What allows seismic events to grow big?: Insights from b-value and fault roughness analysis in laboratory stick-slip experiments

The Gutenberg &#8211; Richter&#8217;s b-value is commonly used to analyze the frequency-magnitude distribution of earthquakes, describing the proportion of small and large seismic events as the first estimation of seismic hazard. Additionally, the b-value has been used as a stress meter, giving some insights into the stress regime in different regions around the world. In this research, a grid-based spatial distribution for the b &#8211; value was estimated in three different areas of Norway: northern (74&#176;-81&#176; N/ 12&#176;-26&#176; E), southern (57&#176;-64&#176;N/3&#176;-12&#176; E), and the ridge zones of Mohns and Knipovich. For this, we used a complete catalog from the years 2000 to 2019, which was obtained from the Norwegian National Seismic Network online database. The magnitude of completeness was estimated separately for each zone both in time and space, covering a total area of ~425,000 km2. Our results show a regional variation of the mean b-value for northern (bnorth = 0.79) and southern (bsouth = 1.03) Norway, and the Ridge (bridge = 0.73), which can be interpreted in terms of the predominant stress regime in the different zones. So far, a few calculations regarding the b-value were previously done in Norway to analyze local intraplate sequences. Then, according to our knowledge, this research corresponds to the first estimation of a regional spatial variation of the b &#8211; value in the country.

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Possible stick-slip behavior before the Rausu landslide inferred from repeating seismic events

Geophysical Research Letters ◽

10.1002/2016gl069288 ◽

2016 ◽

Vol 43 (17) ◽

pp. 9038-9044 ◽

Cited By ~ 10

Author(s):

Masumi Yamada ◽

Jim Mori ◽

Yuki Matsushi

Keyword(s):

Seismic Events ◽

Stick Slip

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The effect of salt in dilatant faults on rates and magnitudes of induced seismicity – first results building on the geological setting of the Groningen Rotliegend reservoirs

Netherlands Journal of Geosciences – Geologie en Mijnbouw ◽

10.1017/njg.2017.19 ◽

2017 ◽

Vol 96 (5) ◽

pp. s87-s104 ◽

Cited By ~ 1

Author(s):

Michael Kettermann ◽

Steffen Abe ◽

Alexander F. Raith ◽

Jan de Jager ◽

Janos L. Urai

Keyword(s):

Rock Salt ◽

Induced Seismicity ◽

Loading Rate ◽

Numerical Models ◽

Fault Zones ◽

Shear Loading ◽

Ductile Material ◽

Seismic Events ◽

Fault Mechanics ◽

Stick Slip

AbstractThe presence of salt in dilatant normal faults may have a strong influence on fault mechanics in the Groningen field and on the related induced seismicity. At present, little is known of the structure of these fault zones. This study starts with the geological evolution of the Groningen area, where, during tectonic faulting, rock salt may have migrated downwards into dilatant faults. These fault zones therefore may contain inclusions of rock salt. Because of its rate-dependent mechanical properties, the presence of salt in a fault may introduce a loading-rate dependency into fault movement and affect the distribution of magnitudes of seismic events. We present a first-look study showing how these processes can be investigated using a combination of analogue and numerical modelling. Full scaling of the models and quantification of implications for induced seismicity in Groningen require further, more detailed studies: an understanding of fault zone structure in the Groningen field is required for improved predictions of induced seismicity. The analogue experiments are based on a simplified stratigraphy of the Groningen area, where it is generally thought that most of the Rotliegend faulting has taken place in the Jurassic, after deposition of the Zechstein. This suggests that, at the time of faulting, the sulphates were already transformed into brittle anhydrite. If these layers were sufficiently brittle to fault in a dilatant fashion, rock salt was able to flow downwards into the dilatant fractures. To test this hypothesis, we use sandbox experiments where we combine cohesive powder as analogue for brittle anhydrites and carbonates with viscous salt analogues to explore the developing fault geometry and the resulting distribution of salt in the faults. Using the observations from analogue models as input, numerical models investigate the stick-slip behaviour of fault zones containing ductile material qualitatively with the discrete element method (DEM). Results show that the DEM approach is suitable for modelling the seismicity of faults containing salt. The stick-slip motion of the fault becomes dependent on shear loading rate with a modification of the frequency–magnitude distribution of the generated seismic events.

