Roger, I had to do a double take on that Sea of Japan earthquake as I had not
remembered it. I checked with PDE listings, they have it as M 6.5 (PAS) and
Mb 6.2 (PDE). After further check, however I found that JMA did list it as a MJ 7.7.
It is not listed in the Pachecho-Sykes Moment magnitude catalog, so I could not confirm
that, so I will accept that it may have been that large. I think the confusion comes
from the great depth - about 600 km of this event. It is often difficult to get good
magnitudes for deep earthquakes. The only other event of about the same size
(M given between 7.6 and 7.8) was an earthquake on June 29, 1898 in the Near Islands
(Aleutians).
It just seemed odd to me that only one large event had been recorded on the
29th of June so curiosity got the best of me.
By the way, for American readers, the largest earthquake within Yellowstone
National Park (Ms 6.1) occurred on June 30, 1975, two days after the Sea of
Japan quake cited by Roger. The Hebgen Lake earthquake of Aug. 18, 1959 (Mw
7.7) actually had it's epicenter outside the Park.