Magnitude Seismic Events Research Articles

Magnitudes of seismic events induced by fluid injections in the Earth’s crust

Magnitudes of seismic events induced by fluid injections in the Earth’s crust

An EGF technique to infer the source parameters of a circular crack growing at a variable rupture velocity

Circular crack models with a constant rupture velocity struggle to effectively model both the amplitude and duration of first P-wave pulses generated by small magnitude seismic events. Assuming a constant rupture velocity is unphysical, necessitating a deceleration phase in the rupture velocity to uphold the causality of the healing process. Moreover, a comprehensive failure model might encompass an initial nucleation phase, typically characterized by an increase of the initial rupture velocity. Studies have demonstrated that quasi-dynamic circular crack models featuring variable rupture velocities can accurately model the shape of the observed first P-wave pulse. Based on these principles, an Empirical Green’s function (EGF) approach was previously formulated to estimate the source parameters of small magnitude earthquakes, called MAIN. In addition to determine the source radius and stress drop, this method also enables the inference of the temporal evolution of rupture velocity. However, this method encounters difficulties when the noise-to-signal ratio in the recordings of smaller earthquakes used as EGF exceeds 5%, a common situation when employing regional-scale recordings of small-magnitude earthquakes as EGF. Through synthetic tests, we demonstrated that, in such instances, the problem of this technique is that the alignment between the onset of P waves of EGF and MAIN is not rightly recovered after the initial inversion step. Consequently, a novel inversion method has been developed to address this issue, enabling the identification of the optimal alignment of P-wave arrivals in EGF and MAIN across all stations. A Bayesian statistical approach is proposed to meticulously investigate the solutions of model parameters and their correlations. Using the new technique on a small magnitude earthquake (ML = 3.3) occurred in Central Italy enabled us to identify the most likely rupture models and examine the issue of correlation among model parameters. Application of Occam’s Razor Principle suggests that, for the investigated event, a circular crack model should be favored over a heterogeneous rupture model.

The Magnitudes of Seismic Events Induced by Fluid Injections into the Earth’s Crust

The Magnitudes of Seismic Events Induced by Fluid Injections into the Earth’s Crust

Identification Of Liquefaction-Potential Zones Using The Gravity Method In Lolu Village, Central Sulawesi

A seismic event of magnitude 7.5 struck the Palu region in Central Sulawesi on September 28, 2018, precipitating a subsequent calamity in the form of a tsunami measuring 4-7 meters in height. This catastrophe was further compounded by the occurrence of liquefaction, leading to extensive devastation and a significant loss of life. In order to identify areas susceptible to liquefaction, it is anticipated that the employment of the gravity method, renowned for its capacity to discern density fluctuations associated with the mass of voluminous materials over a considerable detection range, will prove instrumental. The investigation of parameters and the characterization of liquefaction phenomena in regions previously afflicted by liquefaction disasters can be instrumental in devising strategies for mapping zones that are predisposed to such occurrences. The present study seeks to employ geophysical methods, specifically the gravity method, to delineate zones with the potential for liquefaction within the Lolu Village at Palu City, Central Sulawesi. Through the application of techniques designed to isolate regional and residual anomalies, it is envisaged that a clearer understanding of anomalies situated in shallower regions can be attained, with a specific focus on residential areas. Notably, due to liquefaction, approximately half of the residential areas have shifted a considerable distance of around 132 meters from their original positions. To facilitate the interpretation of subsurface layers, two-dimensional cross-sections are modeled to intersect the displaced and stationary areas. The residual map reveals discernible variations in anomaly values, with lower values observed in the areas that experienced liquefaction-induced movement. Subsurface modeling further demonstrates the presence of three distinct rock layers, namely a sandy layer, a gravel layer, and a rock layer. Additionally, the modeling depicts the formation of canals composed of hard rock, exhibiting varying thicknesses within the surface layer as a consequence of the liquefaction event in 2018. The existence of these canals serves as an indicator that when the sandy layer becomes saturated with water, it will flow along the topographical gradient, following the path of the subterranean canals that have formed.