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SCALING LAWS OF SEISMIC EVENTS — A MODEL WITH FRACTAL GEOMETRY

Fractals ◽

10.1142/s0218348x99000347 ◽

1999 ◽

Vol 07 (04) ◽

pp. 341-351

Author(s):

C. GODANO ◽

M. L. ALONZO

Keyword(s):

Fractal Dimension ◽

Fractal Geometry ◽

Scaling Laws ◽

B Value ◽

Seismic Events ◽

Magnitude Distribution ◽

Transitional State ◽

Contact Points ◽

Omori Law ◽

Local Fluctuations

Most models of earthquakes attempt to reproduce the observed scaling laws of seismic events: the Gutenberg-Richter frequency magnitude distribution, but not the Omori law for aftershocks and the multifractal distribution of hypocenters location. Many of these models are based on the idea of Self-Organized Criticality (SOC). These are dynamic systems which organize themselves into a transitional state and can reproduce the Gutenberg-Richter distribution, but generally do not reproduce the space-time distribution. Here, we suggest a model based on a fractal geometry: the two sides of a fault are modeled by means of a fractal surface. As a first step, one of them is slipped of a random amount with periodic boundary conditions, then new contact points between the surfaces are found. The area surrounded by these points is assumed to be proportional to the area of the earthquake. The size distribution of events is in good agreement with the observed Gutenberg-Richter law and the local fluctuations of the b value are explained in terms of variations of the fractal dimension of the surface. Also the multifractal distribution of earthquakes in space is well-reproduced with global properties not depending on the fractal dimension of the surface. However, we are not able to obtain something similar to the Omori law simply because we do not control the time evolution of the model.

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Indications for different types of brittle failure due to active coal mining using waveform similarities of induced seismic events

Solid Earth ◽

10.5194/se-4-405-2013 ◽

2013 ◽

Vol 4 (2) ◽

pp. 405-422 ◽

Cited By ~ 6

Author(s):

S. Wehling-Benatelli ◽

D. Becker ◽

M. Bischoff ◽

W. Friederich ◽

T. Meier

Keyword(s):

Coal Mining ◽

Brittle Failure ◽

B Value ◽

Mining Activity ◽

Longwall Face ◽

Seismic Events ◽

Single Station ◽

Longwall Panel ◽

Active Coal ◽

Different Types

Abstract. Longwall mining activity in the Ruhr coal mining district leads to mining-induced seismicity. For detailed studies the seismicity of a single longwall panel beneath the town of Hamm-Herringen in the eastern Ruhr area was monitored between June 2006 and July 2007 with a dense temporary network of 15 seismic stations. More than 7000 seismic events with magnitudes between –1.7 ≤ ML ≤ 2.0 were detected and localized in this period. Most of the events occurred in the vicinity of the moving longwall face. In order to find possible differences in the brittle failure types of these events an association of the events to distinct clusters is performed based on their waveform characteristics. This task is carried out using a new clustering algorithm utilizing a network similarity matrix which is created by combining all available 3-component single station similarity matrices. The resultant network matrix is then sorted with respect to the similarity of its rows leading to a sorted matrix immediately indicating the clustering of the event catalogue. Finally, clusters of similar events are extracted by visual inspection. This approach results in the identification of several large clusters which are distinct with respect to their spatial and temporal characteristics as well as their frequency magnitude distributions. Comparable clusters are also found with a conventional single linkage approach, however, the new routine seems to be able to associate more events to specific clusters without merging the clusters. The nine largest observed clusters can be tentatively divided into three different groups that indicate different types of brittle failure. The first group consists of the two largest clusters which constitute more than half of all recorded events. Results of a relative relocation using cross-correlation data suggest that these events are confined to the extent of the mined out longwall and cluster close to the edges of the active longwall at the depth of active mining. These events occur in lockstep with the longwall advance and exhibit a high b value of the Gutenberg–Richter relation (GR) of about 1.5 to 2.5 and consist of small magnitude events. Thus, these events represent the immediate energy release adjacent to the mined out area. The second group consists of clusters located either slightly above or below the depth of active mining and occurring at the current position of the longwall face within the confines of the longwall. They consist of generally stronger events and do not follow GR. This activity might be linked to the failure of more competent layers above and below the mined out seam resulting in larger magnitude events. Finally, one cluster represents seismic activity with a rather low b value below 1 and events located partly towards the north of the longwall which are delayed with respect to the advance of the longwall face. These events are interpreted as brittle failure on pre-existing tectonic structures reactivated by the mining activity.

