@article {Dagnino2014,
	title = {{Scale- and parameter-adaptive model-based gradient pre-conditioner for elastic full-waveform inversion}},
	journal = {Geophysical Journal International},
	volume = {198},
	number = {2},
	year = {2014},
	month = {jun},
	pages = {1130{\textendash}1142},
	publisher = {Oxford University Press},
	abstract = {We present a scale- and parameter-adaptive method to pre-condition the gradient of the parameters to be inverted in time-domain 2-D elastic full-waveform inversion (FWI). The proposed technique, which relies on a change of variables of the model parameters, allows to balance the value of the gradient of the Lam{\'e} parameters and density throughout the model in each step of the multiscale inversion. The main difference compared to existing gradient pre-conditioners is that the variables are automatically selected based on a least squares minimization criteria of the gradient weight, which corresponds to the product of the gradient by a power of the parameter to be inverted. Based on numerical tests made with (1) a modified version of the Marmousi-2 model, and (2) a high-velocity and density local anomaly model, we illustrate that the value of the power helps to balance the gradient throughout the model. In addition, we show that a particular value exists for each parameter that optimizes the inversion results in terms of accuracy and efficiency. For the two models, the optimal power is \~{}2.0-2.5 and and \~{}1.5 for the first and second Lam{\'e} parameters, respectively; and between 3 and 6, depending on the inverted frequency, for density. These power values provide the fastest and most accurate inversion results for the three parameters in the framework of multiscale and multishooting FWI using three different optimization schemes. {\textcopyright} The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.},
	keywords = {Computational seismology, Inverse theory, Numerical approximations and analysis, Seismic tomography},
	issn = {0956-540X},
	doi = {10.1093/gji/ggu175},
	url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84903949166\&partnerID=tZOtx3y1},
	author = {Dagnino, D. and Sallar{\`e}s, V. and Ranero, C. R.}
}
@article {Mel{\'e}ndez2013243,
	title = {{Origin of water layer multiple phases with anomalously high amplitude in near-seafloor wide-angle seismic recordings}},
	journal = {Geophysical Journal International},
	volume = {196},
	number = {1},
	year = {2013},
	pages = {243{\textendash}252},
	abstract = {Water layer multiple seismic phases are recorded at ocean bottom seismometers and hydrophones as arrivals that correspond to the reflection of the primary phases at the sea-free air interface. In regions of low to moderate seabed relief, the shape of these phases mimics that of the primary phases with a traveltime delay that depends on the water layer thickness at the receiver location. Given their longer travel paths, multiple phases should have smaller amplitudes than their corresponding primary phases. However, depending on the geological context it can be relatively common to observe the opposite, which results in the identification of the multiple phases at longer offsets than the primary events. In this paper, we examine the origin of this apparently paradoxical phenomenon by analysing the combined effect of the major factors potentially involved: the source frequency content, the subsurface velocity distribution, the receiver-seafloor distance, the geometrical spreading and attenuation of sound waves and the ambient noise level.We use synthetic modelling to show that for certain combinations of these factors, the interference between the multiple and its reflection at the seafloor is constructive and has a higher amplitude than the primary wave. Our analysis indicates that in the most favourable cases the phases resulting from this interference can be observed at offsets some tens of kilometres longer than their corresponding primary phases, and thus they can provide useful information for velocity modelling. {\textcopyright} The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.},
	keywords = {ambient noise, Controlled source seismology, Controlled-source seismologies, Earthquake effects, Geometrical spread, hydrophone, Numerical approximations and analysis, numerical method, ocea, Seismology, Site effects, Wave propagation},
	issn = {0956540X},
	doi = {10.1093/gji/ggt391},
	url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-84890885715\&partnerID=tZOtx3y1 http://www.scopus.com/inward/record.url?eid=2-s2.0-84890885715\&partnerID=40\&md5=a3729b5c20fafb9373a2a82c94b34990},
	author = {Mel{\'e}ndez, A.a and Sallar{\`e}s, V.a and Ranero, C.R.b R. and Kormann, J.c and Mel{\'e}ndez, A. and Sallar{\`e}s, V.}
}
