Frequency-magnitude Distribution Research Articles

Seismic hazard estimation and medium-term earthquake precursor analysis of North East India: an assessment on large earthquake scenario

The North-Eastern region of India has the distinction of being one of the most seismically active and tectonically complex regions in the world. The region has periodically jolted by a number of large earthquakes. The temporal and spatial frequency-magnitude distribution (FMD) of earthquakes in three major selected regions of North-East India, namely Shillong-Mikir Hills, Arunachal Himalaya, and Assam Foredeep region, are examined in this study. Temporal variation of ‘b’ shows a significant declination prior to a large earthquake, which strongly advocates for a medium-term (months-year) earthquake precursor. Similarly, spatial distribution map is prepared by estimating b-value at every 0.01o×0.01o grid using the nearest 150 events, which is vital in understanding the stress regime of a specific region. The present study critically demonstrates the higher b-value regions associated with minimum seismicity and vice-versa, especially focusing on large earthquake scenario. High anomalies of ‘b’ were found in the regions of Shillong-Mikir hills and Arunachal Himalaya, whereas the Assam-Foredeep region, free from seismic activity for a long period, shows a low. It may be due to the accumulation of stress energy within the region for a long time and could be an alarming sign for future large events.

Seismogenic Potential of the Subduction Zone in Northern Chile

ABSTRACT The northern Chile region of the Nazca subduction zone ruptured in an Mw∼8.5–9.0 earthquake in 1877, which induced a tsunami. The various magnitude estimates of this event are based on the evaluation of historical records, seismic intensities, and/or tide gauge information; however, its actual along-strike extent is debated. Based on geodetic data, the previous studies have suggested that this region has the potential for an Mw 8.2–8.8 event. We re-evaluate the seismic potential of the region, accounting for the buildup rate of moment deficit along the megathrust, the earthquake magnitude–frequency distribution, and the physics of earthquakes. We combine an improved probabilistic estimate of moment deficit rate with results from dynamic models of the earthquake cycle, testing, in particular, the influence of a potential aseismic barrier near the city of Iquique, which may influence the extent and magnitude of large events in this region. We find that Mw 8.8 is the most probable maximum magnitude earthquake in the region, and that the potential barrier likely has a limited impact considering uncertainties. We discuss the effect of the moment deficit rate on the fault, the b-value, and the importance of postseismic processes on our results.

Analysis of seismic magnitude-frequency distribution in northern and central Chile

Analysis of seismic magnitude-frequency distribution in northern and central Chile

Lighting Up a 1 km Fault near a Hydraulic Fracturing Well Using a Machine Learning-Based Picker

Abstract The development of portable nodal array in the recent years greatly improved the seismic monitoring ability across multiple scales. The dense arrays also directly benefit microseismic monitoring by providing relatively low-cost surface recordings. However, the rapid growth of seismic data is accompanied by the increased demand for efficient seismic phase picking. On the other hand, machine learning-based phase picking techniques achieved high stability and accuracy, showing promising potential to replace human labors and traditional automatic pickers. In this study, we applied a state-of-the-art package on newly collected nodal array data around a hydraulic fracturing well in southwestern China. The array consists of up to 85 nodes with an average station spacing of less than a kilometer. Within the hydraulic fracturing stimulation periods, we detected ∼3000 seismic events with magnitude down to ∼−2. After waveform cross-correlation-based relocation, the 1979 relocated events clearly light up a 1 km long fault structure and several fractures. Furthermore, the frequency–magnitude distribution of the catalog exhibits weak bilinear features with relatively low b-value (0.88) and a moderate coefficient of variation (Cv ∼2). The nature and origin of the observed earthquake cluster are then discussed and defined based on the industrial information, high-resolution earthquake catalog, and basic statistics. Finally, we summarized our experience and provided recommendations for applying similar approaches to other local scale, surface microseismic monitoring scenarios.

Cluster Analysis of Seismicity in the Eastern Gulf of Corinth Based on a Waveform Template Matching Catalog.

