Stefan Wiemer

Last Name

Wiemer

First Name

Stefan

ORCID

0000-0002-4919-3283

Organisational unit

02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)

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Publications 1 - 10 of 219

Analysis of hazard and efficiency associated with the stimulation strategy for Enhanced Geothermal Systems
Ritz, Vanille; Rinaldi, Antonio Pio; Wiemer, Stefan (2018)
Geophysical Research Abstracts
Stimulation operations at geothermal sites often cause induced earthquakes that are susceptible of being felt by local populations. Such injection-induced sequences often present specific earthquake-size distributions, presenting both spatial and temporal features ; an example of which being the Basel deep heat mining experiment. Previous studies have already replicated these observations with simplified assumptions. Here, we propose an improvement to these model accounting for a full 3D configuration for stress and fluid flow, and more complex physics based mechanisms (e.g. permeability enhancement, static stress transfer). Our model of a hot dry rock system and its stimulation phase is achieved using a hydro-geomechanical-stochastic simulator: TOUGH2-Seed. We successfully model a seismic cloud comparable to the one observed in Basel, including similar spatio-temporal evolutions of the b-value. Based on this synthetic modelling, we focus on assessing the efficiency of the reservoir creation, introducing a stimulation factor built on permeability enhancement in the stimulated volume. Furthermore, we assess the seismic hazard associated with the fluid injection, estimating the probability of exceeding a certain magnitude event during and after stimulation. The comparison of these factors representing seismic hazard and efficiency allow us to envision a unique tool aiming at a simpler evaluation of injection strategies, reconciling the engineering successfulness goal of a geothermal project and the potentially damaging seismicity resulting from stimulation operations.
Variability of Seismicity Rates and Maximum Magnitude for Adjacent Hydraulic Stimulations
Kwiatek, Grzegorz; Grigoratos, Iason; Wiemer, Stefan (2025)
Seismological Research Letters
We hindcasted the seismicity rates and the next largest earthquake magnitude using seismic and hydraulic data from two hydraulic stimulation campaigns carried out in adjacent (500 m apart) ultra‐deep wells in Finland. The two campaigns performed in 2018 and 2020 took place in the frame of the St1 Helsinki project producing stable, pressure‐controlled induced seismic activity with the maximum magnitudes of 1.7 and 1.2, respectively. The seismicity rates were modeled using simplified physics‐based approaches tailored to varying injection rates. This is the first time that this framework was applied to a cyclical injection protocol. The next largest earthquake magnitude was estimated using several existing models from the literature. Despite the close proximity of the two hydraulic stimulations and associated seismicity, we obtained strongly different parameterizations of the critical model components, questioning the usefulness of a priori seismic hazard modeling parameters for neighboring stimulation. The differences in parameterization were attributed to the contrasting hydraulic energy rates observed in each stimulation, small differences in the fracture network characteristics of the reservoir and resulting seismic injection efficiency, and potentially to variations in the injection protocol itself. As far as the seismicity rate model is concerned, despite a good performance during the 2018 campaign, the fit during the 2020 stimulation was suboptimal. Forecasting the next largest magnitude using different models led to a very wide range of outcomes. Moreover, their relative ranking across stimulations was inconsistent, including the situation when the best‐performing model in the 2018 stimulation turned out to be the worst one in the 2020 stimulation.
Shale fault zone structure and stress dependent anisotropic permeability and seismic velocity properties (Opalinus Clay, Switzerland)
Wenning, Quinn; Madonna, Claudio; Zappone, Alba; et al. (2021)
Journal of Structural Geology
Given shale's potential to serve as both a caprock for geological carbon sequestration and as the host for nuclear waste disposal, this study focuses on the structural characterization around a 1.5–3 m thick fault within the Opalinus Clay host rock and petrophysical characterization of both the host rock and fault core. Seven boreholes were drilled at the Mont Terri Rock laboratory in late 2018 to constrain the orientation of the so-called ‘Main Fault’ and several fracture families within the fault core using core and image logs. Contrary to typical fault models, matrix permeability and seismic velocity measurements show similarities in the host rock and within the Main Fault. In the clay-rich samples, measurements performed in laboratory at varying confining pressures indicate p-wave velocities range from 2.60 to 2.95 km/s perpendicular to foliation and 3.38–3.58 km/s parallel to foliation at near in-situ confining pressures, which increase with similar anisotropy at higher confining pressures (200 MPa). Since the permeability of the host rock and fault zone is very low (10−19–10−21 m2) flow is expected to prevail along fractures, where critical stress fault analysis suggests that potential hydraulically conductive fractures are actually conjugate to the Main Fault trend.
