Earthquakes Continued after COVID-19-related Fracking Shutdown by Laboratory Equipment, April 21, 2021
When hydraulic fracturing operations ground to a halt last spring in the Kiskatinaw area of British Columbia, researchers expected seismic quiescence in the region. Instead, hundreds of small earthquakes occurred for months after operations shut down, according to a new study.
In her presentation at the Seismological Society of America (SSA)’s 2021 Annual Meeting, Rebecca Salvage of the University of Calgary said about 65% of these events could not be attributed to either natural seismicity or active fluid injection from hydraulic fracturing operations.
Salvage and her colleagues instead suggest the latent earthquakes may be the result of aseismic slip, driven by fluid from previous hydraulic fracture injections keeping rock pore pressures elevated.
“Because there are lots of faults in that area, the fluid is becoming trapped in these zones,” Salvage explained. “And as aseismic deformation occurs, which leads to very, very slow slip in these zones, then you get seismicity generated from that process.”
The study by Salvage and her University of Calgary colleague David Eaton offers an unusual glimpse at how hydraulic fracturing may alter the rate of seismicity in a region long after active operations cease.
Their findings may reflect a new background rate of seismicity for the area, Salvage said, “but since this is such an unprecedented situation, we have no idea whether that is the case, and we won’t know until all hydraulic fracturing ceases in the Kiskatinaw Seismic Monitoring and Mitigation Area (KSMMA) entirely, which is unlikely to occur any time in the near future.”
Hydraulic fracturing operations are thought to be the main cause of seismic activity in the Kiskatinaw region, causing thousands of small earthquakes over the past two decades. The area, along with most of western Canada, has very few natural earthquakes. Between 1984 and 2008, before oil and gas operations in the area, seismologists detected only 20 earthquakes in the Kiskatinaw region, Salvage said.
Researchers had just finished installing a new seismic array in the KSMMA in January 2020, hoping to learn more about how active operations were related to earthquakes, particularly those of very small magnitudes.
“Operators in the area have their own small private arrays, but the public sensors in the area were much more scattered and sparse,” said Salvage. “We installed this array thinking, this is going to be great, we’re going to capture all this hydraulic fracturing.”
But when COVID-19 reached the region, operations came to a halt due to a government lockdown which caused plummeting oil and gas prices.
Then the researchers noticed things weren’t entirely quiet. Between April and August 2020, they detected 389 earthquakes during a period of almost no hydraulic fracturing. All of the earthquakes were magnitude 1.2 or smaller, so it wouldn’t be noticeable to anybody that the background seismicity had increased without a seismologist doing the analysis, Salvage said.
The earthquakes didn’t fall into the same patterns that would be expected of hydraulic fracturing-induced seismicity, according to the researchers. The rate of earthquakes persisted over time, instead of declining, and there was no pattern of earthquakes moving away from an initial source, as is often observed during active fluid injection.
Hydraulic fracturing has resumed in the area, along with an uptick in earthquakes.
A few of the papers, many more at link
The Occurrence of Persistent Seismicity in a Hydraulic-Fracturing Dominated Area During Operational Shutdown by Rebecca O. Salvage and Dave W. Eaton, both U of Calgary, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Seismicity in NE British Columbia is usually attributed to ongoing resource development, due to its characteristic temporal and spatial clustering. However, for the first time we have been able to detect seismicity not directly related to these operations, due to the global pandemic of COVID-19 where there was an extended period of anthropogenic quiescence.
A total of 389 events were detected from April to August 2020 within the Kiskatinaw area of British Columbia, encompassing a period of no hydraulic-fracturing operations during a government-imposed lockdown. During this time period, observed seismicity had a maximum magnitude of ML 1.2 but lacked temporal clustering that is often characteristic of hydraulic-fracturing induced sequences.
