Subducting oceanic basement roughness impacts on upper plate tectonic structure and a backstop splay fault zone activated in the southern Kodiak aftershock region of the Mw 9.2, 1964 megathrust rupture, Alaska
Links
- More information: Publisher Index Page (via DOI)
- Open Access Version: Publisher Index Page
- Download citation as: RIS | Dublin Core
Abstract
In 1964, the Alaska margin ruptured in a giant Mw 9.2 megathrust earthquake, the 2nd largest during worldwide instrumental recording. The coseismic slip and aftershock region offshore Kodiak Island was surveyed in 1977 – 1981 to understand the region’s tectonics. We re-processed multichannel seismic (MCS) field data using current standard Kirchhoff depth migration and/or MCS traveltime tomography. Further surveys in 1994 added P-wave velocity structure from wide-angle seismic lines and multibeam bathymetry. Published regional gravity, backscatter, and earthquake compilations also became available at this time.
Beneath the trench, rough oceanic crust is covered by ~3 to 5 km thick sediment. Sediment on the subducting plate modulates the plate interface relief. The accreted prism’s imbricate thrust faults have a complex P-wave velocity structure. Landward, an accelerated increase in P-wave velocities is marked by a backstop splay fault zone (BSFZ) that marks a transition from the prism to the higher rigidity rock beneath the middle and upper slope. Structures associated with this feature may indicate fluid flow. Further upslope, another fault extends >100 km along-strike across the middle slope. Erosion from subducting seamounts leaves embayments in the frontal prism.
Plate interface roughness varies along the subduction zone. Beneath the lower and middle slope, 2.5 D plate interface images show modest relief whereas the oceanic basement image is rougher. The 1964 earthquake slip maximum coincides with the leading/landward flank of a subducting seamount and the BSFZ. The BSFZ is a potentially active structure and should be considered in tsunami hazard assessments.
Suggested Citation
Krabbenhoeft, A., von Huene, R.E., Miller, J.J., Klaeschen, D., 2021, Subducting oceanic basement roughness impacts on upper plate tectonic structure and a backstop splay fault zone activated in the southern Kodiak aftershock region of the Mw 9.2, 1964 megathrust rupture, Alaska: Geosphere, v. 17, no. 2, p. 409-437, https://doi.org/10.1130/GES02275.1.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Subducting oceanic basement roughness impacts on upper plate tectonic structure and a backstop splay fault zone activated in the southern Kodiak aftershock region of the Mw 9.2, 1964 megathrust rupture, Alaska |
| Series title | Geosphere |
| DOI | 10.1130/GES02275.1 |
| Volume | 17 |
| Issue | 2 |
| Publication Date | February 25, 2021 |
| Year Published | 2021 |
| Language | English |
| Publisher | Geological Society of America |
| Contributing office(s) | Central Energy Resources Science Center |
| Description | 29 p. |
| First page | 409 |
| Last page | 437 |
| Country | United States |
| State | Alaska |
| Other Geospatial | Kodiak Island |