Follow-up question. I understand how Richter Scale + depth could be useful, academically. But when communicating with the public, wouldn't it be easier to have a single number - rather than requiring the public to understand the relationship between two different quantities? Maybe: surface-equivalent Richter scale?
Of course transitioning to a new standard would be even more confusing for a while.
In Japan for domestic quakes they always report the Shindo scale (based on surface peak ground acceleration) instead of Magnitude. It’s way more useful a measure IMHO and whenever I see western news report use M it tells me nothing about how bad the quake actually was.
This is why the Shindo scale is favoured in Japan, as it addresses the effects on people and buildings in a particular area, so you can tell just by looking at what is shaking and how much to get an idea of the strength. The worst part of experiencing an earthquake, for me, is realising that anything can happen in the next moments, otherwise it's weirdly normal.
That's exactly how the shindo scale is reported in Japan. They assign a number to every major city on a map, just like temperatures in a weather forecast.
For example, January's big quake was 7 in Ishikawa, but only 2-3 in the Tokyo area.
Of course transitioning to a new standard would be even more confusing for a while.
Edit: apparently there are many different scales in wide use already. https://en.wikipedia.org/wiki/Seismic_magnitude_scales