Six Axis Measurements at Kilauea – More Riddles to Be Solved?

Date: 4/26/2019

Time: 11:15 AM

Room: Puget Sound

Near field recordings and thus finite source inversions of large earthquakes and volcano-induced events very often suffer from unaccounted effects of local tilt, saturation of classical instrumentation, unknown shallow velocity structure and doubtful orientation of the instruments. Recent advances in hardware and software development made it possible to install a very broadband, high sensitive rotational motion sensor based on fibre optical gyroscope technology in very close distance of only two kilometres to the area of activate slumping at the Halema’uma’u pit of Kilauea's summit apparatus. Using this new instrument together with permanent deployed classical instrumentation (i.e., translational seismometer. accelerometer and tilt meter) we were able to record three magnitude Mw5 earthquakes during the 2018 Kilauea summit eruption. The resulting six axis measurement reveals clear rotations around all three coordinate axis. Outstanding is hereby the observation of rotation around the vertical axis, a motion which will not be detectable using classical instrumentation only. We are furthermore able to demonstrate how this six axis measurements can help to improve the location procedure due to its property 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 further will improve the estimation of the source mechanism.

In parts the surprisingly clear static rotations and translations can be verified by simulations using computed moment tensor solution inverted from the local to regional network data as well as with data from a local installed borehole tilt meter. Discrepancies between classical instrumentation can be explained in parts by the near field observation of a finite source and very localised near fault effects.

Presenting Author: Joachim M. Wassermann

Authors