The Corinth Rift, in Central Greece, is one of the most seismically active areas in Europe. In the eastern part of the Gulf of Corinth, which has been the site of numerous large and destructive earthquakes in both historic and modern times, a pronounced earthquake swarm occurred in 2020-2021 at the Perachora peninsula. Herein, we present an in-depth analysis of this sequence, employing a high-resolution relocated earthquake catalog, further enhanced by the application of a multi-channel template matching technique, producing additional detections of over 7600 events between January 2020 and June 2021. Single-station template matching enriches the original catalog thirty-fold, providing origin times and magnitudes for over 24,000 events. We explore the variable levels of spatial and temporal resolution in the catalogs of different completeness magnitudes and also of variable location uncertainties. We characterize the frequency-magnitude distributions using the Gutenberg-Richter scaling relation and discuss possible b-value temporal variations that appear during the swarm and their implications for the stress levels in the area. The evolution of the swarm is further analyzed through spatiotemporal clustering methods, while the temporal properties of multiplet families indicate that short-lived seismic bursts, associated with the swarm, dominate the catalogs. Multiplet families present clustering effects at all time scales, suggesting triggering by aseismic factors, such as fluid diffusion, rather than constant stress loading, in accordance with the spatiotemporal migration patterns of seismicity.

Numerical modeling of cracking behaviors for the rock-inclusion composite under dynamic tensile loading

Rock-inclusion composites have been widely used in underground engineering, however, the impact of inclusions with varying physico-mechanical properties, such as the strength ratio and size, on cracking behaviors under dynamic tensile loading is still unclear. In this study, using a discrete element method (DEM), a series of numerical simulations are performed on the flattened Brazilian disc (FBD) specimens to simulate the split Hopkinson pressure bar (SHPB) tests. The numerical results indicate that both the inclusion size and strength ratio can influence dynamic responses of a rock-inclusion composite. In specimens with weak inclusions, the nominal tensile strength (NTS) value is proportional with the strength ratio but negatively correlated with the inclusion size. Strength ratios are primarily responsible for determining three failure modes in specimens. During the loading process, the characteristics of acoustic emission (AE) events generated from the microcracks in specimens are analyzed in terms of moment magnitude, failure mechanism, b-value, and frequency-magnitude distribution. Additionally, energy partitions evolve synchronously with cracking behaviors in specimens, and all the loading systems show a similar trend of energy conversion. This study may provide a promising DEM model for exploring dynamic tensile failures in rock-inclusion composites and explaining the complicated cracking behaviors in underground engineering.

Temporal Variations of Seismicity Rates and Gutenberg–Richterb-Values for a Stochastic Declustered Catalog: An Example in Central Italy

AbstractOne important aspect of the seismicity is the spatiotemporal clustering; hence, the distinction between independent and triggered events is a critical part of the analysis of seismic catalogs. Stochastic declustering of seismicity allows a probabilistic distinction between these two kinds of events. Such an approach, usually performed with the epidemic-type aftershock sequence (ETAS) model, avoids the bias in the estimation of the frequency–magnitude distribution parameters if we consider a subset of the catalog, that is, only the independent or the triggered events. In this article, we present a framework to properly include the probabilities of any event to be independent (or triggered) both in the temporal variation of the seismic rates and in the estimation of the b-value of the Gutenberg–Richter law. This framework is then applied to a high-definition seismic catalog in the central part of Italy covering the period from April 2010 to December 2015. The results of our analysis show that the seismic activity from the beginning of the catalog to March 2013 is characterized by a low degree of clustering and a relatively high b-value, whereas the following period exhibits a higher degree of clustering and a smaller b-value.

Fault-based probabilistic seismic hazard analysis in regions with low strain rates and a thick seismogenic layer: a case study from Malawi

