Gas production in the Groningen gas field has led to human-induced seismicity. To better understand the potential hazards resulting from future subsurface activities, such as geothermal energy production or underground CO2 storage, numerical modeling is of interest. One area that demands special attention is the shallow subsurface. This region influences hazard strongly, as the amplitude of a seismic wave increases when it transitions from stiff materials deep in the earth into compliant, uncompacted soils near the surface. However, accurately modeling this region is challenging. The lateral resolution of the model should be sufficient to capture the variety in soil types. In addition, uncompacted soil is best modeled as a poro-elastic continuum, rather than purely elastic. Despite these challenges, computational effort must remain limited to allow for stochastic simulations. To accomplish this, Isogeometric Analysis (IGA) is a promising discretization method. It has been reported that, for poro-elasticity, IGA enables local mass conservation [1] and reduces numerical oscillations [2]. For our purpose of modeling wave propagation, IGA presents another potential benefit. In the literature, it has been observed that higher-order Finite Elements (FE) exhibit spurious ”optical” eigenmodes for elasticity problems, while the spectra resulting from higher-order discretizations using splines do not [3]. Thus, higher-order IGA-models can capture a certain range of frequencies using fewer degrees of freedom than than an FE model. Our study focuses on assessing whether this extends to poro-elastic continua. We expect to report on the frequency spectrum of a poro-elastic material, discretized through IGA. This spectrum should contain no optical modes, and display the fast pressure wave, slow pressure wave and the shear wave typical of poro-elasticity [4]. REFERENCES [1] F. Irzal, J.J.C. Remmers, C.V. Verhoosel, R. de Borst, Isogeometric finite element analysis of poroelasticity. Int. J. Numer. Anal. Meth. Geomech. (2013) 37(12), 1891-1907 [2] Y.W. Bekele, E. Fonn, T. Kvamsdal, A.M. Kvarving, S. Nordal, Mixed Method for Iso- geometric Analysis of Coupled Flow and Deformation in Poroelastic Media. Appl. Sci. (2022) 12(6): 2915. [3] J.A. Cottrell, A. Reali, Y. Bazilevs, T.J.R. Hughes, Isogeometric analysis of structural vibrations. Computer Methods in Applied Mechanics and Engineering. (2006) 195(41- 43): 5257-5296. [4] D.M. Smeulders, Experimental Evidence for Slo