The modeling of fault activation, slip, and induced seismicity for geological [formula omitted] storage at a pilot-scale site in the Janggi Basin, South Korea

We investigate the effects of possible fault activation and slip during geological CO2 storage operations numerically. To this end we develop a numerical simulator by coupling a multiphase flow simulator with an existing geomechanics simulator in order to model fault slip and seismic events induced by reservoir pressurization. After validation and verification of the developed coupled simulator, we apply it to a pilot-scale site of geological CO2 storage located in the Janggi Basin, South Korea. We design a fault structure with a fault core and surrounded damage zones, assuming the fault to be activated along the fault core only. Zero-thickness interface elements are employed in the numerical model to represent the fault core. We perform numerical tests with different injection scenarios to evaluate the impact of pore pressure on fault activation and its post-failure behavior. We model occurrence and the magnitude of seismic events, identifying sudden changes of the moment magnitude at the onset of fault activation. Specifically, we take CO2 injection with 100 , 200, 400 ton/day for 20 years, from which the cumulative moment magnitudes (Mw’s) of 1.46, 2.36 and 3.11 are estimated, respectively. However, the maximum instantaneous changes of Mw occur at the onset of fault activation for all the injection cases (i.e., approximately 0.1, 0.36, 0.75, respectively). As the injection rate increases, fault activation occurs early and the magnitude of induced seismicity becomes large, but substantial reduction of the injection rate can weaken following induced seismicity. Interestingly, the location of maximum surface lift does not correspond to the injection well due to heterogeneity of geology and geomechanics. We thus expect relatively low risk of induced seismicity overall within the range of injection rates considered in this study, but monitoring surface uplift and seismic signals is still necessary to prevent any unexpected events due to uncertainty of parameters.

Coupled Hydromechanical Modeling and Assessment of Induced Seismicity at FWU: Utilizing Time-Lapse VSP and Microseismic Data

The objective of this work is to utilize integrated geomechanics, field vertical seismic profile (VSP) and microseismic data to characterize the complex subsurface stress conditions at the Farnsworth Unit (FWU). The model is based on a five-spot sector model extracted from a primary geomechanical model. The five-spot well injection pattern is characterized by extensive reservoir characterization data, such well logs, extracted cores and borehole geophone data, to facilitate the detailed examination of stress changes and microseismic event occurrences. The study utilizes field vertical seismic volumes acquired from the injection well 13-10A. The seismic volumes successfully provided snapshots of the behavior of the reservoir at distinct times. The use of VSP and microseismic data provided direct and indirect estimates of the dynamic stress changes occurring in the overburden, reservoir and underburden rock formations. In order to illuminate the stress regions and identify rocks that have undergone inelastic failure, microseismic event occurrences were utilized. Microseismic activity has been detected at the FWU; further study of its locations, timing, and magnitude was needed to deduce the nature of the changing stress state. The results of the study revealed that microseismic events were successfully modeled within the Morrow B formation. Moment magnitudes of seismic events were within the same magnitudes for events in the reservoir, suggesting the suitability of the model. The results of the study showed that the computed moment magnitudes for seismic events were insignificant to warrant safety concerns. The study findings showed the usefulness of coupled hydromechanical models in predicting the subsurface stress changes associated with CO2 injection. The knowledge gained from this study will serve as a guideline for industries planning to undertake underground CO2 storage, and characterize the subsurface stress changes.

DiTing: A large-scale Chinese seismic benchmark dataset for artificial intelligence in seismology

In recent years, artificial intelligence technology has exhibited great potential in seismic signal recognition, setting off a new wave of research. Vast amounts of high-quality labeled data are required to develop and apply artificial intelligence in seismology research. In this study, based on the 2013–2020 seismic cataloging reports of the China Earthquake Networks Center, we constructed an artificial intelligence seismological training dataset (“DiTing”) with the largest known total time length. Data were recorded using broadband and short-period seismometers. The obtained dataset included 2,734,748 three-component waveform traces from 787,010 regional seismic events, the corresponding P- and S-phase arrival time labels, and 641,025 P-wave first-motion polarity labels. All waveforms were sampled at 50 Hz and cut to a time length of 180 s starting from a random number of seconds before the occurrence of an earthquake. Each three-component waveform contained a considerable amount of descriptive information, such as the epicentral distance, back azimuth, and signal-to-noise ratios. The magnitudes of seismic events, epicentral distance, signal-to-noise ratio of P-wave data, and signal-to-noise ratio of S-wave data ranged from 0 to 7.7, 0 to 330 km, –0.05 to 5.31 dB, and –0.05 to 4.73 dB, respectively. The dataset compiled in this study can serve as a high-quality benchmark for machine learning model development and data-driven seismological research on earthquake detection, seismic phase picking, first-motion polarity determination, earthquake magnitude prediction, early warning systems, and strong ground-motion prediction. Such research will further promote the development and application of artificial intelligence in seismology.

