Inferring earth structure from combined measurements of rotational and translational ground motions

Abstract

We introduce a novel variant of seismic tomography that is based on colocated measurements of rotational and translational ground motions. Our aim is to assess whether rotations may be incorporated successfully into seismic inverse problems to produce better resolved and more realistic tomographic images. Our methodology is based on the definition of apparent S-wave speed as the ratio of rms velocity and rotation amplitudes. The principal advantages of this definition are that ͑1͒ no traveltimes measurements are needed and ͑2͒ the apparent S-wave speed is independent of source magnitude and source timing. We derive finite-frequency kernels for apparent S-wave speed by using a combination of the adjoint method and ray approximation. The properties of these kernels as a function of frequency bandwidth can be illustrated along with their usefulness for seismic tomography. In multifrequency synthetic inversions, we consider local crosshole tomography and regional-scale earthquake tomography.Our results indicate that S-wave speed variations can be retrieved accurately from colocated rotation and translation measurements, suggesting that our methodology is a promising extension of conventional seismic tomography. Further, apparent S-wave speed can be used to increase vertical resolution in teleseismic tomography for local structures.

Reducing nonuniqueness in finite source inversion using rotational ground motions

“…Their potential field of application is multifaceted and involves geophysical exploration, hazard assessment, and seismic engineering [e.g., Takeo, 1998;Wang et al, 2009;Stupazzini et al, 2009;Zembaty, 2009], as well as seismic tomography where the joint processing of translation and rotation data produces unique seismic observables with local sensitivities surrounding the receiver Bernauer et al, 2009Bernauer et al, , 2012b.…”

Can we estimate local Love wave dispersion properties from collocated amplitude measurements of translations and rotations?

“…Since overtones are always present, even for very shallow earthquakes, and separating them from the fundamental mode is very difficult [e.g., van Heijst and Woodhouse , 1997; Beucler et al , 2003; Visser et al , 2007], it seems rather unfeasible to use dispersion curves determined from amplitude ratios as reported here for structural inversion. Instead, an inversion based on the full waveforms as proposed by Bernauer et al [2009] might be a promising alternative.…”

“…[3] One possible application of rotation measurements is structural inversion based on collocated recordings from seismometers and rotation sensors Bernauer et al, 2009]. As has been shown in several previous studies [Igel et al, 2005;Cochard et al, 2006;Igel et al, 2007], waveforms of rotation rate around a vertical axis and transverse horizontal acceleration recorded at the same site show a high similarity in the Love wave part.…”

Global Imaging of the Earth's Deep Interior: Seismic Constraints on (An)isotropy, Density and Attenuation

“…Examples of the former include measurements of rotational ground motions (e.g. Ferreira & Igel, 2009), Bernauer et al, 2009, Earth tides (Latychev et al, 2009) and highly accurate long-period mode splitting . The design of targeted misfit functionals is based on the realization that not all parametrizations are equivalent.…”