Earthquake Measurements

Ok I've just learned something new this morning. I learned that in Japan they measure quakes on a. Scale of 1 to 7. This latest big one was a 6 on their scale.

Since the US doesn't use the richter scale for it's official measurement any more (not since the 1989 quake in San Francisco, CA). The popular theory for this is because if there is a quake in the USA 7.0 or larger, the US government has to pay for ALL damages. This is why we in the USA, will never see a 7.0 or larger quake in large populated areas.

I have seen (shortly after the quake) the actual richter scale ratings by zip code of the Northridge, CA quake in 1994. They ranged from 7's to 8.5's to a 9 in a couple zip codes in the valley.

Since the new US measurements take a larger area into account, the magnitude is reduced dramatically. It only stands to reason that if there is ever a 7.0 or bigger (in a large population area) in the USA, the scale will once again be adjusted to reduce it below 7.0 again.

My question today is this, if Japan rated their quake at a 6 on their scale, and the news media is reporting it as a 9.0. What is the real richter scale rating of this quake?

Again, these are just my thoughts.
Bret