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.

Effect of dynamic loading conditions on the dynamic performance of MP1 energy-absorbing rockbolts: Insight from laboratory drop test

Energy-absorbing rockbolts have been widely adopted in burst-prone excavation support, and their serviceability is closely related to the frequency and magnitude of seismic events. In this research, the split-tube drop test with varying impact energy was conducted to reproduce the dynamic performance of MP1 rockbolts under a wide range of seismic event magnitudes. The test results showed that the impact process could be subdivided into four distinct stages, i.e. mobilization, strain hardening, plastic flow (ductile), and rebound stage, of which strain hardening and plastic flow are the primary energy absorbing stages. As the impact energy per drop increases from 8.1 to 46.7 kJ, the strain rate of the shank varies between 1.20 and 2.70 s−1, and the average impact load is between 240 and 270 kN, which may be considered as constant. The MP1 rockbolt has a cumulative maximum energy absorption (CMEA) of 31.9–40.0 kJ/m, with an average of 35.0 kJ/m, and the elongation rate is 11.4%–14.7%, with an average of 12.7%, both of which are negatively correlated with the impact energy per drop. Regression analysis shows that energy absorption and shank elongation, as well as momentum input and impact duration, conform to the linear relationship. The complete dynamic capacity envelope of MP1 rockbolts is proposed, which reflects the dynamic bearing capacity, elongation, and distinct stages. This study is helpful to better understand the dynamic characteristics of energy-absorbing rockbolts and assist design engineers in robust reinforcement systems design to mitigate rockburst damage in seismically active underground excavations.

EMD based statistical analysis of nighttime pre-earthquake ULF electric field disturbances observed by CSES

To explore the correlation between earthquakes and spatial ultra-low frequency electric field disturbances and to study the phenomenon of seismic ionospheric disturbances, this study uses 3 years of electric field ULF band data from 2019 to 2021 observed by the electric field detector carried by the CSES to identify anomalous disturbances using the anomaly automatic detection algorithm based on empirical mode decomposition for the 2,329 seismic events of magnitude not less than 5.0 and the electric field ULF disturbances in this period are analyzed by Superposed Epoch Analysis, and the statistical results are compared and analyzed in depth by earthquake location and different magnitudes in terms of both spatial and temporal scales and spatial distribution. The results show that: 1) There is a correlation between earthquakes of magnitude not less than 5.0 and ultra-low frequency disturbances in the electric field. The abnormal disturbance mainly occurred 11 days before the earthquake, 2 days before the earthquake to the day of the earthquake, and the location of the earthquake is within 200 km from the epicenter. 2) Sea earthquakes can observe more pre-seismic anomalous electromagnetic disturbances than land earthquakes. 3) In terms of earthquake magnitude, the larger the magnitude, the earlier the pre-earthquake anomalous disturbances appear and the wider the range of anomalies. This study provides an effective way to explain seismic ionospheric phenomena, and also provides a reference for the application of electromagnetic monitoring satellites in earthquake prediction and early warning as well as disaster prevention and mitigation.

