Dynamic Earthquake Triggering Research Articles

Dynamic triggering of small local earthquakes in the central Himalaya

AbstractWe present the first observation of remote dynamic triggering of local microearthquakes in central Himalaya caused by the teleseismic waves from the 2007 Mw 8.5 Sumatra earthquake that occurs ~4500 km away. We find small local earthquakes in the Kumaon‐Garhwal Himalaya triggered by teleseismic long‐period surface waves. Interestingly, an elevated level of seismicity persists for a week or so after the arrival of the teleseismic waves. The teleseismic waves impart ~9 kPa of peak dynamic stresses, suggesting that the Himalayan faults in this area are sensitive to small stress changes. This heightened and protracted seismicity indicates that the transient dynamic stresses may have triggered secondary processes, such as slow slip, that may be responsible for the persistence of this earthquake sequence. The region is thought to be close to a large damaging earthquake in the near future. This study provides improved constraints on the factors controlling the earthquake cycle.

Dynamic triggering of deep earthquakes within a fossil slab

AbstractThe 9 November 2009 Mw 7.3 Fiji deep earthquake is the largest event in a region west of the Tonga slab defined by scattered seismicity and velocity anomalies. The main shock rupture was compact, but the aftershocks were distributed along a linear feature at distances of up to 126 km. The aftershocks and some background seismicity define a sharp northern boundary to the zone of outboard earthquakes, extending westward toward the Vitiaz deep earthquake cluster. The northern earthquake lineament is geometrically similar to tectonic reconstructions of the relict Vitiaz subduction zone at 8–10 Ma, suggesting the earthquakes are occurring in the final portion of the slab subducted at the now inactive Vitiaz trench. A Coulomb stress change calculation suggests many of the aftershocks were dynamically triggered. We propose that fossil slabs contain material that is too warm for earthquake nucleation but may be near the critical stress susceptible to dynamic triggering.

Acoustically induced slip in sheared granular layers: Application to dynamic earthquake triggering

AbstractA fundamental mystery in earthquake physics is “how can an earthquake be triggered by distant seismic sources?” Here we use discrete element method simulations of a granular layer, during stick slip, that is subject to transient vibrational excitation to gain further insight into the physics of dynamic earthquake triggering. Using Coulomb friction law for grains interaction, we observe delayed triggering of slip in the granular gouge. We find that at a critical vibrational amplitude (strain) there is an abrupt transition from negligible time‐advanced slip (clock advance) to full clock advance; i.e., transient vibration and triggered slip are simultaneous. The critical strain is of order 10−6, similar to observations in the laboratory and in Earth. The transition is related to frictional weakening of the granular layer due to a dramatic decrease in coordination number and the weakening of the contact force network. Associated with this frictional weakening is a pronounced decrease in the elastic modulus of the layer. The study has important implications for mechanisms of triggered earthquakes and induced seismic events and points out the underlying processes in response of the fault gouge to dynamic transient stresses.

Granular friction: Triggering large events with small vibrations.

Triggering large-scale motion by imposing vibrations to a system can be encountered in many situations, from daily-life shaking of saltcellar to silo unclogging or dynamic earthquakes triggering. In the well-known situation of solid or granular friction, the acceleration of imposed vibrations has often been proposed as the governing parameter for the transition between stick-slip motion and continuous sliding. The threshold acceleration for the onset of continuous slip motion or system unjamming is usually found of the order of the gravitational acceleration. These conclusions are mostly drawn from numerical studies. Here, we investigate, in the laboratory, granular friction by shearing a layer of grains subjected to horizontal vibrations. We show that, in contrast with previous results, the quantity that controls the frictional properties is the characteristic velocity, and not the acceleration, of the imposed mechanical vibrations. Thus, when the system is statically loaded, the typical acceleration of the vibrations which trigger large slip events is much smaller than the gravitational acceleration. These results may be relevant to understand dynamic earthquake triggering by small ground perturbations.

