Earthquake Triggering Research Articles

On the controversial role of earthquake triggering of the Rigopiano avalanche

Here Nicola Pugno, leading expert in fracture mechanics, deduces by sticking to the facts that (1) there is no evidence of earthquake triggering of the Rigopiano avalanche, (2) earthquake triggering of this avalanche is very unlikely, (3) even if it cannot be proved nor disproved, (4) those earthquakes are equivalent to only a few centimeters of snow precipitation, and (5) even assuming earthquake triggering, the avalanche would have likely occurred the very same day even in absence of earthquakes.

A Hydrofracturing-Triggered Earthquake Occurred Three Years after the Stimulation

Hydrofracturing, used for shale gas exploitation, may induce felt, even damaging earthquakes. On 15 June 2019, an Mw2.8 earthquake occurred, spatially correlated with the location of earlier exploratory hydrofracturing operations for shale gas in Wysin in Poland. However, this earthquake was atypical. Hydrofracturing-triggered seismicity mainly occurs during stimulation; occasionally, it continues a few months after completion of the stimulation. In Wysin, there were only two weaker events during two-month hydrofracturing and then 35 months of seismic silence until the mentioned earthquake occurred. The Wysin site is in Gdańsk Pomerania broader region, located on the very weakly seismically active Precambrian Platform. The historical documents, covering 1000 years, report no natural earthquakes in Gdańsk Pomerania. We conclude, therefore, that despite the never observed before that long lag time after stimulation, the Mw2.8 earthquake was triggered by hydrofracturing. It is possible that its unusually late occurrence in relation to the time of its triggering technological activity was caused by changes in stresses due to time-dependent deformation of reservoir shales. The Wysin earthquake determines a new time horizon for the effect of HF on the stress state, which can lead to triggering earthquakes. Time-dependent deformation and its induced stress changes should be considered in shall gas reservoir exploitation plans.

Tidal modulation of seismicity at the Coso geothermal field

Studying the seismicity triggering response of fault systems to periodic stress fluctuations can improve our understanding of earthquake nucleation, rupture failure processes, and local stress states. Geothermal fields are well known to be susceptible to triggering, as the injection and extraction activities change the local stress and fluid flow conditions. Here, we examine the modulation of earthquakes by Earth tides within California's Coso geothermal field (CGF) and its vicinity. To maximize our resolution to detect modulation of small earthquakes, we take advantage of the new Quake Template Matching catalog in southern California, which has nearly twice as many events in the Coso region as the standard catalog and is complete down to about magnitude 0.3. We observe strong tidal triggering of earthquakes within the CGF, even though the fluctuations of tidal stresses are small (∼2 kPa). The tidally-triggered earthquakes tend to occur near the time of maximum tensile tidal stress. The signal is strongest near the edges of the zone of new production wells, suggesting fluid pressure gradients encourages triggering at tidal periods.

The interrelationship between electrical resistivity and VP/VS ratio: A novel approach to constrain the subsurface resistivity structure in data gap areas in a seismogenic zone

Large man-made water reservoirs promote fluid diffusion and cause critically stressed fault zones underneath to trigger earthquakes. Electrical resistivity is a crucial property to investigate such fluid-filled fault zones. Therefore, we carry out magnetotelluric (MT) investigation to explore an intraplate earthquake zone, which is related to artificial reservoir-triggered seismicity. However, due to surface access restrictions, our data set has a gap in coverage in the middle part of the study area. This data gap region coincides with the earthquake hypocenter distribution in that intraplate earthquake zone. Therefore, it is vital to fill the data gap to obtain the electrical signature of the active seismic zone. To compensate for the data gap, we have developed a relation that connects resistivity with the ratio of seismic P- to S-wave velocity ([Formula: see text]). Using this relation, we estimate a priori resistivity distribution in the data gap region from known [Formula: see text] values during the inversion to compensate for the data gap. A comparison study of the root-mean-square misfits of inversion outputs (with and without data gap filled) proves the effectiveness of the established relation. The inversion output obtained using the established relation brings out fault signatures in the data gap region. To examine the reliability and accuracy of these fault signatures, we occupy a portion of the data gap with new MT sites. We compare the inversion output from this new setup with the inversion output obtained from the established relation and observe that the electrical signatures in both outputs are spatially correlated. Furthermore, a synthetic test on a similar earth model establishes the credibility and robustness of the derived relation.

Detailed 3D Seismic Velocity Structure of the Prague, Oklahoma Fault Zone and the Implications for Induced Seismicity

AbstractThe 2011 Mw 5.7 Prague earthquake is the second largest induced earthquake in Oklahoma, and occurred after decades of wastewater disposal. The local geological structure that led to the triggering of this large earthquake is not well understood. In this study, tomographic inversion of seismic data recorded by a dense local seismic network resulted in a high‐resolution 3D velocity model with three major layers. The model clearly illuminates the geometry and characteristics of the Meeker‐Prague Fault that hosted the 2011 Prague sequence. A conceptual model is proposed to link the tomographic structure to the triggering process of the sequence. The low‐permeability second layer at ∼1.5–3.5 km may be the key that delays the occurrence of the first sizeable earthquake after decades of wastewater injection. However, a low‐shear‐velocity zone within this layer at the intersection of two major faults could have provided a fluid pathway to facilitate downward fluid propagation.

