Laboratory Evidence of Transient Pressure Surge in a Fluid-Filled Fracture as a Potential Driver of Remote Dynamic Earthquake Triggering

Abstract Seismic waves carrying tiny perturbing stresses can trigger earthquakes in geothermal and volcanic regions. The underlying cause of this dynamic triggering is still not well understood. One leading hypothesis is that a sudden increase in the fluid-pore pressure in the fault zone is involved, but the exact physical mechanism is unclear. Here, we report experimental evidence in which a fluid-filled fracture was shown to be able to amplify the pressure of an incoming seismic wave. We built miniature pressure sensors and directly placed them inside a thin fluid-filled fracture to measure the fluid pressure during wave propagation. By varying the fracture aperture from 0.2 to 9.2 mm and sweeping the frequency from 12 to 70 Hz, we observed in the lab that the fluid pressure in the fracture could be amplified up to 25.2 times compared with the incident-wave amplitude. Because an increase of the fluid pressure in a fault can reduce the effective normal stress to allow the fault to slide, our observed transient pressure surge phenomenon may provide the mechanism for earthquake dynamic triggering.

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Fault’s hydraulic diffusivity enhancement during injection induced fault reactivation: application of pore pressure diffusion inversions to laboratory injection experiments

Geophysical Journal International ◽

10.1093/gji/ggaa446 ◽

2020 ◽

Vol 223 (3) ◽

pp. 2117-2132

Author(s):

M Almakari ◽

H Chauris ◽

F Passelègue ◽

P Dublanchet ◽

A Gesret

Keyword(s):

Fluid Flow ◽

Fluid Pressure ◽

Pressure Sensors ◽

Order Effect ◽

Fault Reactivation ◽

Time Range ◽

Hydraulic Diffusivity ◽

Effective Normal Stress ◽

Geological Conditions ◽

Order Of Magnitude

SUMMARY In situ observations of fluid induced fault slip reactivation, as well as the analysis of induced seismicity have demonstrated the complexity of fluid–fault interactions under geological conditions. If fluid flow commonly reactivates faults in the form of aseismic slip or earthquakes, the resulting shear deformation causes strong modifications of the hydraulic properties. In this context, the relationship between slip front and fluid front on deep faults remains not fully understood. In this study, we investigate shear induced fluid flow and hydraulic diffusivity enhancement during fracture shearing in the laboratory. We use a series of injection reactivation tests, conducted under triaxial conditions, at different confining pressures (30, 60 and 95 MPa). The evolution of the fluid pressure along the saw-cut Andesite rock sample was monitored by two pressure sensors, at two opposite locations of the experimental fault. We estimate the history of the effective hydraulic diffusivity (and its associated uncertainties) governing the experimental fault, using the pressure history at two points on the fault. For this, we develop a deterministic and a probabilistic inversion procedure, which is able to reproduce the experimental data for a wide time range of the different experiments. In this study, the hydraulic diffusivity increases by one order of magnitude through the injection experiment. Hydraulic diffusivity changes are mainly governed by the reduction of the effective normal stress acting on the fault plane, with a second-order effect of the shear slip.

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Seismically induced changes in groundwater levels and temperatures following the ML5.8 (ML5.1) Gyeongju earthquake in South Korea

Hydrogeology Journal ◽

10.1007/s10040-021-02328-w ◽

2021 ◽

Author(s):

Soo-Hyoung Lee ◽

Jae Min Lee ◽

Sang-Ho Moon ◽

Kyoochul Ha ◽

Yongcheol Kim ◽

...