Fluid‐driven seismicity activation in northern Nagano region after the 2011 M9.0 Tohoku‐oki earthquake

AbstractThe dynamic triggering of earthquakes is well documented; however, the underlying physical mechanisms remain obscure. Here we analyze the seismicity in northern Nagano, central Japan, following the Tohoku‐oki quake, until the occurrence 13 h later of an Mw6.2 local earthquake. We use waveform detection techniques to identify 17 times more earthquakes than those in the Japan Meteorological Agency catalog. The activation of seismicity in the epicentral region of the Mw6.2 event is weak and delayed, culminating with the occurrence of the moderate shock preceded by two small foreshocks. The seismicity activation to the south is shallower, abundant, and starts during the passage of Tohoku‐oki surface waves of high dynamic stresses. The early activation occurs in areas of relatively high near‐surface fluid temperature, indicating that the dynamic triggering is likely caused by excitation of geothermal crustal fluids. The Mw6.2 Northern Nagano earthquake might have been delay‐triggered by fluid migration from a deep source.

Dynamic triggering of earthquakes is promoted by crustal heterogeneities and bimaterial faults

Remotely triggered earthquakes and aftershocks constitute a great challenge in assessing seismic risk. A growing body of observations indicates that significant earthquakes can be triggered by moderate to great earthquakes occurring at distances of up to thousands of kilometres. Currently we lack the knowledge to predict the location of triggered events. We present numerical simulations showing that dynamic interactions between material heterogeneities (e.g. compliant fault zones, sedimentary basins) and seismic waves focus and enhance stresses sufficiently to remotely trigger earthquakes. Numerical simulations indicate that even at great distances (>100km), the amplified transient dynamic stress near heterogeneities is equivalent to stress levels near the source rupture tip (<5km). Such stress levels are widely considered capable of nucleating an earthquake rupture on a pre-stressed fault. Analysis of stress patterns in dynamic rupture simulations which include a heterogeneous zone with a range of material and geometrical properties reveals various mechanisms of stress enhancement. We conclude that both stiff and weak heterogeneities may focus stress waves to form zones of enhanced stress, and that bimaterial interfaces distort under static and dynamic loading in a way that induces local stress concentrations. Our work provides insights for understanding non-uniform distribution of remotely triggered seismicity and recurrence of such events along complex fault-systems and near magmatic intrusions and geothermal zones.

Limited Dynamic Earthquake Triggering in the Socorro Magma Body Region, Rio Grande Rift, New Mexico

Abstract Dynamic earthquake triggering, the process through which stresses transmitted through the passage of seismic waves can trigger remote faults to fail, has been shown to be fairly common throughout the globe and especially in seismically active areas of high heat flow and geothermal activity. We explore the possibility of dynamic earthquake triggering around the Socorro magma body, a feature within the Rio Grande rift in New Mexico that exhibits high heat flow and heightened seismicity. Because the area fits the environment type in which triggering preferentially occurs, we examine 319 global mainshocks with M w ≥6.0 for the possibility of increased seismicity rates following the passage of the mainshock waves. We examine local event locations and origin times relative to mainshock phase arrivals for patterns distinguishing triggering mainshocks from nontriggering mainshocks. We find a small triggering response during the time period analyzed, unlike following the 2002 Denali fault earthquake (DFE). This small response corresponds to smaller peak dynamic stresses than are found in other triggering studies ( M w >7.0), at a regional to small teleseismic distance (

The Uses of Dynamic Earthquake Triggering

Dynamic triggering of earthquakes by seismic waves is a robustly observed phenomenon with well-documented examples from over 30 major earthquakes. We are now in a position to use dynamic triggering as a natural experiment to probe the reaction of faults to the known stresses from seismic waves. We show here that dynamic triggering can be used to investigate the distribution of stresses required for failure on faults. In some regions, faults appear to be uniformly distributed over their loading cycles with equal numbers at all possible stresses from failure. Regions under tectonic extension, at the interface between locked and creeping faults, or subject to anthropogenic forcing are most prone to triggered failure. Predictions of future seismicity rates based on seismic wave amplitudes are theoretically possible and may provide similar results to purely stochastic prediction schemes. The underlying mechanisms of dynamic triggering are still unknown. The prolonged triggered sequences require a multistage process such as shear failure from rate-state friction coupled to aseismic creep or continued triggering through a secondary cascade. Permeability enhancement leading to drainage or pore pressure redistribution on faults is an alternative possibility.

