Regional moment tensor inversion using rotational observations

There are potential benefits from the addition of 3-C rotational motions to traditional 3-C translational displacements for moment tensor (MT) inversions. The rotational radiation pattern is orthogonal to the shear radiation pattern, thus incorporating rotations is equivalent to gaining another observation point on the focal sphere. We demonstrate this by simulating the curl and displacement wavefields in a half-space for a regional distance station. We also demonstrate the effect of velocity gradients beneath a station on rotational motions compared to displacements. Further investigation is needed to study how this affects the MT inversion. We added rotational Greens functions to regional long-period MT inversion computing spatial gradients from f- k reflectivity synthetics. We used array derived rotational motions from the Piñon Flats Observatory Array in California and Golay arrays deployed during the IRIS Community Wavefield Demonstration Experiment in Oklahoma. Well-constrained MT solutions were estimated for three earthquakes using long-period regional waves with and without rotational ground motions as test cases. Prepared by LLNL under Contract DE-AC52-07NA27344.