Remote Triggering Of Earthquakes Research Articles

Perturbation-induced granular fluidization as a model for remote earthquake triggering.

Studying the effect of mechanical perturbations on granular systems is crucial for understanding soil stability, avalanches, and earthquakes. We investigate a granular system as a laboratory proxy for fault gouge. When subjected to a slow shear, granular materials typically exhibit a stress overshoot before reaching a steady state. We find that short seismic pulses can reset a granular system flowing in steady state so that the stress overshoot is regenerated. This feature is shown to determine the stability of the granular system under different applied stresses in the wake of a perturbation pulse and the resulting dynamics when it fails. Using an analytical aging-rejuvenation model for describing the overshoot response, we show that our laboratory-derived theoretical framework can quantitatively explain data from two fault slip events triggered by seismic waves.

Generic mechanism for remote triggering of earthquakes.

"Remote triggering" refers to the inducement of earthquakes by weak perturbations that emanate from faraway sources, typically intense earthquakes that happen at much larger distances than their nearby aftershocks, sometimes even around the globe. Here, we propose a mechanism for this phenomenon; the proposed mechanism is generic, resulting from the breaking of Hamiltonian symmetry due to the existence of friction. We allow a transition from static to dynamic friction. Linearly stable stressed systems display giant sensitivity to small perturbations of arbitrary frequency (without a need for resonance), which trigger an instability with exponential oscillatory growth. Once nonlinear effects kick in, the blow up in mean-square displacements can reach 15-20 orders of magnitude. Analytic and numerical results of the proposed model are presented and discussed.

Optimally Oriented Remote Triggering in the Coso Geothermal Region

AbstractDefining the nature of faulting, the stress needed to trigger earthquakes, and the stress state of faults remains fundamental to understanding the earthquake cycle. Studying remote dynamic triggering allows us to probe faults to systemically address the fundamental physical mechanisms of faulting. Using 13 years of data (2004–2016) from the EarthScope USArray Transportable Array and the Southern California Seismic Network, we search for remotely triggered seismicity in an extended region encompassing the Coso Geothermal Field (CGF+), California. We first apply a short term to long‐term average ratio detector to high‐pass (5 Hz) filtered waveforms spanning ±5 hr encompassing 211 M ≥ 7 global earthquakes. We visually inspect these waveforms to identify uncatalogued local earthquakes. We use the augmented local earthquake catalog to investigate remote earthquake triggering in the CGF+ region. Of the 211 remote mainshocks, we find 32 (15%) produce a statistically significant increase in seismicity following the P wave arrival in CGF+. An additional nine mainshocks had local earthquakes coincident with the surface waves passage but lacked a significant rate increase. Of the 41 (19%) triggering mainshocks, 28 and 13 exhibit instantaneous and delayed triggering, respectively. We find no correlation between triggering and mainshock depth, peak dynamic stress, nor mainshock focal mechanism type. Instead, results suggest the CGF+ may be optimally oriented for remote triggering from mainshocks in the West Pacific and South America and propose the reason for this is that the transient dynamic stresses align favorably with the local stress field (most compressive horizontal stress, SHmax) to promote triggering.

Going Beyond Rate Changes as the Sole Indicator for Dynamic Triggering of Earthquakes

Remote earthquake triggering is a well-established phenomenon. Triggering is commonly identified from statistically significant increases in earthquake rate coincident with the passage of seismic energy. In establishing rate changes, short duration earthquake catalogs are commonly used, and triggered sequences are not typically analyzed within the context of background seismic activity. Using 500 mainshocks and four western USA 33-yearlong earthquake catalogs, we compare the ability of three different statistical methods to identify remote earthquake triggering. Counter to many prior studies, we find remote dynamic triggering is rare (conservatively, <2% of the time). For the mainshocks associated with remote rate increases, the spatial and temporal signatures of triggering differ. We find that a rate increase coincident in time with mainshock energy alone is insufficient to conclude that dynamic triggering occurred. To classify dynamically triggered sequences, we suggest moving away from strict statistical measurements and instead use a compatibility assessment that includes multiple factors, like spatial and temporal indicators.

Friction weakening by mechanical vibrations: A velocity-controlled process.

