Dendrochronological Dating of Co-Seismic Land-Level Changes Along the Washington Coast

Session: Amphibious Seismic Studies of Plate Boundary Structure and Processes [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Large earthquakes along the Cascadian coastline cause substantial land-level changes and inundate ecosystems with salt water for kilometers inland. Cascadia is expected to experience a catastrophic subduction event (as well as smaller, more frequent events) in the coming centuries, with the seismic moment large enough to generate shaking that would impact the rapidly growing urban area of Seattle’s metropolitan corridor. There remain, however, substantial uncertainties in the recurrence of these events, as well as their potential effects on coastal ecosystems and communities. The turbidite and onshore geological records show multiple magnitude 8+ earthquakes over the past 2000 years. The interpretation of these records, however, could be a misrepresentation of a series of lower magnitude events that occurred within years to decades. Furthermore, the spatial and temporal manifestation of these events on the surface (i.e. the rate and location of subsidence or uplift) along the coast is complex and not well constrained. Here, we show how precise geochronology of tree-ring records from ancient, drowned forests in the Puget Lowlands allow us to date these events and analyze the impacts of coastal climate and extreme events beyond the limited span of instrumental records. These “ghost forests” were killed by co-seismic land level changes, such as rapid subsidence and transition into a tidal environment along the coast or were drowned in fault-dammed lakes. We use dendrochronologic methods on the sub-fossil wood (wood that is dead but not yet fossilized) from these paleolandscapes along the Washington coast to more precisely date coastal subsidence and surface rupture events during the Common Era.

Presenting Author: Jessie K. Pearl

Authors