I-MAG STS Corporation
One prevailing theory asserts that if two tectonic plates are strongly coupled, the stress along their
interface, which can be hundreds of miles long, increases dramatically with time. In particular,
Japan had wisely placed marine GPS sensors along the edge of the Pacific Plate. We do NOT know
how exactly TEPCO modeled the worst-case tsunami, although we are informed it was done using
internally developed software. This was apparently a conscious decision to exclude any earthquakes
older than 1896 on grounds the measurements were too inaccurate. We are not very convinced
mathematically that there is a significant difference if an event that would be measured today as 8.3
was recorded or estimated as a Richter 8.2 or an 8.4. One paper of interest is Minoura, K.; Imamura
F., Sugawara D., Kono Y. & Iwashita T. (2001). "The 869 Jōgan tsunami deposit and recurrence
interval of large-scale tsunami on the Pacific coast of northeast Japan".
Journal of Natural Disaster
Science
23 (2): 83–88. http://wwwsoc.nii.ac.jp/jsnds/contents/jnds/23_2_3.pdf. The city of Tagajō
(多賀城市) was almost completely destroyed by what was estimated to be an 8.6 Richter event. Sand
deposits indicate the tsunami flooded distances of about 2.5 miles inland. Another paper is Satake,
K.; Sawai, Y.; Shishikura, M.; Okamura, Y.; Namegaya, Y. & Yamaki, S. (2007). "Tsunami source of
the unusual AD 869 earthquake off Miyagi, Japan, inferred from tsunami deposits and numerical
simulation of inundation". American Geophysical Union, Fall Meeting 2007, abstract #T31G-03. http:
//adsabs.harvard.edu/abs/2007AGUFM.T31G..03S. And a third paper is Sawai, Y.; Fujii Y., Fujiwara
O., Kamataki T., Komatsubara J., Okamura Y., Satake K. & Shishikura M. (2008). "Marine incursions
of the past 1500 years and evidence of tsunamis at Suijin-numa, a coastal lake facing the Japan
Trench".
Holocene
18 (4): 517–528. Sawai
et alia identified at least two other major tsunamis and
explicitly predicted an 8.1 - 8.3 within 30 years. Alas, the reactors had already been built. It was
likely tempting to conclude that the reactors were high enough above the anticipated flood level, and
that there was a good chance the reactors would be retired before the next big tsunami came.