Global review of human-induced earthquakes

Induced seismicity of the Groningen gas field is caused by the production of gas. Because of the large areal extent of the reservoir, the long history of depletion, and the available data sets (which exist as a result of consequences and public unrest caused by induced seismicity), the field presents a valuable case for studying the relationships among geologic, flow-dynamic, geomechanical, and seismological models. Gas production from the Groningen field started in 1963. Induced seismicity of the field first was recorded in 1991 (ML 2.4). During the subsequent 10 years, induced seismicity stayed at a rate of about five events (ML ≥ 1.5) per year. Starting in 2003, the number of events and magnitudes started to increase. In 2012, the largest event (ML 3.6) occurred, which caused the most damage to date. As a consequence, studies carried out in 2013 have fundamentally changed the way to look at the relationship between induced seismicity and gas depletion. There appears to be a close link between ...

Induced seismicity of the Groningen gas field: History and recent developments

An analytic model now provides quantitative predictions for the effect of void fractions within a granular medium on avalanche statistics. It will help us understand the dynamics of earthquakes as well as plasticity. Slowly sheared granular materials at high packing fractions deform via slip avalanches with a broad range of sizes. Conventional continuum descriptions1 are not expected to apply to such highly inhomogeneous, intermittent deformations. Here, we show that it is possible to analytically compute the dynamics using a simple model that is inherently discrete. This model predicts quantities such as the avalanche size distribution, power spectra and temporal avalanche profiles as functions of the grain number fraction v and the frictional weakening ɛ. A dynamical phase diagram emerges with quasi-static avalanches at high number fractions, and more regular, fluid-like flow at lower number fractions. The predictions agree with experiments and simulations for different granular materials, motivate future experiments and provide a fresh approach to data analysis. The simplicity of the model reveals quantitative connections to plasticity and earthquake statistics.

http://absimage.aps.org/image/MAR12/MWS_MAR12-2011-002498.pdf

A simple analytic theory for the statistics of avalanches in sheared granular materials

This paper presents a Lebedev finite difference scheme on staggered grids for the numerical simulation of wave propagation in an arbitrary 3D anisotropic elastic media. The main concept of the scheme is the definition of all the components of each tensor (vector) appearing in the elastic wave equation at the corresponding grid points, i.e., all of the stresses are stored in one set of nodes while all of the velocity components are stored in another. Meanwhile, the derivatives with respect to the spatial directions are approximated to the second order on two‐point stencils. The second‐order scheme is presented for the sake of simplicity and it is easy to expand to a higher order. Another approach, widely‐known as the rotated staggered grid scheme, is based on the same concept; therefore, this paper contains a detailed comparative analysis of the two schemes. It is shown that the dispersion condition of the Lebedev scheme is less restrictive than that of the rotated staggered grid scheme, while the stability criteria lead to approximately equal time stepping for the two approaches. The main advantage of the proposed scheme is its reduced computational memory requirements. Due to a less restrictive dispersion condition and the way the media parameters are stored, the Lebedev scheme requires only one‐third to two‐thirds of the computer memory required by the rotated staggered grid scheme. At the same time, the number of floating point operations performed by the Lebedev scheme is higher than that for the rotated staggered grid scheme.

Lebedev scheme for the numerical simulation of wave propagation in 3D anisotropic elasticity

/pdf/recent-and-future-developments-in-earthquake-ground-motion-4wjdoetr8w.pdf

Recent and future developments in earthquake ground motion estimation

A seismological model is developed for earthquakes induced by subsurface reservoir volume changes. The approach is based on the work of Kostrov (1974) and McGarr (1976) linking total strain to the summed seismic moment in an earthquake catalog. We refer to the fraction of the total strain expressed as seismic moment as the strain partitioning function, α. A probability distribution for total seismic moment as a function of time is derived from an evolving earthquake catalog. The moment distribution is taken to be a Pareto Sum Distribution with confidence bounds estimated using approximations given by Zaliapin et al. (2005). In this way available seismic moment is expressed in terms of reservoir volume change and hence compaction in the case of a depleting reservoir. The Pareto Sum Distribution for moment and the Pareto Distribution underpinning the Gutenberg-Richter Law are sampled using Monte Carlo methods to simulate synthetic earthquake catalogs for subsequent estimation of seismic ground motion hazard. We demonstrate the method by applying it to the Groningen gas field. A compaction model for the field calibrated using various geodetic data allows reservoir strain due to gas extraction to be expressed as a function of both spatial position and time since the start of production. Fitting with a generalized logistic function gives an empirical expression for the dependence of α on reservoir compaction. Probability density maps for earthquake event locations can then be calculated from the compaction maps. Predicted seismic moment is shown to be strongly dependent on planned gas production.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014JB011663

