Abstract
We present seismic reflection images of the plate interface down to a depth of 65 km across 130,000 km2 offshore Alaska Peninsula. A thin reflection package (<2 km) characterizes the megathrust at depths <24–34 km, marking localized brittle deformation that likely hosts the largest seismic asperities. The reflection band thickness transitions from 2 to 5 km over depths of 24–41 km, suggesting a thickening zone of cumulative deformation and greater heterogeneity corresponding to conditionally stable megathrust behavior. At depths >35–41 km, the reflection package maintains a thickness of 5–6 km and marks the predominantly aseismically slipping megathrust areas. Historic and recent megathrust earthquakes in the southwest Kodiak Asperity and Semidi Segment generally occur within the thin and/or transitional reflection bands. The 2020 Simeonof and earlier M 7+ earthquakes in the Shumagin Gap are estimated to also rupture the shallowest section of megathrust characterized by the thick reflection band (35–41 km depth). Although the shallow part of the plate boundary (<  25 km deep) in the Semidi and Shumagin segments did not rupture in recent 2020 M 7.8 Simeonof and 2021 M 8.2 Chignik earthquakes, the seismic properties of the megathrust suggest it may be capable of earthquake slip in the future, as may have occurred in 1788.
Original language | English (US) |
---|---|
Title of host publication | Tectonics and Seismic Structure of Alaska and Northwestern Canada |
Subtitle of host publication | EarthScope and Beyond |
Publisher | wiley |
Pages | 419-444 |
Number of pages | 26 |
ISBN (Electronic) | 9781394195947 |
ISBN (Print) | 9781394195916 |
DOIs | |
State | Published - Jan 1 2024 |
Keywords
- Alaska peninsula
- Earthquakes
- Lithospheric plates
- Northern cascadia subduction zone
- Subduction zones
- Tsunamis
ASJC Scopus subject areas
- General Earth and Planetary Sciences