Paul Antony Selvadurai

Last Name

Selvadurai

First Name

Paul Antony

ORCID

0000-0002-3846-8333

Organisational unit

03476 - Giardini, Domenico / Giardini, Domenico

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Publications 1 - 10 of 42

Importance of Water-Clay Interactions for Fault Slip in Clay-Rich Rocks
Rast, Markus; Madonna, Claudio; Selvadurai, Paul Antony; et al. (2024)
Journal of Geophysical Research: Solid Earth
Clay-rich rocks are integral to subduction zone dynamics and of practical importance, for example, as barriers in nuclear waste and CO2 repositories. While the effects of swelling strain on the self-sealing capabilities of these rocks are relatively well-established, the implications of polar fluids interacting with charged clay particles on the frictional behavior, and the role of swelling stress in initiating slip in critically stressed faults, remain ambiguous. To address these uncertainties, we conducted triaxial friction experiments using saw-cut samples, with the upper half composed of Opalinus claystone (OPA) and the lower half of Berea sandstone (BER). The frictional strength of the non-wetted OPA-BER interface was estimated based on experiments at confining pressures of 4–25 MPa and constant axial loading rate (0.1 mm/min). Fluid injection friction experiments were performed using decane (non-polar fluid) or deionized water (polar fluid) at 10 and 25 MPa confining pressures and constant piston displacement control. Macroscopic mechanical data were complemented by distributed strain sensing on the sample surface. Compared to decane, the frictional strength of the OPA-BER interface tended to decrease when injecting water, which is attributed to phyllosilicate lubrication and the transition of the OPA from a solid rock to an incohesive mud near the saw-cut surface. When injecting water, slip was initiated during initial hydration of the OPA-BER interface, although the apparent stress state was below the yield stress. To explain this behavior, we propose that the swelling stress is a crucial factor that should be integrated into the effective stress model.
Influence of reservoir geology on seismic response during decameter-scale hydraulic stimulations in crystalline rock
Villiger, Linus; Gischig, Valentin S.; Doetsch, Joseph; et al. (2020)
Solid Earth
We performed a series of 12 hydraulic stimulation experiments in a 20m×20m×20m foliated, crystalline rock volume intersected by two distinct fault sets at the Grimsel Test Site, Switzerland. The goal of these experiments was to improve our understanding of stimulation processes associated with high-pressure fluid injection used for reservoir creation in enhanced or engineered geothermal systems. In the first six experiments, pre-existing fractures were stimulated to induce shear dilation and enhance permeability. Two types of shear zones were targeted for these hydroshearing experiments: (i) ductile ones with intense foliation and (ii) brittle–ductile ones associated with a fractured zone. The second series of six stimulations were performed in borehole intervals without natural fractures to initiate and propagate hydraulic fractures that connect the wellbore to the existing fracture network. The same injection protocol was used for all experiments within each stimulation series so that the differences observed will give insights into the effect of geology on the seismo-hydromechanical response rather than differences due to the injection protocols. Deformations and fluid pressure were monitored using a dense sensor network in boreholes surrounding the injection locations. Seismicity was recorded with sensitive in situ acoustic emission sensors both in boreholes and at the tunnel walls. We observed high variability in the seismic response in terms of seismogenic indices, b values, and spatial and temporal evolution during both hydroshearing and hydrofracturing experiments, which we attribute to local geological heterogeneities. Seismicity was most pronounced for injections into the highly conductive brittle–ductile shear zones, while the injectivity increase on these structures was only marginal. No significant differences between the seismic response of hydroshearing and hydrofracturing was identified, possibly because the hydrofractures interact with the same pre-existing fracture network that is reactivated during the hydroshearing experiments. Fault slip during the hydroshearing experiments was predominantly aseismic. The results of our hydraulic stimulations indicate that stimulation of short borehole intervals with limited fluid volumes (i.e., the concept of zonal insulation) may be an effective approach to limit induced seismic hazard if highly seismogenic structures can be avoided.
Effects of Energy Dissipation on Precursory Seismicity During Earthquake Preparation
Bianchi, Patrick; Selvadurai, Paul Antony; Dal Zilio, Luca; et al. (2024)
Seismica
The b-value of the magnitude distribution of natural earthquakes appears to be closely influenced by the faulting style. We investigate this in the laboratory for the first time by analyzing the moment tensor solutions of acoustic emissions detected during a triaxial compression test on Berea sandstone. We observe systematic patterns showing that faulting style influences the b-value and differential stress. Similar trends are observed in a complementary physics-based numerical model that captures mechanical energy dissipation. Both the differential stress and dissipation are found to be inversely correlated to the b-value. The results indicate that, at late stages of the test, the dissipation increases and is linked to a change in AE faulting style and drop in b-value. The patterns observed in the laboratory Frohlich diagrams could be explained by the integrated earthquake model: damaged rock regions form as microcracks coalesce, leading to strain localization and runaway deformation. The modeling results also align with the micromechanics responsible for dissipation at various stages of the experiment and agrees with moment tensor solutions and petrographic investigations. The integration of physics-based models that can capture dissipative processes of the earthquake cycle could assist researchers in constraining seismic hazard in both natural and anthropogenic settings.