Assessment of post-liquefaction potential in soil displacement on irrigation canal reconstruction project in the Jono Oge and Lolu area, Central Sulawesi, Indonesia

A seismic event of magnitude 7.5 Mw took place in Central Sulawesi in September 2018, marking a significant occurrence in the geological hazard chronicles of Indonesia. The occurrence of liquefaction subsequent to the earthquake significantly damaged the water resource infrastructure in the Sigi Regency. This study aims to evaluate the possible soil displacement resulting from re-liquefaction events occurring in the main irrigation canals in the Jono Oge and Lolu regions. The study used semi-empirical and finite element analysis to compute the lateral displacement index and reconsolidation settlement within the designated study region. The examination of soil displacement is conducted under various groundwater level scenarios, utilizing the most recent soil investigation conducted in 2021. The findings of the study indicate that raising the groundwater level to -3.5 meters will result in significant soil and irrigation canal damage. In the future, it is suggested that limiting the groundwater level below -11 meters in the primary irrigation canal area might effectively mitigate soil lateral displacement and settlement.

Transition From Slow to Fast Injection‐Induced Slip of an Experimental Fault in Granite Promoted by Elevated Temperature

AbstractThe influence of elevated temperature on injection‐induced fault slip is poorly constrained. In this study, at steady‐state elevated temperatures, triaxial shear‐flow experiments on a sawcut fault in granite were conducted to simulate injection‐induced slip of a critically stressed fault. Our results suggest that an elevated temperature favors a more uniform fluid pressure distribution over the fault surface mainly by reducing water viscosity. At temperatures above ambient, a larger perturbation force from the injected fluid is required to reactivate the fault primarily because of the enhanced thermally activated fault healing processes, resulting in a faster fault slip rate upon failure. This study may partially explain the causal link between higher reservoir temperature and higher maximum magnitude of injection‐induced earthquakes in geothermal systems, and the observation that larger magnitude seismic events concentrate near the deeper part of the reservoir, where temperature is higher.

New CNN-based tool to discriminate anthropogenic from natural low magnitude seismic events

SUMMARY With the deployment of high quality and dense permanent seismic networks over the last 15 yr comes a dramatic increase of data to process. In order to lower the threshold value of magnitudes in a catalogue as much as possible, the issue of discrimination between natural and anthropogenic events is becoming increasingly important. To achieve this discrimination, we propose the use of a convolutional neural network (CNN) trained from spectrograms. We built a database of labelled events detected in metropolitan France between 2020 and 2021 and trained a CNN with three-component 60 s spectrograms ranging frequencies from 1 to 50 Hz. By applying our trained model on independent French data, we reach an accuracy of 98.2 per cent. In order to show the versatility of the approach, this trained model is also applied on different geographical areas, a post-seismic campaign from NW France and data from Utah, and reaches an accuracy of 100.0 and 96.7 per cent, respectively. These tests tend to hypothesize that some features due to explosions compared to earthquakes are widely shared in different geographical places. In a first approach, we propose that it can be due to a contrast in the energy balance between natural and anthopogenic events. Earthquake seismic energies seem to be more continuous as a function of frequency (vertical bands features in a spectrogram) and conversely for explosions (horizontal strips).

Detection and study of a high magnitude seismic event from GPS data: Case study of the 2011 Tohoku-Oki earthquake

The advent of GPS provided a new way of measuring surface displacements due to earthquakes by deploying GPS networks within active seismic areas. Japan is located in the confluence of several tectonic plates, hence its seismicity. In order to surveille this activity, one of wider GPS network in the world was deployed, i.e., GEONET. By processing data from 93 GEONET reference stations, we analyze the 2011 Tohoku-Oki earthquake using PPP strategy. We studied the time series during the event setting up a threshold value at we consider the time series are being altered by the earthquake. We also identified the time after the occurrence when the maximum displacements happen. With the study of these two parameters, we aim to show their different behavior as the main shock propagates along the Japan islands, with a focus on a better understanding of the earthquake and its propagation. To achieving this, a least square adjustment method was used to relate epicentral distance to topocentric displacements and the time of detection to epicentral distance. The results show an exponential behavior of the distance-displacement regression versus a linear behavior of the distance-time regression. Besides, we use the former linear regression to calculate and approximation of the velocity of the shock waves.