Selection and characterization of the target fault for fluid-induced activation and earthquake rupture experiments
Achtziger-Zupančič, Peter; Ceccato, Alberto; Zappone, Alba Simona; et al. (2024)
Solid Earth
Performing stimulation experiments at approximately 1 km depth in the Bedretto Underground Laboratory for Geosciences and Geoenergies necessitates identifying and characterizing the target fault zone for on-fault monitoring of induced fault slip and seismicity, which presents a challenge when attempting to understand seismogenic processes. We discuss the multidisciplinary approach for selecting the target fault zone for experiments planned within the Fault Activation and Earthquake Ruptures (FEAR) project, for which the aim is to induce the fault slip and seismicity for an earthquake magnitude of up to 1.0 while enhancing the monitoring and control of fluid-injection experiments.Structural geological mapping, remote sensing, exploration drilling and borehole logging, ground-penetration radar, and laboratory investigations were employed to identify and characterize the target fault - a ductile-brittle shear zone several meters wide with an intensely fractured volume spanning over 100 m. Its orientation in the in situ stress field favors reactivation in normal to strike-slip regimes. Laboratory tests showed slight velocity strengthening of the fault gouge. The fault's architecture, typical for crystalline environments, poses challenges for fluid flow, necessitating detailed hydraulic and stress characterization before each of the FEAR experiments. This multidisciplinary approach was crucial for managing rock volume heterogeneity and understanding implications for the dense monitoring network. Successfully identifying the fault sets the stage for seismic activation experiments commencing in spring 2024.
Extending ERM-CH23 to shallow induced seismicity in Switzerland
Grigoratos, Iason; Bergamo, Paolo; Cauzzi, Carlo Virgilio; et al. (2025)
The risks from induced seismicity remain a persistent and complex issue that needs to be managed. Appropriate modeling of these risks is essential in order to facilitate both the permitting process of certain energy-production projects and the acquisition of insurance against potential losses. For Switzerland, the most relevant causal factors of induced seismicity are likely hydraulic stimulations for Enhanced Geothermal Systems and fluid disposal for storage. The earthquakes that these activities might trigger are expected to be quite shallow, of mostly small to moderate magnitude. Their nucleation mechanism might also differ, compared to tectonic events. Thus, their source characteristics and the attenuation of their ground motion might be partly incompatible with the modeling assumptions adopted by the national Earthquake Hazard Model of Switzerland (SUIhaz2015; Wiemer et al., 2016; Papadopoulos et al., 2024a). This report investigated these issues, as well as, the possibility that the fragility models of the Earthquake Risk Model of Switzerland (ERM-CH23; Wiemer et al., 2023) might warrant modifications for similar reasons.. The results of these investigations highlighted the need to adjust some aspects of the risk model to render it suitable for (shallow) induced seismicity in Switzerland. In the end, new recommendations were made regarding the minimum and maximum magnitude, two new intensity measures were added to the vulnerability models, while major changes were made to the ground shaking branching level. The latter is now magnitude-dependent, only includes spectral acceleration models and was tilted towards lower stress-parameter values. A ready to use version of the updated risk model, called Induced Earthquake Risk Model of Switzerland (IERM-CH25), is now available. Finally, risk calculations, including sensitivity analyses, were conducted for certain scenario earthquakes at selected sites.
Development of 1D Hybrid Hydromechanical Models for Real‐Time Forecasting of Induced Seismicity Rate
Clasen Repollés, Victor; Rinaldi, Antonio Pio; Ciardo, Federico; et al. (2025)
Journal of Geophysical Research: Solid Earth
