Pressure build-up and stress variations within the Earth\u2019s crust in the light of analogue models

Evangelos Moulas,Ernst Willingshofer,Dimitrios Sokoutis

doi:10.1038/s41598-018-38256-1

Evangelos Moulas, Ernst Willingshofer + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-38256-1

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Abstract

Strength contrasts and spatial variations in rheology are likely to produce significant stress differences in the Εarth’s crust. The buildup and the relaxation of stresses have important consequences for the state of stress of the brittle crust, its deformational behaviour and seismicity. We performed scaled analogue experiments of a classic wedge-type geometry wherein we introduced a weak, fluid-filled body representing a low-stress heterogeneity. The experiments were coupled to direct pressure measurements that revealed significant pressure differences from their surrounding stressed matrix. The magnitude of the pressure variations is similar to the magnitude of the differential stress of the strongest lithology in the system. When rocks with negligible differential stresses are considered, their pressure can be more than twice larger than the surrounding lithostatic stress. The values of the pressure variations are consistent with the stresses that are estimated in analytical studies. This behaviour is not restricted to a particular scale or rheology, but it requires materials that are able to support different levels of stress upon deformation. For non-creeping rheological behaviours, the stress and pressure variations are maintained even after deformation ceases, implying that these stress variations can be preserved in nature over geological timescales.

Highlights

The state of stress in the Earth’s upper crust is important for a variety of geodynamic phenomena such as earthquakes, volcanic eruptions and the strain evolution of rocks and regions
We present the results of experiments with direct pressure measurements to show that strength heterogeneities, such as weak bodies embedded in a stressed brittle layer can experience significant (>100%) pressure variations from the initial lithostatic stress
The aim of this study is to show that stress variations that can occur in the crust is controlled from the maximum strength of rocks and from the geometrical configuration and the far-field stress conditions as envisaged by analogue experiments, simple mechanical solutions and thermomechanical modelling

Summary

Introduction

The state of stress in the Earth’s upper crust is important for a variety of geodynamic phenomena such as earthquakes, volcanic eruptions and the strain evolution of rocks and regions. Some of the first mechanical investigations considering the Earth’s crust were based on the study of simple materials that can be used as scaled analogues in space and time[1,2,3] Such models can provide useful insights especially on the evolution of complex strain patterns in deforming regions of the crust and the lithosphere in general[4,5,6]. The aim of this study is to show that stress variations that can occur in the crust is controlled from the maximum strength of rocks and from the geometrical configuration and the far-field stress conditions as envisaged by analogue experiments, simple mechanical solutions and thermomechanical modelling

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