Effect of boundary vibration on the frictional behavior of a dense sheared granular layer

We report results of 3D Discrete Element Method (DEM) simulations aiming at investigating the role of the boundary vibration in inducing frictional weakening in sheared granular layers. We study the role of different vibration amplitudes applied at various shear stress levels, for a granular layer in the stick-slip regime and in the steady-sliding regime. Results are reported in terms of friction drops and kinetic energy release associated with frictional weakening events. We find that larger vibration amplitude induces larger frictional weakening events. The results show evidence of a threshold below which no induced frictional weakening takes place. Friction drop size is found to be dependent on the shear stress at the time of vibration. A significant increase in the ratio between the number of slipping contacts to the number of sticking contacts in the granular layer is observed for large vibration amplitudes. These vibration-induced contact rearrangements enhance particle mobilization and induces a friction drop and kinetic energy release. This observation provides some insight into the grain-scale mechanisms of frictional weakening by boundary vibration in a dense sheared granular layer. In addition to characterizing the basic physics of vibration induced shear weakening, we are attempting to understand how a fault fails in the earth under seismic wave forcing. This is the well know phenomenon of dynamic earthquake triggering. We believe that the granular physics are key to this understanding.

Insights into water level response to seismic waves: A 24 year high‐fidelity record of global seismicity at Devils Hole

AbstractWe studied the 24 year record of water level responses in Devils Hole, Death Valley National Park, NV, to dynamic crustal stresses from earthquakes. The continuous water level record exhibited 219 responses from earthquakes around the world, displaying hydroseismogram and coseismic offset types of response. We found that the water level in Devils Hole is extremely sensitive to earthquakes, and the seismic energy density required to initiate both hydroseismogram and coseismic offset responses is e ~ 10−6 J/m3, 2 orders of magnitude smaller than previously documented. Multiple mechanisms at Devils Hole may be responsible for observed water level responses to distant earthquakes. The hydroseismogram‐type responses are best explained by poroelastic deformation, while coseismic offset responses are likely the result of localized permeability changes. This study could have implication to studying dynamic triggering of earthquakes, as remote earthquakes can lead to pore pressure changes and consequently effective stress changes in fluid‐filled fault zones.

Dynamic mechanisms of earthquake-triggered landslides

Earthquake-triggered landslides usually cause great disasters, and yet their dynamic mechanisms remain poorly understood. This paper will derive a general conceptual landslide model from the geometric and kinematic features of the most landslide masses triggered by the 2008 Wenchuan earthquake. Kinematic characteristics and dynamic processes are simulated here by means of finite element method (FEM) based on the dynamic process of the discontinuous deformable body. The calculated results presented the whole course of landslide motion, and displayed some typical kinematic characteristics such as initiation, sliding, ejection, collision, flying in the air, and climbing of landslides. The simulation result also shows that, under combined seismic inertial forces and gravity, landslides will start to slip once it overcomes the friction between the sliding mass and slip-bed, then it will move from slow to fast along the slippery bed until it ejects from the slip-bed. Moreover, the high frequencies and serious damages by landslides in the Wenchuan earthquake are caused by the strong ground motion on the mountain slopes in and around the epicenter that was dramatically amplified owing to both resonances produced by the seismic event and topographical amplification by seismic motion. In addition, the modeling results suggest that the direction, amplitude, frequency, and duration of strong ground motion have a great influence on the stability of landslide mass. Therefore, the study helps us better understand dynamic mechanism of landslides, seismic hazard assessment, and dynamic earthquake triggering.

Meso-mechanical analysis of deformation characteristics for dynamically triggered slip in a granular medium

The deformation characteristics of a sheared granular layer during stick–slip are studied from a meso-mechanical viewpoint, both in the absence and in the presence of externally applied vibration. The ultimate goal is to characterize the physics of dynamic earthquake triggering, where one earthquake, i.e., slip on one fault, is triggered via the seismic waves radiated by another spatially and temporally distant seismic event. Toward this goal, we performed Discrete Element Method simulations of a two-dimensional packing of disks, mimicking a mature geologic fault. These simulations were used to investigate the affine and non-affine deformations inside the granular layer and their spatial–temporal evolution across the stick–slip cycle. The simulation results show that slip in general is accompanied by the appearance of localized regions with high values of both affine and non-affine deformations. These regions are temporally correlated and are mainly concentrated in a shear zone at the interface between the granular layer and the driving block. Dynamic triggering is found to initiate slip when vibration is applied late in the stick–slip cycle, when the system is close to a critical state. It is also found that vibration itself introduces a large amount of affine and non-affine strains, which leads to the initiation of slip at lower shear stress than an equivalent slip event without vibration.

