Demonstration of seismic exploration techniques

On Monday, November 7th, 2022, in front of the building of the geophysical department in Horvatovac, a demonstration of the MASW method and microseismic disturbance was held. Demonstrations were held by Assoc. PhD. Mario Gazdek from the Faculty of Geotechnical Engineering and Jakov Stanislav Uglešić mag. phys.-geophys. from the Faculty of Science, Department of Geophysics.

MASW (Multichannel Analysis of Surface Waves) is a geophysical seismic method that evaluates the surface stiffness of the soil (solidity) by measuring the velocity of shear waves in 1D, 2D, and 3D. In order to record the produced surface waves, it was necessary to install geophones, simple devices that register the arrival of seismic waves, and connect them to a joint cable (Figures 1 and 2). The geophone profile’s length directly affects the research’s maximum depth, which ranges from 10 to 30 meters. As part of this demonstration, 12 geophones were placed at a distance of 5 m.

Data collection was carried out using an active method, in which an active source, usually a hammer, is used as the source of the seismic wave. Next to the initial geophone or “trigger”, it is necessary to place a metal plate to generate surface seismic waves by hitting the plate with a sledgehammer. The mentioned procedure is repeated several times along the profile of the geophone (Figure 3). After the field data collection of surface waves, data processing follows to obtain a dispersion curve and inversion or calculation of the velocity of propagation of shear waves from Rayleigh waves. The obtained results of all measurements tell us about the strength of the surface layer with a thickness of approximately 30 m (Figure 4).

The second demonstration was measuring microseismic disturbance or HVSR method (Horizontal-to-Vertical Spectral Ratio). It is a simple and fast method for investigating the seismic response of the soil, i.e. for determining the resonant frequency of the soil and the amplification factor. Most scientists consider it suitable for determining the fundamental frequency of buildings.

The measurement was performed with the Tromino instrument (Micromed, Italy), which saves the data in binary files that can be accessed using the Grilla program. After Tromino was attached to the ground and levelled, the 20-minute data recording began (Figure 5).

During the propagation of seismic waves through the ground, there is an amplification of the seismic excitation from the bedrock to the ground surface. By knowing the amplification of the soil and the resonance frequency of the soil oscillation, along with the building’s frequencies, it is possible to estimate the risk of the occurrence of ground-building resonance during an earthquake.

The HVSR method complements the MASW method when investigating the velocity of movement of seismic waves in the surface layer.

Figure 5


Kostolanović, Matej. “Application of surface waves spectral analysis (MASW and SASW) for soil stiffness estimation”, Master thesis, Faculty of Geotechnical Engineering, Varaždin, 2016.

Josip Simunić, Patrick. “Multichannel analysis of surface waves (MASW) and the design values of maximum earthquake by Eurocode 8”, Undergraduate Thesis, Faculty of Geotechnical Engineering, Varaždin, 2017.

Erceg, Petra. “Measurement of the fundamental frequency of the environment and building of the Department of Geophysics”, Master thesis, Faculty of Science, Department of geophysics, Zagreb, 2019.

Filipović, Alen. “Estimation of soil response and resonance of soil- building by measuring micro seismic disturbance”, master thesis, Faculty of Geotechnical Engineering, Varaždin, 2014.