Bob;

The original Richter seismometer was a Wood-Anderson, a fairly low-gain device.

Todays WWSSS stations use Benioffs for the most part.

No, you don't use the same drum. There are at least 6 of them, 3 short-periods and 3 long-periods. mb will come from the short period vertical, Ms from the long periods.

Arrays can really complicate matters because they may have scores of identical instruments laid out in a pattern to facilitate directional detection (for example).

Amazing what you can learn here if you're willing to learn.

Roger