A Multicomponent Large Ringlaser for Seismology: First Observations

During 2016 a large 4-component ring laser structure called "Romy" was built and implemented underground in the Geophysical Observatory of the Ludwig-Maximilians-University (LMU) 20km outside Munich primarily funded by the European Research Council and LMU. The ring laser has a tetrahedral top-down shape with four triangles of 12m side length. The independent triangular He-Ne ring lasers with 12 m side length are expected to resolve rotational motions down to 12 prad/s/sqrt(Hz), allowing us to record below the assumed low-noise model for rotational ground motions in a wide frequency band (e.g., ocean-generated noise, free oscillations, local regional and global earthquakes). Recently, Romy was described in a feature article in Science (Hand, DOI: 10.1126/science.aal1069). We will present the current state of the instrument and discuss the operation principle and quality of the ring laser components. First observations include the ocean-generated noise, the late 2016 earthquake sequence of Italy, and several teleseismic events. We compare ring laser observations from different sites (Gran Sasso Underground Laboratory, Italy, and G-ring Wettzell, Germany) in relation with their local site conditions. We report on future plans to stabilize the ring geometry providing long-term stability for geodetic applications such as the precise measurement of the Earth's complete rotation vector.