The Yakutat microplate, a significant element in the geological framework of southern Alaska, is the latest addition to the collection of accreted terranes in the region. This microplate has been gradually transported northward along transform faults that run parallel to the margin, specifically the Queen Charlotte and Fairweather faults. Its eventual encounter with the continental margin of southern Alaska has led to ongoing collisions that yield intricate seismotectonic interactions, contributing to the formation of an active seismic belt.
Historically, this area has experienced several powerful seismic events. In 1899, two major earthquakes, measuring magnitudes of M8.1 and M8.2, dramatically reshaped the landscape of the Yakutat Bay area, causing up to 40 feet of uplift in some areas and land subsidence of approximately 6 feet. More recently, in 1958, the M7.7 Lituya Bay Earthquake ruptured from the head of Yakutat Bay along the Fairweather Fault, triggering a massive landslide into Lituya Bay that generated a tsunami wave towering at an astonishing 1,720 feet. Additionally, the 1972 M7.4 Saint Elias Earthquake further demonstrated the seismic volatility of the region.
In the offshore context, the Transition Fault stands out as a notable geological structure, marking the boundary between the Yakutat microplate and the Pacific Plate, while the northern Gulf of Alaska fault zone continues to be a point of interest. Significant seismic activity has been recorded in this area over the years, with noteworthy earthquakes such as the M7.7 event in 1987 and the M7.8 event in 1988, both of which resulted in substantial ground movements felt across the southern and southeastern Alaskan coasts. Although the Transition Fault has not been responsible for significant earthquakes aside from a M6.7 event in 1973, the coastal region remains characterized by a high level of background seismicity, witnessing hundreds of earthquakes annually, predominantly shallow and located within a 50-mile coastal zone.
This persistent seismic activity in the Yakutat region is a reminder of the dynamic nature of Earth’s tectonic processes. The ongoing study of these interactions not only enhances our understanding of geophysical phenomena but also underscores the importance of earthquake preparedness in communities situated in seismically active areas.