Triggered creep as a possible mechanism for delayed dynamic triggering of tremor and earthquakes

The passage of radiating seismic waves generates transient stresses in the Earth’s crust that can trigger slip on faults far away from the original earthquake source. The triggered fault slip is detectable in the form of earthquakes 1‐3 and seismic tremor 4‐7 . However, the significance of these triggered events remains controversial 8,9 , in part because they often occur with some delay, long after the triggering stress has passed. Here we scrutinize the location and timing of tremor on the San Andreas fault between 2001 and 2010 in relation to distant earthquakes. We observe tremor on the San Andreas fault that is initiated by passing seismic waves, yet migrates along the fault at a much slower velocity than the radiating seismic waves. We suggest that the migrating tremor records triggered slow slip of the San Andreas fault as a propagating creep event. We find that the triggered tremor and fault creep can be initiated by distant earthquakes as small as magnitude 5.4 and can persist for several days after the seismic waves have passed. Our observations of prolonged tremor activity provide a clear example of the delayed dynamic triggering of seismic events. Fault creep has been shown to trigger earthquakes 10‐12 , and we therefore suggest that the dynamic

Dynamic triggering of shallow earthquakes near Beijing, China

SUMMARY We perform a comprehensive analysis of dynamic triggering around the Babaoshan and Huangzhuang-Gaoliying faults near Beijing, China. The triggered earthquakes are identified as impulsive seismic arrivals with clear P and S waves in 5 Hz high-pass-filtered three-component velocity seismograms during the passage of large amplitude body and surface waves of large teleseismic earthquakes. We find that this region was repeatedly triggered by four earthquakes in East Asia, including the 2001 Mw 7.8 Kunlun, 2003 Mw 8.3 Tokachi-oki, 2004 Mw 9.2 Sumatra and 2008 Mw 7.9 Wenchuan earthquakes. In most instances, the microearthquakes coincide with the first few cycles of the Love waves, and more are triggered during the large-amplitude Rayleigh waves. Such an instantaneous triggering by both the Love and Rayleigh waves is similar to recent observations of remotely triggered ‘non-volcanic’ tremor along major plate-boundary faults, and can be explained by a simple Coulomb failure criterion. We are able to locate five of the earthquakes triggered by the Kunlun and Tokachi-oki earthquakes. These events occurred at shallow depth (<5 km) above the background seismicity near the boundary between NW-striking Babaoshan and Huangzhuang-Gaoliying faults and the Fangshan Pluton. We suggest that these triggered earthquakes occur near the transition between the velocity strengthening and weakening zones in the top few kilometres of the crust, and are likely driven by relatively large dynamic stresses on the order of few tens of KPa.

A physical model for widespread near‐surface and fault zone damage induced by earthquakes

I present a rigorous unifying interpretation of the well‐documented widespread near‐surface and fault zone damage induced by earthquakes by simulating three‐dimensional dynamic rupture propagation on a vertical strike‐slip fault. Stresses in the crust are depth‐dependent and material response is governed by the Drucker‐Prager yield criterion. I show that material yielding induced by seismic waves under the low confining pressure causes widespread near‐surface damage. Because the confining pressure increases with depth, the yielding zone at depth is narrowly confined near the fault, but its thickness broadens dramatically near the surface, forming a “flower‐like” damage zone. The fault zone damage at depth is induced by large dynamic stresses associated with the rupture front, while is induced by strong seismic waves ahead of the rupture front near the Earth's surface. These results have important implications for the formation and evolution of fault zones and possibly for the dynamic triggering of earthquakes as well.

Global ubiquity of dynamic earthquake triggering

Surface waves that were generated by 12 out of 15 earthquakes with magnitudes greater than 7 since 1990 led to a global increase in the number of small earthquakes. This suggests that dynamic triggering of earthquakes is common and is independent of the tectonic environment. Earthquakes can be triggered by local changes in the stress field (static triggering1,2,3,4,5,6,7) due to nearby earthquakes or by stresses caused by the passage of surface (Rayleigh and Love) waves from a remote, large earthquake (dynamic triggering8,9,10,11,12,13,14,15,16,17,18). However, the mechanism, frequency, controlling factors and the global extent of dynamic triggering are yet to be fully understood. Because Rayleigh waves involve compressional and dilatational particle motion (volumetric changes) as well as shearing, whereas Love waves only involve shearing, triggering by either wave type implies fundamentally different physical mechanisms. Here, we analyse broadband seismograms from over 500 globally distributed stations and use an automated approach to systematically identify small triggered earthquakes—the low-amplitude signals of such earthquakes would normally be masked by high-amplitude surface waves. Our analysis reveals that out of 15 earthquakes studied of magnitude (M) greater than 7.0 that occurred after 1990, 12 are associated with significant increases in the detection of smaller earthquakes during the passage of both the Love and Rayleigh waves. We conclude that dynamic triggering is a ubiquitous phenomenon that is independent of the tectonic environment of the main earthquake or the triggered event.