SUMMARY Historical and instrumental earthquake catalogs in low strain rate regions are not necessarily indicative of the long-term spatio-temporal distribution of seismicity. This implies that probabilistic seismic hazard analysis (PSHA) should also consider geologic and geodetic data through fault-based seismogenic sources. However, it is not always clear how on-fault magnitude-frequency distributions (MFDs) should be described and, if the seismogenic layer is especially thick, how fault sources should be extrapolated down-dip. We explore these issues in the context of a new PSHA for Malawi, where regional extensional rates are 0.5–2 mm yr−1, the seismogenic layer is 30–40-km thick, the instrumental catalog is ∼60 yr long and fault-based sources were recently collated in the Malawi Seismogenic Source Model. Furthermore, Malawi is one of several countries along the East African Rift where exposure to seismic hazard is growing, but PSHA does not typically consider fault sources. We use stochastic event catalogs to explore different fault source down-dip extents and MFDs. Our PSHA indicates that hazard levels are highest for a Gutenberg–Richter on-fault MFD, even at low probabilities of exceedance (2 per cent in 50 yr), whilst seismic hazard levels are also sensitive to how relatively short (<50 km) fault sources are extrapolated down-dip. For sites close to fault sources (<40 km), seismic hazard levels are doubled compared to previous instrumental-seismicity based PSHA in Malawi. Cumulatively, these results highlight the need for careful fault source modelling in PSHA of low strain rate regions and the need for new fault-based PSHA elsewhere in the East Africa Rift.

Physics-Based Forecasting of Induced Seismicity at Groningen Gas Field, The Netherlands: Post Hoc Evaluation and Forecast Update

Abstract Induced seismicity due to natural gas extraction from the Groningen reservoir, The Netherlands, has been occurring since the early 1990s. Prospective forecasts of the possible maximum earthquake magnitude for different gas extraction scenarios have previously been published. However, their accuracy and continued relevance are unknown. Here, we evaluate our prior Groningen seismicity forecast and propose a revised model. We compare the forecast to earthquakes that occurred after its publication, between 1 February 2017 and 1 July 2022. We used volume scaling to account for actual gas extraction being 35% less than considered in the forecast. After this correction, we found that the forecast slightly underestimated the number of M ≥2.5 events. However, it was consistent with the largest event in that period, an M 3.4. Then, we updated the forecast model for a new depressurization scenario, testing its pseudoprospective (out-of-sample) performance using L-test and N-test. This revision considered two possible magnitude–frequency distributions (MFD): (1) tapered Gutenberg–Richter (GR), in which induced ruptures are confined within the reservoir, and (2) unbounded GR, in which ruptures can propagate into the underburden. A tapered GR is the more likely scenario due to clear rollover in the MFD and a lack of events beneath the reservoir. However, we cannot exclude the possibility of an unbounded GR, because direct stress measurements in the underburden are not currently available. For the period 2021–2030, this new forecast suggests a 1% likelihood that the largest event will exceed M 3.8 for the tapered model and M 5.4 for the unbounded model.

The SWADE model for landslide dating in time series of optical satellite imagery

Landslides are destructive natural hazards that cause substantial loss of life and impact on natural and built environments. Landslide frequencies are important inputs for hazard assessments. However, dating landslides in remote areas is often challenging. We propose a novel landslide dating technique based on Segmented WAvelet-DEnoising and stepwise linear fitting (SWADE), using the Landsat archive (1985–2017). SWADE employs the principle that vegetation is often removed by landsliding in vegetated areas, causing a temporal decrease in normalized difference vegetation index (NDVI). The applicability of SWADE and two previously published methods for landslide dating, harmonic modelling and LandTrendr, are evaluated using 66 known landslides in the Buckinghorse River area, northeastern British Columbia, Canada. SWADE identifies sudden changes of NDVI values in the time series and this may result in one or more probable landslide occurrence dates. The most-probable date range identified by SWADE detects 52% of the landslides within a maximum error of 1 year, and 62% of the landslides within a maximum error of 2 years. Comparatively, these numbers increase to 68% and 80% when including the two most-probable landslide date ranges, respectively. Harmonic modelling detects 79% of the landslides with a maximum error of 1 year, and 82% of the landslides with a maximum error of 2 years, but requires expert judgement and a well-developed seasonal vegetation cycle in contrast to SWADE. LandTrendr, originally developed for mapping deforestation, only detects 42% of landslides within a maximum error of 2 years. SWADE provides a promising fully automatic method for landslide dating, which can contribute to constructing landslide frequency-magnitude distributions in remote areas.