Hypocenters occurred within a corridor orientated NW-SE, similar to previous years, with focal depths near the target Montney formation or shallower (<2.5 km). Based on the Gutenberg-Richter relationship, we estimate that a maximum of 21% of the detected events during lockdown may be attributable to natural seismicity, with a further 8% possibly due to dynamic triggering of seismicity from teleseismic events. However, the remaining ~70% of events cannot be attributed to a primary activation process (e.g. tectonic forces, fluid injection) and has no obvious trigger (e.g. enhanced pressurization at the onset of seismicity). We deem this to be latent seismicity, which shows an unusually long delay following an activation processes. We can exclude direct pore-pressure diffusion from the most recent fluid injection, as there is no clear pattern of temporal or spatial seismicity migration. If elevated pore pressure from previous injections became trapped in the sub-surface, this could explain the localization of seismicity within an operational corridor, but it does not explain the latency of seismicity on a timescale of months. Aseismic creep on weak surfaces such as faults, in response to tectonic stresses, in addition to trapped elevated pore-pressure could play a role in stress re-loading to sustain the observed pattern of seismicity
A 3D Stochastic Modelling Approach for Induced Seismicity Risk Mitigation by Dave W. Eaton, University of Calgary, and R. S. Eyre, ASEISMIC Solutions Inc., Calgary, Canada, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Anthropogenic fluid injection into the subsurface is known to produce induced seismicity. Efforts to quantify induced-seismicity risk and to develop mitigation strategies are hampered by a dearth of numerical schemes that can accommodate realistic Earth models while capturing the full spectrum of applicable physics. Several models have been proposed to explain the mechanisms of fault activation by fluid injection. The most common is an increase in pore pressure within the fault zone, which leads to a reduction in effective normal stress acting on the fault. Alternatively, poroelastic coupling between hydraulic fractures and the rock matrix is capable of altering fault-loading conditions without any hydraulic connection. More recently, it has been recognized that aseismic slip triggered by the two mechanisms above may play a major in loading unstable regions of a fault. Here, we present a new 3D stochastic approach to modelling injection-induced seismicity, whereby each of these mechanisms are accounted for. Uncertainties in input parameters are addressed stochastically to provide a probabilistic assessment of induced-seismicity risk. Regions of modelled faults that exceed the assigned failure criteria are mapped and provide estimates for the magnitudes of any seismic events that may occur. Due to the stochastic approach, probabilities for the expected maximum magnitudes of events and the sensitivities of results to the different input parameters can be analyzed. This type of modelling can be used to give a site-specific assessment of how the probability of generating an induced event changes, based on different treatment designs. Case studies from western Canada are used to evaluate the applicability of this approach for unconventional oil and gas development; this methodology also has potential for other industries, including geothermal energy and gigatonne-scale carbon dioxide storage.
Statistical Modelling of Induced Seismicity in the Western Canada Sedimentary Basin by S. Kothari, R. Shcherbakov and Gail Atkinson, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
In western Canada, there has been an increase in seismic activity linked to anthropogenic energy-related operations including conventional hydrocarbon production, wastewater fluid injection, and, more recently, hydraulic fracturing (HF). Statistical modelling and characterization of the space, time, and magnitude distributions of the seismicity are vital for a better understanding of induced earthquake processes and development of forecasting models. In this work, a statistical analysis of the seismicity in the Western Canada Sedimentary Basin was performed across past and present time periods by utilizing a compiled earthquake catalog for Alberta and eastern British Columbia. Specifically, the interevent space-time distance distributions of earthquakes were studied using the nearest-neighbor distance (NND) method. Additionally, the frequency-magnitude statistics and aftershock parameters of several clusters were analyzed using the Gutenberg-Richter relation and the epidemic-type aftershock sequence model.
The results suggest that recent regional changes in the NND distributions, namely, a disproportionate increase in loosely and tightly clustered seismic activity over time, are unnatural and likely due to the rise in HF operations for the development of unconventional resources.
It is concluded that both these loosely and tightly clustered earthquake subpopulations differ measurably from what may be the region’s tectonic seismic activity.
Additionally, HF treatments have a greater probability of triggering swarm-like sequences that sharply spike the seismicity rate and are characterized by larger Gutenberg-Richter b values. In contrast, conventional production and wastewater disposal operations largely trigger loosely clustered activity with more typical magnitude occurrence distributions.
