Luca Dal Zilio

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Dal Zilio

First Name

Luca

ORCID

0000-0002-5642-0894

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Publications 1 - 10 of 20

Harnessing the potential of digital twins in seismology
Dal Zilio, Luca; Giardini, Domenico; Carbonell, Ramon; et al. (2023)
Nature Reviews Earth & Environment
Digital twins - virtual replicas of natural systems - are emerging as promising tools for assessing seismic hazard and for aiding disaster decision-making and earthquake rapid response. However, to truly harness their potential, the challenges of exascale computing must be tackled to create systems that are capable of adapting to ever-evolving earthquake dynamics.
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.
Community-Driven Code Comparisons for Three-Dimensional Dynamic Modeling of Sequences of Earthquakes and Aseismic Slip
Jiang, Junle; Erickson, Brittany A.; Lambert, Valère R.; et al. (2022)
Journal of Geophysical Research: Solid Earth
Dynamic modeling of sequences of earthquakes and aseismic slip (SEAS) provides a self-consistent, physics-based framework to connect, interpret, and predict diverse geophysical observations across spatial and temporal scales. Amid growing applications of SEAS models, numerical code verification is essential to ensure reliable simulation results but is often infeasible due to the lack of analytical solutions. Here, we develop two benchmarks for three-dimensional (3D) SEAS problems to compare and verify numerical codes based on boundary-element, finite-element, and finite-difference methods, in a community initiative. Our benchmarks consider a planar vertical strike-slip fault obeying a rate- and state-dependent friction law, in a 3D homogeneous, linear elastic whole-space or half-space, where spontaneous earthquakes and slow slip arise due to tectonic-like loading. We use a suite of quasi-dynamic simulations from 10 modeling groups to assess the agreement during all phases of multiple seismic cycles. We find excellent quantitative agreement among simulated outputs for sufficiently large model domains and small grid spacings. However, discrepancies in rupture fronts of the initial event are influenced by the free surface and various computational factors. The recurrence intervals and nucleation phase of later earthquakes are particularly sensitive to numerical resolution and domain-size-dependent loading. Despite such variability, key properties of individual earthquakes, including rupture style, duration, total slip, peak slip rate, and stress drop, are comparable among even marginally resolved simulations. Our benchmark efforts offer a community-based example to improve numerical simulations and reveal sensitivities of model observables, which are important for advancing SEAS models to better understand earthquake system dynamics.
Seismic coupling and Hazard assessment of the Himalaya
Michel, Sylvain; Stevens, Victoria; Dal Zilio, Luca; et al. (2023)
Himalaya, Dynamics of a Giant 3: Current Activity of the Himalayan Range
This chapter provides a description of what is currently known in the Himalaya about regional and local seismicity, the surface strain budget, the seismically active structures and how to incorporate these elements into seismic hazard assessment. It describes current surface strain rate and how such surface deformation informs us on the state of the main faults that might rupture in the future. The chapter considers surface deformation rates as measured by Global Navigation Satellite System at instrumented sites over whole Himalayan range and derive a probabilistic model of coupling of the Main Himalayan Thrust. It presents the evaluation of seismic hazard using ground motion prediction equations to derive maps of peak ground acceleration expected at certain probability levels during the next decades. The chapter concludes by stating that, although risk can be mitigated to some level, seismic hazard and all subsequent related hazards in Himalaya is high and will remain as such at all times.
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.
Incorporating Full Elastodynamic Effects and Dipping Fault Geometries in Community Code Verification Exercises for Simulations of Earthquake Sequences and Aseismic Slip (SEAS)
Erickson, Brittany A.; Jiang, Junle; Lambert, Valère; et al. (2023)
Bulletin of the Seismological Society of America
