Creepmeter at IPOC

All the installed instruments use 12 mm thick invar rods as length standards, which are firmly attached to a concrete foundation on one side of the fault and pass through a PVC pipe to the far side of the fault. The creepmeters are buried at a depth of 30 - 70 cm, in order to increase the signal-to-noise ratio. We use a LVDT (linear variable differential transformer) with a linear range of 50mm to monitor the relative displacement of the free end of the rod relative to the fixation point. Displacement is converted to voltage change and stored on a data logger with a sampling rate of 2/min. The temperature at the rod is also continuously measured with the same sampling rate but we store only an average of 10 min to decrease the data volume and correct the thermal expansion and contraction of the length standard. The length of the instrument is dependent on the geometry at each site and ranges between 2 and 9 m. One station per target fault is also equipped with a weather station to control effects of humidity and air pressure changes. The time of each data logger is synchronised via GPS automatically. All instruments are equipped with an Inmarsat/BGAN satellite link and data is sent to the GFZ ftp server every third day.

Collocated with three of the creepmeters, we operate broadband seismometers to investigate triggered displacement events. The CHO1 site is equipped with seismometer CHOM (Guralp CMG-3ESP, sampling frequency 100Hz) since 2011 (collaboration with Monika Sobiesiak). CAR3 is equipped with a Trillium seismometer (sampling frequency 100 Hz) since 2014. MEJ3 is equipped with a Trillium seismometer (sampling frequency 100Hz) since 2017 (collaboration with Pablo Salazar, UCN).