Abstract: The present invention refers to a method for determining the rigidity of a geological layer in terms of propagation velocity of the elastic waves within a geological system delimited by a free surface (2) and comprising at least one first geological layer (6) having a second rigidity and a second geological layer (5) having a second rigidity and being arranged below the first geological layer, said first and second layer being separated from each other by an interface (3), the method comprising the steps of: positioning a source (4) suitable to generate seismic waves in the second geological layer (5), whose rigidity is intended to be measured; activating said source of seismic waves; detecting at least one seismic signal by means of at least one sensor arranged coupling with the free surface, and determining—from at least one seismic signal—a shear velocity of the elastic waves in the second layer and thus indicating the rigidity of the second layer.

Abstract: Portable seismograph (1) comprising a support and containment structure (2), a bottom portion (3) of which is made of a material having a seismic impedance value ranging between 2×105 and 4×106 kg/m2s, three sensors (4) placed orthogonally to one another, each comprising at least one electrodynamic or capacitive transducer and, attached to the bottom portion (3), a level (11) to position the support and containment structure horizontally, a control unit (5) connected to the sensors (4) for viewing, managing the acquisition mode, recording and processing the data, a power source (9), and means for coupling to the ground (12; 21) designed not perturb the seismic tremor detectable by the sensors (4).