Frictional weakening by vibrations was first invoked in the 70s to explain unusual fault slips and earthquakes, low viscosity during the collapse of impact craters or the extraordinary mobility of sturzstroms, peculiar rock avalanches which travels large horizontal distances. This mechanism was further invoked to explain the remote triggering of earthquakes or the abnormally large runout of landslides or pyroclastic flows. Recent experimental and theoretical works pointed out that the key parameter which governs frictional weakening in sheared granular media is the characteristic velocity of the vibrations. Here we show that the mobility of the grains is not mandatory and that the vibration velocity governs the weakening of both granular and solid friction. The critical velocity leading to the transition from stick-slip motion to continuous sliding is in both cases of the same order of magnitude, namely a hundred microns per second. It is linked to the roughness of the surfaces in contact.

Delayed Dynamic Triggering of Disposal‐Induced Earthquakes Observed by a Dense Array in Northern Oklahoma

AbstractRecent increases in earthquake occurrence rates in Oklahoma have been linked to the injection of large volumes of saltwater, a byproduct of oil and gas extraction. Here we present a detailed study of remote earthquake triggering in an area of active injection‐induced seismicity in northern Oklahoma using data from the LArge‐n Seismic Survey in Oklahoma (LASSO) temporary array and nearby permanent broadband seismic stations. We estimate changes in earthquake rates and calculate the Coulomb failure stress changes on potential receiver faults due to passing teleseismic surface waves. A statistically significant increase in seismicity is observed ∼8 hr after the 16 April 2016 Mw 7.8 Ecuador earthquake. The Coulomb stress changes associated with the Ecuador earthquake are on the order of ∼1 kPa. Physical mechanisms consistent with the observed dynamic stress threshold include failure driven by activation of aseismic slip or hydrological response of the fault system.

Absence of remote earthquake triggering within the Coso and Salton Sea geothermal production fields

AbstractGeothermal areas are long recognized to be susceptible to remote earthquake triggering, probably due to the high seismicity rates and presence of geothermal fluids. However, anthropogenic injection and extraction activity may alter the stress state and fluid flow within the geothermal fields. Here we examine the remote triggering phenomena in the Coso geothermal field and its surrounding areas to assess possible anthropogenic effects. We find that triggered earthquakes are absent within the geothermal field but occur in the surrounding areas. Similar observation is also found in the Salton Sea geothermal field. We hypothesize that continuous geothermal operation has eliminated any significant differential pore pressure between fractures inside the geothermal field through flushing geothermal precipitations and sediments out of clogged fractures. To test this hypothesis, we analyze the pore‐pressure‐driven earthquake swarms, and they are found to occur outside or on the periphery of the geothermal production field. Therefore, our results suggest that the geothermal operation has changed the subsurface fracture network, and differential pore pressure is the primary controlling factor of remote triggering in geothermal fields.

Exploring remote earthquake triggering potential across EarthScopes' Transportable Array through frequency domain array visualization

AbstractTo better understand earthquake source processes involved in dynamically triggering remote aftershocks, we use data from the EarthScope Transportable Array (TA) that provide uniform station sampling, similar recording capabilities, large spatial coverage, and, in many cases, repeat sampling at each site. To avoid spurious detections, which are an inevitable part of automated time domain amplitude threshold detection methods, we develop a frequency domain earthquake detection algorithm that identifies coherent signal patterns through array visualization. This method is tractable for large data sets, ensures robust catalogs, and delivers higher resolution observations than what are available in current catalogs. We explore seismicity rate changes local to the TA stations following 18 global main shocks (M ≥ 7) that generate median peak dynamic stress amplitudes of 0.001–0.028 MPa across the array. From these main shocks, we find no evidence of prolific or widespread remote dynamic triggering in the continental U.S. within the main shock's wave train or following main shock stress transients within 2 days. However, limited evidence for rate increases exist in localized source regions. These results suggest that for these data, prolific, remote earthquake triggering is a rare phenomenon throughout a wide range of observable magnitudes. We further conclude that within the lower range of previously reported triggering thresholds, surface wave amplitude does not correlate well with observed cases of dynamic triggering. We propose that other characteristics of the triggering wavefield, in addition to specific conditions at the site, will drive the occurrence of triggering at these amplitudes.