Numerical modeling of earthquake dynamics and derived insight for seismic hazard relies on credible, reproducible model results. The sequences of earthquakes and aseismic slip (SEAS) initiative has set out to facilitate community code comparisons, and verify and advance the next generation of physics‐based earthquake models that reproduce all phases of the seismic cycle. With the goal of advancing SEAS models to robustly incorporate physical and geometrical complexities, here we present code comparison results from two new benchmark problems: BP1‐FD considers full elastodynamic effects, and BP3‐QD considers dipping fault geometries. Seven and eight modeling groups participated in BP1‐FD and BP3‐QD, respectively, allowing us to explore these physical ingredients across multiple codes and better understand associated numerical considerations. With new comparison metrics, we find that numerical resolution and computational domain size are critical parameters to obtain matching results. Codes for BP1‐FD implement different criteria for switching between quasi‐static and dynamic solvers, which require tuning to obtain matching results. In BP3‐QD, proper remote boundary conditions consistent with specified rigid body translation are required to obtain matching surface displacements. With these numerical and mathematical issues resolved, we obtain excellent quantitative agreements among codes in earthquake interevent times, event moments, and coseismic slip, with reasonable agreements made in peak slip rates and rupture arrival time. We find that including full inertial effects generates events with larger slip rates and rupture speeds compared to the quasi‐dynamic counterpart. For BP3‐QD, both dip angle and sense of motion (thrust versus normal faulting) alter ground motion on the hanging and foot walls, and influence event patterns, with some sequences exhibiting similar‐size characteristic earthquakes, and others exhibiting different‐size events. These findings underscore the importance of considering full elastodynamics and nonvertical dip angles in SEAS models, as both influence short‐ and long‐term earthquake behavior and are relevant to seismic hazard.
Localization of Brittle Failure During Triaxial Rock Tests: Insight From Laboratory and Numerical Modeling
Bianchi, Patrick; Selvadurai, Paul Antony; Salazar Vásquez, Antonio Felipe; et al. (2022)
Due to the difficulty to retrieve direct measurements and observations in the field, we use laboratory and numerical models to study and better understand localization processes prior to mainshocks. We use a triaxial machine (LabQuake) to perform a failure test on an intact sample of Berea sandstone confined at 20 MPa. Employing in-house developed conical-type piezo- electric transducers (PZT), which are absolutely calibrated and exhibit a flat and broadband response between 100 kHz and 1.5 MHz, we are able to investigate the acoustic emission (AE) clouds by relocating the single events and by computing their focal mechanisms and scalar seismic moments. The PZT sensors are also used actively to account for velocity and anisotropy changes in the sample during the test. Further, we capture the heterogeneous spatial distribution of the surface strain field by deploying fiber optics cables on the sample surface. All these measurements are used to validate numerical simulations of the experiment using a two- dimensional continuum-based and fully coupled seismo-hydro-mechanical poro-visco-elasto- plastic modelling tool (H-MEC). By combining laboratory observations with numerical models, we are able to study physical mechanisms (e.g., viscous compaction of pores and rock damage) which potentially explain the observed localization processes that produces both acoustic emissions and surface strain concentrations occurring prior to the main fracture of the sample.
Subduction earthquake cycles controlled by episodic fluid pressure cycling
Dal Zilio, Luca; Gerya, Taras (2022)
Lithos
In subduction zones, fluids are often invoked to explain slip processes on the megathrust, from great earthquakes to slow-slip events and tectonic tremors. However, it is unclear how the transient evolution of pore-fluid is controlled by depth-dependent variations in hydraulic properties over a broad range of timescales concomitant with the full spectrum of seismic and aseismic slip. In this study, we leverage a newly-developed fully dynamic hydro-mechanical earthquake cycle modeling framework to simulate fluid-driven seismic and aseismic fault slip. By assimilating geological, geophysical, and laboratory data in a physics-based model of fault dynamics, we investigate the role of hydraulic properties on-fault in controlling the predominant slip mode along the subduction megathrust. Results indicate that fluid-driven shear cracks nucleate due to a competing mechanism between the compaction of pores and the dynamic self-pressurization of fluids inside the megathrust, whereas the subsequent propagation of dynamic ruptures is self-sustained by solitary pore-pressure waves. While models with uniform hydraulic properties yield