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

Abstract

In Alaska, the Denali fault (Figure 1b) is a remarkable strike-slip system extending over 2,000 km in length. It has been active since at least 65 Ma, has accommodated hundreds of kilometers of dextral motion, and has maintained a relatively stable curvature since 45 Ma (Benowitz et al., 2022;Regan et al., 2020). 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 (

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

“…We collected eight representative 3-D shear-wave velocity models. Since the arrival of the EarthScope TA in Alaska, there have been a large number of velocity models published using data from the EarthScope TA stations and the Alaska regional network stations (e.g., Jiang et al, 2018;Martin-Short et al, 2018;Gou et al, 2019;Feng & Ritzwoller, 2019;Berg et al, 2020;Yang & Gao, 2020;Esteve et al, 2020;Audet et al, 2019;Nayak et al, 2020;Esteve et al, 2021;Gama et al, 2022b;Liu et al, 2022). To narrow down the velocity models for this synthesis work, we select velocity models that satisfy the following conditions: 1) covers most of mainland Alaska, 2) provides isotropic seismic velocities, 3) uses part or all EarthScope TA data, 4) includes surface wave data to aid with the vertical resolution, 5) is available as a digital velocity model through IRIS Earth Model Collaboration or personal communications, 6) provides absolute velocities or perturbations with an explicitly known reference model, and 7) covers at least the continental crust in depth.…”

“…The EarthScope TA stations have a nominal spacing of about 85 km, while some places, such as central Alaska and the Wrangell Volcanic Field, are covered with denser regional arrays. Among the eight velocity models, the Y2020 model (Yang & Gao, 2020) covers only central and southern Alaska (Figure 2b) while the M2018 (Martin-Short et al, 2018) and G2022 (Gama et al, 2022b) models cover most of Alaska. The rest of the velocity models cover the entire Alaska region.…”

“…The outlines are estimated using the velocity model at the depth of about 30 km for all models. W2018 -model by Ward and Lin (2018), J2018 -model by Jiang et al (2018), M2018 -model by Martin-Short et al (2018), F2019 -model by Feng and Ritzwoller (2019), B2020 -model by Berg et al (2020), Y2020 -model by Yang and Gao (2020), N2020 -model by Nayak et al (2020), G2022 -model by Gama et al (2022b). See Table 1 for more information about these velocity models.…”

“…However, the recent TA deployment has greatly improved the coverage for estimating crustal thickness and allows for continuous analysis across the entire state. Here we compare crustal thickness estimates across Alaska Gao, 2020), N2020 (Nayak et al, 2020), and G2022 (Gama et al, 2022b). Major faults (thick green lines) are shown for reference.…”

“…In addition to the seven studies selected for comparison, other measures of crustal thickness in Alaska also exist. Among studies that solve for 3D velocity structure, those that jointly invert surface wave dispersion with P receiver functions (e.g., Martin-Short et al, 2018;Feng & Ritzwoller, 2019;Berg et al, 2020) or with S receiver functions (e.g., Gama et al, 2021Gama et al, , 2022b typically provide sharper resolution of the depth of the Moho velocity gradient than other approaches. However, the studies in these groups that sample mainland Alaska are represented in the analysis of shear-wave velocity models in Section 2.1 and their crustal thickness results are not explicitly considered in this section.…”