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Seismic b-Value for Foreshock AE Events Preceding Repeated Stick-Slips of Pre-Cut Faults in Granite

Applied Sciences ◽

10.3390/app8122361 ◽

2018 ◽

Vol 8 (12) ◽

pp. 2361 ◽

Cited By ~ 2

Author(s):

Xinglin Lei ◽

Shinian Li ◽

Liqiang Liu

Keyword(s):

Shear Stress ◽

Dynamic Range ◽

Triaxial Compression ◽

Sampling Rate ◽

Maximum Amplitude ◽

Seismic Hazard Assessment ◽

Confining Pressure ◽

B Value ◽

Stick Slip ◽

Shear Rupture

In this study, the b-values for acoustic emission (AE) events during stick-slip cycles of pre-cut faults in granite (as an analogue of unfavorably oriented immature faults) under triaxial compression (confining pressure: 40 MPa) are investigated. Using a multi-channel AE waveform recording system and two peak detectors, we recorded AE waveforms at 16 bits and at a sampling rate of 25 MHz, as well as the maximum amplitude of AE events with a dynamic range of 55 dB. For stick-slip events, the b-value decreases from 1.2 to 1.5 to approximately 0.6 as the shear stress increases, and then quickly jumps back to 1.0 to 1.3 immediately prior to the dynamic stress drop. The minimum b-value coincides with the maximum event rate and a stress level of 70 to 95% of the shear strength. It is also observed that the AE activity during each cycle was linked with the pre-failure fault slip, which accounts for 30% of the dynamic slip. Our results on b-value evaluation preceding repeated stick-slips can be used as an indicator of the degree of fault maturity and shear stress acting on the fault, which is important in seismic hazard assessment and earthquake prediction, especially for the injection-induced seismicity for fields in which reactivated shear rupture of unfavorable and immature faults or tensile fractures is important.

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Stress drop–magnitude dependence of acoustic emissions during laboratory stick-slip

Geophysical Journal International ◽

10.1093/gji/ggaa524 ◽

2020 ◽

Vol 224 (2) ◽

pp. 1371-1380

Author(s):

Aglaja Blanke ◽

Grzegorz Kwiatek ◽

Thomas H W Goebel ◽

Marco Bohnhoff ◽

Georg Dresen

Keyword(s):

Grain Size ◽

Stress Drop ◽

Source Parameters ◽

Corner Frequency ◽

Strong Increase ◽

Stick Slip ◽

Fault Roughness ◽

Average Grain Size ◽

Seismic Stress ◽

Stress Drops

SUMMARY Earthquake source parameters such as seismic stress drop and corner frequency are observed to vary widely, leading to persistent discussion on potential scaling of stress drop and event size. Physical mechanisms that govern stress drop variations are difficult to evaluate in nature and are more readily studied in controlled laboratory experiments. We perform two stick-slip experiments on fractured (rough) and cut (smooth) Westerly granite samples to explore fault roughness effects on acoustic emission (AE) source parameters. We separate large stick-slip events that generally saturate the seismic recording system from populations of smaller AE events which are sensitive to fault stresses prior to slip. AE event populations show many similarities to natural seismicity and may be interpreted as laboratory equivalent of natural microseismic events. We then compare the temporal evolution of mechanical data such as measured stress release during slip to temporal changes in stress drops derived from AEs using the spectral ratio technique. We report on two primary observations: (1) In contrast to most case studies for natural earthquakes, we observe a strong increase in seismic stress drop with AE size. (2) The scaling of stress drop with magnitude is governed by fault roughness, whereby the rough fault shows a more rapid increase of the stress drop–magnitude relation with progressing large stick-slip events than the smooth fault. The overall range of AE sizes on the rough surface is influenced by both the average grain size and the width of the fault core. The magnitudes of the smallest AE events on smooth faults may also be governed by grain size. However, AEs significantly grow beyond peak roughness and the width of the fault core. Our laboratory tests highlight that source parameters vary substantially in the presence of fault zone heterogeneity (i.e. roughness and narrow grain size distribution), which may affect seismic energy partitioning and static stress drops of small and large AE events.

