IPOC Creep

IPOC Creep is an array of 11 creepmeters installed along 4 active segments oft eh Atacama Fault Zone in Northern Chile. Installation of instruments started in 2008 within the framework of the Integrated Plate-boundary Observatory Chile (IPOC) and was completed in 2011. All installations are designed by the authors and follow a general concept, but are adapted to each site specifically. All the installed instruments use solid 12 mm thick invar rods as length standards, which are firmly attached to a concrete foundation in the hanging wall of the fault and pass through a PVC pipe to the footwall side of the fault where it is fixed to another concrete foundation. 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 range of 50 mm to monitor the relative displacement of the free end of the rod relative to the fixation point. Displacement is measured as voltage change and stored on a data logger with a sampling rate of 1/min (2008-2011 and 2/min (since 2011). Temperature at the rod is continuously measured with the same sampling rate to correct for 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. More specific information on each site can be found on http://www.ipoc-network.org/index.php/observatory/creepmeter.html . The Data is stored as time series since the initial start of operation of each creepmeter until July 2016. Data format is asci and contains 4 columns: 1st column Date[D.M.Y] 2nd column Time [HH:MM:SS] 3rd column ReferenceSensor[V]The reference signal is a steady signal of 1V and fluctuations indicate general voltage fluctuations in the setup. By normalizing to the reference signal it is possible to correct for these voltage changes. 4th column CreepSensor[V]The measured voltage of the CreepSensor is linearly proportional to the actual displacement. It can be converted to micrometers as follows: Displacement(µm) = (CreepSensor(t2)[V] - CreepSensor(t1)[V]) * 10000.