Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

Study of Historical Earthquakes in Japan 287Table 2. Comparison of Large Earthquakes Off the Coast of Northeastern JapanType Date d M Number of felt aftershocks Rem.year.mo.da (OE) (ON) Tokyo Ha Mo Mi S F 0 N H Hn A(a,) (b.12 1896.06.15 144 393 6.8 (1) 0 62 95 (1)4 1897.02.20 141.9 38.1 7.4 0 (2)4 1897.08.05 143.3 38.1 7.6 2+(1) 1+(3)4 1915.11.01 142.9 38.3 7.5 1+(1) (4) (2)3 1933.03.03 144.7 39.1 8.3 1 0 29 17 3 14 3 (3)5 1938.05.23 141.4 36.7 7.1 1 3 6 5 12 5 21 23 (4)5 1938.11.05 141.7 37.1 7.7 12 8 16 26 29 77 164 91 (5)1793.02.17 142.4 38.3 7.1 2 70 ? 69 170 184 (6)(a.) = within 7 days after the main shock; (b.) = 8 to 30 days after the main shock.Ha = Hachinohe; Mo = Morioka; Mi = Miyako; S = Sendai; F = Fukushima; 0 = Onahams;N = Nakamura; H = Hazama-machi; Hn = Hanamaki; A = Aomori.Parentheses in columns (a.) and (b.) indicate epicenter is not certain, but consideredas aftershock by the present author.Remarks: (1) = felt aftershock in June; (2) = felt earthquake in November; (3) = all feltearthquakes in March; (4) = all felt earthquakes in May and June; (5) = felt earthquakein November; (6) = felt earthquake within one week after the main shock.Table 3. Comparison Between 1793 Kansei Earthquake and Other TypicalEarthquakes Occurring off the Coast of Northeastern JapanType Typical earthquake referred Tsunami Distribution Number ofof intensity aftershocksEdo General1 Off Tokachi earthquake X X X 0(1677, 1763, 1856)2 Off Sanriku earthquake(reverse type, 1896)0 Q' X 03 Off Sanriku earthquake 0 0 X X(normal type, 1933)4 Off Miyagi Pref. earthquake X 0 X X(1897-1, 1897-2, 1915)5 Off F'ukushima Pref.earthquake (1938)X (> X 0Type = classification due to epicentral area and fault movement. Edo = former namefor Tokyo. Similarity to 1793 Kansei earthquake: 0 = good; C, = moderate; X = bad.(*) = isoseismal is aimilar, but the value of intensity is different.from Table 4 that reverse type earthquakes take place 30-40 years after a type 1event, therefore the next reverse fault type earthquake may take place circa theyear 2000. The interval between earthquakes is longer when the energy release bythe previous earthquake is large, and is average (about 100 years), when the energyrelease by the previous one is average. So, the prediction of the year for the nextoff-Sanriku earthquake of reverse type depends upon the estimation of the releasedenergy by the 1896 earthquake.