Keyword(s):

South Korea ◽

Groundwater Level ◽

Seismic Waves ◽

Groundwater Resources ◽

Fluid Pressure ◽

Water Levels ◽

Aquifer System ◽

Groundwater Levels ◽

Monitoring Wells ◽

Gyeongju Earthquake

AbstractHydrogeological responses to earthquakes such as changes in groundwater level, temperature, and chemistry, have been observed for several decades. This study examines behavior associated with ML 5.8 and ML 5.1 earthquakes that occurred on 12 September 2016 near Gyeongju, a city located on the southeast coast of the Korean peninsula. The ML 5.8 event stands as the largest recorded earthquake in South Korea since the advent of modern recording systems. There was considerable damage associated with the earthquakes and many aftershocks. Records from monitoring wells located about 135 km west of the epicenter displayed various patterns of change in both water level and temperature. There were transient-type, step-like-type (up and down), and persistent-type (rise and fall) changes in water levels. The water temperature changes were of transient, shift-change, and tendency-change types. Transient changes in the groundwater level and temperature were particularly well developed in monitoring wells installed along a major boundary fault that bisected the study area. These changes were interpreted as representing an aquifer system deformed by seismic waves. The various patterns in groundwater level and temperature, therefore, suggested that seismic waves impacted the fractured units through the reactivation of fractures, joints, and microcracks, which resulted from a pulse in fluid pressure. This study points to the value of long-term monitoring efforts, which in this case were able to provide detailed information needed to manage the groundwater resources in areas potentially affected by further earthquakes.

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Fluid pressure waves trigger earthquakes

Geophysical Journal International ◽

10.1093/gji/ggu469 ◽

2015 ◽

Vol 200 (3) ◽

pp. 1279-1283 ◽

Cited By ~ 7

Author(s):

Francesco Mulargia ◽

Andrea Bizzarri

Keyword(s):

Oil And Gas ◽

Nonlinear Partial Differential Equation ◽

Active Faults ◽

Fluid Pressure ◽

Rock Joints ◽

Pressure Waves ◽

Earthquake Triggering ◽

Oil And Gas Exploration ◽

Exploration And Production ◽

Von Mises

Abstract Fluids—essentially meteoric water—are present everywhere in the Earth's crust, occasionally also with pressures higher than hydrostatic due to the tectonic strain imposed on impermeable undrained layers, to the impoundment of artificial lakes or to the forced injections required by oil and gas exploration and production. Experimental evidence suggests that such fluids flow along preferred paths of high diffusivity, provided by rock joints and faults. Studying the coupled poroelastic problem, we find that such flow is ruled by a nonlinear partial differential equation amenable to a Barenblatt-type solution, implying that it takes place in form of solitary pressure waves propagating at a velocity which decreases with time as v ∝ t [1/(n − 1) − 1] with n ≳ 7. According to Tresca-Von Mises criterion, these waves appear to play a major role in earthquake triggering, being also capable to account for aftershock delay without any further assumption. The measure of stress and fluid pressure inside active faults may therefore provide direct information about fault potential instability.

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Seismic wave attenuation due to fluid pressure diffusion at the mesoscopic scale: an experimental and numerical study

10.5194/egusphere-egu21-16072 ◽

2021 ◽

Author(s):

Samuel Chapman ◽

Jan V. M. Borgomano ◽

Beatriz Quintal ◽

Sally M. Benson ◽

Jerome Fortin

Keyword(s):

