Determination of the velocity of seismic waves for the location of seismic station of Zatriq, Kosovo

1 Introduction

The experience from the last earthquake that took place in the surrounding of Istog in March 2010 has shown that expansion of the network for detailed monitoring of the local seismic activity needs to be installed in Kosovo. One of the secondary seismic stations is that of Zatriq.

It is important to fulfill certain conditions on obtaining of high-quality records of seismic waves and defining of earthquake parameters [1–5]. This is necessary for high-quality seismological data in seismology and the earthquake engineering. The accuracy of the earthquake parameters, the hypo central depth, the hypo central time, and the geographical coordinates of the epicenter, depend on a number of factors:

• The model includes: the geometry of the layers, their physical characteristics (velocity of the seismic waves, the density of matter), the homogeneity, or the inhomogeneity and alike.

• The geometrical distribution of the locations of the seismological stations.

• The quality of the installed seismological equipment.

• The geotechnical characteristics of the locations where the seismological stations are installed.

• The spectral components of the seismic tremor at the selected locations.

In addition to the criteria for the selection of locations for the installation of seismological stations, such as choice of network geometry, natural conditions, seismic characteristics, seismic vibrations, relief, climatic conditions, conditions for the realization of works, the possibility of purchasing the land to be used, conditions for electricity supply, and ensuring telecommunication conditions for uninterrupted data transfer are also the criterion for determining the speed of seismic waves [6–10]. Considering the above, the configuration, i.e., the geometry of the network of seismological stations in Kosovo should be carefully selected. The stations should also be located in the vicinity of clearly differentiated epicentral areas as well as in areas of intersection of tectonic structures where there has not yet been significant seismic activity [11–17]. It should also be mentioned that the operation of the seismological network will contribute to obtain deeper knowledge about the seismic risk both for the entire territory of Kosovo and for local areas that are of particular importance and for which micro-zoning should be done. The planned seismological station covers the geological media of the main geotectonic units and the main neotectonic structures in the territory of Kosovo. Exploring the data on the recorded earthquakes should provide an answer about the relation between the seismic activity of the foci and the tectonic structures in the Kosovo territory.

2 Methods

Seismic refraction method is applied to determine the velocities of seismic P and S waves and definition of the thickness of the surface cover and the method of seismic reflection to define the local structural-tectonic structure and the boundaries of the subsurface geological media from which microseismic vibration and seismic noise could be generated.

Seismic refraction and reflection methods are realized through:

• Seismograph Geotech12-channel seismic digital.

• Vertical and horizontal geophones with natural frequency of 12 and 26 Hz.

• Hammer with a mass of 8 kg for signal excitation.

Analytical analysis and interpretation of the measured data have been done by applying the Seisplus set of computer program. The interpretation of the data enabled the determination of the speed of the primary and secondary seismic waves at the location of the possible secondary seismic station of Zatriq.

3 Results

The refraction profile extends to a length of 120 m (RP-1 in the N–S direction). The realized refraction scheme and the location of the seismological station are given in Figure 1.

Figure 1

The refraction scheme and the location of the seismological station.

According to the results from the refraction investigations, as shown in Figure 2, two elastic media are present at the site: (1) surface loose layer of peridotite and dunite at a depth of 2–3 m in the higher and down to 6 m in the lower part of the terrain with values of seismic velocities of Vp = 575–1,300 m/s and Vs = 325–680 m/s and (2) compact peridotite and dunite below the surface layer with values of seismic velocities of Vp = 4,450 m/s and Vs = 2,360 m/s. The seismological station is located in the higher part of the terrain (in the first half of the refraction profile) in the vicinity of the antenna transmitter.

Figure 2

Refraction investigations.

In Figure 3, the thickness of the peridotite and dunite amounting to over 300 m has been displayed. On the surface, these are cracked and loose and their compactness is increased at depth exceeding 80–100 m. No fault has been found to exist in the vicinity of the seismological station. According to the values of the seismic velocities, the thickness of the loose rock and the expression T = 4 h/Vs, an increase in microseismic vibrations with a dominant period of about 0.12–0.16 s (f = 8.33–6.25 Hz) are expected at this location. In the literature there is also important that interesting results were obtained in some other works [18–38].

Figure 3

The thickness of the peridotite and dunite amounts to over 300 m.

4 Conclusion

The refraction investigations enabled the definition of the values of seismic Vp and Vs velocities of the geological media at the sites down to the depth of about 30–50 m. The thickness of the loose surface and disintegrated layer to be removed while installing the seismometers in the seismological stations. The microlocations of the seismological stations on the most compact parts of the refraction profile where the thickness of the surface layer is the lowest, i.e., less than a few meters of the foci and the tectonic structures in the Kosovo territory. The planned telemetric network of seismological stations covers the entire territory of Kosovo and enables complete monitoring of the seismic activity of the autochthonous foci and the foci in the neighboring countries, i.e., it will enable detailed investigation and definition of the contemporary seismic regime. The same network of seismological stations can also be equipment with seismological instruments for recording of strong earthquakes for the need of earthquake engineering and ecological protection of the human environment. Therefore, from the data of primary and secondary seismic velocity values, the investigated location in Zatriq in Kosovo fulfills the seismological conditions for the construction of the secondary seismic station, something that will affect the more successful monitoring of seismic activity in Kosovo, the region and beyond.