Here is a photo of my roughly half size rip off of a Sprengnether seismometer. Unlike the original, this instrument uses an lvdt as the sensor. That's a six inch scale in the foreground.

Also, here is a link to the paper that I presented in 2005 about using crossed flexures as pivots for a seismometer.
http://www.aspe.net/publications/Annual_2005/PAPERS/5FLEX/1859.PDF