Seismic Wave ◽

Seismic Waves ◽

Wave Attenuation ◽

Fluid Pressure ◽

Fluid Distribution ◽

Mesoscopic Scale ◽

Seismic Wave Attenuation ◽

X Ray ◽

Pressure Diffusion ◽

Attenuation And Dispersion

<p>Monitoring of the subsurface with seismic methods can be improved by better understanding the attenuation of seismic waves due to fluid pressure diffusion (FPD). In porous rocks saturated with multiple fluid phases the attenuation of seismic waves by FPD is sensitive to the mesoscopic scale distribution of the respective fluids. The relationship between fluid distribution and seismic wave attenuation could be used, for example, to assess the effectiveness of residual trapping of carbon dioxide (CO2) in the subsurface. Determining such relationships requires validating models of FPD with accurate laboratory measurements of seismic wave attenuation and modulus dispersion over a broad frequency range, and, in addition, characterising the fluid distribution during experiments. To address this challenge, experiments were performed on a Berea sandstone sample in which the exsolution of CO2 from water in the pore space of the sample was induced by a reduction in pore pressure. The fluid distribution was determined with X-ray computed tomography (CT) in a first set of experiments. The CO2 exosolved predominantly near the outlet, resulting in a heterogeneous fluid distribution along the sample length. In a second set of experiments, at similar pressure and temperature conditions, the forced oscillation method was used to measure the attenuation and modulus dispersion in the partially saturated sample over a broad frequency range (0.1 - 1000 Hz). Significant P-wave attenuation and dispersion was observed, while S-wave attenuation and dispersion were negligible. These observations suggest that the dominant mechanism of attenuation and dispersion was FPD. The attenuation and dispersion by FPD was subsequently modelled by solving Biot&#8217;s quasi-static equations of poroelasticity with the finite element method. The fluid saturation distribution determined from the X-ray CT was used in combination with a Reuss average to define a single phase effective fluid bulk modulus. The numerical solutions agree well with the attenuation and modulus dispersion measured in the laboratory, supporting the interpretation that attenuation and dispersion was due to FPD occurring in the heterogenous distribution of the coexisting fluids. The numerical simulations have the advantage that the models can easily be improved by including sub-core scale porosity and permeability distributions, which can also be determined using X-ray CT. In the future this could allow for conducting experiments on heterogenous samples.</p>

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Fluid-induced aseismic fault slip outpaces pore-fluid migration

Science ◽

10.1126/science.aaw7354 ◽

2019 ◽

Vol 364 (6439) ◽

pp. 464-468 ◽

Cited By ~ 36

Author(s):

Pathikrit Bhattacharya ◽

Robert C. Viesca

Keyword(s):

Pore Fluid ◽

Fluid Injection ◽

Fluid Migration ◽

Aseismic Slip ◽

Earthquake Triggering ◽

Effective Normal Stress ◽

Shear Rupture ◽

Stress Changes ◽

Slip History ◽

Rupture Model

Earthquake swarms attributed to subsurface fluid injection are usually assumed to occur on faults destabilized by increased pore-fluid pressures. However, fluid injection could also activate aseismic slip, which might outpace pore-fluid migration and transmit earthquake-triggering stress changes beyond the fluid-pressurized region. We tested this theoretical prediction against data derived from fluid-injection experiments that activated and measured slow, aseismic slip on preexisting, shallow faults. We found that the pore pressure and slip history imply a fault whose strength is the product of a slip-weakening friction coefficient and the local effective normal stress. Using a coupled shear-rupture model, we derived constraints on the hydromechanical parameters of the actively deforming fault. The inferred aseismic rupture front propagates faster and to larger distances than the diffusion of pressurized pore fluid.

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DynTriPy: A Python Package for Detecting Dynamic Earthquake Triggering Signals

Seismological Research Letters ◽

10.1785/0220200216 ◽

2020 ◽

Vol 92 (1) ◽

pp. 543-554

Author(s):

Naidan Yun ◽

Hongfeng Yang ◽

Shiyong Zhou

Keyword(s):

Large Scale ◽

Seismic Analysis ◽

Parallel Architecture ◽

Global Scale ◽

Earthquake Triggering ◽

Process Data ◽

Dynamic Triggering ◽

Earthquake Interaction ◽

High Level ◽

Python Package

Abstract Long-term and large-scale observations of dynamic earthquake triggering are urgently needed to understand the mechanism of earthquake interaction and assess seismic hazards. We developed a robust Python package termed DynTriPy to automatically detect dynamic triggering signals by distinguishing anomalous seismicity after the arrival of remote earthquakes. This package is an efficient implementation of the high-frequency power integral ratio algorithm, which is suitable for processing big data independent of earthquake catalogs or subjective judgments and can suppress the influence of noise and variations in the background seismicity. Finally, a confidence level of dynamic triggering (0–1) is statistically yielded. DynTriPy is designed to process data from multiple stations in parallel, taking advantage of rapidly expanding seismic arrays to monitor triggering on a global scale. Various data formats are supported, such as Seismic Analysis Code, mini Standard for Exchange of Earthquake Data (miniSEED), and SEED. To tune parameters more conveniently, we build a function to generate a database that stores power integrals in different time and frequency segments. All calculation functions possess a high-level parallel architecture, thoroughly capitalizing on available computational resources. We output and store the results of each function for continuous operation in the event of an unexpected interruption. The deployment of DynTriPy to data centers for real-time monitoring and investigating the sudden activation of any signal within a certain frequency scope has broad application prospects.

