How hot is a lab-earthquake?

Frictional heating in faults during seismic slip induces a temperature increase on the rubbing contacts and within the slipping zone which activates deformation processes and chemical reactions resulting in dynamic weakening.

An independent measurement of temperature would allow to correlate frictional strength with temperature and to constrain the deformation processes and associated chemical reactions activated during seismic slip. So far, in-situ temperature measurements performed at high acquisition rates (from kHz to MHz) and high spatial resolution (< 0.1 mm²) were impossible to achieve due to the large thermal inertia of traditional techniques (i.e., thermocouples). As a consequence, temperatures in the slipping zone sheared at seismic slip rates (1 m/s) were often modelled numerically using the frictional power (shear stress x slip rate) dissipated on the slipping zone as an input parameter, but by making poorly constrained estimates about (1) the partitioning of the dissipated power between frictional heating and wear processes or, worse, (2) other energy sinks that would result in the buffering of the temperature increase (e.g., endothermic reactions).

Here we reproduced earthquake slip in the laboratory via high velocity friction experiments (SHIVA rotary apparatus, INGV, Rome) performed on Carrara marble rock samples, slid at 20 MPa effective normal stresses, slip rates ranging from 0.03 to 6 m/s, up to 20 m of total displacement. During the experiments, the bulk temperature of the slipping zone was measured at acquisition rate of 1 kHz with optical fibers conveying the IR radiation from the hot rubbing surfaces to a two-color pyrometer.

Our data provide the first real-time measurements of the bulk temperature developing by frictional heating and of the dependence of frictional heating with slip rate and displacement during seismic slip in carbonate-built rocks. These and future similar experiments will shed light on the mechanics of carbonate-hosted earthquakes, a main hazard in the Mediterranean and other areas worldwide.