Enhanced Remote Earthquake Triggering at Fluid-Injection Sites in the Midwestern United States

A recent dramatic increase in seismicity in the midwestern United States may be related to increases in deep wastewater injection. Here, we demonstrate that areas with suspected anthropogenic earthquakes are also more susceptible to earthquake-triggering from natural transient stresses generated by the seismic waves of large remote earthquakes. Enhanced triggering susceptibility suggests the presence of critically loaded faults and potentially high fluid pressures. Sensitivity to remote triggering is most clearly seen in sites with a long delay between the start of injection and the onset of seismicity and in regions that went on to host moderate magnitude earthquakes within 6 to 20 months. Triggering in induced seismic zones could therefore be an indicator that fluid injection has brought the fault system to a critical state.

Laboratory observation of acoustic fluidization in granular fault gouge and implications for dynamic weakening of earthquake faults

AbstractSeveral lines of evidence, including remote triggering of earthquakes and modulation of seismic tremor by Earth tides, suggest that faults weaken when subject to shaking and dynamic stresses associated with the passage of seismic waves. However, the origin of such dynamic weakening is poorly understood. Here we explore the role of acoustic resonance for dynamic fault weakening using laboratory measurements. Experiments were conducted using a split Hopkinson pressure bar assembly, with dynamic stressing via impact loading. Samples were composed of crushed rock particles from mine tailings with a particle size distribution similar to that found in a natural fault gouge. We used pulse‐shaper techniques and carefully evaluated dynamic stresses recorded at the front and rear of the sample to ensure that dynamic force balance was satisfied. Our experiments document acoustic‐induced fluidization and dramatic dynamic weakening. Frictional strength and elastic modulus of a simulated fault gouge are reduced by a factor of 5–10 via acoustic fluidization. We find a threshold acoustic pressure for fluidization that varies systematically with gouge zone properties. Our observations could help explain dynamic fault weakening and triggering of earthquake fault slip by dynamic stressing.

Unraveling the apparent magnitude threshold of remote earthquake triggering using full wavefield surface wave simulation

Empirical studies with earthquake catalogs suggest that large events (M &gt; 5) are rarely triggered in significant numbers by passing surface waves at remote distances from main shocks. Triggered, small (M &lt; 5) earthquakes are routinely associated with the passage of surface waves from large (M &gt; 7) main shocks. Since large earthquakes involve larger rupture areas, we study the spatial and temporal characteristics of dynamic stress change for clues. Using a 3D finite element method, we model the complete wavefield from the 2002 M= 7.9 Denali earthquake recorded near the Wasatch Front in Utah, where details about triggered seismicity are known. In particular, we load our model with a displacement seismogram to acquire a time series of the stress change tensor and model failure of a representative normal fault based on these stress changes. We note that the stress‐change regime varies rapidly between favoring strike‐slip, thrust, and normal faulting, with durations lasting ∼1–4 s. We find that these stress regimes usually affect only some fraction of a fault surface at any given time. Stress amplitudes also vary, meaning that ideal conditions for triggering are short‐lived and spatially limited. Stress conditions can also rapidly reverse to regimes that inhibit slip. Given these stressing conditions, we conclude that it may be difficult for a larger rupture area to experience the temporally and spatially coherent stress change necessary to develop into a large magnitude earthquake.

Stabilizing Stick-Slip Friction

Even the most regular stick-slip frictional sliding is always stochastic, with irregularity in both the intervals between slip events and the sizes of the associated stress drops. Applying small-amplitude oscillations to the shear force, we show, experimentally and theoretically, that the stick-slip periods synchronize. We further show that this phase locking is related to the inhibition of slow rupture modes which forces a transition to fast rupture, providing a possible mechanism for observed remote triggering of earthquakes. Such manipulation of collective modes may be generally relevant to extended nonlinear systems driven near to criticality.