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Equivalent viscoelastic solids for heterogeneous fluid-saturated porous rocks

Geophysics ◽

10.1190/1.3008544 ◽

2009 ◽

Vol 74 (1) ◽

pp. N1-N13 ◽

Cited By ~ 104

Author(s):

J. Germán Rubino ◽

Claudia L. Ravazzoli ◽

Juan E. Santos

Keyword(s):

Monte Carlo ◽

Seismic Waves ◽

Fluid Pressure ◽

Porous Rocks ◽

Quality Factors ◽

Shear Tests ◽

Viscoelastic Solids ◽

Shear Moduli ◽

Phase Velocities ◽

Biot’S Equations

Different theoretical and laboratory studies on the propagation of elastic waves in real rocks have shown that the presence of heterogeneities larger than the pore size but smaller than the predominant wavelengths (mesoscopic-scale heterogeneities) may produce significant attenuation and velocity dispersion effects on seismic waves. Such phenomena are known as “mesoscopic effects” and are caused by equilibration of wave-induced fluid pressure gradients. We propose a numerical upscaling procedure to obtain equivalent viscoelastic solids for heterogeneous fluid-saturated rocks. It consists in simulating oscillatory compressibility and shear tests in the space-frequency domain, which enable us to obtain the equivalent complex undrained plane wave and shear moduli of the rock sample. We assume that the behavior of the porous media obeys Biot’s equations and use a finite-element procedure to approximate the solutions of the associated boundary value problems. Also, because at mesoscopic scales rock parameter distributions are generally uncertain and of stochastic nature, we propose applying the compressibility and shear tests in a Monte Carlo fashion. This facilitates the definition of average equivalent viscoelastic media by computing the moments of the equivalent phase velocities and inverse quality factors over a set of realizations of stochastic rock parameters described by a given spectral density distribution. We analyzed the sensitivity of the mesoscopic effects to different kinds of heterogeneities in the rock and fluid properties using numerical examples. Also, the application of the Monte Carlo procedure allowed us to determine the statistical properties of phase velocities and inverse quality factors for the particular case of quasi-fractal heterogeneities.

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Swelling Behaviour and Permeability of Compacted Bentonites at High Salinity as Infl uenced by Fluid Pressure Changes

Radioactive waste ◽

10.25283/2587-9707-2020-2-109-119 ◽

2020 ◽

Vol 11 (2) ◽

pp. 109-119

Author(s):

A. Yu. Meleshyn ◽

Keyword(s):

Hydraulic Fracturing ◽

Fluid Pressure ◽

Swelling Pressure ◽

Swelling Behaviour ◽

Geological Repository ◽

Before And After ◽

Pressure Surge ◽

One Year ◽

Pressure Changes ◽

Peak Pattern

This study presents results of two series of permeameter experiments with 15 bentonites compacted to a bulk density of 1.6 g/cm3 before and after one-year contact with a model clay porewater with a salinity of 155 g/l. For four original bentonites, a double-peak pattern of swelling pressure evolution was revealed, which was observed previously only at much lower salinities. For 80 % of bentonites, swelling pressure and permeability were in the range of 0.8—4.8 MPa and 7·10−20—3·10−18 m2 (for original ones) as well as 0.5—2.2 MPa and 4·10−19—6·10−18 m² (for ones after one-year contact). A fl uid pressure surge of 12.6 MPa caused no hydraulic fracturing of original bentonites. This observation challenges the validity of threshold values of a few MPa for onset of hydraulic fracturing in compacted bentonites proposed earlier using an alternative experimental method. Yet, this fl uid pressure surge and a moderate one of 0.3 MPa caused a decrease of swelling pressure by up to 66 % — an effect, which need to be accounted for when designing and assessing the performance of bentonite-based barriers in a geological repository.

