Crustal Structure in Alaska From Receiver Function Analysis

• Published in: Geophysical research letters 2019-02, Vol.46 (3), p.1284-1292
• Main Authors: Zhang, Ying, Li, Aibing, Hu, Hao
• Format: Article
• Language: English
• Subjects: Alaska; Buoyancy; Crustal structure; Crustal thickness; Crustal Vp/Vs; Earth mantle; Elevation; Function analysis; H‐κ stacking; Isostasy; Magma; Moho; Mountains; Ocean surface topography; Oceanic crust; Receiver function; Subduction (geology); Thickness; Topography; Topography (geology); Upper mantle
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL081011

New maps of crustal thickness and Vp/Vs in Alaska and western Canada were obtained using P receiver functions recorded at 198 stations from the USArray Transportable Array and the Alaska Regional Network. Our results indicate that topography and Moho depth are correlated as crustal thickness varies from 28 to 43 km across Alaska. A thick crust occurs under the mountains in the south and north with relatively thin crust in central Alaska. The deepest crustal root beneath the Brooks Range may have lost its buoyancy based on Airy isostasy. In addition, a buoyant upper mantle is required to support the high topography in east central Alaska. Vp/Vs is determined between 1.7 and 1.8 beneath most of Alaska except a high average of 1.9 in the south central region. We attribute this high Vp/Vs to the underplating of Yakutat and Pacific oceanic crust. Plain Language Summary We have developed the first statewide maps of crustal thickness and Vp/Vs in Alaska and western Canada. The observed crustal thickness generally correlates with surface topography, and the Denali Fault is associated with a sharp step of crustal structure variation. A deep Moho and high Vp/Vs are imaged under southern Alaska following the outline of the subducting Yakutat and Pacific slab, probably caused by the underplated oceanic crust. The thin crust in east central Alaska is not enough to compensate the elevation. A buoyant upper mantle at the northeastern edge of the Yakutat slab is required for maintaining local isostasy. The thickest crust under the Brooks Range overcompensates the elevation, suggesting a densified crustal root. Key Points The maps of crustal thickness and Vp/Vs are produced in Alaska and western Canada The Moho depth in Alaska largely correlates with the topography High Vp/Vs is observed in south central Alaska, probably due to the underplated oceanic crust