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Offshore Site Effects in Alaska: Geologic Factors and Pervasive Small-strain Nonlinearity

Description: 

The importance of site amplification and the geologic factors controlling it are well understood for onshore sedimentary basins, while offshore site amplification has not been addressed adequately, despite its significance for slope stability during great earthquakes including compounding hazards from earthquake-triggered submarine landslides, and for the quantitative interpretation of the turbidite record as a paleoseismic proxy. In this study, we investigate linear and nonlinear site amplification using waveforms of regional and teleseismic earthquakes recorded by 75 ocean bottom seismometers from the Alaska Amphibious Community Seismic Experiment (AACSE), spanning Kodiak Island and the Alaska Peninsula, across water depths of up to ~5 km. We derive a linear amplification factor using a generalized inversion framework, and compare the site terms with ground motion model predictions. We also compare site terms with geomorphic parameters, such as slope angle and water depth, which illuminate geologic controls on offshore ground motion variability. Additionally, we search for evidence of nonlinearity by evaluating the amplitude dependence of site period, derived from horizontal-to-vertical spectral ratios. Preliminary results show that some stations exhibit nonlinear dynamic softening at relatively low peak ground acceleration, even approaching the level of seismic ambient noise.

Session: Subaqueous Evidence for Earthquakes, Coseismic Landslides, Tsunamis and other Cascading Hazards [Poster]

Type: Poster

Date: 4/15/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Litong Huang

Student Presenter: Yes

Invited Presentation: 

Poster Number: 161

Authors