Earthquake Dynamics Research Articles

Converging Research Fields Need Converging Communities

The seismological community consists of researchers in academia, government, and industry working on a wide range of research topics that include: earthquake dynamics, induced seismicity, deep earth structure, the exploration and production of reservoirs, and hazard analysis. In practice, the results of this research are presented at various conferences and in journals that fall under the auspices of professional societies, such as the Seismological Society of America (SSA), the American Geophysical Union (AGU), and the Society of Exploration Geophysicists (SEG). There are a number of converging trends in the seismological community despite the broad range of topics studied. In exploration geophysics, microseismicity enjoys increasing importance in a number of applications. Induced seismicity is a side-effect of hydrofracturing carried out to produce tight gas reservoirs and is used to diagnose fluid migration. Characterization and monitoring of induced seismicity is used for the exploration and production of hydrocarbons and is important in geothermal energy production and carbon …

A Tale of Two Earthquakes

Networks of GPS detectors can provide a detailed picture of the dynamics of earthquakes before, during, and after the event.

Modeling and simulating an aftershock process caused by a strong earthquake in the Barents Sea shelf

The paper considers an aftershock process caused by an Mw = 6.1 earthquake which occurred on 21 February 2008 in the Storfjord channel (Spitsbergen). The earthquake was the strongest in the history of seismic monitoring on the Barents Sea shelf. To study the aftershock process, some relaxation models of aftershock decay rate and the Epidemic-type Aftershock-sequences (ETAS) model of triggered seismicity were fitted. It was shown that the aftershock process was a superposition of two subprocesses relaxation and trigger. Each of the subprocesses was simulated using a relevant model. Based on the modeling, a hypothesis of Storfjord seismicity connected with fluid effect on the local stress field was suggested. GCMD TERMS: Solid Earth; Seismology; Earthquake Dynamics / Earthquake

A window into the complexity of the dynamic rupture of the 2011 Mw 9 Tohoku-Oki earthquake

The 2011 Mw 9 Tohoku-Oki earthquake, recorded by over 1000 near-field stations and multiple large-aperture arrays, is by far the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in earthquake source dynamics. Here we conduct a high resolution array analysis based on recordings from the USarray and the European network. The mutually consistent results from both arrays reveal rupture complexity with unprecedented resolution, involving phases of diverse rupture speed and intermittent high frequency bursts within slow speed phases, which suggests spatially heterogeneous material properties. The earthquake initially propagates down-dip, with a slow initiation phase followed by sustained propagation at speeds of 3 km/s. The rupture then slows down to 1.5 km/s for 60 seconds. A rich sequence of bursts is generated along the down-dip rim of this slow and roughly circular rupture front. Before the end of the slow phase an extremely fast rupture front detaches at about 5 km/s towards the North. Finally a rupture front propagates towards the south running at about 2.5 km/s for over 100 km. Key features of the rupture process are confirmed by the strong motion data recorded by K-net and KIK-net. The energetic high frequency radiation episodes within a slow rupture phase suggests a patchy image of the brittle-ductile transition zone, composed of discrete brittle asperities within a ductile matrix. The high frequency is generated mainly at the down-dip edge of the principal slip regions constrained by geodesy, suggesting a variation along dip of the mechanical properties of the mega thrust fault or their spatial heterogeneity that affects rise time.

Leon Knopoff (1925–2011)

Interests in earthquake dynamics and music were driven by a seismologist's passion for understanding the physics behind pattern recognition.

Slip Sequences in Laboratory Experiments Resulting from Inhomogeneous Shear as Analogs of Earthquakes Associated with a Fault Edge

Faults are intrinsically heterogeneous with common occurrences of jogs, edges and steps. We therefore explore experimentally and theoretically how fault edges may affect earthquake and slip dynamics. In the presented experiments and accompanying theoretical model, shear loads are applied to the edge of one of two flat blocks in frictional contact that form a fault analog. We show that slip occurs via a sequence of rapid rupture events that initiate from the loading edge and are arrested after propagating a finite distance. Each successive event extends the slip size, transfers the applied shear across the block, and causes progressively larger changes of the contact area along the contact surface. Resulting from this sequence of events, a hard asperity is dynamically formed near the loaded edge. The contact area beyond this asperity is largely reduced. These sequences of rapid events culminate in slow slip events that precede a major, unarrested slip event along the entire contact surface. We suggest that the 1998 M5.0 Sendai and 1995 off-Etorofu earthquake sequences may correspond to this scenario. Our work demonstrates, qualitatively, how the simplest deviation from uniform shear loading may significantly affect both earthquake nucleation processes and how fault complexity develops.

