1900 Kodiak earthquake

1900 Kodiak Island earthquake
1900 Kodiak earthquake is located in Alaska
1900 Kodiak earthquake
Location within Alaska
UTC time
  • 1900-10-09 12:28:30
ISC event
USGS-ANSS
Local date
  • October 9, 1900
Local time
  • about 2:30 a.m.
Magnitude
Depth
  • 20 km (12 mi)[1]
Epicenter57°24′00″N 151°00′00″W / 57.400°N 151.000°W / 57.400; -151.000[1]
Areas affectedDistrict of Alaska, United States
Max. intensityMMI VIII (Severe)[3]
TsunamiNo significant tsunami documented[2]

The 1900 Kodiak Island earthquake occurred offshore of Kodiak Island in the District of Alaska on October 9, 1900, at 12:28:30 UTC, or about 2:30 a.m. local time.[1][4] The current United States Geological Survey event page lists the earthquake at 7.9 Mw, while a 2021 reanalysis estimated a moment magnitude of 7.6–8.0 and placed the epicentral area about 95 km (59 mi) southeast of the town of Kodiak.[1][2] Older historical catalogs assigned a magnitude of 8.3 and a slightly different epicentral location.[3]

The earthquake strongly shook Kodiak and nearby Woody Island, damaged buildings and a wharf, and was followed by numerous felt aftershocks.[5][2] It was probably the largest known earthquake worldwide in 1900.[4]

Tectonic setting

Kodiak Island lies above the eastern part of the Alaska–Aleutian subduction zone, where the Pacific Plate is subducted beneath the North American Plate. Southern Alaska is one of the most seismically active parts of the United States; the southern margin of the state follows the Alaska–Aleutian megathrust, where convergence produces large earthquakes and tsunamis.[6][7]

The offshore Kodiak region is structurally complex. The incoming Pacific Plate, the plate boundary, and the accretionary wedge south of Kodiak contain faults capable of producing large earthquakes; the same broad margin also ruptured during the 1964 Mw 9.2 Alaska earthquake.[2] Mapping of the Kodiak segment has identified active upper-plate structures, including faults related to the Kodiak shelf fault zone and the Ugak fault, a likely source of the local Kodiak tsunami generated in 1964.[8]

Earthquake

The earthquake occurred early in the instrumental era. Written observations were sparse because Kodiak had no telegraph connection in 1900, and news could leave the island only by ship.[4] Modern work has combined preserved written accounts with early seismograms recorded at distant stations. The 2021 reanalysis used felt reports and arrival times from global seismic stations, including records from Victoria, and Cape Town to estimate an epicentral area centered near 57.4° N, 151.0° W.[2]

A 1988 USGS intensity catalog listed the event at 12:28 UTC, magnitude 8.3, depth 25 km (16 mi), and epicenter 58.00° N, 152.00° W.[3] The current USGS event page gives a revised magnitude of 7.9 Mw, depth 20 km (12 mi), and epicenter 57.400° N, 151.000° W.[1] Because the earthquake predates modern instrumental networks in Alaska, these values are not equivalent in precision to those for recent earthquakes.

The source mechanism has not been resolved. The 2021 reanalysis proposed three possible source regions: rupture on the subduction interface, an earthquake within the subducted oceanic lithosphere, or faulting within the accretionary wedge offshore of Kodiak Island. The absence of evidence for a significant tsunami was identified as an important constraint on future source modeling.[2]

Impact and aftershocks

The maximum reported shaking reached intensity VIII (Severe) on the Modified Mercalli intensity scale at Kodiak–Woody Island in the 1988 USGS catalog.[3] The wharf at Woody Island was partly destroyed, and chimneys, windows, and crockery were broken at Kodiak.[5] The town of Kodiak was small and isolated at the time; it had about 340 residents, and local accounts became known outside the island only after later ships carried news away.[4]

The earthquake was felt over a wide area. A Weather Bureau observer at Tyonek, hundreds of kilometers north of Kodiak, described violent shaking, and a slight shock was reported at Coal Harbor on Unga Island, about 570 km (350 mi) southwest of Kodiak.[5] Felt reports were also compiled from locations such as Seldovia, Valdez, and Yakutat.[3]