Hydraulic stimulations play an important role in Enhanced Geothermal Systems (EGS) byincreasing the permeability of the host rock and facilitating more efficient fluid circulation and heat extraction.However, fluid injection operations are unavoidably accompanied by induced earthquakes. Adaptive TrafficLight Systems (ATLS) have been proposed as seismic risk mitigation tools for EGS stimulations. An ATLSscheme aims to provide real‐time, adaptive, and time‐dependent probabilistic seismic forecasts by leveragingthe latest available data during ongoing industrial operations. Critical to ATLS are numerical models capable ofrobustly forecasting the temporal evolution of induced seismicity, while properly accounting for uncertainties.In this work, we present two classes of 1D hybrid hydromechanical models for real‐time forecasting of inducedearthquakes. We retrospectively apply these models to data sets from hydraulic stimulations performed at fourdifferent spatial scales: Grimsel Test Site (2017), Bedretto Underground Laboratory for Geoenergy andGeosciences (2022), Utah FORGE (2022), and Basel Deep Heat Mining project (2006). We compare themodels' forecasting performance and real‐time applicability. We found that a nonlinear pressure solution thataccounts for both reversible and irreversible permeability changes, coupled with an analytical probabilitydensity‐based approach to simulate seismicity, is more suitable for industrial‐scale applications. A stochasticapproach that explicitly simulates seismicity, albeit simplified and improved for computational efficiency,exhibits greater variability in performance and remains computationally expensive for industrial‐scale casesinvolving large seismic data sets and high spatial resolution requirements.
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.
A Prospective Evaluation of Borehole Distributed Acoustic Sensing Technologies for Detecting and Locating Out‐of‐Network Microseismicity
Lanza, Federica; Tuinstra, Katinka B.; Rinaldi, Antonio P.; et al. (2024)
Geophysical Monograph Series ~ Distributed Acoustic Sensing in Borehole Geophysics
Downhole distributed acoustic sensing (DAS) has proven effective in monitoring microseismicity produced during hydraulic stimulations. It is also a promising tool for monitoring microseismicity occurring beyond the stimulation region. Downhole DAS arrays exhibit reduced sensitivity to surface noise compared to surface deployments, and they can remain in place undisturbed after operations cease, unlike downhole geophones. Identifying and locating microseismicity occurring at remote distances is crucial for reservoir monitoring, allowing us to assess stress conditions and the presence of pre-existing faults. Here, we evaluate the potential of downhole DAS in detecting and locating out-of-network microseismicity through two case studies: a field-scale investigation at the Frontier Observatory for Research in Geothermal Energy (FORGE) site in Utah and a mesoscale experiment in the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) in Switzerland. We demonstrate that DAS data have sufficient quality to detect and locate low-magnitude earthquakes (M < 0) occurring several hundred meters away. However, azimuthal ambiguity is unavoidable when only a single vertical borehole is available. We show that DAS signal characteristics and location capabilities perform equally at different scales, ranging from full-reservoir scale to mesoscale. Our evaluation supports the employment of longer-term experiments to explore downhole DAS suitability for passive microseismic monitoring.
Corrigendum to “Hydraulic stimulation and fluid circulation experiments in underground laboratories: Stepping up the scale towards engineered geothermal systems” by Gischig et al. https://doi.org/10.1016/j.gete.2019.100175
Gischig, Valentin S.; Giardini, Domenico; Amann, Florian; et al. (2020)
Geomechanics for Energy and the Environment
The bound growth of induced earthquakes could de-risk hydraulic fracturing
Schultz, Ryan; Lanza, Federica; Dyer, Ben; et al. (2025)
Communications Earth & Environment
The world’s energy supply depends critically on hydraulic fracturing (HF) to access otherwise uneconomical resources. Unfortunately, HF also has the potential to induce larger earthquakes – with some projects being prematurely terminated because of perceived earthquake risks. To de-risk HF, we use a suite of statistical tests to discern if some physical process has restricted the growth of earthquake magnitudes. We show that all stage stimulations at both UK PNR-1z and Helsinki St1 indicate bound fracture growth, implying a more controllable operation. Contrastingly, stimulations at Utah FORGE and UK PNR-2 sequentially transitioned into unbound fault reactivation. The problematic stages (that ultimately led to the termination of PNR-2) are clearly distinguishable. We postulate that our research can discriminate fracture stimulation from fault reactivation, contributing to the de-risking of HF operations worldwide. Our statistical tests provide a framework for model falsification, which can guide physical insights into the bounding processes.

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Stefan Wiemer

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