MPI-OpenMP hybrid simulations using boundary integral equation and finite difference methods for earthquake dynamics and wave propagation: Application to the 2007 Niigata Chuetsu-Oki earthquake (Mw6.6)

Abstract For the past two decades, the combination between the boundary integral equation method (BIEM) and the finite difference method (FDM) has provided a powerful approach for simulating the dynamic rupture process along a complex fault system and the resultant seismic wave radiation and propagation for the purpose of understanding the physics of seismology and the generation of strong ground motion by large earthquakes. In the many-core architecture currently in use, it can be useful to take advantage of hybrid MPI-OpenMP programming. In this study, we are investigating the Mw6.6, 2007 Niigata Chuetsu-Oki, Japan, earthquake. In the BIEM simulation of the dynamic rupture process, MPI-OpenMP hybrid programming is 24 to 38% faster than MPI programming on the same resource using 8 to 16 nodes (with 8 cores). In the FDM simulation on the wave propagation, hybrid programming is 25 to 37% faster. This performance allows us to investigate this earthquake using various parameter settings. First we obtain the frictional parameters based on the proposed kinematic finite source model using BIEM, then model both the spontaneous dynamic rupture propagation and wave radiation by combining BIEM and FDM. It is found that on the given asperities, the peak stress can reach 20 MPa and reduced stress, -20 MPa. Dynamic rupture simulations require a barrier around the southernmost asperity so that this asperity is ruptured in a reverse manner. This effect can be observed very locally in the wave radiation. Furthermore, we observe that the dynamic rupture propagation between two cross-cutting segments generates a more complex wavefield. The change in fault geometry may be dominant over the asperities on a single plane for this earthquake.

Intraplate seismicity in Canada: a graph theoretic approach to data analysis and interpretation

Abstract. Intraplate seismicity occurs in central and northern Canada, but the underlying origin and dynamics remain poorly understood. Here, we apply a graph theoretic approach to characterize the statistical structure of spatiotemporal clustering exhibited by intraplate seismicity, a direct consequence of the underlying nonlinear dynamics. Using a recently proposed definition of "recurrences" based on record breaking processes (Davidsen et al., 2006, 2008), we have constructed directed graphs using catalogue data for three selected regions (Region 1: 45°−48° N/74°−80° W; Region 2: 51°−55° N/77°−83° W; and Region 3: 56°−70° N/65°−95° W), with attributes drawn from the location, origin time and the magnitude of the events. Based on comparisons with a null model derived from Poisson distribution or Monte Carlo shuffling of the catalogue data, our results provide strong evidence in support of spatiotemporal correlations of seismicity in all three regions considered. Similar evidence for spatiotemporal clustering has been documented using seismicity catalogues for southern California, suggesting possible similarities in underlying earthquake dynamics of both regions despite huge differences in the variability of seismic activity.

Microwave stimulation of plasticity in an earthquake source

It is suggested to stimulate the slow relaxation of elastic energy of deformation stress in an earth-quake source by microwave radiation, which intensifies the motion of dislocations, decreases the yield limit, and increases the plasticity. This phenomenon, known in solid-state physics as magnetoplasticity, can be used to retain an earthquake source far from the critical regime capable of developing into a catastrophic earth-quake by stimulating a slow relaxation of the source. The available evidence for the influence of magnetic storms on the dynamics of earthquakes is generally consistent with the concept of stimulated magnetoplasticity as a means of preventing catastrophic earthquakes, proposed in the present communication.

On the transient behavior of frictional melt during seismic slip

In a recent work on the problem of sliding surfaces under the presence of frictional melt (applying in particular to earthquake fault dynamics), we derived from first principles an expression for the steady state friction compatible with experimental observations. Building on the expressions of heat and mass balance obtained in the above study for this particular case of Stefan problem (phase transition with a migrating boundary), we propose here an extension providing a full time‐dependent solution (including the weakening transient after pervasive melting has started, the effect of eventual steps in velocity, and the final decelerating phase). A system of coupled equations is derived and solved numerically. The resulting transient friction and wear evolution yield a satisfactory fit (1) with experiments performed under variable sliding velocities (0.9–2 m s−1) and different normal stresses (0.5–20 MPa) for various rock types and (2) with estimates of slip weakening obtained from observations on ancient seismogenic faults that host pseudotachylite (solidified melt). The model allows us to extrapolate the experimentally observed frictional behavior to large normal stresses representative of the seismogenic Earth crust (up to 200 MPa), high slip rates (up to 9 m s−1), and cases where melt extrusion is negligible. Though weakening distance and peak stress vary widely, the net breakdown energy appears to be essentially independent of either slip velocity or normal stress. In addition, the response to earthquakelike slip can be simulated, showing a rapid friction recovery when slip rate drops. We discuss the properties of energy dissipation, transient duration, velocity weakening, restrengthening in the decelerating final slip phase, and the implications for earthquake source dynamics.