Estimates for the Effective Permeability of Intact Granite Obtained from the Eastern and Western Flanks of the Canadian Shield
Selvadurai, Patrick; Blain-Coallier, A.; Selvadurai, Paul Antony (2020)
Minerals
Granitic rock from the western part of the Canadian Shield is considered as a potential host rock for the siting of a deep geological repository for the storage of heat-emitting high-level nuclear fuel waste. The research program focused on the use of surface permeability measurements conducted at 54 locations on a 300 mm cuboid of granite, obtained from the Lac du Bonnet region in Manitoba, to obtain an estimate for the effective permeability of the cuboid. Companion experiments are conducted on a 280 mm cuboid of granite obtained from Stanstead, Quebec, located in the eastern part of the Canadian Shield. The surface permeabilities for the cuboids of granite are developed from theoretical relationships applicable to experimental situations where steady flow is initiated at a sealed annular surface region with a pressurized central domain. The experimental values for the surface permeability are used with a kriging procedure to estimate the permeability variations within the cuboidal region. The spatial variations of permeability are implemented in computational models of the cuboidal regions to determine the one-dimensional permeabilities in three orthogonal directions. The effective permeability of the granite cuboids is estimated by appeal to the geometric mean. The research provides a non-destructive methodology for estimating the effective permeability of large specimens of rock and the experiments performed give estimates for the effective permeability of the two types of granitic rock obtained from the western and eastern flanks of the Canadian Shield.
High-Resolution Seismo-hydromechnic Monitoring in Mesoscale Multi-stage Stimulation Experiment
Plenkers, Katrin; Krietsch, Hannes; Gischig, Valentin; et al. (2019)
AGU Fall Meeting Abstracts
From Labquakes to Megathrusts: Scaling Deep Learning Based Pickers Over 15 Orders of Magnitude
Shi, Peidong; Meier, Men‐Andrin; Villiger, Linus; et al. (2024)
Journal of Geophysical Research: Machine Learning and Computation
The application of machine learning techniques in seismology has greatly advanced seismological analysis, especially for earthquake detection and seismic phase picking. However, machine learning approaches still face challenges in generalizing to data sets that differ from their original training setting. Previous studies focused on retraining or transfer-learning models for these scenarios, but require high-quality labeled data sets. This paper demonstrates a new approach for augmenting already trained models without the need for additional training data. We propose four strategies—rescaling, model aggregation, shifting, and filtering—to enhance the performance of pre-trained models on out-of-distribution data sets. We further devise various methodologies to ensemble the individual predictions from these strategies to obtain a final unified prediction result featuring prediction robustness and detection sensitivity. We develop an open-source Python module quakephase that implements these methods and can flexibly process input continuous seismic data of any sampling rate. With quakephase and pre-trained ML models from SeisBench, we perform systematic benchmark tests on data recorded by different types of instruments, ranging from acoustic emission sensors to distributed acoustic sensing, and collected at different scales, spanning from laboratory acoustic emission events to major tectonic earthquakes. Our tests highlight that rescaling is essential for dealing with small-magnitude seismic events recorded at high sampling rates as well as larger magnitude events having long coda and remote events with long wave trains. Our results demonstrate that the proposed methods are effective in augmenting pre-trained models for out-of-distribution data sets, especially in scenarios with limited labeled data for transfer learning.
Aseismic strain localization prior to failure and associated seismicity in crystalline rock
Salazar Vásquez, Antonio Felipe; Selvadurai, Paul Antony; Bianchi, Patrick; et al. (2024)
Scientific Reports
Recent laboratory tests and large-scale observations have revealed the complex interplays between aseismic and seismic deformation, as well as the progressive localization of the rock failure process. To investigate these processes, we conducted triaxial tests that combined distributed strain sensing (DSS) with acoustic emission (AE) sensors. Progressive strain localization was detected by DSS at 80% of the peak stress but did not produce measurable AEs. Closer to the peak stress, regions exhibiting strain localizations began to show clusters of AEs. This reveals that DSS measurements are more informative during the preparatory stage of brittle rock failure. The frequency-magnitude distribution of the AEs showed an inverse correlation with the volumetric deformation rate a few seconds preceding catastrophic failure. Our results are consistent with recent large-scale observations and offer crucial insights into progressive failure assessment.
On the Influence of a Dilatant Asperity Patch on the Seismic Moment
Selvadurai, Paul Antony; Selvadurai, Antony Patrick S. (2025)
Journal of Elasticity
