We report on the modification of the optical and mechanical properties of a silicon 1D optomechanical crystal cavity due to thermo-optic effects in a high phonon/photon population regime. The cavity heats up due to light absorption in a way that shifts the optical modes towards longer wavelengths and the mechanical modes to lower frequencies. By combining the experimental optical results with finite-difference time-domain simulations, we establish a direct relation between the observed wavelength drift and the actual effective temperature increase of the cavity. By assuming that the Young's modulus decreases accordingly to the temperature increase, we find a good agreement between the mechanical mode drift predicted using a finite element method and the experimental one. ; Spanish projects TAPHOR MAT2012-31392 ; Navarro-Urrios, D.; Gomis-Bresco, J.; Capuj, NE.; Alzina, F.; Griol Barres, A.; Puerto García, D.; Martínez Abietar, AJ. (2014). Optical and mechanical mode tuning in an optomechanical crystal with light-induced thermal effects. Journal of Applied Physics. 116(9):93506-93510. doi:10.1063/1.4894623. ; Senia ; 93506 ; 93510 ; 116 ; 9