A seismological model for earthquakes induced by fluid extraction from a subsurface reservoir

A Monte Carlo approach to probabilistic seismic‐hazard analysis is developed for a case of induced seismicity associated with a compacting gas reservoir. The geomechanical foundation for the method is the work of Kostrov (1974) and McGarr (1976) linking total strain to summed seismic moment in an earthquake catalog. Our Monte Carlo method simulates future seismic hazard consistent with historical seismic and compaction datasets by sampling probability distributions for total seismic moment, event locations and magnitudes, and resulting ground motions. Ground motions are aggregated over an ensemble of simulated catalogs to give a probabilistic representation of the ground‐motion hazard. This approach is particularly well suited to the specific nature of the time‐dependent induced seismicity considered. We demonstrate the method by applying it to seismicity induced by reservoir compaction following gas production from the Groningen gas field. A new ground‐motion prediction equation (GMPE) tailored to the Groningen field has been derived by calibrating an existing GMPE with local strong‐motion data. For 2013–2023, we find a 2% chance of exceeding a peak ground acceleration of 0.57 g and a 2% chance of exceeding a peak ground velocity of 22  cm/s above the area of maximum compaction. Disaggregation shows that earthquakes of M w  4–5, at the shortest hypocentral distances of 3 km, and ground motions two standard deviations above the median make the largest contributions to this hazard. Uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes.

A Monte Carlo Method for Probabilistic Hazard Assessment of Induced Seismicity due to Conventional Natural Gas Production

The exponential rise of induced seismicity with increasing stress levels in the Groningen gas field and its implications for controlling seismic risk

Measurements of the strains and earthquakes induced by fluid extraction from a subsurface reservoir reveal a transient, exponential-like increase in seismicity relative to the volume of fluids extracted. If the frictional strength of these re-activating faults is heterogeneously and randomly distributed, then progressive failures of the weakest fault patches account in a general manner for this initial exponential-like trend.

Allowing for the observable elastic and geometric heterogeneity of the reservoir, the spatio-temporal evolution of induced seismicity over 5 years is predictable without significant bias using a statistical-physics model of poro-elastic reservoir deformations inducing extreme threshold frictional failures of previously inactive faults. This model is used to forecast the temporal and spatial probability density of earthquakes within the Groningen natural gas reservoir, conditional on future gas production plans. Probabilistic seismic hazard and risk assessments based on these forecasts inform the current gas production policy and building strengthening plans.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2017JB014356

Extreme Threshold Failures Within a Heterogeneous Elastic Thin Sheet and the Spatial‐Temporal Development of Induced Seismicity Within the Groningen Gas Field

Effective-medium theories can be used to predict reflection coefficients of an interface between an unfractured layer overlying a fractured half-space. In 2D and 3D computer simulations, we analyze wavefields that are emitted by an explosion line or point source and reflected from a fractured area in a digital rock model. The reflection coefficients from the simulations are compared to several predictions given by static effective-medium theories. The agreement between our numerical results and the theoretical reflection coefficients is best for differential effective-medium schemes in 2D as well as in 3D. This result agrees with previously published numerical static and numerical transmission-time experiments. By varying the wavelength to crack-length ratio, we consider the application range of different effective-medium theories. We observe good agreement with theoretical predictions even for a ratio equal to 9. An angle-dependent analysis of the reflected amplitude of our numerical results is also compared to results given by effective-medium theory in combination with exact reflection-coefficient formulas. As expected, the fluctuations of the reflection coefficients decrease for wider angles. In our 3D digital rock models, we vary the crack density and the infill of the crack (i.e., water [cold and hot] and oil [cold and hot]).

S. J. Oates

Papers

A seismological model for earthquakes induced by fluid extraction from a subsurface reservoir

A Monte Carlo Method for Probabilistic Hazard Assessment of Induced Seismicity due to Conventional Natural Gas Production

The exponential rise of induced seismicity with increasing stress levels in the Groningen gas field and its implications for controlling seismic risk

Extreme Threshold Failures Within a Heterogeneous Elastic Thin Sheet and the Spatial‐Temporal Development of Induced Seismicity Within the Groningen Gas Field

A numerical study on reflection coefficients of fractured media