Large Seismic Events Research Articles

Fracture caging in a lab fault to prevent seismic rupture during fluid injection

Seismic risk associated with deep fluid injection is a major holdback for geothermal energy development. Currently adopted mitigation measures include traffic light protocol and cyclic stimulation methods that retroactively limit injection pressures and flowrates based on observed seismic activity to hopefully reduce the likelihood of triggering large seismic events. Fracture caging presents an alternative proactive approach to seismicity mitigation that does not require flow rate or injection pressure limits. The caging concept is to pre-drill boundary wells around injection wells to contain all injected fluid. Prior experimental and numerical work demonstrated successful caging of tensile hydraulic fractures but did not investigate caging in shear faults. To fill this knowledge gap, this study focuses on caging of injection-induced shear fractures in a critically stressed lab-scale shear fault. Experiment variables include mechanical versus hydraulic shearing and cage size by varied well spacing. Acoustic activity was monitored using two calibrated acoustic emission systems, each having a different sensitivity bandwidth. This constitutes what we call Caged Geothermal Systems (CGS) as a modified version of Enhanced Geothermal Systems (EGS), but with CGS using more wells, an accelerated drilling timetable, much higher flow rate limits, and less proppant. We demonstrate successful caging in a lab-scale shear fault with a high recovery of the injected fluid and prevention of large critical rupture events.

Seismic radial anisotropy in southeastern Tibetan Plateau and its implications for regional geodynamic evolution

The southeastern Tibetan Plateau exhibits intricate crustal tectonics, encompassing recent seismic megathrust events. Previous research suggested the presence of north-south-oriented channelized viscous flow within the crust. However, recent investigations have unveiled a notable northeast-southwest-oriented geological structure, potentially rigid, intersecting with the presumed crustal channelized flow. Several questions persist regarding the composition of the northeast-southwest-oriented structure, the continuity of crustal channelized flow, and the interplay between them. In this study, dispersion data from a dense seismic array are employed to significantly refine regional crustal models for shear wave velocity and radial anisotropy through ambient noise tomography. The resulting high-resolution model further reveals the style of the crustal deformation and supports the interpretation that the northeast-southwest structure, which shows higher velocity and significant negative radial anisotropy, results from mafic material at the base of crust, obstructing the crustal channelized flow. However, the northeast-southwest structure is not as rigid as the Sichuan Block and exhibits depth-dependent deformation. The interpretation proves useful in further understanding regional earthquake focal mechanisms and strain distribution. Additionally, this research identified a region of generalized negative radial anisotropy in the crust of the western Chuan-Dian fragment, suggesting a reduced horizontal channel crustal flow in this area. Drawing upon various geophysical and geological evidence, we present a geodynamic evolution model, proposing a sequence of events: Permian plume activity resulting in mafic material at the base of the crust near Anninghe-Zemuhe fault, northward advancement of the east Himalayan syntaxis inducing crustal compressional stress field, reduced lower crustal channel flow in the western Chuan-Dian fragment leading to the regional east-west extension, and initiation of the Xianshuihe fault causing shift of strain concentration and depth-dependent deformation near the Anninghe-Zemuhe fault. The geodynamic model provides valuable insights into the regional distribution of crustal strain and the underlying mechanisms of large seismic events.

Classifying Seismic Events Linked to Solar Activity: A Retrospective LSTM Approach Using Proton Density

The influence of solar activity on seismic activity is a subject of debate. Previous studies have shown that there is sometimes a correlation and sometimes a contradiction between solar activity maxima and large earthquakes. Long-term memory neural network is used to study the relationship between solar activity and seismic activity. This study emphasizes retrospective classification rather than direct prediction, refining the LSTM architecture to maximize classification accuracy and processing data from the Solar and Heliospheric Observatory and the U.S. Geological Survey earthquake catalogs. A declustering technique is used to select large seismic events and weighted learning corrects for class imbalances. The LSTM model accurately classified earthquakes (84.47%) and proton density variations. The results support the theory that solar activity, in particular proton density, can anticipate earthquake events.

