On the potential of recording earthquakes for global seismic tomography by low‐cost autonomous instruments in the oceans

Simons, Frederik J.; Nolet, Guust; Georgief, Paul; Babcock, J.; Regier, L. A.; Davis, Russ E

doi:10.1029/2008jb006088

Cited by 43 publications

(40 citation statements)

References 101 publications

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“…The intrinsic time-domain nature of the procedure is a benefit when forward and adjoint wavefield modeling is carried out using software such as the open-source spectralelement package SPECFEM (Komatitsch et al, 2005). Finally, as may become more important in the future, when field data will be analyzed, wavelets are an excellent nonlinear denoising tool (Donoho and Johnstone, 1994;Simons et al, 2009).…”

Section: Discussionmentioning

confidence: 99%

Multiscale adjoint waveform tomography for surface and body waves

2015

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International audienceWe have developed a wavelet-multiscale adjoint scheme for the elastic full-waveform inversion of seismic data, including body waves (BWs) and surface waves (SWs). We start the inversion on the SW portion of the seismograms. To avoid cycle skipping and reduce the dependence on the initial model of these dispersive waves, we commence by minimizing an envelope-based misfit function. Subsequently, we proceed to the minimization of a waveform-difference (WD) metric applied to the SWs only. After that, we fit BWs and SWs indiscriminately using a WD misfit metric. In each of these three steps, we guide the iterative inversion through a sequence of nested subspace projections in a wavelet basis. SW analysis preserves a wealth of near-surface features that would be lost in conventional BW tomography. We used a toy model to illustrate the dispersive and cycle-skipping behavior of the SWs, and to introduce the two ways by which we combat the nonlinearity of waveform inversions involving SWs. The first is the wavelet-based multiscale character of the method, and the second the envelope-based misfit function. Next, we used an industry synthetic model to perform realistic numerical experiments to further develop a strategy for SW and joint SW as well as BW tomography. The effect of incorrect density information on wave-speed inversions was also evaluated. We ultimately formalize a flexible scheme for full-waveform inversion based on adjoint methods that includes BWs and SWs, and also considers P- and S-wave speeds, as well as density. Our method is applicable to waveform inversion in exploration geophysics, geotechnical engineering, regional, and global seismology.Read More: http://library.seg.org/doi/10.1190/geo2014-0461.

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Section: Discussionmentioning

confidence: 99%

Multiscale adjoint waveform tomography for surface and body waves

2015

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“…Teleseismic P‐waves arriving at the ocean bottom are refracted into the water column and generate acoustic signals, which are of particular interest as their arrival times can be used in seismic tomography. Simons et al [2009] have proposed to use autonomous freely‐drifting underwater robots (called MERMAID, short for Mobile Earthquake Recording in Marine Areas by Independent Divers) equipped with hydrophones. By changing its buoyancy, the robot is able to dive to and remain at a certain depth.…”

Section: Introductionmentioning

confidence: 99%

Automatic discrimination of underwater acoustic signals generated by teleseismic P-waves: A probabilistic approach

Sukhovich

Irisson²,

Simons

et al. 2011

Geophys. Res. Lett.

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We propose a new probabilistic scheme for the automatic recognition of underwater acoustic signals generated by teleseismic P‐waves recorded by hydrophones in the ocean. The recognition of a given signal is based on the relative distribution of its power among different frequency bands. The signal's power distribution is compared with a statistical model developed by analyzing relative power distributions of many signals of the same origin and a numerical criterion is calculated, which can serve as a measure of the probability for the signal to belong to the statistical model. Our recognition scheme was applied to 6‐month‐long continuous records of seven ocean bottom hydrophones (OBH) deployed in the Ligurian Sea. A maximum of 94% of all detectable teleseismic P‐waves recorded during the deployment of the OBHs were recognized correctly with no false recognitions. The proposed recognition method will be implemented in autonomous underwater robots dedicated to detect and transmit acoustic signals generated by teleseismic P‐waves.

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“…Uncorrelated, additive Gaussian noise would be easy to remove using thresholded waveletdenoising techniques (e.g., Simons et al, 2009). On the other hand, jointly estimating and fully characterizing structural and signal-generated noise would be so involved that we continue to focus on the performance of the algorithm as applied to noise-free data for the sake of simplicity and brevity.…”

Section: Multiscale Seismogramsmentioning

confidence: 99%

Multiscale adjoint waveform-difference tomography using wavelets

Yuan

Simons

2014

GEOPHYSICS

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Full-waveform seismic inversions based on minimizing the distance between observed and predicted seismograms are, in principle, able to yield better-resolved earth models than those minimizing misfits derived from traveltimes alone. Adjoint-based methods provide an efficient way of calculating the gradient of the misfit function via a sequence of forward-modeling steps, which, using spectral-element codes, can be carried out in realistically complex media. Convergence and stability of full-waveform-difference adjoint schemes are greatly improved when data and synthetics are progressively presented to the algorithms in a constructive multiscale approximation using a (bi)orthogonal wavelet transform. Wavelets provide the nonredundant spectral decomposition that paves the way for the inversion to proceed successively from long-wavelength fitting to detailed exploration of the phases in the seismogram. The choice of wavelet class and type, the initial depth of the multiscale decomposition, and the minimization algorithms used at every level continue to play crucial roles in our procedure, but adequate choices can be made that test successfully on 2C elastic seismograms generated in toy models, as well as in the industry-standard 2D Marmousi model. Although for simplicity our inversion ignored surface waves by prior tapering and filtered removal, those also appeared to be very well matched in the final model.

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On the potential of recording earthquakes for global seismic tomography by low‐cost autonomous instruments in the oceans

Cited by 43 publications

References 101 publications

Multiscale adjoint waveform tomography for surface and body waves

Multiscale adjoint waveform tomography for surface and body waves

Automatic discrimination of underwater acoustic signals generated by teleseismic P-waves: A probabilistic approach

Multiscale adjoint waveform-difference tomography using wavelets

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