Numerical modelling of spatially and temporally distributed on-fault induced seismicity: implication for seismic hazards

Induced seismicity is strongly related to various engineering projects that cause anthropogenic in-situ stress change at a great depth. Hence, there is a need to estimate and mitigate the associated risks. In the past, various simulation methods have been developed and applied to induced seismicity analysis, but there is still a fundamental difference between simulation results and field observations in terms of the spatial distribution of seismic events and its frequency. The present study aims to develop a method to simulate spatially distributed on-fault seismicity whilst reproducing a complex stress state in the fault zone. Hence, an equivalent continuum model is constructed, based on a discrete fracture network within a fault damage zone, by employing the crack tensor theory. A fault core is simulated at the center of the model as a discontinuous plane. Using the model, a heterogeneous stress state with stress anomalies in the fault zone is first simulated by applying tractions on the model outer boundaries. Subsequently, the effective normal stress on the fault plane is decreased in a stepwise manner to induce slip. The simulation result is validated in terms of the b-value and other seismic source parameters, hence demonstrating that the model can reproduce spatially and temporally distributed on-fault seismicity. Further analysis on the parameters shows the variation of frequency-magnitude distribution before the occurrence of large seismic events. This variation is found to be consistent with field observations, thus suggesting the potential use of this simulation method in evaluating the risk for seismic hazards in various engineering projects.

A weakening-healing law to simulate stick-slip behavior of rock joint and the associated seismicity

The variation of frictional strength of asperities is one of the fundamental mechanisms that govern earthquake cycles. The rate - and - state friction (RSF) law has been widely employed to explain earthquake phenomena. In RSF, the frictional strength of fault depends upon the current slipping velocity and the conditions on the slipping surface (i.e., the state), which depends partly on the prior sliding history. In this study, we proposed a simplified weakening-healing law to describe the slip behavior of individual asperity. In the weakening-healing law, the friction strength linearly decreases to the residual value with shear displacement when slip occurs, and immediately recovers to its original value once slip terminates. In the numerical model, a power-law distribution is used to introduce asperity heterogeneity (e.g., size, frictional strength, and stiffness) on a rock joint. A displacement-based moment tensor method is used to calculate the seismic moment during fault slipping. The simulated b-value (magnitude-frequency distribution) and its evolution during stick-slip phases are compared with published experiments. Slip nucleation, growth, coalescence, and the associated spatial-temporal behavior of the simulated seismicity are delineated. Although this preliminary study focuses on simplified conditions (small-scale smooth rock joint sheared under constant normal pressure and shear rate), our method successfully duplicates laboratory observed stick-slip behavior, b-value evolution, slip nucleation process, etc., providing a promising way to mimic more realistic natural earthquake phenomena.

Variations of the seismic b-value along the Dead Sea transform

The frequency-magnitude distribution follows the Gutenberg-Richter empirical law, in which the scaling between small and large earthquakes is represented by the b-value. Laboratory experiments have shown that the b-value is related to fault mechanics with an inverse dependency to the differential stress, as was also inferred from observational datasets through relations with earthquake depth and style of faulting. In this study, we aim to obtain a better understanding of the geological structure and tectonics along the Dead Sea transform (DST), by examining relations of the b-value to three source parameters: the earthquake depth, the seismic moment release, and the predominant style of faulting. We analyse a regional earthquake catalogue of ∼20,300 earthquakes that were recorded between 1983 and 2020 in a regional rectangle between latitudes 27.5°N−35.5°N and longitudes 32°E−38°E. We convert the duration magnitudes, Md, to moment magnitudes, Mw, applying a new regional empirical relation, by that achieving a consistent magnitude type for the entire catalogue. Exploring the variations in the b-value for several regions along and near the DST, we find that the b-value increases from 0.93 to 1.19 as the dominant style of faulting changes from almost pure strike-slip, along the DST, to normal faulting at the Galilee, northern Israel. Focusing on the DST, our temporal analysis shows an inverse correlation between the b-value and the seismic moment release, whereas the spatial variations are more complex, showing combined dependencies on seismogenic depth and seismic moment release. We also identify seismic gaps that might be related to locking or creeping of sections along the DST and should be considered for hazard assessment. Furthermore, we observe a northward decreasing trend of the b-value along the DST, which we associate to an increase of the differential stress due to structural variations, from more extensional deformation in the south to more compressional deformation in the north.

