## 3 Results  
### Constrained Thermal Regime Benetath the Alaskan Continental Wedge  
Two-dimensional thermal models have been constructed with nonlinear mantle rheology to study 17 global subduction zones, including the Alaskan subduction zone [23]. The models incorporate slab mantle (or interplate) decoupling, which has been suggested to apply to NE Japan [24; 25] based on the hypothesis that the observed surface heat flow above the cold forearc mantle is low in contrast to the hot arc and backarc mantle [23; 26]. However, this slab-mantle (or interplate) decoupling hypothesis relies on limited observations in NE Japan and Cascadia. The new development of surface heat flow measurements has included bottom-simulating reflectors [27; 28], terrestrial boreholes and marine heat probes [29; 30], and Hi-net boreholes [31], which are not used in Furukawa [24] but indicate the presence of forearc medium-high heat flow values (50-140 or 150 mW/m\({}^{2}\)) located in NE Japan and Cascadia (Figure 2), which implies a much warmer forearc mantle than  
Figure 1: Study region in Alaska. Seafloor age and surface heat flow observations in Alaska are included. The colored solid circles represent the observed surface heat flow obtained from the global heat flow database [19]. The ocean seafloor age and its distribution are provided by EarthByte [15]. The light blue dotted line indicates the model boundary. The red (inside the model region) and purple (outside the model region) curves represent iso-depth contours of the upper surface of the subducted oceanic plate, with two adjacent lines separated by 20 km (Slab2) [12]. previously thought. Therefore, plate decoupling in thermal modeling, which significantly affects the subduction thermal regime, is still controversial. The thermal results are shown in Figure 3c,d. We found that the thermal models without plate decoupling result in a subduction regime via calculation, which better fits the observation of surface heat flow and seismicity distribution. Therefore, we suggest constraining the modeled thermal regime primarily by the integrated and updated observations for surface heat flow, which include the observations from bottom-simulating reflectors [27; 28], terrestrial boreholes and marine heat probes [29; 30], Hi-net boreholes [31], and Currie depths [20]. The Currie depth estimation [20] data cover global subduction zones and are a good reference for calculating the thermal regime on the shallow megathrusts. Compared with the result of temperature variation along the profile crossing the Augustine volcano (Figure 3) [23] in Alaska, we found that the slab geometry updated in Alaska by Slab2.0 [12] provides a high-resolution slab topography involving a slab depth of 100--115 km beneath the Augustine volcano, while the slab geometry [32] obtained by using seismic reflection and refraction data and earthquake distribution suggests a slab depth beneath Augustine volcano of approximately 85 km, as adopted by [PERSON] and [PERSON] [23] (Figure 3). This geometric difference greatly affects the calculated subduction thermal regime. In addition, the interplate temperature predicted by our models gradually  
Figure 2: Integrated heat flow observations were based on the Global Heat Flow Database [19] and further combined with bottom-simulating reflectors [27; 28], terrestrial boreholes, marine heat probes [29; 30], and Hi-net boreholes [31]. The integrated observation of surface heat flow in NE Japan shows gradually changing values from the cold trench to the hot arc and then to the medium backarc. However, we found a forearc medium heat flow region (50–140/150 mW/m\({}^{2}\)) in NE Japan and Cascadia, indicating that plate coupling occurs at a forearc depth of 40–80 km. The plate decoupling hypothesis is not robustly constrained by heat flow observations. (**a**) Northeast Japan. (**b**) Cascadia.