Comparison analysis of the ETAS model with Gutenberg–Richter (GR), Tapered-GR and characteristic magnitude distributions

SUMMARY In this paper, we carry out a comparison analysis of the Epidemic Type Aftershock Sequence (ETAS) model for the earthquake process, embedded with the three main exponential-type distributions adopted in practical applications to describe the magnitudes of seismic events, that are, the Gutenberg–Richter (GR), the tapered Gutenberg–Richter (TGR) and the CHaracteristic (CH) frequency–magnitude distributions (FMDs). The first law is a pure-power decreasing function, while both the other two introduce a more rapid decay in the tail of the distribution: a soft taper in the TGR model and a sharp cut-off in the CH one. To perform the comparison, we first investigate some theoretical features of the ETAS model with CH-distributed magnitudes (ETAS-CH), which have not been deeply analysed in the literature as much as for ETAS-TGR and ETAS-GR. In particular, we explicitly compute the branching ratio, we analyse its asymptotics in relation to its parameters, and we derive the proper stability conditions. We then move to the comparison among the three ETAS-GR, ETAS-TGR and ETAS-CH processes, to highlight differences and similarities. This is done by carrying out both a theoretical analysis, mainly focused on the three models’ branching ratios and the relative sensitivity, and a simulation analysis of realistic synthetic catalogues to compare the processes’ numbers, events’ magnitude distribution and temporal evolution. The results we obtained show that the ETAS-TGR and ETAS-CH processes have very similar features. They both have also less restrictive non-explosion conditions than for ETAS-GR; in fact, differently from this latter case, their branching ratios exist for any value of the parameters and are lower than the one of ETAS-GR, to which they converge for large magnitudes.

Macroseismic intensity-based catalogue of earthquakes in Ecuador

Earthquake magnitude catalogues and peak ground acceleration (PGA) maps for Ecuador may be found in several studies, however, there are rare works on the characterisation of the epicentral macroseismic intensities associated with earthquakes. In view of the concept that macroseismic intensity enables us to categorise the extent and severity of damage to buildings and structures caused by an earthquake, this study aims to compile a macro-seismic intensity-based catalogue of earthquakes in Ecuador, characterise the epicentral macroseismic intensities associated to seismogenic sources and perform a comparison with the National Seismic Hazard Map. This paper is the first that presents a catalogue of earthquakes with macroseismic intensities ≥VII and a series of maps of earthquake epicentres according to intensity, focal depth, data and magnitude of seismic events in Ecuador, based on the study of historical and instrumental records from 1900 to 2021. The obtained data shows that 95% of the territory of Ecuador has a PGA 0.1 g, which corresponds to seismic intensities greater than VII, while regions with seismicityVIII (ag = 0.2 g) constitute 86%, and 3.8% of the territory of Ecuador has very high seismicity (IX), where the PGA exceeds 0.5 g. This information suggests that the normative National Seismic Hazard Map of Ecuador underestimate the hazard mainly in the south-east and in the Central Andes of Ecuador, and require an actualization.

Temporal-spatial characterization of mining-induced seismicity in the vicinity of a dyke – A case study

Major faults and dykes are common geological discontinuities in underground mines and can often contribute to significant failures such as coal bursts during mining. The failure mechanisms of faults have been widely studied, whereas the seismic characteristics associated with dykes have been rarely investigated for mine dynamic hazard risk management. This research aimed to characterize the seismic behavior near an intrusive dyke that intersected with the roadways in an underground longwall coal mine in Australia. The temporal-spatial variations of seismic multi-parameters around the stiff dyke were analyzed, including clustered seismicity, event locations, Es/Ep ratio, b-value and correlation with the released seismic energy. Four stages were defined based on the evolutions of seismic characteristics. The rock fractures initiated near the dyke when the longwall face was 400 m from the dyke. The seismicity started to increase when the longwall was <100 m from the dyke and decreased drastically after the longwall mined 50 m past the dyke. The seismic events were concentrated at the inbye side of the dyke and propagated to the outbye side of the dyke as the longwall mined through the dyke. The spatial distribution of Es/Ep ratios and temporal variations of the b-value indicated that higher magnitude seismic events dominated by shear failures occurred in the hanging wall of the dyke, suggesting more sudden seismic energy release and escalating seismic risks around the roadways at the inbye side of the dyke. Meanwhile, when the longwall was mining through the dyke, even though the seismicity was intensive, seismic energy was more frequently and gently released so that stress was not significantly accumulated to induce any major failures at the outbye side of the dyke. The results demonstrated that the geological features of the dyke and the longwall mining progress had a controlling effect on the seismic characteristics in the time-space domain. The comprehensive analysis of seismic multi-parameters reliably revealed the rock mass response near a major dyke and can provide guidance for assessing and managing the risks of dynamic mining hazards around dykes.

