Relocations of Earthquakes (1899–1917) in South-Central Alaska

Abstract

I have relocated 18 earthquakes occurring in the south-central Alaska region between 1899 and 1917 using a bootstrap relocation technique. Locations of events within the Yakutat region suggest that the 1899 sequence began on 4 September with a M S = 7.9 event within the area of the Pamplona fault zone/western Transition fault zone, rupturing the western portion of the North American/Pacific plate interface. A M S = 7.4 event on 10 September appears to have ruptured the offshore portion of the plate interface to the east of the 4 September event. This was followed by a M S = 8.0 event that likely ruptured the onshore and down-dip portion of the plate interface. A M S = 7.0 event in 1908 may have ruptured a small portion of the plate interface between the 4 September and 10 September events. Events occurring between 1911 and 1916 in the Prince William Sound region appear to be slab events occurring in similar locations to more recent seismicity. Within the Kodiak region the 1900 earthquake of M S = 7.7 has a location consistent with the rupture of the Kodiak asperity which also ruptured during the 1964 great Alaska earthquake. Other large magnitude Kodiak events appear to be associated with regions of recent seismicity, including the Karluk Lake area of southwestern Kodiak Island and the Albatross Basin located offshore southeast of Kodiak Island. Space-time seismicity patterns since 1899 indicate that magnitude 6 to7 events have occurred with regularity in the Kodiak Island region; that there has been a lack of magnitude ‡ 6 events in the Prince William Sound region since 1964, and that the Yakutat region has remained notably quiescent at the magnitude ‡ 6 level.

Landslides and Megathrust Splay Faults Captured by the Late Holocene Sediment Record of Eastern Prince William Sound, Alaska

“…1) may lie along the L1 and L2 faults (at depth) and suggest that these faults may rupture independently of the large megathrust earthquakes. Although it is not clear whether pre-1964 M w > 7 earthquakes initiated in the upper plate, Doser (2006) relocated older earthquakes to lie beneath eastern PWS in the vicinity of Orca Bay. Finally, using empirical relationships for subsurface rupture lengths from Wells and Coppersmith (1994), slip along the ∼60 km length of the L1/L2 faults beneath Orca Bay could independently support an M w 7 earthquake.…”

Tsunami inundation maps of Port Valdez, Alaska

“…3; Doser, 2006), shaking was felt in Valdez to the extent "that men were made dizzy and could not stand, houses and forests were disturbed, and there were earthquake water waves in Port Valdez" (Tarr and Martin, 1912, p. 66). There was also a report stating that a ship, docked near the Lowe River in 12 m (40 ft) of water, could not anchor at the same spot with 60 m (200 ft) of cable after the earthquake (Coulter and Migliaccio, 1966), which suggests there was a significant submarine landslide at this location.…”

“…This M S 6.9 earthquake had an epicenter beneath western Prince William Sound (Doser, 2006). It was a series of four shocks of different duration in the northwest-southeast direction.…”

“…The M S 7.2 earthquake occurred in the middle of Prince William Sound (Doser, 2006). The submarine cables were again broken in Port Valdez.…”

Revision of Time-Independent Probabilistic Seismic Hazard Maps for Alaska

“…Review of the plate tectonic and geodetic constraints on the slip rate (DeMets and Dixon, 1999;Fletcher and Freymueller, 2003) suggests that a slip rate of 12 mm/yr is more appropriate. The low number of large earthquakes on the fault, however, seem to be at odds with this slip rate, although it is possible that some the large earthquakes in 1899 could be associated with this fault (Doser, 2006). On the subduction zone to the west it is clear that a variable, but perhaps substantial, fraction of the slip is accommodated as aseismic slip (Pacheco and others, 1993).…”