Aftershocks were numerous. The USGS impact summary describes about 50 slight aftershocks continuing through the following day, and later catalog entries list additional felt shocks at Kodiak on October 11, 12, and 13.[5][3]

Tsunami question

A damaging tsunami has not been documented for the 1900 event. The absence of a significant tsunami is notable because large offshore earthquakes in southern Alaska commonly raise tsunami concerns. Wilfred Hudson Osgood, a Smithsonian biologist camped near sea level at Women's Bay, west of Kodiak, recorded the earthquake and aftershocks but did not record a tsunami. A log from the U.S. Revenue Cutter Manning, which was anchored in Kodiak harbor, also noted the shaking but not a tsunami.[4]

Later studies treat this negative evidence cautiously. The 2021 reanalysis did not rule out all water-level disturbance, but it found no evidence for a significant tsunami and used that absence as a constraint when considering whether the rupture occurred on the plate interface, within the subducting slab, or on faults in the accretionary wedge.[2]

Significance

The earthquake is significant as a large, early-instrumental event near the Kodiak segment of the Alaska–Aleutian margin. Its reassessment changed the inferred epicentral area from older historical-catalog locations near Kodiak Island to an offshore area southeast of Kodiak, north of the plate boundary.[2][3] It also illustrates the limitations of Alaska earthquake records before local seismic networks: the event was large enough to be recorded globally, but the sparse local record leaves its rupture geometry and precise source mechanism uncertain.[2][4]

The event remains relevant to regional hazard analysis because the Kodiak area includes both the megathrust that produced the 1964 Alaska earthquake and active upper-plate faults capable of local tsunami generation.[2][8] Paleoseismic and tsunami-hazard studies along the Alaska–Aleutian margin continue to use historical earthquakes together with geologic evidence because the written record is too short to define the full recurrence behavior of the subduction zone.[9]

See also

References

  1. 1 2 3 4 5 6 "M 7.9 – Kodiak Island region, Alaska". Earthquake Hazards Program. United States Geological Survey. Retrieved June 29, 2026.
  2. 1 2 3 4 5 6 7 8 9 10 11 Tape, Carl; Sykes, Lynn; Lomax, Anthony (2021). "The 1900 Mw 7.6–8.0 earthquake offshore of Kodiak Island, Alaska". Bulletin of the Seismological Society of America. 111 (2): 1080–1109. doi:10.1785/0120200273.
  3. 1 2 3 4 5 6 7 8 Brockman, Stanley R.; Espinosa, A. F.; Michael, J. A. (1988). Catalog of intensities and magnitudes for earthquakes in Alaska and the Aleutian Islands, 1786–1981 (Report). U.S. Geological Survey Bulletin. United States Geological Survey. doi:10.3133/b1840. Retrieved June 29, 2026.
  4. 1 2 3 4 5 6 Rozell, Ned (March 5, 2021). "Finding the great earthquake of 1900". Alaska Science Forum. Geophysical Institute, University of Alaska Fairbanks. Retrieved June 29, 2026.
  5. 1 2 3 4 "M 7.9 – Kodiak Island region, Alaska: Impact". Earthquake Hazards Program. United States Geological Survey. Retrieved June 29, 2026.
  6. ↑ "Earthquakes & Tsunamis". Popular Geology. Alaska Division of Geological & Geophysical Surveys. Retrieved June 29, 2026.
  7. ↑ "An Introduction to the Geology of the Aleutian Islands". NOAA Ocean Exploration. National Oceanic and Atmospheric Administration. Retrieved June 29, 2026.
  8. 1 2 Ramos, Marlon D.; Liberty, Lee M.; Haeussler, Peter J.; Humphreys, Robert John (2022). "Upper-plate structure and tsunamigenic faults near the Kodiak Islands, Alaska, USA". Geosphere. 18 (5): 1474–1491. doi:10.1130/GES02486.1. Retrieved June 29, 2026.
  9. ↑ Ryan, Holly F.; von Huene, Roland; Wells, Ray E.; Scholl, David W.; Kirby, Stephen; Draut, Amy E. (2012). History of earthquakes and tsunamis along the eastern Aleutian-Alaska megathrust, with implications for tsunami hazards in the California Continental Borderland (PDF) (Report). U.S. Geological Survey Professional Paper. United States Geological Survey. doi:10.3133/pp1795A. Retrieved June 29, 2026.

Further reading

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