P wave
It is also named primary (sonic) wave, compression wave, longitudinal wave. Generally it is an elastic space wave. During seismic events it is the fastest (and therefore primary) of the three generated seismic waves (besides, S wave and superficial wave) with a velocity vp of 5.5 to 7.2 km/s in the Earth’s crust and 7.8 to 8.5 km/s in the Earth’s mantle. Generally vp increases with density. It is called compression wave because particles move along (or longitudinally with) the direction of propagation leading to elastic compression and extension of a rock volume during an earth quake. In an isotropic medium the velocity of the P wave vp can be described by the following equation:
vp = 0.5*[{E*(1-ν)}/{ρ*(1-2ν)*(1+ν)}]
with E as Young’s modulus, ν as the Poisson’s ratio and ρ as density.
Poisson's ratio
The dimensionless ν describes the deformation behaviour of a rock body in terms of the negative ratio between radial strain ε33 and axial strain ε11:
ν = δε33/δε11.
Usually the Poisson's ratio is calculated as the ratio between the gradients of the load paths of the unload-load cycle for both, the radial and the axial ε-σ1 curves of a given uniaxial/triaxial test.
Generally ν ranges between 0.1 and 0.5. In rocks it rarely exceeds 0.3. Exceptions include weakly consolidated sandstone and very soft claystone where ν can reach a value of 0.45). Brittle rocks have a low Poisson’s ratio.
Pore pressure
Pp is the pressure exerted by the brine within the pore space of a rock which counteracts the applied (external) stress Sij.
Porosity
The porosity of a specimen stands for the volume of all its voids (pores and open cracks) in relation to the total volume of the specimen. Using the bulk density ρb and the grain density ρg, the effective porosity φeff is calculated by the following equation:
φeff = 1 – (ρb/ρg)
News
With the recent acquisition of the state-of-the-art DIL 502 Expedis® Select thermal dilatometer from Netzsch, we are expanding our capabilities for the precise analysis of the thermal properties of rocks and mineral materials. We are now able to determine the coefficient of thermal expansion in accordance with DIN EN 14581:2004, ASTM D4535-13e1. (2013) or using a measurement program specifically tailored to the customer’s needs (for more information, see Thermal Dilatometer).
The project, which was funded by the Free State of Thuringia, was co-financed by the European Union through the European Regional Development Fund (EFRE).
This year’s EAGE GET Conference and Exhibition is taking place in Germany:
Gesteinslabor Dr. Eberhard Jahns will again be taking part as an exhibitor this year. From 2 to 6 November 2026, you can find us at Stand 31 at the HCC in Hannover.
We would be delighted to welcome you to our stand.
Gesteinslabor Dr. Eberhard Jahns is project and research partner within the HENRI (Hydrogen Energy Reservoir) project.
Our main focus is on determining the impact of H2 on the cap rock. Besides other parameters, we measure the capillary threshold pressure using various gases and gas mixtures of hydrogen and methane.
Results were presented at the third HENRI conference in Bratislava in September 2025
We are pleased to be part of the Dutch subsurface research for geothermal heat SCAN.
Further information can be found on the official homepage:
https://scanaardwarmte.nl/english/