Universality in solar flare, magnetic storm and earthquake dynamics using Tsallis statistical mechanics

The universal character of the dynamics of various extreme phenomena is an outstanding scientific challenge. We show that X-ray flux and D s t time series during powerful solar flares and intense magnetic storms, respectively, obey a nonextensive energy distribution function for earthquake dynamics with similar values for the Tsallis entropic index q . Thus, evidence for universality in solar flares, magnetic storms and earthquakes arise naturally in the framework of Tsallis statistical mechanics. The observed similarity suggests a common approach to the interpretation of these diverse phenomena in terms of driving physical mechanisms that have the same character.

Mesh dependence and slip complexity in earthquake fault models

AbstractWe study the origins of mesh dependence in earthquake dynamics and show that mesh sensitivity in numerical models of earthquake rupture can unearth new, exciting physical phenomena, and provide hidden clues to discovering the physics underlying earthquake complexity. We show (in agreement with previous numerical studies of dynamic rupture at faults) that coarse meshes or discrete models produce more interesting physics because these numerical simulations produce richer spatio‐temporal complexity at faults over multiple earthquake cycles. These discrete models are desirable as they reproduce the observed Gutenberg–Richter power‐law frequency magnitude distribution of earthquakes more accurately. However, this complexity is lost as the mesh size is refined, which is undersirable from a physical point of view. We investigate this mesh sensitivity by analysing the higher‐order perturbative terms introduced into numerical models with coarse meshes. The introduction of these higher‐order, nonlinear terms into standard continuum models generally used to describe earthquake dynamics may provide a key to reproducing earthquake complexity while partially removing the associated mesh dependence without the need to modify the underlying mesh. This is a first step towards deriving a physical law capable of reproducing the scale‐invariant behaviour in earthquake sizes and reconciling continuum and discrete models of earthquake rupture. Copyright © 2009 John Wiley & Sons, Ltd.

Pulse-like and crack-like dynamic shear ruptures on frictional interfaces: experimental evidence, numerical modeling, and implications

Destructive large earthquakes occur as dynamic frictional ruptures along pre-existing interfaces (or faults) in the Earth’s crust. One of the important issues in earthquake dynamics is the local duration of relative displacement or slip. Seismic inversions show that earthquakes may propagate as self-healing pulse-like ruptures, with local slip duration being much shorter than the overall rupture duration. Yet many classical models produce crack-like ruptures, with local slip durations comparable to the overall rupture duration. We study rupture modes in an experimental set up designed to mimic a fault prestressed both in compression and in shear. Our experiments demonstrate systematic variation from crack-like to pulse-like rupture modes as nondimensional shear prestress is decreased. The results of our experiments are consistent with theories of ruptures on interfaces with velocity-weakening friction. To consider the possibility that slip-weakening friction can also result in such rupture mode transition in the presence of the dynamic nucleation procedure employed by the experimental setup, we conduct numerical simulations with linear slip-weakening friction. In the simulations, we use the parameter regimes that were shown in previous studies to reproduce supershear transition distances obtained in the same experimental setup. We find that simulations with linear slip-weakening friction are unable to reproduce pulse-like ruptures, even in the presence of the dynamic initiation procedure. Our experimental results and simulations imply that velocity-weakening friction plays an important role in dynamic behavior of shear ruptures and needs to be included in earthquake models.