The effect of acoustic waves on stick-slip behaviour in sheared granular media, with implications to earthquake processes

We are studying the effects of acoustic waves on sheared granular material, with two goals in mind: one is to understand the intriguing physics that arises in this experimental system, and the other is to see if such experiments offer insight into earthquake processes, in particular the phenomenon where one earthquake triggers another nearby, or distant, earthquake ('dynamic earthquake triggering'). We conducted laboratory experiments of stick-slip in granular media using a double-direct, shear apparatus, while applying low amplitude vibration as well as pulsed waves. We find that vibration and pulses significantly perturb the shearing behaviour of the granular material, and that the manifestation of vibration is extremely complex, including strong material memory of the acoustic perturbation, that persists. We note that the wave disturbance must take place near the critical point, where the granular material is near failure, otherwise no effect is observed. Also, horizontal loads on the system can eliminate the effect if they arelarge (⩾4-5 MPa).

Observations and models of dynamic earthquake triggering

Seismologists have long accepted the idea that step-function perturbations to the deformation field acting on a fault can change its likelihood of, or 'trigger', failure as fault slip. We review the observations that have lead to the very recent recognition that transient perturbations (e.g., associated with seismic waves) also affect failure probabilities, and more broadly, observations of the spatial and temporal variations in both triggering deformations and triggered responses. Many of these cannot be explained by conventional models of earthquake nucleation, requiring consideration of ideas developed in other disciplines, such as those describing and explaining nonlinear dynamic elasticity from rock-mechanics. In addition to the scientific challenges, these observations and models significantly impact earthquake forecasts and hazard assessments. We focus on observations of natural earthquakes and from the rock-mechanics laboratory, and some of the explanatory models that we and others have proposed. While many of these observations and models are just being vetted now, even newer ones related to slow aseismic fault slip and non-volcanic tremor (seismic radiation that scales very differently from that from earthquakes) may lead to substantive modifications and advances. We conclude with a few tantalizing examples as a prelude to a companion presentation.

Dynamic triggering of earthquakes

After an earthquake, numerous smaller shocks are triggered over distances comparable to the dimensions of the mainshock fault rupture, although they are rare at larger distances. Here we analyse the scaling of dynamic deformations (the stresses and strains associated with seismic waves) with distance from, and magnitude of, their triggering earthquake, and show that they can cause further earthquakes at any distance if their amplitude exceeds several microstrain, regardless of their frequency content. These triggering requirements are remarkably similar to those measured in the laboratory for inducing dynamic elastic nonlinear behaviour, which suggests that the underlying physics is similar.

Nonlinear dynamics, granular media and dynamic earthquake triggering

The 1992 magnitude 7.3 Landers earthquake triggered an exceptional number of additional earthquakes within California and as far north as Yellowstone and Montana. Since this observation, other large earthquakes have been shown to induce dynamic triggering at remote distances--for example, after the 1999 magnitude 7.1 Hector Mine and the 2002 magnitude 7.9 Denali earthquakes--and in the near-field as aftershocks. The physical origin of dynamic triggering, however, remains one of the least understood aspects of earthquake nucleation. The dynamic strain amplitudes from a large earthquake are exceedingly small once the waves have propagated more than several fault radii. For example, a strain wave amplitude of 10(-6) and wavelength 1 m corresponds to a displacement amplitude of about 10(-7) m. Here we show that the dynamic, elastic-nonlinear behaviour of fault gouge perturbed by a seismic wave may trigger earthquakes, even with such small strains. We base our hypothesis on recent laboratory dynamic experiments conducted in granular media, a fault gouge surrogate. From these we infer that, if the fault is weak, seismic waves cause the fault core modulus to decrease abruptly and weaken further. If the fault is already near failure, this process could therefore induce fault slip.