Joyner Lecture: Are Small Earthquakes a Big Deal? by Julian J. Bommer, Imperial College London. Introduced by SSA President John Townend, Victoria U of Wellington, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Earthquake engineering has traditionally focused on protecting society against the effects of large-magnitude earth-quakes but in recent years there has been increasing interest regarding the impact of smaller earthquakes. This has been driven partly by the occurrence of some low-magnitude earth-quakes that have caused unexpected levels of damage and particularly by the heightened concern regarding earthquakes of anthropogenic origin. A number of case histories of small magnitude events reported to have caused damage are then reviewed, highlighting in each case the specific factors contributing to the impact—and in some cases arguing that the physical impact may have been exaggerated.
The lecture re-visits the often misunderstood rationale behind the exclusion of smaller magnitude earthquakes from probabilistic seismic hazard analysis as being related to the risk posed by such events.
This is followed by a global analysis of small-to-moderate magnitude earthquakes to ascertain the likelihood of these resulting in damage and/or injury, also considering the generally shallower depths of induced events. Consideration is also given to the question of the smallest magnitudes of relevance to hazards other than ground shaking, including liquefaction and surface rupture. The lecture concludes with some insights regarding if and when smaller earthquakes should be a concern as well as discussing the challenges associated with modeling the resulting hazard and risk that such events can pose.
Shallow Induced Seismicity in Sichuan, China: A Coupled Flow–Geomechanics Modeling Analysis by C. Liu, J. Choo, F. Liu, H. Yang, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
On 25 February 2019, an ML 4.9 (Mw 4.3) earthquake occurred in the Rongxian County, Sichuan, China, presumably related to hydraulic fracturing operations in the Weiyuan Shale Gas Field. The earthquake was located at a depth of ~1 km, which is extremely shallower than the typical locations of induced earthquakes. This peculiarity has attracted detailed investigations into the mechanism of the 2019 Rongxian ML 4.9 earthquake. Recently, Yang et al. (2020) and Wang et al. (2020) have suggested that the earthquake was triggered by reactivation of the Molin fault – located around the same depth as the mainshock – as a result of poroelastic stress change followed by the hydraulic fracturing operations. Nevertheless, the precise mechanism of the shallow earthquake still remains elusive. To shed light on the mechanism of the 2019 Rongxian earthquake, we conduct a computational analysis of the earthquake sequence based on a coupled flow–geomechanics model. Using the extended finite element method (XFEM), the computational model incorporates the full two-way coupling of fluid flow and geomechanical processes on faults as well as off-fault domains. The main findings from the numerical analysis will be discussed.
Spatial-Temporal Evolution Pattern of Earthquakes Illuminated by Machine Learning Method and Waveform Correlation in Weiyuan Shale Gas Field, Sichuan China by W. Wong, J. Zi, P. Zhou, H. Zang, J. Su, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
The rapid development of hydraulic fracturing activities in the Sichuan Basin, China, has immediately followed by a surge of seismicity since 2015. In 2019, 3 magnitude 4+ earthquakes and 2 magnitude 5+ earthquakes struck the Weiyuan Shale Gas Field, causing casualties and damages.
Albeit multiple research groups have conducted extensive studies on these major earthquakes, the centroid depth and inducing mechanisms are still in controversies. In contrast to most of the previous analysis based on a diffusive earthquake catalog constructed from phase arrivals on the local network, we aim to construct a high-resolution catalog using machine learning detector and waveform cross correlation, so as to derive spatial-temporal evolution of seismicity. In our study, we use the PhaseNet, a U-shaped neural network to automatically pick P and S arrivals from the 9 permanent stations across the Weiyuan area. The P and S arrival onset selection by the machine learning method has shown systematic improvements when compared to the catalog phase picks. The arrivals are associated with a grid search method and the events are located by VELEST. Then they are relocated by the double-difference algorithm with the arrival cross-correlation. The newly constructed catalogs detected one-third more earthquakes than the network catalog, despite using one-fourth of the available data from August 2018 to March 2019. The distribution of the earthquakes has delineated unmapped subsurface fault geometry possibly led to the 2019 Mw 5.0 earthquake in September, by far the largest earthquake in the region. The seismicity patterns display high spatial-temporal correlation of multiple earthquake clusters with the hydraulic fracturing wells, confirming a causal link between the emerged seismicity and the hydraulic fracturing in the region.