This paper proposes a novel procedure to examine the influences of friction, dilatancy, and normal stresses at fault zones on the estimation of seismic moment. For illustrative purposes, the study focuses on a circular frictional dilatant patch located within a frictionless pre-compressed fault zone undergoing relative shear. When dilatancy occurs, the interface beyond the dilatant region may experience separation due to the normal stresses acting on the fault plane, affecting the deformational response of the pre-stressed asperity. This approach allows for an evaluation of the normal stress on the dilatant region, leading to a re-interpretation of the conventional definition of seismic moment. We compare our model against a comprehensive catalog of earthquakes spanning 16 orders of magnitude, utilizing seismologically inferred source properties as well as data from two separate experimental studies that directly measure the shear-dilatant response of shear fractures in both laboratory and field settings. Our findings indicate that friction-induced dilatancy exerts minimal influence on the estimation of seismic moment. However, we emphasize that the discrepancies between our direct measurements and inferred estimates of seismic moment highlight the need for focused campaigns and in situ and on-fault assessments of earthquake mechanics. Plain Language summary. The conventional definition of the Seismic Moment has been central to unifying information from plate tectonics, geology, geodesy, and seismology. It looks at how the ground moves along a fault plane and the strength of the surrounding rocks. However, it often overlooks other factors that might affect this movement, such as the stress on the fault and the local topography that can induce additional physical responses. This study explores how these additional factors, particularly a process called dilatancy, can change our understanding of the seismic moment. The authors found that while these factors do play a role, they have a minimal impact on the traditional definition of seismic moment initially proposed by Aki in 1966.
Revisiting Piezoelectric Sensor Calibration Methods Using Elastodynamic Body Waves
Wu, Rui; Selvadurai, Paul Antony; Chen, Chaojian; et al. (2021)
Journal of Nondestructive Evaluation
The application of absolutely calibrated piezoelectric (PZT) sensors is increasingly used to help interpret the information carried by radiated elastic waves of laboratory/in situs acoustic emissions (AEs) in nondestructive evaluation. In this paper, we present the methodology based on the finite element method (FEM) to characterize PZT sensors. The FEM-based modelling tool is used to numerically compute the true Green’s function between a ball impact source and an array of PZT sensors to map active source to theoretical ground motion. Physical-based boundary conditions are adopted to better constrain the problem of body wave propagation, reflection and transmission in/on the elastic medium. The modelling methodology is first validated against the reference approach (generalized ray theory) and is then extended down to 1 kHz where body wave reflection and transmission along different types of boundaries are explored. We find the Green’s functions calculated using physical-based boundaries have distinct differences between commonly employed idealized boundary conditions, especially around the anti-resonant and resonant frequencies. Unlike traditional methods that use singular ball drops, we find that each ball drop is only partially reliable over specific frequency bands. We demonstrate, by adding spectral constraints, that the individual instrumental responses are accurately cropped and linked together over 1 kHz to 1 MHz after which they overlap with little amplitude shift. This study finds that ball impacts with a broad range of diameters as well as the corresponding valid frequency bandwidth, are necessary to characterize broadband PZT sensors from 1 kHz to 1 MHz.
Pre-Failure Strain Localization in Siliclastic Rocks: A Comparative Study of Laboratory and Numerical Approaches
Bianchi, Patrick; Selvadurai, Paul Antony; Dal Zilio, Luca; et al. (2024)
Rock Mechanics and Rock Engineering
We combined novel laboratory techniques and numerical modeling to investigate (a) seismic preparatory processes associated with deformation localization during a triaxial failure test on a dry sample of Berea sandstone. Laboratory observations were quantified by measuring strain localization on the sample surface with a distributed strain sensing (DSS) array, utilizing optical fibers, in conjunction with both passive and active acoustic emission (AE) techniques. A physics-based computational model was subsequently employed to understand the underlying physics of these observations and to establish a spatio-temporal correlation between the laboratory and modeling results. These simulations revealed three distinct stages of preparatory processes: (i) highly dissipative fronts propagated towards the middle of the sample correlating with the observed acoustic emission locations; (ii) dissipative regions were individuated in the middle of the sample and could be linked to a discernible decrease of the P-wave velocities; (iii) a system of conjugate bands formed, coalesced into a single band that grew from the center towards the sample surface and was interpreted to be representative for the preparation of a weak plane. Dilatative lobes at the process zones of the weak plane extended outwards and grew to the surface, causing strain localization and an acceleration of the simulated deformation prior to failure. This was also observed during the experiment with the strain rate measurements and spatio-temporally correlated with an increase of the seismicity rate in a similar rock volume. The combined approach of such laboratory and numerical techniques provides an enriched view of (a)seismic preparatory processes preceding the mainshock.

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Paul Antony Selvadurai

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