Evaluating the thresholds for predicting post-earthquake debris flows: Comparison of meteorological, hydro-meteorological and critical discharge approaches

Post-earthquake debris flows pose significant hazards in mountainous regions following large seismic events. Evaluating the thresholds for predicting the occurrence of these flows is crucial. However, the absenting of comparison for different predicting methods hampers progress in improving and updating predictions for debris flows. In this study, based on on-site measurements of post-earthquake debris flows in an active catchment during the first year following the 2022 Luding Ms6.8 earthquake, 30 debris-flow events were identified and observed. We established and compared three distinct methods—namely, the meteorological approach, the hydro-meteorological approach, and the critical discharge approach for predicting the occurrence of post-earthquake debris flows. Additionally, we introduced a factor called absolute energy to improve the accuracy of the traditional meteorological approach. Absolute energy is defined as the sum of squared values within a time series. Our findings indicate that the hydro-meteorological model outperforms others in predicting post-earthquake debris flows, whereas the meteorological approaches especially the intensity–duration (I–D) thresholds exhibit suboptimal performance. Furthermore, the updated meteorological model incorporating absolute energy demonstrates improved predictive capability compared to traditional meteorological approaches like intensity–duration (I–D) thresholds. We argue that this comparative analysis will aid in selecting the suitable method for predicting post-earthquake debris flows.

Characteristics of the seismogenic zone in an arc-continent collision belt: insights from seismic b values in Eastern Taiwan

Eastern Taiwan overlies a suture zone between the Eurasian Plate and the Philippine Sea Plate and is characterized by frequent earthquakes, often resulting in significant disasters. Notably, the region exhibits characteristics such as a high frequency of earthquakes and a short recurrence period for intense seismic events. While prior research has explored seismic b values across various periods in Taiwan, detailed investigations of the b value in the eastern region are lacking. This study employs the earthquake catalog compiled by the Taiwan Central Weather Administration to analyze spatial–temporal variations in b values in eastern Taiwan. The analysis encompasses seismic events occurring between January 1996 and June 2019. The seismic catalog is divided into three distinct time periods related to large seismic events: period I, 1996–2003 (the Chengkung earthquake); period II, 2003–2013 (the Ruisui earthquake); and period III, 2013–2019 (the Hualien earthquake). Our results indicate that most seismic events with a magnitude greater than 6 are associated with low b values. The overall b value increases during period II and then decreases substantially during period III. Although the estimated b values changed slightly, but the uncertainty in b values remained stable in this study. The epicenters of large earthquakes often overlap with areas with lower b values, especially in plate suture zones, which means that areas with lower b values usually have a higher probability of larger earthquakes. Given the extremely high potential for a catastrophic earthquake, mitigating measures should be adopted at all times.Graphical

Abnormal low-magnitude seismicity preceding large-magnitude earthquakes

Unraveling the precursory signals of potentially destructive earthquakes is crucial to understand the Earth’s crust dynamics and to provide reliable seismic warnings. Earthquake precursors are ambiguous, but recent experimental studies suggest that robust warning signs may precede large seismic events in the short (day-to-months) term. Here, we show that the M6.4-M7.1 2019 Ridgecrest sequence (California) and the M7.1 2018 Anchorage earthquake (Alaska) were preceded by up to ~3 months of tectonic unrest on regional scales, as evidenced by abnormal low-magnitude seismicity spreading over the ~15-25% of Southern California and Southcentral Alaska. This precursory unrest has been discovered with an algorithm that integrates an innovative random forest machine learning approach and statistical features built from earthquake catalogs. Supported by a novel suite of finite element solid mechanics models, we propose that precursory, abnormal, low-magnitude seismicity arises if the pore fluid pressure within large fault segments escalates significantly as they approach failure, which leads to major uneven changes in the regional stress field. Our findings and method may open up new perspectives for surveillance agencies to anticipate when a region approaches an earthquake of great magnitude weeks to months before it occurs.