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Seismic and Aseismic Preparatory Processes Before Large Stick–Slip Failure

Pure and Applied Geophysics ◽

10.1007/s00024-020-02605-x ◽

2020 ◽

Vol 177 (12) ◽

pp. 5741-5760 ◽

Cited By ~ 2

Author(s):

Georg Dresen ◽

Grzegorz Kwiatek ◽

Thomas Goebel ◽

Yehuda Ben-Zion

Keyword(s):

Shear Strain ◽

Triaxial Compression ◽

Strain Partitioning ◽

Compression Tests ◽

Event Correlation ◽

Stick Slip ◽

Relative Contribution ◽

Fault Roughness ◽

Preparation Phase ◽

Aseismic Deformation

AbstractNatural earthquakes often have very few observable foreshocks which significantly complicates tracking potential preparatory processes. To better characterize expected preparatory processes before failures, we study stick-slip events in a series of triaxial compression tests on faulted Westerly granite samples. We focus on the influence of fault roughness on the duration and magnitude of recordable precursors before large stick–slip failure. Rupture preparation in the experiments is detectable over long time scales and involves acoustic emission (AE) and aseismic deformation events. Preparatory fault slip is found to be accelerating during the entire pre-failure loading period, and is accompanied by increasing AE rates punctuated by distinct activity spikes associated with large slip events. Damage evolution across the fault zones and surrounding wall rocks is manifested by precursory decrease of seismic b-values and spatial correlation dimensions. Peaks in spatial event correlation suggest that large slip initiation occurs by failure of multiple asperities. Shear strain estimated from AE data represents only a small fraction (< 1%) of total shear strain accumulated during the preparation phase, implying that most precursory deformation is aseismic. The relative contribution of aseismic deformation is amplified by larger fault roughness. Similarly, seismic coupling is larger for smooth saw-cut faults compared to rough faults. The laboratory observations point towards a long-lasting and continuous preparation process leading to failure and large seismic events. The strain partitioning between aseismic and observable seismic signatures depends on fault structure and instrument resolution.

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Numerical evidences of almost convergence of wave speeds for the Burridge–Knopoff model

SN Applied Sciences ◽

10.1007/s42452-020-03856-y ◽

2020 ◽

Vol 2 (12) ◽

Author(s):

C. Mascia ◽

P. Moschetta

Keyword(s):

Numerical Approximation ◽

Seismic Event ◽

Numerical Estimate ◽

Propagation Speed ◽

Seismic Events ◽

Almost Convergence ◽

Stick Slip ◽

Wave Speeds ◽

Temporal Averaging ◽

Predictor Corrector

AbstractThis paper deals with the numerical approximation of a stick–slip system, known in the literature as Burridge–Knopoff model, proposed as a simplified description of the mechanisms generating earthquakes. Modelling of friction is crucial and we consider here the so-called velocity-weakening form. The aim of the article is twofold. Firstly, we establish the effectiveness of the classical Predictor–Corrector strategy. To our knowledge, such approach has never been applied to the model under investigation. In the first part, we determine the reliability of the proposed strategy by comparing the results with a collection of significant computational tests, starting from the simplest configuration to the more complicated (and more realistic) ones, with the numerical outputs obtained by different algorithms. Particular emphasis is laid on the Gutenberg–Richter statistical law, a classical empirical benchmark for seismic events. The second part is inspired by the result by Muratov (Phys Rev 59:3847–3857, 1999) providing evidence for the existence of traveling solutions for a corresponding continuum version of the Burridge–Knopoff model. In this direction, we aim to find some appropriate estimate for the crucial object describing the wave, namely its propagation speed. To this aim, motivated by LeVeque and Yee (J Comput Phys 86:187–210, 1990) (a paper dealing with the different topic of conservation laws), we apply a space-averaged quantity (which depends on time) for determining asymptotically an explicit numerical estimate for the velocity, which we decide to name LeVeque–Yee formula after the authors’ name of the original paper. As expected, for the Burridge–Knopoff, due to its inherent discontinuity of the process, it is not possible to attach to a single seismic event any specific propagation speed. More regularity is expected by performing some temporal averaging in the spirit of the Cesàro mean. In this direction, we observe the numerical evidence of the almost convergence of the wave speeds for the Burridge–Knopoff model of earthquakes.

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Stick-slip failure in heterogeneous sheared fault with a variety of fault roughness

Physics of The Earth and Planetary Interiors ◽

10.1016/j.pepi.2020.106587 ◽

2020 ◽

Vol 309 ◽

pp. 106587

Author(s):

Xiaoping Zhou ◽

Yundong Shou ◽

Luhao Yang ◽

Yi He

Keyword(s):

Stick Slip ◽

Fault Roughness

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