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A New Generation of High-Precision Dating Techniques for Coseismically-Killed or Damaged Trees

Description: 

Dendrochronological techniques are uniquely high precision, establishing the exact calendar year of formation for each tree ring in a sample set. Thus, if a tree was killed by seismic activity, the exact calendar year and even season of the earthquake can be determined by establishing the year of the final ring formed under the bark. If trees have been disturbed but not killed, growth or anatomical anomalies can also place seismic events in time.

High dating precision is typically accomplished via crossdating in which synchronous, time-specific growth patterns are matched among trees of a given species and region, beginning with live-collected trees, and extending back in time with dead-collected trees. There are, however, important limitations, even assuming wood is well preserved. Dead-collected trees must contain ring sequences long enough (usually 150 years or more) to establish confident growth-pattern matches. There must also be sufficient year-to-year growth variability and a minimum of irregularities or distortions. Yet wood samples often violate these criteria, especially roots, which are often the best-preserved part of dead trees.

Newly emerging techniques are likely to help overcome limitations of dating with ring widths. First, the oxygen-18 content of tree rings often covaries among trees, and even species, more strongly than width. Preliminary data in the Pacific Northwest indicates that wood samples with short sequences, distorted rings, and little year-to-year growth variability can be crossdated using oxygen-18. Single-year cosmogenic spikes in radiocarbon, known as “Miyake Events,” provide another new approach for one-year dating precision of paleo-earthquakes. Finally, “wiggle matching” multidecadal series of radiocarbon values from tree rings may narrow uncertainties to within a year or two for wood that lived within the past several thousand years. Combined, these techniques could enable the dating of wood samples, including roots, that could not have been crossdated using ring widths, and initiate a new generation of high-resolution paleoseismic reconstructions.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - III

Type: Oral

Date: 5/1/2024

Presentation Time: 02:45 PM (local time)

Presenting Author: Bryan

Student Presenter: No

Invited Presentation: Yes

Authors