Absence of Near-Trench Early Triggering during the 2012 Mw 7.2 Indian Ocean Strike-Slip Earthquake: Evidence from One-Day Aftershocks

AbstractDynamic earthquake triggering is a widely accepted mechanism of earthquake interaction, which plays a vital role in seismic hazard estimation, although its efficacy at regional distances is under debate. The 2012 Mw 7.2 Indian Ocean event is one of the first reported events to produce dynamic stress triggering at regional distances using backprojection (BP) techniques. Alternatively, the coherent radiators in BP images can be interpreted as localized water reverberation phases. We present further evidence against near-trench triggering during this event. We collected 24 hr seismic recordings of two nearby stations located near the trench. We adopted a waveform denoising algorithm and detected 125 aftershocks using two regional seismic stations with a minimum magnitude of ML∼2.7 and completeness magnitude of ML∼3.6, whereas none of these aftershocks occurred near the trench. The absence of immediate (within one day) aftershocks near the trench suggest the absence of dynamic triggering during the offshore mainshock.

Studies of Artificial Water Reservoir Triggered Earthquakes at Koyna, India: A Summary

Abstract Anthropogenic seismicity has been observed due to filling of artificial water reservoirs, geothermal and natural oil/gas production, and gold/coal mining under favorable geological conditions. Among these, artificial water reservoir triggered seismicity (RTS) is most prominent, with over 200 sites globally where RTS has been observed, including 5 sites where earthquakes exceeding M 6 magnitude occurred. Koyna, located near the west coast of India in stable Deccan Volcanic Province is the most prominent site where the largest RTS event of M 6.3 occurred in 1967, and the RTS has continued till now, for near field study of earthquakes. Here we present a summary of (a) global RTS, (b) scientific work carried in the Koyna region, (c) characterizing RTS, and (d) establishing a 3 km deep Pilot Borehole laboratory as a precursor to setting up of a ~ 7 km deep bore hole laboratory. The work being carried out is providing necessary inputs for the design of the ~ 7 km deep borehole laboratory for the near field studies of RTS and shed light on the geneses of earthquakes in general and RTS.

Pore Fluid Pressure Imaging of the Mt. Pollino Region (Southern Italy) From Earthquake Focal Mechanisms

AbstractFocal mechanisms of selected earthquakes, recorded in the Mount Pollino region (southern Italy) from 2010 through 2014, are used to infer the pore fluid pressure at hypocenter depths. The 3‐D excess pore pressure field provides evidence that the sequence occurs in a fluid‐filled volume with values reaching 35 MPa. The mechanisms underlying this swarm‐like sequence and the triggering of earthquakes are investigated by computing the cumulative static Coulomb stress change at hypocenter depths and analyzing the pore‐pressure diffusion mechanism. The results indicate that static Coulomb stress change was lower than 0.01 MPa, which is the value generally assumed as threshold for the triggering, and seismicity distribution was actually driven by pore‐pressure diffusion with relatively low diffusivity value. This latter mechanism could also explain the delayed triggering of the two larger eventsML4.3 andML5.0, respectively, that occurred about 150 days apart.

Possible influence of static and viscoelastic stress perturbations in Musgrave block (Central Australia) earthquake sequence

The spatial and temporal distribution of earthquakes inside continental interiors, where tectonic loading rate is negligible, is much more complicated than plate boundary regions. On 30 March 1986, the moment magnitude (Mw) 5.7 Marryat Creek earthquake occurred in the Musgrave Block of central Australia. Subsequent earthquakes include the1989 Ml 5.6 Uluru, 2012 Mw 5.2 Pukatja, 2013 Mw 5.6 Mulga Park, and 2016 Mw 6.0 Petermann earthquakes. In this study, I explore whether coseismic and viscoelastic Coulomb stress changes following the 1986 Marryat Creek earthquake could have played a role in influencing the basic spatiotemporal characteristics of this earthquake sequence. I find that coseismic stress change does not successfully explain earthquake triggering in the area. I then explore this issue using a viscoelastic stress change model with a range of rheology parameters. In some models, the magnitude of viscoelastic stress change is higher than coseismic stress changes and may be of sufficient magnitude to be considered within an earthquake triggering context. Moreover, I also hypothesize that these earthquakes may have occurred due to dynamic stress triggering or other processes such as fluid migration, nonlinear friction, and/or aseismic deformation, which due to the small distribution of seismic networks across the area I have not been able to investigate in detail. However, I cannot dismiss the possibility that these earthquakes occurred randomly, with no identifiable stress triggering relationships among them.

