We manage in the Institut Cartografic and Geologic de Catalunya a BB network with 20 stations in Catalonia (NE Spain). Our experience with sensors CMG3-T and STS-2 is correct. Both have a nice BB response and technically they are very performant. Unfortunately Guralp Company, does not offer a correct maintenance service: not serious, very late answers...really very bad. Streikheisen and Nanometrics companies offer nice services.

Hi Xavier and Maximiliano.

I also work with Guralp systems. Recently I have purchased a CMG-6TD model for a total amount of 12000 euros. It is impossible to purchase other seismometer with digitizer integrated, with these characteristics, for this cost. Is a 30 s to 100 Hz seismometer with 8 Gb flash memory, GPS antenna, and wi-fi antenna integrated, among other accessories.

I agree with Xavier concerning the Spanish maintenance service. From some years ago I directly contact with Guralp, not with distributors.

STS2 are good

There are many options among BB seismometers these days. We have a few different types in our department including STS-2's (which are fantastic, but expensive). We also have a variety of Guralp sensors (3T, 3ESP, 40T, 6TD, etc.) and Trilliums (T120 and T240). Reftek also makes a BB sensor (RT151), which seems very good. Metrozet also makes BB seismometers, but I have no direct experience with them. Of all of the ones that I am familiar with I think the Trillium is the best combination of robustness, performance and cost. We have not had great luck with the 3T's. They might work fine in an observatory setting, but they don't seem to travel well. Ours have been broken more than they have been working.

Jose is correct that the 6TD is unusual in being the only BB seismometer in its price range that includes a digitizer, but it doesn't compare to a Trillium, STS2 or RT151 for signal to noise ratio, nor for long period performance.