6C Recordings at Active Volcanoes

San Francisco (CA)

Near field recordings and thus finite source inversions of volcano-induced events often
suffer from unaccounted effects of local tilt, saturation of classical instrumentation,
unknown shallow velocity structure and doubtful orientation of the instruments. In addition,
if the station number is limited the results of moment tensor inversions are very often not
well constrained. Recent advances in hardware development made it possible to install
several very broadband, high sensitive rotational motion sensor, based on fibre optical
gyroscope technology, in very close distance of an activate volcano, i.e. on Stromboli
volcano in 2016 and 2018, respectively. Using this new instrument together with classical
instrumentation (i.e., translational seismometer, infra sound and tilt meter) we were able to
record four weeks of permanent strombolian activity at Stromboli during these two
experiments. The resulting six axis measurements reveal clear rotations around all three
coordinate axis. We are furthermore able to demonstrate how this six axis measurements
can help to improve the location procedure due to the property of a fiver optic gyro to act
as a physical wave polariser. We also demonstrate the application of a single site shallow
velocity estimation using volcanic background noise only, which will further improve the
reliability of the source mechanism estimate. As a concluding step we will demonstrate
how the use of sparse 6C measurement might be able to reduce the ambiguity of moment
tensor inversions of volcano related signals.