Rapid Fluid Injection Into a Low Permeability Laboratory Fault Promotes Seismic Swarms by S.B.L. Cebry and G.C. McLaskey, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Fluid injection, from activities such wastewater disposal, hydraulic stimulation, or enhanced geothermal systems, decreases effective normal stress on faults and promotes slip.
Earthquake nucleation models suggest the slip at low effective normal stress will be stable and aseismic—contrary to observed increases in seismicity that are often attributed to fluid injection. We conducted laboratory experiments using a biaxial loading apparatus that demonstrate how an increase in fluid pressure can induce “stick-slip” events along a 0.76 m preexisting saw-cut fault in a poly(methyl methacrylate) (PMMA) sample. We compared slip events generated by externally squeezing the sam-ple (shear-triggered) to those due to direct fluid injection (fluid-triggered) and studied the effects of injection rate and stress levels. Shear-triggered slip events began on a localized nucleation patch and slip smoothly accelerated from slow and aseismic to fast and seismic. Fluid-triggered slip events initiated far more abruptly and were associated with swarms of tiny foreshocks. These foreshocks were able to bypass the smooth nucleation process and jump-start a mainshock resulting in an abrupt initiation. Analysis of these foreshocks indicates that the injection of fluid into a low permeability fault promotes heterogeneous stress and strength which can cause many events to initiate—some of which grow large. To further expand this study, experiments using the same procedure were conducted on a biaxial apparatus with a 3 m long, saw-cut fault in a granite sample. This second set of experiments high-lights the strong effect of stress heterogeneities on resulting fault slip behavior. We conclude that while a reduction in effective normal stress stabilizes fault slip, rapid fluid injection into a low permeability fault increases multi-scale stress/strength heterogeneities which can initiate small seismic events that have the potential to grow rapidly, even into low stress regions.
Understanding Controls on Maximum Induced Earthquake Magnitudes by K. Kroll, E. S. Cachran, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Injection of fluids into the subsurface for industrial operations, such as waste-water disposal, geothermal energy production, and carbon sequestration is known to cause earthquakes.
Forecasts of the hazard associated with such induced seismicity often require estimates of the maximum possible magnitude (Mmax) that may occur near a given site. Scaling relationships suggest that maximum magnitudes or expected numbers of earthquakes are related to the volume of fluid injected into the subsurface; however, notable induced events such as the M5.5 2017 Pohang, South Korea event defy this scaling. To understand the controls on Mmax, we perform a suite of 3-D physics-based earthquake simulations with rate- and state-dependent friction, where we systematically vary the area of the pressurized region and the amplitude of the initial homogeneous or heterogeneous shear stress. Using the resulting catalogs, we explore the conditions that result in pressure-controlled ruptures (confined within the pressurized area) versus runaway ruptures that extend well outside the pressurized zone. We find that proposed empirical scal-ing laws correctly predict Mmax when shear stresses are farther from failure (<=90% of maximum shear stress) and for short wavelength, high amplitude stress fields.
Runaway ruptures are observed for higher initial shear stresses and smoother stress fields without low stress barriers to impede rupture. In these cases, runaway ruptures occur early after the onset of injection and are rarely proceeded by extensive foreshock activity.
Prepared by LLNL under Contract DE-AC52-07NA27344.
Distinguishing the Causal Factors of Induced Seismicity in West Texas: Hydraulic Fracturing Versus Wastewater Disposal by I. Grigoratos, A. Savvaidis, E. Rathje, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Identifying the direct cause of elevated seismicity rates in areas of multiple oil and gas activities has always been a challenging issue that is lacking a homogeneous response. A good example, is the Delaware basin, in West Texas, where the seismicity has been gradually increasing since 2009. In this study, we are examining the recent surge in the area expanding the framework presented in Grigoratos et al. (2020; 10.1785/0120200079) to daily hydraulic fracturing (HF) operations and pressure-driven modeling of wastewater disposal (SWD). Our analysis hindcasts seismicity rates of M ≥ 1.5 events after 2017 on a 5km grid using volume and pressure data as input, and compares them against the null hypothesis of tectonic loading. In the end, each block is assigned a p-value between 0 and 1, indicating our statistical confidence for the causal relationship of each human activity.