Remotely triggered seismicity in north China following the 2008 M w 7.9 Wenchuan earthquake

We conduct a systematic survey of remote triggering of earthquakes in north China following the 2008 Mw 7.9 Wenchuan earthquake. We identify triggered earthquakes as impulsive seismic energies with clear P and S arrivals on 5 Hz high-pass-filtered three-component velocity seismograms during and immediately after the passage of teleseismic waves. We find clearly triggered seismic activity near the Babaoshan and Huangzhuang-Gaoliying faults southwest of Beijing, and near the aftershock zone of the 1976 MW 7.6 Tangshan earthquake. While several earthquakes occur during and immediately after the teleseismic waves in the aftershock zone of the 1975 Mw 7.0 Haicheng earthquake, the change of seismicity is not significant enough to establish the direct triggering relationship. Our results suggest that intraplate regions with active faults associated with major earthquakes during historic or recent times are susceptible to remote triggering. We note that this does not always guarantee the triggering to occur, indicating that other conditions are needed. Since none of these regions is associated with any active geothermal or volcanic activity, we infer that dynamic triggering could be ubiquitous and occur in a wide range of tectonic environments.

Suspension rheology under oscillatory shear and its geophysical implications

Abstract Dynamic strain generated by seismic waves is often invoked to explain coseismic responses to earthquakes, such as liquefaction, dilatancy and the remote triggering of earthquakes and eruptions. In order to expand our understanding of the conditions under which such responses occur, we measure the rheology of non-Brownian particle suspensions under oscillatory shear at frequencies corresponding to the seismic band (0.1–10 Hz). We characterize the changes in rheology as a function of volumetric particle packing fraction (0.2–0.6), particle diameter (9, 39 μm), and the viscosity of the suspending fluid (0.97, 12.14 Pas). By varying the stress (corresponding to a strain range 10− 5

Quantifying the remote triggering capabilities of large earthquakes using data from the ANZA Seismic Network catalog (southern California)

Various studies have examined remote earthquake triggering in geothermal areas, but few studies have investigated triggering in nongeothermal areas. We search the ANZA (southern California) network catalog for evidence of remote triggering. Using three statistical tests (binomial, Kolmogorov‐Smirnov, and Wilcoxon rank sum), we determine the significance of the rates and timing of earthquakes in southern California following large teleseismic events. To validate our statistical tests, we identify 20 local main shocks (ML ≥ 3.1) with obvious aftershock sequences and 22 local main shocks (ML ≥ 3.0) that lack obvious aftershock sequences. Our statistical tests quantify the ability of these local main shocks to trigger aftershocks. Assuming that the same triggering characteristic (i.e., a particular seismic wave amplitude, perhaps in a specific frequency band) is evident for both local and remote main shocks, we apply the same tests to 60 remote main shocks (mb ≥ 7.0) and assess the ability of these events to trigger seismicity in southern California. We find no obvious signature of remote triggering. We find minimal differences between the spectral amplitudes and maximum ground velocities of the local triggering and nontriggering earthquakes. Similar analysis of a select few of our remote earthquakes shows that the related ground motion regularly exceeds that of local earthquakes both at low frequencies and in maximum velocity. This evidence weakly suggests that triggering requires larger amplitudes at high frequencies and that a maximum ground velocity alone is not the primary factor in remote triggering. Our results are complex, suggesting that a triggering threshold, if it exists, may depend on several factors.

EARTHQUAKE TRIGGERING BY STATIC, DYNAMIC, AND POSTSEISMIC STRESS TRANSFER

▪ Abstract Earthquake triggering is the process by which stress changes associated with an earthquake can induce or retard seismic activity in the surrounding region or trigger other earthquakes at great distances. Calculations of static Coulomb stress changes associated with earthquake slip have proven to be a powerful tool in explaining many seismic observations, including aftershock distributions, earthquake sequences, and the quiescence of broad, normally active regions following large earthquakes. Delayed earthquake triggering, which can range from seconds to decades, can be explained by a variety of time-dependent stress transfer mechanisms, such as viscous relaxation, poroelastic rebound, or afterslip, or by reductions in fault friction, such as predicted by rate and state constitutive relations. Rapid remote triggering of earthquakes at great distances (from several fault lengths to 1000s of km) is best explained by the passage of transient (dynamic) seismic waves, which either immediately induce Coulomb-type failure or initiate a secondary mechanism that induces delayed triggering. The passage of seismic waves may also play a significant role in the triggering of near-field earthquakes.

