The development in society means that infrastructure like ballasted railway systems is facing challenges due to requests for a increased number of high-speed trains and heavier freight trains. This implies that ballasted railways get an increased impact from larger dynamic loads. The question is how the ballasted railways are today affected by dynamic loading and how will an increase in train speed and weight change the soil behavior within the railway embankment. A method of investigating soil behavior is via geophysical measurements. Accelerometers are commonly used for vibration measurements and by installing them on trains, measurements are possible to perform for complete railway sections. The knowledge of Eigen frequencies for various track components and soil layers are essential when considering frequency analysis of accelerometer measurements. Specifically, this means that the analysis is about detecting resonance of different components. From the actual case study, a good correlation is obtained between the expected Eigen frequencies and the measurement results. Thus, an assessment of the dynamic loadings influences on various soil layers and ballast has been possible to perform. Resonance of a soil layer means that the particles will be rearranged and degraded. For the case when saturated soil layers are subjected to resonance a phenomenon called liquefaction can occur if the pore pressures increases to the level were soil layers lose their effective stresses. Therefore, the most critical finding in this study is liquefaction because it leads to a loss in bearing capacity followed by settlements. Old railway tracks where little or no information exists of the soil conditions are the most suitable areas were this measurement and analysis method is of special use. Consequently, conventional borehole sampling can be reduced.