Near-Real Prediction of Earthquake-Triggered Landslides on the Southeastern Margin of the Tibetan Plateau

Earthquake-triggered landslides (ETLs) feature large quantities, extensive distributions, and enormous losses to human lives and critical infrastructures. Near-real spatial prediction of ETLs can rapidly predict the locations of coseismic landslides just after a violent earthquake and is a vital technical support for emergency response. However, near-real prediction of ETLs has always been a great challenge with relatively low accuracy. This work proposes an ensemble prediction model of EnPr by integrating machine learning tree models and a deep learning convolutional neural network. EnPr exhibits relatively strong prediction and generalization performance and achieves relatively accurate prediction of ETLs. Six great seismic events occurring from 2008 to 2022 on the southeastern margin of the Tibetan Plateau are selected to conduct ETL prediction. In a chronological order, the 2008 Ms 8.0 Wenchuan, 2010 Ms 7.1 Yushu, 2013 Ms 7.0 Lushan, and 2014 Ms 6.5 Ludian earthquakes are employed for model training and learning. The 2017 Ms 7.0 Jiuzhaigou and 2022 Ms 6.1 Lushan earthquakes are adopted for ETL prediction. The prediction accuracy merits of ACC and AUC attain 91.28% and 0.85, respectively, for the Jiuzhaigou earthquake. The values of ACC and AUC achieve 93.78% and 0.88, respectively, for the Lushan earthquake. The proposed EnPr algorithm outperforms the algorithms of XGBoost, random forest (RF), extremely randomized trees (ET), convolutional neural network (CNN), and Transformer. Moreover, this work reveals that seismic intensity, high and steep relief, pre-seismic fault tectonics, and pre-earthquake road construction have played significant roles in coseismic landslide occurrence and distribution. The EnPr model uses globally accessible open datasets and can therefore be used worldwide for new large seismic events in the future.

Stress spatial distributions, the Gutenberg–Richter and Omori–Utsu laws

We investigate several earthquake models in one and two dimensions of space and analyze in these models the stress spatial distribution. We show that the statistical properties of stress distribution are responsible for the distribution of earthquake magnitudes, as described by the Gutenberg–Richter (GR) law. A series of predictions is made based on the analogies between the stress profile and one-dimensional random curves or two-dimensional random surfaces. These predictions include the b-value, which determines the ratio of small to large seismic events and, in two-dimensional models, we predict the existence of aftershocks and their temporal distribution, known as the Omori–Utsu law. Both the GR and Omori–Utsu law are properties which have been extensively validated by earthquake observations in nature.

Cyclical hydraulic pressure pulses reduce breakdown pressure and initiate staged fracture growth in PMMA

Using unique experimental equipment on large bench-scale samples of Polymethylmethacrylate, used in the literature as an analogue for shale, we investigate the potential benefits of applying cyclical hydraulic pressure pulses to enhance the near-well connectivity through hydraulic fracturing treatment. Under unconfined and confined stresses, equivalent to a depth of up to 530 m, we use dynamic high-resolution strain measurements from fibre optic cables, complemented by optical recordings of fracture development, and investigate the impact of cyclical hydraulic pressure pulses on the number of cycles to failure in Polymethylmethacrylate at different temperatures. Our results indicate that a significant reduction in breakdown pressure can be achieved. This suggests that cyclic pressure pulses could require lower power consumption, as well as reduced fluid injection volumes and injection rates during stimulation, which could minimise the occurrence of the largest induced seismic events. Our results show that fractures develop in stages under repeated pressure cycles. This suggests that Cyclic Fluid Pressurization Systems could be effective in managing damage build-up and increasing permeability. This is achieved by forming numerous small fractures and reducing the size and occurrence of large fracturing events that produce large seismic events. Our results offer new insight into cyclical hydraulic fracturing treatments and provide a unique data set for benchmarking numerical models of fracture initiation and propagation.

