These accelerometers weren't defective, they were on bad locations. It's funny that they think bedrock might be bad as well. That's the trouble with classic accelerometers, they are never used until the big earthquake, and you can never tell if the location is good. Since I had such bad experience with these things, I always insisted on wide-range broadband seismometers, which you could calibrate for site effects. Seismic intensity for housing could then be calculated using standard amplification techniques.