Friday, March 11, 2011

Great Cascadia Earthquake of 1700 M9.0

Yesterday's humongous earthquake in Japan is already listed in Wikipedia as the 7th biggest earthquake, based on its Magnitude of 8.9. Wow! I was drawn to #6, Great Cascadia Earthquake, as it was on the North American Continent---the home continent, with a Magnitude of 9.0.

The date and time of the Great Cascadia Earthquake in Oregon, Washington, and BC, was reconstructed by several methods. In particular, detailed Japanese descriptions/records of a Tsunami in the year 1700 made it possible, four hundred years later, to reconstruct the time of the Great Cascadia Earthquake. They arrived at an estimate of the evening (about 21:00 local time) of 26 January 1700. The paper is unavailable to download, as it is published in the journal Nature:
K Satake, K Shimazaki, Y Tsuji, K Ueda. Time and size of a giant earthquake in Cascadia inferred from Japanese tsunami records of January 1700. Nature 379, 246-249 (1996).

The Abstract:

GEOLOGICAL evidence shows that great earthquakes have occurred in the recent prehistoric past in the Cascadia subduction zone, off the Pacific coast of North America. The most recent event (or series of events) is dated at about 300 years ago, but the precise date and magnitude have not been determined. Geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4, although this information is important for the assessment of future hazard. We have found several tsunami records in Japan from AD 1700 with no indication of a local cause. Historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in South America, Alaska or Kamchatka, leaving Cascadia as the most likely source of this tsunami. The estimated time of the earthquake is the evening (about 21:00 local time) of 26 January 1700. The magnitude is estimated as 9 from the tsunami heights, in which case the earthquake ruptured the entire length of the Cascadia subduction zone2. These estimates are consistent with Native American legends that an earthquake occurred on a winter night.

A review is found in html:here.

Tree ring studies (including one by Yamaguchi et al. have also corroborated the 1700 date. And on Google Scholar one notes several studies of sediment layering in estuaries along the Oregon Coast.

I am particularly drawn to the paper by Ludwin et al.: an estimate--perhaps not as accurate as the above, but more fun to read---from pacific Northwest native stories: Downloadable here. From an analysis of Native Stories (accounts including oral remembrances of great grandchildren) they arrived at a close estimate, as referenced by Satake et al.:

The stories were told between 1860 and 1964. Figure 2 tabulates the accounts
and gives estimated date ranges. Date range minima and maxima are 1400 and 1825. All estimates span the interval between 1690 and 1715, and the average value of the mid-points of the date ranges is 1690. Discarding the earliest and latest midpoints yields an average midpoint date of 1701. This is remarkably consistent with the 1700 date of the most recent CSZ earthquake.

Here is a list of the historical 24 earthquakes of highest magnitude,
from Wikipedia. Notice that on the very day of the 7th Earthquake,
this was added to the Wikipedia record.

1May 22, 1960Valdivia, Chile1960 Valdivia earthquake9.5
2March 27, 1964Prince William Sound, USA1964 Alaska earthquake9.2
3December 26, 2004Sumatra, Indonesia2004 Indian Ocean earthquake9.1
4November 4, 1952Kamchatka, Russia (then USSR)Kamchatka earthquakes9.0 1
5August 13, 1868Arica, Chile (then Peru)1868 Arica earthquake9.0 2
6January 26, 1700Pacific Ocean, Japan and USA and Canada1700 Cascadia earthquake9.03
7March 11, 2011Sendai, Japan2011 Sendai earthquake8.94
8February 27, 2010Maule, Chile2010 Chile earthquake8.8
9January 31, 1906Ecuador–Colombia1906 Ecuador-Colombia earthquake8.8
10November 25, 1833Sumatra, Indonesia1833 Sumatra earthquake8.8
11February 4, 1965Rat Islands, Alaska, USA1965 Rat Islands earthquake8.7
12November 1, 1755Lisbon, Portugal1755 Lisbon earthquake8.7 5
13July 8, 1730Valparaiso, Chile1730 Valparaiso earthquake8.7 6
14March 28, 2005Sumatra, Indonesia2005 Sumatra earthquake8.6
15March 9, 1957Andreanof Islands, Alaska, USA1957 Andreanof Islands earthquake8.6
16August 15, 1950Assam, India – Tibet, China1950 Medog earthquake8.6
17September 12, 2007Sumatra, IndonesiaSeptember 2007 Sumatra earthquakes8.5
18October 13, 1963Kuril Islands, Russia (USSR)1963 Kuril Islands earthquake8.5 7
19February 1, 1938Banda Sea, Indonesia (Dutch East Indies)1938 Banda Sea earthquake8.5
20February 3, 1923Kamchatka, Russia (USSR)Kamchatka earthquakes8.5 7
21November 11, 1922Atacama Region, Chile1922 Vallenar earthquake8.5 8
22May 24, 1751Concepción, Chile (Kingdom of Chile)1751 Concepción earthquake8.5
23October 20, 1687Lima, Peru (Viceroyalty of Peru)1687 Peru earthquake8.5
24December 16, 1575Valdivia, Chile (Kingdom of Chile)1575 Valdivia earthquake8.5

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