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Frictional slip weakening and shear-enhanced crystallinity in simulated coal fault gouges at subseismic slip rates

10.5194/se-2020-43 ◽

2020 ◽

Author(s):

Caiyuan Fan ◽

Jinfeng Liu ◽

Luuk B. Hunfeld ◽

Christopher J. Spiers

Keyword(s):

Steady State ◽

Normal Stress ◽

Hold Time ◽

Shear Bands ◽

Fluid Pressure ◽

Organic Content ◽

Local Conditions ◽

Frictional Properties ◽

Effective Normal Stress ◽

Fault Gouges

Abstract. Previous studies show that organic-rich fault patches may play an important role in promoting unstable fault slip. However, the frictional properties of rock materials with near 100 % organic content, e.g. coal, and the controlling microscale mechanisms, remain unclear. Here, we report seven velocity stepping (VS) and one slide-hold-slide (SHS) friction experiments performed on simulated fault gouges prepared from bituminous coal, collected from the upper Silesian Basin of Poland. These experiments were performed at 25–45 MPa effective normal stress and 100 °C, employing sliding velocities of 0.1–100 μm s−1, using a conventional triaxial apparatus plus direct shear assembly. All samples showed marked slip weakening behaviour at shear displacements beyond ~ 1–2 mm, from a peak friction coefficient approaching ~ 0.5 to (near) steady state values of ~ 0.3, regardless of effective normal stress or whether vacuum dry flooded with distilled (DI) water at 15 MPa pore fluid pressure. Analysis of both unsheared and sheared samples by means of microstructural observation, micro-area X-ray diffraction (XRD) and Raman spectroscopy suggests that the marked slip weakening behaviour can be attributed to the development of R-, B- and Y- shear bands, with internal shear-enhanced coal crystallinity development. The SHS experiment performed showed a transient peak healing (restrengthening) effect that increased with the logarithm of hold time at a linearized rate of ~ 0.006. We also determined the rate-dependence of steady state friction for all VS samples using a full rate and state friction approach. This showed a transition from velocity strengthening to velocity weakening at slip velocities > 1 μm s−1 in the coal sample under vacuum dry conditions, but at > 10 μm s−1 in coal samples exposed to DI water at 15 MPa pore pressure. This may be controlled by competition between dilatant granular flow and compaction enhanced by presence of water. Together with our previous work on frictional properties of coal-shale mixtures, our results imply that the presence of a weak, coal-dominated patch on faults that cut or smear-out coal seams may promote unstable, seismogenic slip behaviour, though the importance of this in enhancing either induced or natural seismicity depends on local conditions.

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Permeability Evolution of an Intact Marble Core during Shearing under High Fluid Pressure

Geofluids ◽

10.1155/2021/8870890 ◽

2021 ◽

Vol 2021 ◽

pp. 1-18

Author(s):

Yuan Wang ◽

Yu Jiao ◽

Shaobin Hu

Keyword(s):

Normal Stress ◽

Laser Scanning ◽

Shear Failure ◽

Fluid Pressure ◽

Shear Displacement ◽

Permeability Evolution ◽

Fracture Permeability ◽

Effective Normal Stress ◽

High Fluid ◽

High Fluid Pressure

The progressive shear failure of a rock mass under hydromechanical coupling is a key aspect of the long-term stability of deeply buried, high fluid pressure diversion tunnels. In this study, we use experimental and numerical analysis to quantify the permeability variations that occur in an intact marble sample as it evolves from shear failure to shear slip under different confining pressures and fluid pressures. The experimental results reveal that at low effective normal stress, the fracture permeability is positively correlated with the shear displacement. The permeability is lower at higher effective normal stress and exhibits an episodic change with increasing shear displacement. After establishing a numerical model based on the point cloud data generated by the three-dimensional (3D) laser scanning of the fracture surfaces, we found that there are some contact areas that block the percolation channels under high effective stress conditions. This type of contact area plays a key role in determining the evolution of the fracture permeability in a given rock sample.

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