Tilt polarity

The raw data in volts are converted to mm and inspected for data quality. Increasing voltages always correspond to water-level up (ie the ground going down relative to the water surface).

Inflation of an offshore magma chamber will cause the tunnels to tilt down to the north. This results in the water rising in the northernmost sensors (see figure opposite). As a result graphs depicting North-South time series (or NW-SE etc) will rise as time progresses - ie increasing N-S tilt indicates inflation.

Tilt can be displayed as water level differences (shown here in mm) or as an angular rotation about an horizontal axis (in micro-radians normalized by water-pipe length). The differenced data are immune to water level changes caused by leaks or thermal expansion.

Twice each day the town of Pozzuoli is tilted down towards the Bay of Naples by the tidal loading of the Mediterranean. The peak to peak tilt 1 km from the shore measured by the 250 m N/S water pipe is roughly 0.5 mm. This large non-tectonic signal can be suppressed by sea level measurement followed by subsequent data processing.

Interruptions to the data can be caused by power failures and lightning strikes. An automatic alarm is emailed to a group of responsible scientists should power be interrupted.

 

Tilt data Pozzuoli

Data from a few days of data in August 2009 from the two tunnels transmitted via the Iridium satelite are shown here. Incoming data with a latency of 15 minutes to 2 hours may be viewed at

www.datagarrison.com, user <geo> password <hobo>

Calibrated 12-bit data in mm may be downloaded as numerical text listings of 30 minute averages with time in GMT. 16-bit data sampled once per minute are recorded by local data loggers for more detailed analysis.

North Tunnel

The six sensors in the north tunnel provide two measures of N/S tilt, each 120 m long, and three combinations in other azimuths with lengths of roughly 100 m. The data below are shown as water level differences in mm.

The figure below shows two weeks of data for three axes of tilt from six combinations of sensors. The upward trend indicates inflation of the offshore magma chamber, or coastal unloading caused by lowering of sea level.

South Tunnel

Six sensors here are linked to three independent water pipes. Two 70-m-long tiltmeters are parallel to each other and in a NW/SE direction. A third 15 m long tiltmeter measures NE/SW tilt. The following is an example of transmitted 12 bit data 30 minute averaged samples from the Iridium satellite link. Water level differences in mm.