Seismic reflection is a technique used to study the subsurface structure of the seafloor. It involves emitting sound waves from a source (such as an air gun) and recording the reflected waves using hydrophones or geophones. By analyzing the travel time and amplitude of the reflected waves, researchers can infer the composition and structure of the underlying sediments and rock layers. This information is vital for understanding geological processes, identifying potential oil and gas reserves, and assessing geohazards like earthquakes and tsunamis. The difference between these two methods is that seismic reflection measures the time of a seismic wave that is approximately vertically reflected on a surface of different density and travels to the geophone. The generation of a seismic wave is the same as that of seismic refraction.

Seismic refraction is based on measuring the propagation time of elastic seismic waves, from sources to geophones, through subsurface geological structures. The waves bounce and break at the material boundaries of different densities and deformation properties.

A seismic wave is generated on the surface by striking a hammer or a vibrator. The wave arrival on the surface is detected by measuring sensors - geophones.

Seismic refraction measures the wave time traveling from a source to a layer of varying density, along with the layer and back to the geophone. Placing the geophone along the direction gives a 2D profile of the wave propagation velocities. For 3D velocity profiles, multiple lines of geophones are placed on predefined grids on the terrain.

The marine seismic refraction method is used to explore the foundation soil on the seabed.

The refraction method is based on the refraction of elastic waves at the boundary between two media, the velocities of which satisfy the positive vertical gradient requirement. Elastic waves deliberately caused at the ground surface begin to propagate at the velocity of the first medium. For this method, the most important wave is the one arriving at the boundary at the critical angle or at the angle of total refraction. The wave further expands along the boundary at the velocity of the lower medium and then returns to the ground surface (according to the Huygens principle), where it acts upon the planted geophones. The time that elapses between the emission and reception of seismic waves depends on the depth of the investigated structures of the foundation soil and on the propagation velocity of seismic waves along the path of their propagation, from the source, through the refractor, and back to the receiver. To initiate a mechanical force, ie an artificially induced seismic wave, various devices are used to strike the ground surface and transmit the mechanical force below the surface. The st diagrams (s-distance, t-time) are derived from the arrangement geometry of geophones and "ignition" points at the ground surface and from the registered times of the first arrivals of the elastic wave. Direct methods and inverse modeling methods are applied to obtain the depths and the spatial arrangement of elastic discontinuities from the st diagram.

Unlike ground seismic investigation methods, marine seismic investigation methods use hydrophones instead of geophones, while air guns are used to provoke seismic waves. Hydrophones (piezoelectric geophones) are used in boreholes and marine measurements due to their sensitivity to pressure changes. The weight lies on a series of plates made of a piezoelectric crystal (quartz, tourmaline, or barium titanate). The soil's downward acceleration decreases the apparent weight of the mass and vice versa, which alters the pressure on the plates and creates electrical voltage within them. The air gun is a device that injects a bubble of highly compressed air into the water. The frequency spectrum depends on the amount of air inside the bubble, on air pressure, and on water depth (Šumanovac, 2007).