Our results indicate that more seismicity clusters than previously identified are associated with HF.
In the center of Reeves county, in particular, HF is associated with a uniform array of more than thirty 5km blocks, and is not limited to scattered sequences as in other parts of the state. Furthermore, although shallow SWD is linked to several sequences, it is not responsible for the vast majority of events, as previously reported. Finally, large parts of the Delaware basin, especially around the city of Pecos, are affected by both oil and gas activities, with better depth resolution needed to fully decouple causality.
Stress Field Variations and Earthquake Source Mechanisms Associated with Wastewater Induced Seismicity in Southern Kansas, USA by A. Amemoutou, P. Martinez-Garzon, G. Kwiatek, M. Bohnhoff, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
During the last 10 years, a strong increase of seismicity rates was observed in the conterminous USA and linked to the injection of huge amounts of wastewater from oil and gas production in unconventional hydrocarbon reservoirs.
Here, we calculated 549 moment tensors of induced earthquakes with a moment magnitude MW ≤ 4.9 in southern Kansas to study their source mechanisms and their relation to injection activity. We observed that approximately 17% of the analyzed events had significant non-double-couple components, and these events mostly occurred near the two largest local earthquakes (the MW 4.9 Milan and MW 4.3 Harper earthquakes). Then, we inverted for the stress field orientation and determined that most of the region lies within a transtensional stress regime, with a maximum horizontal stress σHmax trend-ing N75°E. Furthermore, in the epicentral area of the MW 4.9 Milan earth-quake, the σHmax trend is rotated to about S80°E. Locally, we also highlighted two areas that display a change in the stress field orientation with depth, from transtensional above 5.5 km depth to strike-slip deeper in the basement. Finally by relating the resolved fault geometries to the obtained local stress field orientation, we find that most of the activated fault planes were optimally oriented to the current stress field and thus small stress perturbations caused by the water injection could lead to failure.
Insights on the Criticality of Faults From Dense Monitoring of Induced Seismicity from Moment Tensor Based Stress Inversion by A. Baig, Nanometrics, Kanata, Canada, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Seismic monitoring of waste-water injection, hydraulic fracturing, and other processes has increased across North America. With the increased injection concerns about induced seismicity have risen, and traffic-light systems (TLS) have become a model for managing the risk of shutting down operations. While locations and magnitudes are necessary input for these TLS, seismic monitoring can yield more products providing a detailed level of understanding of the geological and geomechanical setting of the array, allowing for pro-active versus reactive reservoir management. In this paper, I detail how the advanced products of a monitoring system—high-precision locations, moment tensors, and stress inversions derived therefrom—can be used to answer questions on the criticality of the faults, that gives insight into the triggering mechanisms. I look at an example in North America where sequences of large events have been detected over a number of hydraulic fracture completions. Large events, characterized by magnitude above ML2, are selected for moment tensor inversion. By selecting the moment tensors for events within 20km of a grid point, I obtain a relatively high-resolution stress map using a stochastic stress inversion (if at least 10 mechanisms are within that radius). Simultaneously, cross-correlation-based repicking and double difference relocation is used to define lineations associated with faults. By clustering the high-precision locations, these faults can be identified and imaged. Frequently, especially in strike-slip stress regimes in sedimentary basins, this workflow results in the first discovery of such faults as other geophysical means are not amenable. Finally, I assess how critically stressed these faults are in the moment-tensor determined stress regime by calculating the shear and normal stresses on these faults.
What Induced Seismicity From CO2 Injection Can Tell Us About Fluid Migration Pathways by S. Williams-Stroud, H. Leetaru, R. Bauer, S. Greenberg, N. Langet, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Monitoring of induced seismicity before, during, and after injection of super-critical CO2 is being used to help determine pathways the fluid takes during migration over time and to assess the risk of felt seismicity the Illinois Basin – Decatur Project (IBDP). The microseismic activity at the site primarily indicates locations where existing fractures and faults were reactivated. Some microseismic events were large enough to determine focal mechanisms, but no injection-related felt seismicity has been detected. Most of the induced seismicity occurs below the reservoir in fractured low porosity/permeability igneous basement rocks. The reservoir itself, the Cambrian Mt. Simon Sandstone, has high porosity and permeability, with much less common fracturing and faulting. The temporal development of the microseismicity at IBDP indicates stress perturbations that migrate to the north and west of the injection location, concentrated in elongated clusters with NE-SW orientations.
