...

ONC is purchasing two seismometer systems that will be deployed on the Endeavour Segment of the Juan de Fuca Ridge during the 2017 operations and maintenance cruise season. The instruments included in the CFI proposal “Biogeochemical monitoring of mid-ocean ridge axis processes using the NEPTUNE Canada cabled observatory” (Coogan, et al.). A cabled seismometer string with three sensors (70-100m separation) will be installed at the Main Endeavour Field (see map below) and a battery powered stand alone system (that is cable ready) will be installed at High Rise (south of the Regional Circulation North site).

Discussion

Following on from Giorgio’s email below, both the weak-motion velocity and weak-motion acceleration responses will be flat from 120 s to 200 Hz (within 3 dB). In fact, the acceleration response can reach DC, allowing you to resolve any long-period tilt, so this is possible depending on what signals you want to record. The main difference between the two responses is the level of gain (sensitivity) at different parts of the response spectrum.

Attached is a simple illustration that I recently made that describes the advantages of the velocity vs acceleration response in terms of the different monitoring applications that you may wish to use the Maris for.

For me, the decision of acceleration/velocity might depend on whether you are planning on co-locating the Maris installations with any other instrument (e.g. strong motion accelerometer). The velocity response will also be more susceptible to any long-period ocean / current / tidal noise.

Another factor to consider is the maximum size of signal that you wish to record – i.e. the clip level. If you could let us know what order of clip level you would like, then we can start to think about designing the optimum sensor sensitivity.

I hope this gives you a bit more background, but don’t hesitate to ask if you have further questions.