5:00-6:00 PM Networking
6:00-7:00 PM Dinner
7:00-8:00 PM Presentation
Megathrusts and tree-rings: high precision dating of the penultimate great earthquake in southern Alaska
A “ghost forest” of dead trees at Girdwood in Alaska records coseismic subsidence from the March 1964 M9.2 earthquake. Below the roots of these trees, a buried layer of stumps records similar coastal subsidence during the penultimate great earthquake here about 700-900 years ago. This talk will describe ongoing efforts to obtain a precise kill-date for these older stumps using tree-ring crossdating and radiocarbon wiggle-matching. A precise date would give the exact year of the penultimate great earthquake, show the length of the most recent cycle of stress accumulation and release for the northeastern end of the Alaska-Aleutian megathrust, and enable future studies to document regional evidence for coseismic land disturbance from the penultimate great earthquake. In addition to these outcomes for paleoseismology, this work is giving insight into tree-ring crossdating in the rugged maritime area of southern Alaska and into apparent offsets between radiocarbon ages in coastal Alaska and the IntCal20 calibration curve.