## 5 Conclusions  
Through 3-D thermal models and phase diagrams of hydrous minerals in the subducted Pacific plate, the 3-D subduction thermal structure and the petrological metamorphic distribution beneath Alaska are investigated. We draw the following conclusions:  
1. The metamorphosed and downgoing oceanic crust containing bound water releases a large amount of fluid, which results in the recurrence of fast and slow earthquakes beneath south-central and southwestern Alaska by elevated pore fluid pressure and hydrofracturing. 2. The seismic transition zone and the slow slip events (SSEs) identified beneath the Upper Cook Inlet coincide with the slab metamorphic dehydration regions. 3. The slow earthquakes observed beneath Alaska with quasi-stable fault slip preferentially occur, accompanied by high dehydration and temperatures. Fast earthquakes occur updip along the dehydration zones under conditionally low temperatures and dehydration. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app122111139/s1](https://www.mdpi.com/article/10.3390/app122111139/s1)]([https://www.mdpi.com/article/10.3390/app122111139/s1](https://www.mdpi.com/article/10.3390/app122111139/s1)). References [76; 77; 78; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96] are mentioned in the Supplementary Materials file. The Supplementary Materials include Figure S1 Seafloor age and surface heat flow observations in Alaska; Figure S2. Comparison between the observation and calculation of surface heat flow; Figure S3. Refocus on plate decoupling assumption and the observation of surface heat flow in NE Japan; Figure S4. The integrated observation of surface heat flow in NE Japan and Cascadia; Figure S5. Comparison between our model result and [PERSON] and [PERSON] (2009); Figure S6. Comparison of the subduction P-T conditions between this study (blue curve), previous thermal models (other colored curves) and the observation of exhumed rocks (colored ellipses and diamonds); Figure S7. Conceptual sketch of the temperature-dehydration diagram for roughly estimated seismic (fast and slow earthquakes) and asesismic slips in different subduction zones based on this study and our previous series study; Table S1: Model Parameters; Table S2: Parameters for all domains. **Author Contributions:** [PERSON]. conceived the original idea, designed the 3-D thermomechanical code, performed the numerical experiments, and interpreted the results. [PERSON] and [PERSON] elaborated on the numerical study, and [PERSON], [PERSON] ([PERSON]) and [PERSON] ([PERSON]) provided comments. All authors discussed the results and interpretations and participated in writing the paper. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was supported by funds from the Pioneer Hundred Talents Program of the Chinese Academy of Sciences and the Second Tibetan Plateau Scientific Expedition and Research Program (2019 QZKK0708). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Data are available in the figures and tables or from the authors upon reasonable request. The ParaView data for this paper are available at [[https://data.tpdc.ac.cn/en/data/8b266d22-fea7-4259-9a5f-8](https://data.tpdc.ac.cn/en/data/8b266d22-fea7-4259-9a5f-8) ac0 bd9e7869/]([https://data.tpdc.ac.cn/en/data/8b266d22-fea7-4259-9a5f-8](https://data.tpdc.ac.cn/en/data/8b266d22-fea7-4259-9a5f-8) ac0 bd9e7869/) and accessed on 4 December 2020. **Acknowledgments:** We thank [PERSON] for sharing the original Stag3D code developed in this study. We also thank [PERSON] and [PERSON] for their constructive comments, which allowed us to improve this paper. We thank IRIS for their earthquake catalog at [[http://geoserver.iris.edu/](http://geoserver.iris.edu/)]([http://geoserver.iris.edu/](http://geoserver.iris.edu/)) (accessed on 1 January 2020).