Mapping the Lithosphere and Asthenosphere Beneath Alaska With Sp Converted Waves

Abstract

The global distribution of partial melt in the asthenosphere is still widely debated. In subduction zones, seismic velocity and attenuation models have been used to trace the generation and transport of partial melt in the mantle wedge from just above the subducting slab to the arc (e.g.,

Synthesis of the Seismic Structure of the Greater Alaska Region: Continental Lithosphere

“…We observe four notable crustal thickness patterns as revealed by the preferred reference model for Alaska (Figure 11b). 1) The crust across much of interior Alaska, approximately between the Alaska Range to the south and the Brooks Range to the north, is about 25-35 km thick, similar to the observations from previous studies (e.g., Woollard et al, 1960;Clarke & Silver, 1991;Searcy et al, 1996;Ai et al, 2005;Rossi et al, 2006;Veenstra et al, 2006;Brennan et al, 2011;Allam et al, 2017;Miller et al, 2018;Martin-Short et al, 2018;Zhang et al, 2019;Haney et al, 2020;Gama et al, 2021Gama et al, , 2022aGama et al, , 2022bMann et al, 2022).…”

“…The depth of 120 km would include the total thickness of the upper plate lithosphere over most of the study area, with the exception of some of the thickest lithosphere in northern Alaska (Miller et al, 2018;Gama et al, 2021Gama et al, , 2022b. However, in central Alaska, the lithosphere is much thinner (Gama et al, 2022a), and a maximum depth of 120 km would also include the asthenospheric mantle. Hence we use the depth range of 40-120 km for the mantle clustering analysis, to capture variations in the structure of the mantle lithosphere of the continental plate while avoiding too much dilution of the lithospheric structure by the asthenospheric mantle.…”

Variations in Lithospheric Thickness Across the Denali Fault and in Northern Alaska

“…The observed variations in the thickness and velocity of the upper plate mantle lithosphere across the Denali fault and Hines Creek fault/Northern Foothills Thrust Belt are spatially correlated (at distances of <50 km) with the -changes in Moho depth and velocity across these faults found in prior studies (Allam et al, 2017;Brennan et al, 2011;Gama et al, 2022;Haney et al, 2020;Mann et al, 2022;Martin-Short et al, 2018;Miller, O'Driscoll, et al, 2018;Rossi et al, 2006;Veenstra et al, 2006;Ward, 2015). In addition, the northward decrease in crustal thickness noted at the Hines Creek Fault in prior studies (e.g., Allam et al, 2017;Martin-Short et al, 2018;Miller, O'Driscoll, et al, 2018;Miller, Roeske, & Benowitz, 2018;Rossi et al, 2006) is also evident in the Vs model (cross-section C, Figure 3).…”

“…Sp information was derived from a common conversion point (CCP) stack of Sp receiver functions (Gama et al., 2022) based on 449 broadband stations in Alaska (Figure 1a) (network information provided in the Data Availability Statement section), including 153 stations of the NSF EarthScope Transportable Array. For earthquakes larger than Mw 5.8, recorded between 1986 and 2021, 73,500 Sp receiver functions were calculated from waveforms filtered with a 2–100 s bandpass.…”

“…The Denali fault also plays a fundamental role in the mechanics of how shortening due to subduction in southern Alaska is partitioned into upper plate deformation (e.g., Jadamec et al., 2013). However, while abundant evidence exists for offsets in crustal thickness and velocity across the Denali fault and the adjacent Hines Creek fault (Allam et al., 2017; Brennan et al., 2011; Gama et al., 2022; Haney et al., 2020; Mann et al., 2022; Martin‐Short et al., 2018; Miller, O’Driscoll, et al., 2018; Miller, Roeske, & Benowitz, 2018; Rossi et al., 2006; Veenstra et al., 2006; Ward, 2015) the connection of the Denali fault to structures in the deeper mantle lithosphere has remained uncertain. In a new model of shear‐wave velocity structure obtained from joint inversion of surface wave and converted body wave data, we find that the Denali fault lies above a transition in lithospheric thickness.…”