Hydrological and tectonic strain forces measured from a karstic cave using extensometers

TL;DR

This study uses extensometers inside a karst cave to measure hydrological and tectonic strain forces, revealing how water level changes influence fissure network strain and estimating local fault deformation rates.

Contribution

It introduces a method for monitoring hydrological and tectonic strains in karst environments using capacitive extensometers and analyzes their responses to water level variations.

Findings

Strain contracts linearly during water recharge.

Strain extends exponentially during water discharge.

Estimated fault deformation rate is approximately 0.03 mm/yr.

Abstract

In order to monitor the hydrological strain forces of the karst micro fissure networks and local fault activities, six capacitive extensometers were installed inside a karstic cave near the midi-fault in Belgium. From 2004 to 2008, the nearby Lomme River experienced several heavy rains, leading to flooding inside the Rochefort cave. The highest water level rose more than thirteen meters, the karstic fissure networks were filled with water, which altered the pore pressure of the cave. The strain response to the hydrological induced pore pressure changes are separately deduced from fifteen events when the water level exceeded six meters. The strain measured from the extensometer show a linear contraction during the water recharge and a nonlinear exponential extension releasing during the water discharge. The sensitivity and stability of the sensor are constrained by comparing continuously observed tidal strain waves with a theoretical model. Finally, a local fault deformation rate around $0.03 \pm 0.002$mm/yr is estimated from more than four years' records.