Auxiliary material for Paper 2011GCGC003592 Structure and serpentinization of the subducting Cocos plate offshore Nicaragua and Costa Rica H.J.A. Van Avendonk Jackson School of Geosciences, University of Texas Institute for Geophysics, Austin, Texas, USA W.S. Holbrook Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, USA D. Lizarralde Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA P. Denyer Escuela Centroamericana de Geologia, University of Costa Rica, San Pedro, Costa Rica Van Avendonk, H. J. A., W. S. Holbrook, D. Lizarralde, and P. Denyer (2011), Structure and serpentinization of the subducting Cocos plate offshore Nicaragua and Costa Rica, Geochem. Geophys. Geosyst., 12, Q06009, doi:10.1029/2011GC003592. Introduction: The Auxiliary Material to Paper 2011GCGC003592 consists of one PDF document. This material consists of additional calculations and figures that support the conclusions of the paper. The methods used in these analyses are explained in Section 4 of Paper 2011GCGC003592. 1.2011gc003592-txts01.pdf The auxiliary material is divided in two sections. Section 1 is a display of eleven ray-tracing diagrams and data panels for individual OBSs on transect SERP. These figures are labeled S1 to S11. Section 2 illustrates parts of the model covariance matrix that is derived from the inversion of seismic refraction data. The covariance matrix gives us an estimate of uncertainties in the model parameters. These uncertainties are shown in Figure S12.