## 1 Introduction  
As a tram travels, sets of vibrations occur, which are transmitted to the bedrock. The intensity of these vibrations depends on the type and age of trans in operation, the structure and condition of the roadbed, the local geological composition, and distance from the railway yard. Vibrations formed in this way can have an adverse effect on the surrounding structures, people living near these structures, and on the technologies situated in them. Experimental measurements are therefore necessary in order to obtain data that represent such vibrations. To implement seismic measurements using standard seismic stations, a method using a fiber optic interferometer may serve as an alternative. Fiber-optic interferometers (such as Mach-Zehnder, Sagnac, Michelson, or Fabry-Perot) are well known for their ability to make high-precision measurements of optical path differences or changes induced by a refractive index change in the interferometer or physical displacement [1]. The inherent advantages of fiber-optic interferometers are their small size, electrical passivity, immunity to electromagnetic interference (EMI), and low attenuation (which allows the measuring point to be separated from the point of evaluation). Electrical and electromagnetic sensors currently used to monitor rail transport have problems with reliability in their function. A primary reason for this reduced reliability is the new traction drives of rail vehicles, which generate electromagnetic interference and signal contamination caused by the traction return current in rails. Another problem with electrical detection systems is low resistance to the effect of or damage from atmospheric discharge. In devices with metallic connections, undesirable conductive loops are closed over these electrically-conductive circuits, which are very hard to treat [2; 3]. By using the proposed fiber-optic interferometric sensor, which is designed with regard to materials characterized by EMI, these problems can be eliminated. This article focuses, except the innovative detection of passing tram rail vehicles, on the partial comparison of the original data obtained during experimental measurements of the dynamic response of the rock mass beneath the railway rolling stock using both mentioned methods. Monitoring the effect of vibrations, i.e., maximum amplitudes and frequencies, is highly important due to their effect both on building structures and humans. Vibrations from the source are spread via the rock mass and attenuated depending on increasing distance. Vibrations in near-surface sediments can be strengthened; resonant vibrations are caused in the near-surface layer, and the duration of vibrations is prolonged because of freely-vibrating near-surface sediments. Frequencies themselves then play a highly important role in potential structural damage to buildings, especially if the resonance of an object's frequency and the frequency of the load source is achieved. The long-term effect of vibrations on buildings may include the formation of cracks in plaster and masonry or other defects. The scope of the maximum amplitudes and frequencies of measured values are defined for railway transport in ISO 4866:2010 [4]:  
* maximum range of shifts: 1-200 \(\upmu\)m,
* maximum range of vibration speed amplitude: 0.2-50 mm\(\cdot\)s\({}^{-1}\),
* maximum range of acceleration amplitude: 0.02-1 m\(\cdot\)s\({}^{-2}\),
* frequency range: 1-80 Hz. Seismic stations [5; 6; 7] made by recognized companies come equipped with speed and acceleration sensors and are commonly used to measure the effect of vibrations or to detect rail vehicles. Time records are generated showing the passing of a vehicle. Frequency spectra are subsequently calculated in the relevant software. The cost of these devices is often in the thousands of U.S. dollars [8; 9; 10]. This study used a Gaia 2T apparatus with ViGeo2 seismic sensor station as a reference seismic station to an interferometric sensor.