
- NATURAL HAZARDS;
- 4564 Tsunamis and storm surges;
- OCEANOGRAPHY: PHYSICAL