A Low Noise Model for Rotational Ground Motions

<p>The quantitative low/high noise models (L/HNM) for translational ground motions (e.g., Petersen 1993) based on many observations of acceleration power-spectral densities has been extremely successful for the evaluation of site quality, as well as the development of seismic sensors for passive experiments on Earth. No such L/HNM exists for rotational ground motions, primarily because 1) there are close to no direct sensors that measure below the Earth&#8217;s smallest rotational motions (large ring laser are currently the most sensitive instruments), and 2) small-scale seismic arrays can be used to derive rotational motions, but are limited in frequency range. A (even approximate) rotational L/HNM would be useful in particular for the development of new rotation sensors considering the numerous possible applications of 6 degree-of-freedom observations in terrestrial and planetary seismology as well as ocean bottom observations. As the terrestrial low-noise motion is primarily dominated by surface waves, the well-known connection between plane surface waves and rotational motions can be used to estimate rotational motions from classic seismometer records using local velocity information. We propose a methodology to derive a rotational L/HNM and support the model by ring laser and seismic array observations.</p>