Alaska geology and plate tectonics have not been well understood due to an active Yakutat plate, believed to be part of the remains of an ancient Kula plate, not being acknowledged to exist in Alaska. It is positioned throughout most of southcentral Alaska beneath the North American plate and above the NNW subducting Pacific plate. The Kula? plate and its eastern spreading ridge were partially "captured" by the North American plate in the Paleocene. Between 63 Ma and 32 Ma, large volumes of volcanics erupted from its subducted N-S striking spreading ridge through a slab window. The eruptions stopped at 32 Ma, likely due to the Pacific plate flat-slab subducting from the south beneath this spreading ridge. At 28 Ma, magmatism started again to the east; indicating a major shift to the east of this "refusing to die" spreading ridge. The captured Yakutat plate has also been subducting since 63 Ma to the WSW. It started to change to WSW flat-slab subduction at 32 Ma, which stopped all subduction magmatism in W and SW Alaska by 22 Ma. The Yakutat plate subduction has again increased with the impact/joining of the coastal Yakutat terrane from the ESE about 5 Ma, resulting in the Cook Inlet Quaternary volcanism of southcentral Alaska. During the 1964 Alaska earthquake, sudden movements along the southcentral Alaska thrust faults between the Yakutat plate and the Pacific plate occurred. Specifically, the movements consisted of the Pacific plate moving NNW under the buried Yakutat plate and of the coastal Yakutat terrane, which is considered part of the Yakutat plate, thrusting WSW onto the Pacific plate. These were the two main sources of energy release for the E part of this earthquake. Only limited movement between the Yakutat plate and the North American plate occurred during this 1964 earthquake event. Buried paleopeat age dates indicate the thrust boundary between the Yakutat plate and North American plate will move in about 230 years, resulting in a more "continental" type megathrust earthquake for southcentral Alaska. There are, therefore, at least two different types of megathrust earthquakes occurring in southcentral Alaska: the more oceanic 1964 type and the more continental type. In addition, large "active" WSW oriented strike-slip faults are recognized in the Yakutat plate, called slice faults, which represent another earthquake hazard for the region. These slice faults also indicate important oil/gas and mineral resource locations.

This paper examines in a very broad fashion the formation of geothermal resources at lithospheric subduction zones. Regions of highly silicic calc‐alkaline Quaternary volcanoes and/or plutons have been identified as prime candidates for having high‐temperature hydrothermal systems. Regions of large tholeiitic Quaternary volcanoes have been identified as prime candidates for having large moderate‐temperature hydrothermal systems. In addition, active magmatic, phreatomagnetic, and/or tectonic fracturing must be occurring in order to keep any moderate to high temperature hydrothermal system from chemically sealing. Connate, meteoric and/or oceanic water sources must also be present. Owing to tectonic and magmatic processes, volcanic arcs of subduction zones represent regions of the crust that have anomalously high mechanical and heat energy. Such arc regions are expected to contain significantly more moderate to high temperature hydrothermal systems than what is presently known. Many of these arcs are briefly discussed with respect to their potential for containing such resources.

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The November 30, 2018 M 7.1 earthquake near Anchorage, Alaska was caused by a deep normal fault. It was limited to a Yakutat plate as based on a new proposed tectonic model which reflected the movement of a block of this westsouthwest subducting plate into the Cook Inlet subduction zone. This movement was strongly influenced by a deeper and faster north-northwest subducting Pacific plate. It is evident that the Cook Inlet subduction zone has two distinct subducting plates in contrast to the Aleutian subduction zone to the immediate southwest which has just one. Similar normal fault events also exist for the region, but ones comparable to the November 30 size are unknown. However other deep to shallow M 7± earthquakes associated with large strike-slip faults in the Yakutat plate have been common and are called slice faults. In addition, varying types of megathrust earthquakes occur. The great 1964 Alaska earthquake reflected a sudden megathrust slip principally between the Pacific and the Yakutat plates for the offshore region of southcentral Alaska. Based on paleoseismic data a similar oceanic megathrust is expected in about 800 years. Paleoseismic evidence and the mechanics of the November 30 event indicate more continental megathrust earthquakes also occur along the bottom and top of the Yakutat plate with the Pacific and the North American plates, respectively. In fact, based on this paleoseismic data and on present crustal folding for the Cook Inlet region, a more continental megathrust earthquake is expected in about 230± years which would be due to west-southwest thrusting between the Yakutat and the North American plates. The November 30, 2018 earthquake would be small compared with such a predicted megathrust, but it is a very important precursor to it. The November 30 event also helps to confirm the existence of a Redoubt slice fault within the Yakutat plate by defining its boundaries and nature. Collectively these elements verify the existence of a west-southwest subducting Yakutat plate with its regional strike-slip slice faults which helps to explain the seismicity and some of the complex geology of southcentral Alaska.