A study of fluid overpressure microstructures from the creeping segment of the San Andreas fault

Evidence of episodic fluid overpressure events noted in samples from the San Andreas Fault Observatory at Depth (SAFOD) have remained largely uncorrelated in terms of their collective significance for seismic history of the fault zone. The compositional and microstructural correlations sought in this study could shed light on questions about potential for major seismic events in the creeping segment of the SAF in central California. We used quantitative energy dispersive spectroscopy (EDS), Cathodoluminescence (CL) and Scanning Electron Microscope (SEM) imaging, and electron backscatter diffraction (EBSD) analysis to acquire geochemical and microstructural data from a suite of twenty SAFOD core samples including the damage zone and the active core of the fault. The results indicate intermittent coseismic fluid overpressure events that overprint the background aseismic creep across the fault. Analysis of trace elements and deformation in the coseismic calcite vein generations and their associated hydrothermal mineral phases indicate progressive uplift and exhumation followed by an asymmetric incursion of meteoric water into the damage zone. The same analysis suggests that the actively creeping intervals act as permeability barriers. Our results are in overall agreement with recent studies of the SAF in central California that indicate large seismic events have occurred intermittent with aseismic creep in recent geological time or suggest future potential for such events.

Impact of Lossy Compression Errors on Passive Seismic Data Analyses

Abstract New technologies such as low-cost nodes and distributed acoustic sensing (DAS) are making it easier to continuously collect broadband, high-density seismic monitoring data. To reduce the time to move data from the field to computing centers, reduce archival requirements, and speed up interactive data analysis and visualization, we are motivated to investigate the use of lossy compression on passive seismic array data. In particular, there is a need to not only just quantify the errors in the raw data but also the characteristics of the spectra of these errors and the extent to which these errors propagate into results such as detectability and arrival-time picks of microseismic events. We compare three types of lossy compression: sparse thresholded wavelet compression, zfp compression, and low-rank singular value decomposition compression. We apply these techniques to compare compression schemes on two publicly available datasets: an urban dark fiber DAS experiment and a surface DAS array above a geothermal field. We find that depending on the level of compression needed and the importance of preserving large versus small seismic events, different compression schemes are preferable.

Enhancing post-seismic landslide susceptibility modeling in China through a time-variant approach: a spatio-temporal analysis

ABSTRACTThe pre-phase landslides will have a legacy effect on future landslides, changing the landslide susceptibility. This study attempts to establish a reasonable post-seismic landslide susceptibility model and analyze the spatio-temporal characteristics of landslide susceptibility in the Jiuzhaigou MS7.0 earthquake-struck region. Firstly, an integrated ‘space-ground’ monitoring technology is used to establish a multi-temporal post-seismic landslide dataset. Then, the buffer analysis method documents the spatio-temporal characteristics of post-seismic landslides. Thirdly, the distance is selected as an indicator to quantify the legacy effect. An improved time-variant model is established to evaluate the post-seismic landslide susceptibility. Finally, the spatio-temporal characteristics of landslide susceptibility are generalized, to sum up the changing law. Our results show that the post-seismic landslides are gradually closer to the pre-phase landslides with time. Distance is a critical factor in measuring the impact of pre-phase landslides on future landslides, which can improve the assessment accuracy of the post-seismic landslide susceptibility model. After a large seismic event, the correlation between landslide susceptibility and earthquakes gradually weakens. Post-seismic landslide prevention should focus on the pre-phase landslide expansion triggered by rainfall. Moreover, it should clean up the landslide deposits in time and reasonably dredge the debris flows to avoid secondary geological disasters.

A Tectonic Origin for the Largest Marsquake Observed by InSight

AbstractThe S1222a marsquake detected by InSight on 4 May 2022 was the largest of the mission, at 4.7. Given its resemblance to two other large seismic events (S1000a and S1094b), which were associated with the formation of fresh craters, we undertook a search for a fresh crater associated with S1222a. Such a crater would be expected to be ∼300 m in diameter and have a blast zone on the order of 180 km across. Orbital images were targeted and searched as part of an international, multi‐mission effort. Comprehensive analysis of the area using low‐ and medium‐resolution images reveals no relevant transient atmospheric phenomena and no fresh blast zone. High‐resolution coverage of the epicentral area from most spacecraft are more limited, but no fresh crater or other evidence of a new impact have been identified in those images either. We thus conclude that the S1222a event was highly likely of tectonic origin.

