Tsunami Hight H and Tsunami Magnitude Mt

                         September 26, 2003
                         by Abe, K.
                         ERI, Tokyo Univ. 

A tsunami magnitude Mt was estimated for
Tokachi-Oki, Hokkaido, Japan, tsunami of Sept
25, 2003 (UT).

A formula is Mt = log H + log X + 5.80
(Ref. Abe, K., PEPI, 27, 1981)
H: maximum amplitude on tide gage record in meter
X: epicentral distance in km

             H(max amp)  X    Mt
Urakawa      1.3         100  7.9
Kushiro      1.2         100  7.9
Nemuro       0.9         200  8.1
Hachinohe    1.0         250  8.2
Hakodate     0.8         260  8.1
Miyako       0.6         320  8.1
Kamaishi     0.5         360  8.1
Ofunato      0.2         390  7.7
Ayukawa      0.2         470  7.8
Onahama      0.2         620  7.9

The average from ten data is 7.98.  Thus Mt is <8.0>.
This value is close to Ms=8.0 and Mw=8.1 of the USGS
solution.  The Tokachi-Oki event is not a tsunami
earthquake.  The previous Tokachi-Oki event occurred
on March 4, 1952, and its Mt is 8.2.