Boundary integral equations for dynamic rupture propagation on vertical complex fault system in half-space: Theory

The boundary integral equation method (BIEM) is now widely used in numerical studies on earthquake rupture dynamics, and is proved to be a powerful tool to deal with problems on complex fault system. However, since this method heavily lies on the specific forms of Green’s function and only the Green’s function in full-space has a closed analytic expression, it is usually limited to a full-space medium. In this study, as a first step to extend this method to an arbitrary complex fault system in half-space, the boundary integral equations (BIEs) for dynamic strike-slip on vertical complex fault system in half-space are derived based on exact Green’s function for isotropic and homogeneous half-space. Effect of the geometry of the complex fault system are dealt with carefully. Final BIEs is composed of two parts: contribution from full-space, which has been thoroughly investigated by Aochi and his co-workers by using the Green’s function for full-space, and that from free surface, which is studied in detail in this study.

Failure processes in elastic fiber bundles

The fiber bundle model describes a collection of elastic fibers under load. the fibers fail successively and for each failure, the load distribution among the surviving fibers change. Even though very simple, the model captures the essentials of failure processes in a large number of materials and settings. We present here a review of fiber bundle model with different load redistribution mechanism from the point of view of statistics and statistical physics rather than materials science, with a focus on concepts such as criticality, universality and fluctuations. We discuss the fiber bundle model as a tool for understanding phenomena such as creep, and fatigue, how it is used to describe the behavior of fiber reinforced composites as well as modelling e.g. network failure, traffic jams and earthquake dynamics.

Entropy production and self-organized (sub)criticality in earthquake dynamics

We derive an analytical expression for entropy production in earthquake populations based on Dewar's formulation, including flux (tectonic forcing) and source (earthquake population) terms, and apply it to the Olami-Feder-Christensen numerical model for earthquake dynamics. Assuming the commonly observed power-law rheology between driving stress and remote strain rate, we test the hypothesis that maximum entropy production (MEP) is a thermodynamic driver for self-organized 'criticality' (SOC) in the model. MEP occurs when the global elastic strain is near-critical, with small relative fluctuations in macroscopic strain energy expressed by a low seismic efficiency, and broad-bandwidth power-law scaling of frequency and rupture area. These phenomena, all as observed in natural earthquake populations, are hallmarks of the broad conceptual definition of SOC (which has, to date, often included self-organizing systems in a near but strictly subcritical state). In the MEP state, the strain field retains some memory of past events, expressed as coherent 'domains', implying a degree of predictability, albeit strongly limited in practice by the proximity to criticality and our inability to map the natural stress field at an equivalent resolution to the numerical model.

Slip-stick and the evolution of frictional strength

The evolution of frictional strength has great fundamental and practical importance. Applications range from earthquake dynamics to hard-drive read/write cycles. Frictional strength is governed by the resistance to shear of the large ensemble of discrete contacts that forms the interface that separates two sliding bodies. An interface's overall strength is determined by both the real contact area and the contacts' shear strength. Whereas the average motion of large, slowly sliding bodies is well-described by empirical friction laws, interface strength is a dynamic entity that is inherently related to both fast processes such as detachment/re-attachment and the slow process of contact area rejuvenation. Here we show how frictional strength evolves from extremely short to long timescales, by continuous measurements of the concurrent local evolution of the real contact area and the corresponding interface motion (slip) from the first microseconds when contact detachment occurs to large (100-second) timescales. We identify four distinct and inter-related phases of evolution. First, all of the local contact area reduction occurs within a few microseconds, on the passage of a crack-like front. This is followed by the onset of rapid slip over a characteristic time, the value of which suggests a fracture-induced reduction of contact strength before any slip occurs. This rapid slip phase culminates with a sharp transition to slip at velocities an order of magnitude slower. At slip arrest, 'ageing' immediately commences as contact area increases on a characteristic timescale determined by the system's local memory of its effective contact time before slip arrest. We show how the singular logarithmic behaviour generally associated with ageing is cut off at short times. These results provide a comprehensive picture of how frictional strength evolves from the short times and rapid slip velocities at the onset of motion to ageing at the long times following slip arrest.

Influence of strong electromagnetic discharges on the dynamics of earthquakes time distribution in the Bishkek test area (Central Asia)