High energy events as a combined effect of human impact and geoenvironmental factors - the case study based on GNSS data

In the Upper Silesian Coal Basin (USCB) mining region in Poland, coal production has been gradually reduced for many years. Nevertheless, the number of high-energy tremors remains at a similar level or decreases much slower than production. We analyze this problem in the aspect of geological setting and on the base of geodetic data. We explain the paradox by specific interaction between man-induced and natural tectonic stress as seasonal hydrological effects. Anomalous energies released during large seismic events exceeded the predetermined threshold, typical for mining tremors in the area. Further, the authors point out the seasonal occurrence of these events. Temporal variations of distances between continuously operating GNSS (Global Navigation Satellite Systems) reference stations were analyzed, and linear strain, inferred from these geodetic observations, corresponded to high-energy tremors in the area. Consequently, the seismic events usually occurred when the analyzed baseline performance demonstrated significant seasonal increases or decreases of evaluated temporal distribution of strain. The aim of the analysis was to evaluate the relationships between the characteristics of the time series of deformations and the occurrence of seismic tremors of energy E ≥ 3 x 107J occur. Seasonal occurrences of high-energy seismic events as the energy they released suggest the influence of environmental factors.

Constraints for the Martian Crustal Structure From Rayleigh Waves Ellipticity of Large Seismic Events

AbstractFor the first time, we measured the ellipticity of direct Rayleigh waves at intermediate periods (15–35 s) on Mars using the recordings of three large seismic Martian events, including S1222a, the largest event recorded by the InSight mission. These measurements, together with P‐to‐s receiver functions and P‐wave reflection times, were utilized for performing a joint inversion of the local crustal structure at the InSight landing site. Our inversion results are compatible with previously reported intra‐crustal discontinuities around 10 and 20 km depths, whereas the preferred models show a strong discontinuity at ∼37 km, which is interpreted as the crust‐mantle interface. Additionally, we support the presence of a shallow low‐velocity layer of 2–3 km thickness. Compared to nearby regions, lower seismic wave velocities are derived for the crust, suggesting a higher porosity or alteration of the whole local crust.

The Observed Inefficiency of Explosions to Produce Large Aftershocks: Båth’s Law for Explosions is 2.5

Abstract Underground explosions are observed to produce fewer and smaller aftershocks than similar size earthquakes. The seismic magnitude difference Δmx between an explosion and its largest aftershock is an expression of Båth’s law for explosions. Based on an analysis of a compilation of aftershock studies from Soviet testing at the Semipalatinsk test site in Kazakhstan and observations from American testing at the Nevada National Security Site (NNSS), we find that the average magnitude difference for explosions Δmx‾ is about 2.5. Based on the NNSS data, two standard deviations of Δmx is about 1.5. In all the cases studied, from ton to megaton yield, from shallow to overburied depth, and chemical or nuclear source, no explosion aftershock has been larger than the explosion that preceded it. In fact, the two events at the NNSS with the largest aftershock magnitudes relative to the explosion are associated with the collapse of the cavity created by the explosion. This is similar to observations from North Korean testing at the Punggye-ri Test Site, where the largest seismic event following the test is attributed to the collapse after the 2017 explosion and is from 0.8 to 2 magnitude units less than the mainshock.

Numerical investigation of interactions between hydraulic and pre-existing opening-mode fractures in crystalline rocks based on a hydro-grain-based model

Hot dry rock (HDR) is deep geothermal reservoir rock predominantly containing granite, whose physical and mechanical properties are governed by heterogeneous crystal structures. However, the fluid conductivity of intact granite with ultra-low permeability cannot be reformed using existing techniques. Complex fracture networks must be created by connecting hydraulic fractures with natural fractures developed in reservoirs. In this study, we introduce the wall barrier method into the novel hydro-grain-based model (hydro-GBM) to build a prefractured granite model at the mineral grain scale. This model enables investigation of the effects of the stress environment, mineral spatial distribution, and fluid injection rate on hydraulic fracturing characteristics. Microcracks around the inner tips of pre-existing fractures reproduce the initiation, propagation, and coalescence behaviors similar to experimental results. Mineral spatial distributions induce random changes in the propagation paths of hydraulic fractures. Increasing the fluid injection rate delays the deflection of hydraulic fractures and extends the propagation distance along the major axes of pre-existing fractures. The average activity level and proportion of large seismic events are reduced by injecting low-rate fluid. In summary, our results reveal the interactions between hydraulic and pre-existing fractures and provide a valuable reference for constructing an efficient enhanced geothermal system (EGS) for deep reservoirs.