Horizontal fluid migration occurring in the Mt. Simon sandstone could be the dominant pathway for transmission of fluid and pressure away from the injection well to locations that are hydrologically connected to the basement rocks.
To address the potential of upward migration of fluid pressure to cause slip on faults in overlying rocks that could lead to loss of top seal integrity, microseismic monitoring was combined with measurements of pressure and chemistry from subsurface monitoring wells. Shallow monitoring at the site surface has confirmed no CO2 leakage to the surface.
We suggest that that fluid directional pathway is either accommodated by horizontal migration within the Mt. Simon, or by open fractures in the basement with orientations that connect the NE-SW oriented reactivated faults.
We use this integrated data set to create a fault and fracture model that is consistent with the interpretation of the seismic reflection data and the observed microseismicity as a basis on which to test the potential for induced slip on existing fault planes and the risk for induced felt seismicity.
Mechanisms Inducing Earthquakes in the Weiyuan Shale Gas Field, Sichuan, China, Inferred From Dense Array Recordings by H. Yang and J. Zi, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
As one of the major shale gas blocks in China, the Weiyuan shale gas field has been actively developed since 2010, accompanying numerous hydraulic fracturing (fracking) activities. Accordingly, the number of earthquakes has been increasing drastically, with a few damaging earthquakes (M>4) in 2019, some of which led to fatalities in the region. Due to the relatively sparse seismic network, locations of these earthquakes bear appreciable uncertainties, in particular on focal depths. Thus, it remains unclear what mechanisms are dominant of inducing earthquakes in Weiyuan. Since April 2020, we have deployed a dense temporary array consisting of more than 130 short-period seismom-eters, forming a number of mini arrays. During the two-month deployment period, numerous earthquakes with magnitudes up to 3 have been recorded. We apply the machine learning detector, PhaseNet, to identify P and S arrivals. Then we associate the events and locate them by the double-difference method. The location results show a few different earthquake clusters. One cluster that well located within our mini-array stations exhibits clear lineations and temporal migration parallel to the horizontal wells, indicating that they are fracking-induced earthquakes. The earthquakes delineate dipping geometries and locate within 1 km below the Wufeng-Longmaxi formation where fracking was conducted, suggesting that they are likely induced by pore pressure diffusion. Benefiting from the temporary dense array, our location results with unprecedented resolution in the region advance our understanding of mechanisms of induced earthquakes in the Weiyuan shale gas field.
Dynamic Triggering and the State of Stress in Oklahoma by R. A. Alfaro, T. Chen, and X. Ma, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Induced seismicity has increased significantly in Oklahoma resulting from massive wastewater injection. Oklahoma has been subjected to several M ≥ 5 earthquakes including the Prague, Cushing, Fairview, and Pawnee earth-quakes. In order to understand the mechanisms leading to earthquake failure, we examine seismicity leading up to these moderate earthquakes in Oklahoma and search for earthquake-triggering incited by natural transient stresses generated by the seismic waves of large remote earthquakes. We analyze ~7 years of data (2010-2016) from the Oklahoma Seismic Network, EarthScope’s USArray Transportable Array (TA), and temporary local networks. We investigate 957 teleseismic earthquakes wit M ≥ 6 and flag events that significantly increase seismicity throughout Oklahoma following the arrival of the teleseismic wave arrivals. We observe patterns of triggered seismicity indicative of evolving stress-state leading up to several large earthquake failures.
