Source: TEPCO

External event TEPCO response
1966 Fukushima Daiichi 1 nuclear power plant ordered Tsunami defences based on 1960 Chilean earthquake, water level +3.122m
Jul-01 Earthquake research promotion HQ releases long-term evaluation (hereafter, 'Contention of headquarters'. Japan Society of Civil Engineers (JSCE) considers it and adopts probabilistic evaluation method (but lacking data on past tsunami in the Fukushima prefecture-Oki region, there is no wave source model)
Feb-02 JSCE publishes 'Tsunami evaluation technology for nuclear power stations' Safety evaluation based on this is implemented. Countermeasures include raising pumps, drafting new procedures and making buildings watertight. Water level defences raised to +5.4-5.7m
2003-2005 JSCE considers the probabilistic evaluation method TEPCO follows JSCE's delilberations, and considers the method as well
Jul-06 JSCE summarises result of its considerations TEPCO implements a trial analysis with a probabilistic evaluation method, published at ICONE 14 conference
Sep-06 Regulatory guide for reviewing seismic design revised to include a clear description of safety risks of tsunami caused by earthquakes, and to include an instruction for back-check of earthquake resistance Earthquake resistance back-check assessment begins
Jul-07 Chuetsu-Okii earthquake strikes in Nigata prefecture
Mar-08 Interim earthquake resistance report submitted (excluding tsunami evaluations intended to be included in the final report)
April-October 08 Received draft dissertation about 869 AD Jogan tsunami by Dr Satake of National Institute of Advanced Industrial Science & Technology Preliminary calculation conducted against the Contention of headquarters. TEPCO requests that JSCE revise the wave source models and tsunami evaluation technology
Dec-08 TEPCO conducts preliminary calculations concerning the Jogan tsunami
Feb-09 Satake explains the Jogan tsunami research to NISA TEPCO requests JSCE to consider Jogan tsunami
Apr-09 Satake releases final dissertation (concluding that additional surveys were required to fix wave source models)
Jun-09 Joint working group points out mention of Jogan earthquake pointed out in discussion of TEPCO interim report
Jul-09 NISA evaluates interim back-check report, and concludes 'appropriate responses based on the results and achievement of Jogan tsunami investigation'
August-September 2009 Implements safety evaluation and takes necessary countermeasures based on Tsunami Evaluation Technology, considering latest ocean floor topography data and tidal wave level for final back-check report. Tsunami defences raised to: 5.4-6.1m
Nov-09 Tsunami sediment survey starts
Mar-10 Tsunami sediment survey ends
Jan-11 Dissertation about the results of the tsunami survey contributed to the Japan Geoscience Union; it found that no Jogan tsunami sediment was found in the south of Fukushima prefecture.
Mar-11 Report explained to NISA
Mar-11 Earthquake hits northeastern Japan off coast of Tohoku, causing tsunami more than 14m high