Analysis of a Potential Correlation between Seismicity and Production in Kiruna Mine on a Mine-wide and an Extraction Block Scale

The creation of cavities in the underground results in stress redistributions and energy changes in the rock mass. Zones with increased stresses and zones with lower stresses develop. The energy changes manifest themselves amongst others in changes in potential energy, absorption of energy in the formation of fracture zones, and release of energy such as seismic energy. To prevent damage to infrastructure and personnel, it is important to understand the mechanisms of energy changes as a result of mining. As far as seismic energy release is concerned, it is important to understand to relationship between large scale mineral extraction and mining induced seismicity. One coarse way to do this is to correlate for specific areas the cumulated tons of mined rock multiplied by the depth of extraction and multiplied by the gravitational acceleration to get the unit of energy, which is a rough assessment of the mining-induced energy changes, with the cumulated released seismic energy, which is derived from the seismic monitoring system. This correlation is studied for Kiruna Mine on a mine-wide scale and on an extraction block scale for the years 2014 to 2020. The results show that there is a reasonable correlation between the mining-induced energy changes and the seismic energy release not only on a mine-wide scale but also on an extraction block scale. Periods of decreased seismic energy release are followed either by a period of increased seismic activity or by one or a series of large seismic event. Accordingly, periods of decreased seismic activity can be considered as an indicator for a likely increase in future seismic activities. More detailed investigations should be made to find out the cause for the lack of energy release. A disadvantage of this method is that it does not reveal the exact area and reason for the decrease in seismicity. Therefore, additional rock mechanics analysis is needed to understand the background of the change in energy release.

Clustering Analysis of Seismicity in the Anatolian Region with Implications for Seismic Hazard.

The Anatolian region is one of the most seismically active tectonic settings in the world. Here, we perform a clustering analysis of Turkish seismicity using an updated version of the Turkish Homogenized Earthquake Catalogue (TURHEC), which contains the recent developments of the still ongoing Kahramanmaraş seismic sequence. We show that some statistical properties of seismic activity are related to the regional seismogenic potential. Mapping the local and global coefficients of variation of inter-event times of crustal seismicity which occurred during the last three decades, we find that territories prone to major seismic events during the last century usually host globally clustered and locally Poissonian seismic activity. We suggest that regions with seismicity associated with higher values of the global coefficient of variation of inter-event times, CV, are likely to be more prone to hosting large earthquakes in the near future than other regions characterized by lower values, if their largest seismic events have the same magnitude. If our hypothesis is confirmed, clustering properties should be considered as a possible additional information source for the assessment of seismic hazard. We also find positive correlations between global clustering properties, the maximum magnitude and the seismic rate, while the b-value of the Gutenberg-Richter law is weakly correlated with them. Finally, we identify possible changes in such parameters before and during the 2023 Kahramanmaraş seismic sequence.

S1222a—The Largest Marsquake Detected by InSight

AbstractNASA's InSight has detected a large magnitude seismic event, labeled S1222a. The event has a moment magnitude of 4.7, with five times more seismic moment compared to the second largest event. The event is so large that features are clearly observed that were not seen in any previously detected events. In addition to body phases and Rayleigh waves, we also see Love waves, minor arc surface wave overtones, and multi‐orbit surface waves. At long periods, the coda event exceeds 10 hr. The event locates close to the North‐South dichotomy and outside the tectonically active Cerberus Fossae region. S1222a does not show any evident geological or tectonic features. The event is extremely rich in frequency content, extending from below 1/30 Hz up to 35 Hz. The event was classified as a broadband type event; we also observe coda decay and polarization similar to that of very high frequency type events.