Yakyak alaska8/26/2023 Because the yak and any older Paleocene through Miocene colliding terranes would have been driven by PAC and NA, these slices could be considered a hybrid type of sliver.ġ.2 Tectonics of the great 1964 Alaska earthquake They are likely caused by the oblique collision of yak and even earlier terranes with YAK (Fig. These regional slice faults are not transforms because they lack plate tectonic boundaries, nor slivers (Jarrard, 1986) since they lie perpendicular to the motion of the PAC and strike along the YAK motion. Exposures have not been well documented but numerous southwest and west-southwest striking faults have been described within the 10+km wide Montana Creek slice fault (MC) zone (Glen, 2004 McGee, 1978 Werdon et al., 2002). To a degree these slice faults also extend up through the overlying North American plate. They extend west-southwest through the YAK into the Cook Inlet subduction zone and are associated with its volcanoes (Fig. This moving YAK has pronounced offsets caused by differential movements of large west-southwest elongated blocks named slices that are bound by long strike-slip fault zones, called slice faults (Reeder, 2016). 1) which has been partially filled by Wrangell volcanic deposits in its southeast region. The southern part of YAK has moved to the west-southwest from the east faster than its northern part, forming a crustal gap resulting in the large Copper Valley (Fig. This subduction increased when the yak attached/joined the YAK in the Prince William Sound region from the southeast about 5 million years ago (Arkle et al., 2013 Cox and Engebretson, 1985 Reeder, 2016). In opposition to the PAC, the YAK part of the Yakutat plate is subducting more slowly to the west-southwest. It is positioned throughout most of southcentral Alaska beneath the North American plate (NA) and above the less rigid and less seismic north-northwest subducting Pacific plate (PAC). YAK is likely the remains of an ancient Kula plate (Atwater, 1989) and in its eastern part probably consists of numerous thrusted layers of Kula and/or other ancient plates such as the Resurrection, Farallon or even older plates (Bradley et al., 1993 Page et al., 1986). The yak is the Yakutat terrane (also called Yakutat microplate). Key words: megathrust earthquake, new tectonic model, paleoseismic data, precursor earthquake, recurrence earthquake, slice fault, Yakutat plate IntroductionĪlaska geology and plate tectonics have not been well understood due to an unacknowledged active Yakutat plate (YAK&yak) that consists of YAK and yak (Fig. 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. 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. The Novemearthquake would be small compared with such a predicted megathrust, but it is a very important precursor to it. 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. 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. Based on paleoseismic data a similar oceanic megathrust is expected in about 800 years. 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. In addition, varying types of megathrust earthquakes occur. 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. Similar normal fault events also exist for the region, but ones comparable to the November 30 size are unknown. 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. This movement was strongly influenced by a deeper and faster north-northwest subducting Pacific plate. It was limited to a Yakutat plate as based on a new proposed tectonic model which reflected the movement of a block of this west-southwest subducting plate into the Cook Inlet subduction zone. The NovemM 7.1 earthquake near Anchorage, Alaska was caused by a deep normal fault.
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