Seismicity Scenarios for the Remaining Operating Period of the Gas Field in Groningen, Netherlands

AbstractIn recent years, induced seismicity at the Groningen gas field caused increasing public concern and became a critical factor for future gas production plans. Zöller and Holschneider (2016) estimated the upper bound of the 90% confidence interval for the maximum possible magnitude based on the earthquake catalog until 2016 and found M 4.4. In this study, we show that the updated estimate for earthquake activity until 2022 decreases to M 4.0. For the 95% confidence interval, the upper bound that was infinite for the catalog until 2016 decreases to the value M 4.2 for the updated catalog. Because the frequency–magnitude distribution is stable within the uncertainties, it is likely that the growth of the earthquake catalog since 2016 has led to decreasing uncertainties and thus to smaller confidence intervals. Second, we find that a model based on rate-and-state dependent friction with additional aftershocks fits the available data well. Despite the overall decreasing earthquake rate resulting from decreasing production volumes, scenario calculations based on simulated pressure and compaction data indicate a considerable probability that the maximum expected magnitude in the next 30 yr exceeds the maximum observed magnitude from the past 30 yr.

Statistical study on the regional characteristics of seismic activity in and around Japan: frequency-magnitude distribution and tidal correlation

AbstractWe propose a statistical analysis method to identify common features of seismic activity that are indistinguishable from most other seismicity, and to find anomalous activity that differs from these common features. Using the hypocenter catalog of earthquakes which occurs in and around Japan during the past 20 years, we apply this method for the parameters of the frequency-magnitude distribution and a parameter that expresses the correlation of seismicity with tides as indices, with a focus on objectively understanding the regional characteristics of seismicity. As a result, we extracted a "typical" probability density distribution of each index value common to the most analysis regions and "anomalous" regions with index-value distributions that differ significantly from the typical distributions. In terms of the frequency-magnitude distribution, most estimated values of indices in the anomalous activity areas can be explained as variations corresponding to the effects of fluids, interplate coupling, and stress fields that control faulting styles that have been pointed out in previous studies. By extracting typical index values for the frequency-magnitude distribution, common features of the frequency-magnitude distribution that depend on the earthquake occurrence interval were identified. Although seismicity showed no clear correlation with tides, the index value for tidal correlation changes to reflect the proportion of earthquakes occurring in a series of periods shorter than the tidal period; it is therefore useful as an index to capture the characteristics of such earthquake occurrence intervals. We also show that the typical probability density distribution of these index values can be represented by existing models or their extensions. By using the proposed models as a reference, it is possible to quantify the degree of anomaly using the same concept as that of the method presented here; hence, such a method should be applicable to monitor seismic activity. Graphical Abstract

Spatio-temporal evolution of ground motion intensity caused by reservoir-induced seismicity at the Pertusillo artificial lake (southern Italy)

We investigate the spatiotemporal evolution of ground motion caused by reservoir-induced seismicity at the Pertusillo artificial lake in southern Italy. The area has a strong seismogenic potential, having been affected in the past by the 1857, Mw 7.0 Basilicata earthquake. We consider ∼1,000 microearthquakes that occurred from 2001 to 2018 and were recorded by a local network of nine seismic stations. The ground motion intensity associated with microseismicity allows us to identify two periods, each lasting approximately 2 years. They are characterized by a high rate of events but exhibit different source properties and spatial distributions. In the first period, the seismicity is spatially clustered close to the lake, on faults with different orientations and kinematics. In the second period, the seismicity is distributed along the Monti della Maddalena faults. Comparing the ground motion intensities of the two periods, we observe that events that occurred in the first period are associated with higher stress levels than others, in agreement with the b-values of the respective frequency-magnitude distributions. We compare the temporal evolution of the ground motion intensity with the rainfall and water levels measured at the artificial lake, as well as with the discharge of a ∼80 km distant spring, which is strictly controlled by climate trends. The results provide information about the regional processes acting on the southern Apennines. Our results show that the microseismicity is clearly associated with the Pertusillo artificial lake in the first period, whereas in the second period is a result of a combination of local effects due to water table oscillations of the lake itself, regional tectonics, and the poroelastic and elastic phenomena associated with carbonate rocks hosting aquifers.