From 08/01/1983 to 28/03/1990, at the Bishkek ElectroMagnetic (EM) test site (Northern Tien Shan and Chu Val- ley area, Central Asia), strong currents, up to 2.5 kA, were released at a 4.5 km long electrical (grounded) dipole. This area is seismically active and a catalogue with about 14100 events from 1975 to 1996 has been analyzed. The seismic catalogue was divided into three parts: 1975-1983 first part with no EM experiments, 1983-1990 second part during EM experiments and 1988-1996 after experiments part. Qualitative and quantitative time series non- lin- ear analysis was applied to waiting times of earthquakes to the above three sub catalogue periods. The qualitative approach includes visual inspection of reconstructed phase space, Iterated Function Systems (IFS) and Recurrence Quantification Analysis (RQA). The quantitative approach followed correlation integral calculation of reconstruct- ed phase space of waiting time distribution, with noise reduction and surrogate testing methods. Moreover the Lem- pel-Ziv algorithmic complexity measure (LZC) was calculated. General dynamics of earthquakes' temporal distri- bution around the test area, reveals properties of low dimensional non linearity. Strong EM discharges lead to the increase in extent of regularity in earthquakes temporal distribution. After cessation of EM experiments the earth- quakes' temporal distribution becomes much more random than before experiments. To avoid non valid conclusions several tests were applied to our data set: differentiation of the time series was applied to check results not affected by non stationarity; the surrogate data approach was followed to reject the hypothesis that dynamics belongs to the colored noise type. Small earthquakes, below completeness threshold, were added to the analysis to check results robustness.

Constitutive parameters for earthquake rupture dynamics based on high-velocity friction tests with variable sliprate

To reproduce the dynamic rupture process of earthquakes, the fault geometry, initial stress distribution and a frictional constitutive law on the fault are important parameters as initial and boundary conditions of the system. Here, we focus on the frictional constitutive relation on the fault. During a high-speed rupture, fault strength decreases as slip develops which can be described by a slip weakening equation. To understand the physical process of stress breakdown during the dynamic rupture of earthquakes, we investigated the friction behavior of rocks in the laboratory by direct measurements of traction evolution with slip in response to a given slip history. We employed a high-speed rotary shear apparatus introduced at National Research Institute for Earth Science and Disaster Prevention (NIED). This apparatus has a capability of sliding with predefined variable velocities using a servo-controlled system. We used a pair of granite cylindrical specimens with a diameter of 25 mm. As an input signal, we used a regularized Yoffe function to investigate the scale dependence of fracture energy and slip weakening distance (D c). We observed a positive correlation between D c and total slip, keeping the maximum slip velocity constant. These conditions correspond to those for earthquakes with the same stress drop and varying magnitudes. Finally, we used a real fault motion; a fault parallel velocity seismogram observed at PS10, 3 km away from the surface fault trace and above the high slip region during the 2002 Denali, Alaska, earthquake. We compared the seismological fracture energy with the corresponding D c. The relation is linear with an inflection point at D c = 0.2 m, where the gradient changes. Another interesting feature is that the maximum value of D c is about 4m even if the total slip exceeds 12 m.

The twelfth Mallet–Milne lecture

This twelfth Mallet–Milne lecture marks 22 years of the series. These lectures, organised by the Society for Earthquake and Civil Engineering Dynamics (SECED), are named in honour of Robert Mallet (1810–1881) and John Milne (1850–1913), nineteenth century pioneers of seismology in Britain. The bi-ennial Mallet–Milne lectures are given by internationally recognised experts in the field of earthquake engineering on topics close to their own professional interests but also of relevance to the broader earthquake engineering community. The Mallet–Milne lectures have covered many different aspects of earthquake engineering, primarily from a technical perspective including the broader issues of policy for disaster prevention. Three of the lectures in the series have been dedicated to issues related to engineering seismology and seismic hazard assessment. In the First Mallet–Milne lecture, ‘Engineering Seismology’, Prof. Nicholas Ambraseys of Imperial College, London described a new approach to the assessment of liquefaction potential and a re-evaluation of twentieth century seismicity in Turkey. In the Fifth Mallet–Milne Lecture, ‘From Earthquake Acceleration to Seismic Displacements’, Prof. Bruce Bolt of the University of California at Berkeley focussed on the destructive nature of near field ground motions containing high energy pulses that are usually referred to as ‘fling’—a term the lecturer himself was responsible for coining. In the Eighth Mallet–Milne lecture, ‘Living with Earthquakes: Know your Faults’, Dr. James Jackson of Cambridge University addressed the identification and characterisation of active geological faults. Dr Jackson illustrated the major advances made in the ability of seismologists to determine the source parameters for earthquakes, in the understanding of the relationship between crustal deformations and geomorphology and in the developments of remote technologies that allow rapid and accurate measurements of deformation on the Earth’s surface. The other seven Mallet–Milne lectures have considered how the seismic community may use technical knowledge, model testing and common sense to ensure appropriate design.