Remotely Triggered Seismicity in the Yellowstone National Park Region by the 2002 Mw 7.9 Denali Fault Earthquake, Alaska

Coincident with the arrival of low-frequency, large-amplitude surface waves of the Mw 7.9 Denali fault earthquake (DFE), an abrupt increase in seismicity was observed in the Yellowstone National Park region, despite the large epicentral distance of 3100 km. Within the first 24 hr following the DFE mainshock, we located more than 250 earthquakes, which occurred throughout the entire Yellowstone Na- tional Park region. The elevated seismicity rate continued for about 30 days and followed a modified Omori law decay with a P value of 1.02 ! 0.07. For a declus- tered earthquake catalog, the seismicity following the 2002 DFE uniquely stands out with a significance of 30r. The increase in seismicity occurred over all magnitude bands. In general, we observed that seismicity following the DFE outlined the spatial pattern of past seismicity routinely observed in the Yellowstone National Parkregion. However, we found significant differences in triggered seismicity inside and outside the caldera. Earthquakes inside the Yellowstone caldera occurred preferentially as clusters close to major hydrothermal systems, were of larger magnitude, and seis- micity decayed more rapidly. This suggests that either different trigger mechanisms were operating inside and outside the caldera or that the crust responded differently to the same trigger mechanism depending on its different mechanicalstate.Compared with other sites that experienced remote earthquake triggering following the 2002 DFE, Yellowstone showed the most vigorous earthquake activity. We attribute this to strong directivity effects of the DFE, which caused relatively large peak dynamic stresses (0.16-0.22 MPa) in Yellowstone, and to the volcanic nature of Yellowstone.

Did the 7/9/1999 M5.9 Athens Earthquake Come with a Warning?

Prior to the 7/9/1999 MS = 5.9 Athens earthquake, regional seismicity has exhibited a power-law increase, of the form �� = K +A(tc −t) n ,w hereis estimated using an expression log � = cM + d and tc is the time of the culminating event. Such changes appeared after the 17/8/1999 M7.4 Izmit event. We quantified the performance of the power law vs. the null hypothesis of constant seismic release rates, by defining the curvature C as the ratio of the power law fit RMS/linear fit RMS, so that the smaller C is, the better the power law behaviour. By mapping C, we have established a critical radius of 110 km and observed that the region of correlated accelerating seismic release extended from the N. Aegean, through Euboea and Attica to the SW Peloponnese. A few days prior to the Athens event, min(C) was centred at the epicentral area and numerical simulation yielded tc = 1999.676 and predicted MS = 5.77. Seismicity rates returned to normal (quasi-constant) after the Athens event. We interpret this effect as critical point behaviour, following remote excitation of a broad area by stress redistribution due to the Izmit event which, at Athens, has triggered 'premature' failure of a fault nearing its load bearing capacity. If this is correct, we have documented a case of remote earthquake triggering by another earthquake, as well as insight into the mechanisms produ- cing it. As a corollary, we note that a large event may beget another large event in its broader region of interaction, which may be preceded by characteristic precursory seismicity changes.

Remote Earthquake Triggering along the Dead Sea Fault in Syria following the 1995 Gulf of Aqaba Earthquake (Ms = 7.3)

Copyright 2000, Seismological Society of America. See also: http://www.seismosoc.org/publications/srl.html; http://atlas.geo.cornell.edu/deadsea/publications/Mohamad2000_SRL.htm

Viscosity of oceanic asthenosphere inferred from remote triggering of earthquakes

A sequence of large interplate earthquakes from 1952 to 1965 along the Aleutian arc and Kurile-Kamchatka trench released accumulated stresses along nearly the entire northern portion of the Pacific Plate boundary. The postseismic stress evolution across the northern Pacific and Arctic basins, calculated from a viscoelastic coupling model with an asthenospheric viscosity of 5 x 10(17) pascal seconds, is consistent with triggering of oceanic intraplate earthquakes, temporal patterns in seismicity at remote plate boundaries, and space-based geodetic measurements of anomalous velocity over an area 7000 by 7000 kilometers square during the 30-year period after the sequence.