Effect of mining and geology on mining-induced seismicity – A case study

Mining-induced seismicity is a commonly occurring phenomenon in underground mines. This poses a greater challenge to the safety of the mining operation. This paper presents a case study of the Young-Davidson mine in northern Ontario, Canada, where seismic events of magnitude Mn 2.0+ have been observed at mining depths of 600 to 800 m below the surface. The occurrence of large seismic events at such shallow depths is the key issue of this study. A comprehensive study of the microseismic database has been conducted to discern the root causes for the unusually strong seismic activities recorded at shallow depths. The effects of mining activities in the vicinity of two dykes intersecting the orebody on the seismic response are investigated. Variation of the b-value derived from the magnitude-frequency distribution is examined, and moment tensor inversion for three large seismic events is carried out to determine the source mechanisms. It is shown from this investigation that the influence of the sill pillar is more critical, leading to high mining-induced stress and the occurrence of large events. While the findings from this research are specific to this case study, they could be used to shed light on the causes of induced seismicity at other mines with similar conditions.

Spatio‐temporal variation in b‐value prior to the 26 November 2021 Mizoram earthquake of northeast India

In this study, the variation in frequency magnitude distribution factor (b‐value) before the main shock has been assessed for the 26 November 2021 Mizoram earthquake (Mw 6.1) in northeast India. The study area covering the Indo‐Burma Ranges is divided into square grids of equal dimension and spatial mapping of the b‐value for each square grid has been carried out. The maximum likelihood method is implemented for the estimation of the b‐value of each grid. The epicentral location of the 26 November 2021 Mizoram earthquake (Mw 6.1) is found to be in the intermediate b‐value square grid. The temporal variation in the b‐value indicates a considerable decline in the b‐value before the occurrence of the main event. The depth‐wise variation in the b‐value suggests an antithetical relationship between the b‐value and crustal stress. The spatio‐temporal and depth‐wise fluctuation in the b‐value results have been strengthened by employing a non‐parametric Kolmogorov–Smirnov (K–S) test. Based on our study, we infer that interplate earthquakes occur mostly in the upper crust of the study region.

The September 26, 2019 Silivri Earthquake (MW=5.6), NW Türkiye

The September 26, 2019 Silivri earthquake (MW=5.6-5.8) occurred along the North Anatolian Fault Zone segments extending beneath the Marmara Sea. In the present study the teleseismic P waveforms and 20-year long background seismicity of the earthquake (MW=5.6-5.8) have been analyzed. Point-source inversion of the teleseismic P waveforms revealed that the earthquake was due to oblique faulting and released a seismic moment of 3.2 x 1017 Nm (MW=5.6). The frequency-magnitude distributions (FMDs) for the background seismicity have been calculated after the 1999 İzmit earthquake. The considerable decrease of b-value of the FMD before the 2019 Silivri earthquake has been interpreted as stress increase along the fault segments.

A preliminary report on seismicity declustering methods and completeness magnitude in eastern Sunda Arc

Data declustering separates mainshocks from both foreshocks and aftershocks while a reliable estimate of completeness magnitude is a key point in seismic parameter determination. These play a role in seismicity-related work. In this preliminary study, we reported seismicity in two Indonesian provinces, namely NTB and NTT, as part of eastern Sunda Arc using the USGS catalogue during 1970-2021 based on performance of three declustering methods (Gardner and Knopoff, Reasenberg, Uhrhammer). These methods were tested along with three techniques of M c determination (MAXC, EMR, BC) provided by ZMAP to estimate minimum magnitude cut-offs, leading to an accurate completeness magnitude. After careful examination, the Reasenberg and BC techniques were proved to be suitable for characterising seismicity in the regions of interest, where M c was calculated under a linear assumption of the cumulative frequency-magnitude distribution (FMD), widely known as the Gutenberg-Richter law. The results revealed that b and a parameters are influenced by the choice of a specific declustering algorithm and calculation of M c. NTT was found to have a higher level of seismicity than NTB and seismicity rates in the southern part of both provinces were higher than those in the northern part. However, the number of strong ground motion with M w ≥ 6.5 in the northern area was larger than that in the southern, indicating the potency of Flores Back-arc Thrust for generating large earthquakes hence possible tsunamis.