This implies that the earthquake was an intraslab earthquake within that plate, rather than at the plate boundary between the Pacific and North American Plates beneath the Anchorage area. The depth and mechanism are consistent with faulting within the down-going Pacific Plate. A fault dipping at 29° towards the east gives the best match to the observed seismic waveforms. The focal mechanism shows that the earthquake was a result of normal faulting. The earthquake had a magnitude of 7.1 on the moment magnitude scale using a centroid moment tensor inversion of the W-phase. This earthquake is more similar to the 2001 Nisqually earthquake located near Tacoma, Washington, than to the 1964 megathrust earthquake. Though earthquakes are common in Alaska, they often occur out at sea. The 1964 earthquake, with a magnitude of 9.2, was the largest earthquake in American history and the second largest to ever be recorded anywhere in the world. The region has experienced severe earthquakes in the past, including several megathrust earthquakes. Near Anchorage, the plates are converging at a rate of 57 mm per year. Southern Alaska lies at the eastern end of the Aleutian Trench, where the Pacific Plate is subducting beneath the North American Plate. The National Tsunami Warning Center-itself located inside the quake zone, in Palmer, Alaska, 42 miles (68 km) northeast of Anchorage-issued tsunami warnings for nearby coastal areas, including Cook Inlet and the Kenai Peninsula, but they were lifted shortly after. The earthquake could be felt as far away as Fairbanks.
It was followed six minutes later by a magnitude 5.7 aftershock centered 2.5 miles (4.0 km) north-northwest of the municipality. The earthquake's epicenter was near Point Mackenzie, about 10 miles (16 km) north of Anchorage, and occurred at a depth of 29 miles (47 km). AKST (17:29 UTC), a magnitude 7.1 earthquake hit Anchorage in South Central Alaska.
#Alaska quake center series#
This broad zone of seismicity includes a series of predominantly thrust faults, and a 1943 M7.0 earthquake may have originated in this band.61☂0′46″N 149★7′18″W / 61.346°N 149.955°W / 61.346 -149.955 The diffuse zone of seismicity between Cook Inlet and the Denali Fault may mark a deformation zone between the Bering microplate to the west and the southern Alaska block to the east.
The Castle Mountain Fault, which passes 25 miles (40 km) north of Anchorage, exhibits geological evidence of Holocene offsets and generated the 1984 M5.6 Sutton Earthquake. The April 1933 M6.9 earthquake, which caused considerable damage in Anchorage, appears to have occurred on such a structure. Mapped geological structures in upper Cook Inlet are capable of generating strong earthquakes. (3) Crustal seismicity in this region can be attributed to three major sources: the faults and folds of the Cook Inlet basin, the Castle Mountain Fault, and the wide band of diffuse seismicity extending from northern Cook Inlet to the Denali Fault. Both produced significant ground shaking in the Southcentral region and resulted in structural damage to buildings and infrastructure. The 2016 M7.1 Iniskin and the 2018 M7.1 Anchorage earthquakes are the most recent notable intermediate-depth events. In southern and central Alaska, this seismicity abates at a depth of approximately 140 miles (225 km), reflecting the down-dip extension of the Pacific Plate. This zone extends along the Aleutian Arc, Alaska Peninsula, and Cook Inlet and terminates beneath the northern foothills of the Alaska Range. (2) Intermediate-depth seismicity (below 20 miles/32 km) occurs in the Wadati-Benioff Zone, where the subducting Pacific Plate descends towards the mantle beneath the North American Plate. The 1964 M9.2 Great Alaska Earthquake, which is still the second largest earthquake ever recorded worldwide, originated under Prince William Sound. (1) The strongest earthquakes in Southcentral Alaska are generated by the megathrust fault that marks the contact zone between the subducting Pacific and overriding North American plates. Tectonic Setting of Southern AlaskaEarthquakes in Southcentral Alaska are produced by a number of different tectonic features.
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