Modeling Injection Induced Stress Changes in the Fort Worth Basin by L. A. Quinones and H. Deshon, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Ongoing seismicity within the crystalline basement of the Fort Worth Basin (FWB), Texas, has been causally linked to the injection of wastewater into the thick, directly overlying, limestone Ellenburger formation. The majority of earthquakes in the basin are located within 10 km of at least one fluid injection well with the exceptions being earthquakes located in the most northeastern portion of the basin. This includes the Dallas-Irving earthquake sequence of M3.4+ earthquakes directly below the densely populated urban area. Spatiotemporal correlation between earthquake and injection activities has led to the conclusion that pore fluid pressure and/or poroelastic stress changes induce seismicity on pre-existing, well-oriented normal faults, even at 10s of kms distance. Here, we create a 3D fully-coupled geomechanical model to examine injection related time-dependent stress changes along faults within the FWB. The model incorporates updated 3D geometries and parameters of the main geologic formations, fault geometries from using earthquake and 3D seismic reflection data, and updated fluid injection data. Parameter testing of the model has focused on three aspects of the system: connectivity of the Ellenburger across the eastern boundary of the basin, which in prior FWB models is assumed to coincide at the intersection of the Ouachita Thrust Front and top of the Ellenburger formation; the matrix permeability of the Ellenburger formation; and the spatial distribution, width and permeability of faults. We find that treating the eastern boundary of the model as an impermeable feature leads to increased stress changes that better match observed seismicity. We show that assumptions regarding the matrix permeability of the Ellenburger have a greater influence on the absolute value of stress change than the connectivity of the NE-SW trending fault systems. We observe peak injection associated stress changes in the basin of >2 MPa for regions with high injection activities, however stress changes in the Dallas-Irving sequence area are <0.1 MPa for all end member parameterizations.
One-Year Seismic Hazard and Risk Maps Due to Wastewater Disposal in Oklahoma by I. grigoratos, P. Bazzurro, E. Rathje, and A. Savvaidis, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
In the past decade, several parts of the United States, including Oklahoma, have experienced unprecedented seismicity rates that have been attributed to wastewater disposal activities carried out by the oil and gas industry.
In this study, we perform a probabilistic assessment of the time-dependent seismic hazard in Oklahoma and incorporate these results into an integrated seismic risk model to assess the evolution of the state-wide economic losses, including a conservative forecast through 2030. Our risk model employs an injection-driven earthquake rate model, a region-specific ground motion model, a recent Vs30 map, HAZUS exposure data and updated vulnerability curves for both structural and non-structural elements, and contents. The calculations are performed using a stochastic Monte Carlo based approach implemented in the OpenQuake software engine. The resulting seismic hazard maps illustrate the incompatibility of the regional seismic provisions with the recent seismicity.
In 2015 in particular, the induced seismic hazard in several places in Oklahoma was higher than along the San Andreas fault. During the peak of seismicity in 2015, the seismic risk was 275 times higher than the background level, with the vast majority of losses originating from damages to non-structural elements (66%) and contents (20%).
We believe that our seismic risk model is a significant upgrade to previous efforts, with our loss estimates being in reasonable agreement with the paid insurance claims. Even though our risk estimates are fairly stable overall, they show significant sensitivity to the Ground Motion Model selection. Finally, our risk model can be adopted in an ongoing manner, helping stakeholders to quantify the benefits of various risk mitigation measures and to define acceptable production levels.
Machine-Learning-Facilitated Earthquake Detection and Characterization Near the Weiyuan Shale Gas Blocks, Sichuan, China by P. Zhou, W. L. Ellsworth, H. Yang , Y. Tan, G. C. Beroza, M. Sheng, R. Chu, www.srl-online.org Volume 92, Number 2B, April 2021 12 14, Seismological Research Letters
Increasing seismicity in shale gas blocks of the Sichuan Basin, China, presents a challenge for rapid analysis and characterization of earthquake sequences, which is critical for seismic hazard assessment and risk mitigation. We analyze the early stages of the Weiyuan, Sichuan, earthquake sequence, which was potentially induced by hydraulic fracking (HF) starting in early 2015, during the 1-year time period from November 2015 to November 2016. The densely clustered small earthquakes were initially detected and located using a dedicated temporary network of 50 stations covering the Weiyuan Shale Gas Blocks and a machine-learning-based phase picker—PhaseNet. Both P- and S-phases are picked and associated for location.