to regular seismic cycles of complete megathrust ruptures, a depth-varying fault permeability leads to the emergence of complex aperiodic sequences characterized by partial and complete ruptures, aftershocks, and transient aseismic slip. Further parameter analysis shows that the slip response on-fault primarily depends on fault permeability and porosity, which in turn control the poroelastic compaction, the storage capacity, and the hydraulic diffusion length. Four slip response patterns are revealed by the parameter space, including seismic events, slow-slip events, oscillatory decay with time, and stable aseismic creep. Our findings provide new insights into the interplay between pore-fluid, mechanical, and fault slip processes, and suggest that solid-fluid interactions and the permeability architecture play a key role in controlling the predominant slip mode on subduction megathrusts.
Modeling the 3D Dynamic Rupture of Microearthquakes Induced by Fluid Injection
Mosconi, Francesco; Tinti, Elisa; Casarotti, Emanuele; et al. (2025)
Journal of Geophysical Research: Solid Earth
Understanding the dynamics of microearthquakes is a timely challenge with the potential to address current paradoxes in earthquake mechanics, and to better understand earthquake ruptures induced by fluid injection. We perform fully 3D dynamic rupture simulations caused by fluid injection on a target fault for Fault Activation and Earthquake Ruptures experiments generating Mw <= 1 earthquakes. We investigate the dynamics of rupture propagation with spatially variable stress drop caused by pore pressure changes and assuming different slip-weakening constitutive parameters. We show that the spontaneous arrest of propagating ruptures is possible by assuming a high fault strength parameter S, that is, a high ratio between strength excess and dynamic stress drop. In faults with high S values (low rupturing potential), even minor variations in Dc (from 0.45 to 0.6 mm) have a substantial effect on the rupture propagation and the ultimate earthquake size. Modest spatial variations of dynamic stress drop determine the rupture mode, distinguishing self-arresting from run-away ruptures. Our results suggest that several characteristics inferred for accelerating dynamic ruptures differ from those observed during rupture deceleration of a self-arresting earthquake. During deceleration, a decrease of peak slip velocity is associated with a nearly constant cohesive zone size. Moreover, the residual slip velocity value (asymptotic value for a crack-like rupture) decreases to nearly zero. This means that an initially crack-like rupture becomes a pulse-like rupture during spontaneous arrest. These findings highlight the complex dynamics of small induced earthquakes, which differ from solutions obtained from conventional crack-like models of earthquake rupture.
Seismic Response of Hectometer-Scale Fracture Systems to Hydraulic Stimulation in the Bedretto Underground Laboratory, Switzerland
Obermann, Anne; Rosskopf, Martina; Durand, Virginie; et al. (2024)
Journal of Geophysical Research: Solid Earth
We performed a series of hydraulic stimulations at 1.1 km depth in the Bedretto underground laboratory, Switzerland, as part of an overall research strategy attempting to understand induced seismicity on different scales. Using an ultra-high frequency seismic network we detect seismic events as small as Mw < −4, revealing intricate details of a complex fracture network extending over 100 m from the injection sites. Here, we outline the experimental approach and present seismic catalogs as well as a comparative analysis of event number per injection, magnitudes, b-values, seismogenic index and reactivation pressures. In our first-order seismicity analysis, we could make the following observations: The rock volume impacted by the stimulations in different intervals differs significantly with a lateral extent from a few meters to more than 150 m. In most intervals multiple fractures were reactivated. The seismicity typically propagates upwards toward shallower depth on parallel oriented planes that are consistent with the stress field and seem to a large extent associated with preexisting open fractures. This experiment confirms the diversity in seismic behavior independent from the injection protocol. The overall seismicity patterns demonstrate that multi-stage stimulations using zonal isolation allow developing an extended fracture network in a 3D rock volume, which is necessary for enhanced geothermal systems. Our stimulations covering two orders of magnitude in terms of injected volume will give insights into upscaling of induced seismicity from underground laboratory scale to field scale.

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