Seismic hazard calculation using the equivalent magnitude obtained from numerical modelling

Numerical modelling is widely used to estimate seismic potential in mines. Several numerical methods, along with different interpretation techniques, allow estimating the seismic potential at different stages of a mine or tunnel construction. However, none of the existing methods considers the magnitude of seismic events as a distribution of values, rather all methods focus on obtaining a single value representative of the seismic conditions for each excavation stage. The objective of this study was to develop a method based on the implicit generation of a synthetic distribution of seismic data and on the results of numerical modelling, providing a means to decompose the modelling results into a statistical distribution of maximum magnitudes. The results of this method provide a statistical distribution of the maximum magnitudes, based on existing plastic modelling results and assumptions about the failure mechanism. This work provides an engineering tool to evaluate the probability of the maximum seismic event.

Tectonic geomorphology along the transverse basement fault (Moradabad fault) in the Ganga basin: A nexus between the Himalayan tectonics and the pre-Himalayan transverse basement structure

The present study focuses on the neotectonic perspective of a subsurface basement fault, i.e., the Moradabad Fault (MF) in the Ganga basin. This is a ∼163 km long NE-SW trending prominent pre-Himalayan subsurface structure that participated in many phases of tectonic movement during and after the Himalayan orogeny. At present, it is deep-buried under the alluvium, and frequent geomorphic readjustments are seen in the fluvial archives around this fault. The datasets presented here include tectono-geomorphological analysis, transverse-tectonic analysis, previous seismic records from the earthquake catalogs and the associated seismites, and the Ground Penetrating Radar (GPR) studies. The available geological maps limit the northern end of the MF at the Himalayan front, and further northward, it is marked as lineaments. However, the recent geological evidence such as the river alignment, river confluence, landslides, faceted spurs, triangular facets, truncated spurs, fault scarps, structural terraces, and the alignment of the low to moderate magnitude seismic events having parallel trends with the MF may conclude that it is not just a matter of coincidence. However, these features are likely aligned due to the post-Himalayan reactivation-regeneration of the basement structures. It is, therefore, argued that these linear structures showing active deformation are the extension of the MF into the Himalayas, and hence the lineament terminology for these structures should be abolished. The MF has a curved fault-line with the existence of the releasing bend in a transtensional regime. The up-thrown block shows the signs of compression, evidenced by the geomorphological signatures. The fault-bend is characterized by oblique deformation may be accommodated by oblique-slip faulting or dip-slip fault displacements. Tectonic geomorphological characteristics, morphostratigraphic record, GPR data, seismic events, and the basement contour model suggest the Moradabad fault is neotectonically active and is influenced by the Himalayan tectonics.

ВЫБОР ЭНЕРГЕТИЧЕСКОЙ ХАРАКТЕРИСТИКИ ДЛЯ УНИФИЦИРОВАННОГО СЕЙСМИЧЕСКОГО КАТАЛОГА КЫРГЫЗСТАНА

The paper substantiates the choice of the Rautian KP class as the main energy characteristic for the unified catalog of Kyrgyzstan.KP class introduced into the practice of seismological observations by T.G. Rautian in 1960 and widely used in the USSR and post-Soviet countries. Comparison of the calibration function σ(∆) used to calculate the energy class of the KP for four independent catalogs containing the most complete information on seismic events in Kyrgyzstan is presented. The need to recalculate the KP of seismic events included in the KNET catalog obtained at the Research Station of the Russian Academy of Sciences has been revealed. A good agreement between of the new KP values with the KP values for common events from other seismic catalogs of Kyrgyzstan is shown. The obtained KP values for the KNET catalog can be used to compile when compiling the composite catalog without violating the uniformity of the methodology for calculating the magnitude of seismic events.