Our primary catalog contains more than 70,000 earthquakes, about 60 times as many earthquakes as appear in the catalog of the Chinese Earthquake Network Center (CENC), which only used the sparsely distributed permanent stations. We also measure the local magnitude and achieve a magnitude of completeness of ML 0. We calibrate the velocity model and refine locations of earthquakes, with magnitudes –0.5 ≤ ML ≤ 3.5. Finally, we located ~43,000 earthquakes that form several spatially compact clusters with the double-difference relocation algorithm and an improved velocity model. Most clustered earthquakes during this time were spatially correlated with HF wells but not with mapped faults. We found clusters of events, most likely induced by HF, showing migration patterns in the Wei202 and Wei204 blocks. Our results demonstrate the applicability of a machine-learning phase picker to a dense seismic network. The algorithms can be run in real time, facilitating rapid characterization of earthquake sequences as they develop.
Refer also to:
Prof Rebecca Harrington on frac quakes in western Canada: “The earthquakes do originate from industrial activities.” Research team from Ruhr-Universität Bochum (Germany) and McGill University (Canada) investigating when frac’ing shakes the earth
Frac waste quakes in Oklahoma keep rising, 4.1M felt 801 km away. Press not reporting it. Authorities diddle & daudle instead of hiring replacement for seismologist Austin Holland. What are Oklahoma authorities afraid of? Studying tens of thousands of frac quakes no one has time for?
Matt Skinner, Oklahoma Corporation Commission – “When we call up OGS (Oklahoma Geological Survey), and they can’t get their computers to come up, that’s a problem.” …
Austin Holland, Oklahoma Geological Survey – “Last year we recorded, or were actually able to locate more than 5000 earthquakes and we probably had another 10,000 that our systems have identified, that we didn’t have a chance to look at.” …
2016: New news or old? Frac’ing, not waste injection, causing earthquakes in Western Canada. Diana Daunheimer calls out U of Calgary’s David Eaton: “So why are you getting the details on this issue so very wrong Mr. Eaton?”
… For the report, in the May-June edition of Seismological Research Letters, the team of 13 scientists surveyed seismic activity between 1985 and 2015 in the Western Canada Sedimentary Basin (WCSB), an area of 454,000 square kilometres near the border between Alberta and B.C., and looked at 12,289 fracking wells and 1,236 waste-water disposal wells.
… “There’s been this growing tide over the last few years” of one-off reports linking an earthquake with fracking activity, she said, but this new report puts them “all together in a more systematic way.”
– Western University professor of geophysics Gail M. Atkinson
“There’s a mixture of science and the whole social-political aspect of this.”
You bet there is Mr. Eaton! Of critical importance is that the political, social, synergy and funding aspects of the oil and gas industry greatly degrades the science and dissemination of factual information and regulations. Wouldn’t you agree?
How long has industry actually known, but vehemently denied hydraulic fracturing causes seismicity? Likely decades, since at least 1985.
“Fracking involves pumping high-pressure fluids underground to create tiny cracks in rock to release natural gas or oil”
Fracking also involves high pressure gas completions as well. Cracks are not always tiny, some fracs propagations have been logged (communicating with other wells bores) at over a kilometre in distance. The average propagation from industry records is approximately 200-400m. That’s some “tiny” crack, which then has the potential (which never existed prior to fracking the formation) to connect to a natural fracture, that may be tens or hundreds of kilometres in distance. Induced and unmanageable chaos.
“Alberta’s energy regulator has already changed regulations for the industry as a result of the Fox Creek earthquakes.”
Subsurface Order #2, which is the interim measure put in place by the AER to “regulate” seismic events, is only relevant to the Fox Creek play based pilot area. The ridiculous stop light system does not apply to any other area or operator in the province that is causing seismicity, such as is in operations around Rocky Mountain House and Cardston. The AER has only implemented regulations for a small portion of operators in a specific area, not the industy as a whole.
“Scientists are aware of the pressure they face getting the issue right, Eaton said.”
So why are you getting the details on this issue so very wrong Mr. Eaton?
Why not tell everyone about how the AER has swept all frac monitoring, previously reported by AGS, under their non-transparent, 100% industry funded, corporate regulatory system?