Slow Slip Triggers the 2018 Mw 6.9 Zakynthos Earthquake Within the Weakly Locked Hellenic Subduction System, Greece

AbstractSlow slip events (SSEs) at subduction zones can precede large‐magnitude earthquakes and may serve as precursor indicators, but the triggering of earthquakes by slow slip remains insufficiently understood. Here, we combine geodetic, Coulomb wedge and Coulomb failure‐stress models with seismological data to explore the potential causal relationship between two SSEs and the 2018 Mw 6.9 Zakynthos Earthquake within the Hellenic Subduction System. We show that both SSEs released up to 10 mm of aseismic slip on the plate‐interface and were accompanied by an increase in upper‐plate seismicity rate. While the first SSE in late 2014 generated only mild Coulomb failure stress changes (≤3 kPa), that were nevertheless sufficient to destabilize faults of various kinematics in the overriding plate, the second SSE in 2018 caused stress changes up to 25 kPa prior to the mainshock. Collectively, these stress changes affected a highly overpressured and mechanically weak forearc, whose state of stress fluctuated between horizontal deviatoric compression and tension during the years preceding the Zakynthos Earthquake. We conclude that this configuration facilitated episodes of aseismic and seismic deformation that ultimately triggered the Zakynthos Earthquake.

Spatiotemporal Evolution of Pore Pressure Changes and Coulomb Failure Stress in a Poroelastic Medium for Different Faulting Regimes

AbstractSpatial distribution of aftershocks has been explained by the co‐seismic static Coulomb Failure Stress changes (ΔCFS) to some extent. In practice, the earth's crust is porous medium saturated with fluid filling pores, cavities, cracks, and faults. The pore fluid flow plays an important role in the evolution of the stress field in porous medium of the earth. The ΔCFS can be influenced by the co‐seismic pore pressure changes and the post‐seismic pore fluid flow. In order to understand such impacts, we built 3D fault‐slip finite element models to study the evolution of the pore pressure changes and the ΔCFS based on the fully coupled poroelastic theory. The strike‐slip, reverse, and normal faulting models were investigated separately. The patterns of co‐seismic ΔCFS were similar to the elastic stress changes on a homogeneous half‐space, but there were considerable differences in details especially in the near‐fault area when considering co‐seismic pore pressure change. Due to post‐seismic pore fluid flow, the near‐field stress shadow narrowed gradually in the strike‐slip model. In the reverse faulting model, both the near‐field stress shadow and enhanced areas expanded. In the normal faulting model, the stress shadow near the epicenter reduced. The pore pressure changes decayed sharply at the beginning and then gradually approached to zero because the system evolves to drained conditions. These results can help us to understand the effect of pore fluid flow on Coulomb Failure Stress evolution and might improve the understanding of earthquake triggering and aftershock forecasting.

Debris Flow Risk Reduction in Malaysia: From Science-Policy to Multi-Stakeholder Actions

Debris flows remained the deadliest and disastrous geological disasters in Malaysia. The two-decade records from 1995 until 2015 highlighted at least 23 events have occurred regardless of fatalities, and locations. The fatal event was induced by a typhoon recorded in Keningau, Sabah in 1996 with the highest human losses of 302, and economic losses of RM 458.9 million. To date, Malaysia has no dedicated national policy, framework, and standard operating procedure to address this sediment-related disaster in a holistic manner. Moreover, a dedicated, responsible government agency for managing debris flow risk reduction remained elusive. This study aims at providing insights for debris flow disaster risk reduction (DRR) by addressing risk governance, including multi-sectoral agencies roles and responsibilities for different triggering factors, i.e., earthquakes, and intense and prolonged rainfall, and DRR investment towards co-developing an integrated national action plan for reducing current risk, preventing future risk, and strengthening resilience. This study explores various methods to better understand local profiles and suitable methods to assess geological hazard risk processes, activities and impact towards redefining a comprehensive risk assessment method in Malaysia. A case study of recent event in Mesilau watershed induced by the earthquake and rainfall, as a result of 2015 Sabah Earthquake was selected for this study. This study elaborates the significance uses of scientific- and social-based study in promoting science-policy and multi-stakeholders action planning for reducing sediment-based disaster risk in the near future. This includes: (i) the mapping and characterizing the watershed area, (ii) modelling the past debris flow event, and (iii) engaging with the community and stakeholder to gather more local inputs.

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.

Dynamic earthquake triggering response tracks evolving unrest at Sierra Negra volcano, Galápagos Islands.

The propensity for dynamic earthquake triggering is thought to depend on the local stress state and amplitude of the stress perturbation. However, the nature of this dependency has not been confirmed within a single crustal volume. Here, we show that at Sierra Negra volcano, Galápagos Islands, the intensity of dynamically triggered earthquakes increased as inflation of a magma reservoir elevated the stress state. The perturbation of short-term seismicity within teleseismic surface waves also increased with peak dynamic strain. Following rapid coeruptive subsidence and reduction in stress and background seismicity rates, equivalent dynamic strains no longer triggered detectable seismicity. These findings offer direct constraints on the primary controls on dynamic triggering and suggest that the response to dynamic stresses may help constrain the evolution of volcanic unrest.

Precursory tidal triggering and b value variation before the 2011 Mw 5.1 and 5.0 Tengchong, China earthquakes

Recent studies have suggested that tidal triggering may preferentially occur when a region is critically stressed, and that tidal stresses provide a potential tool for forecasting earthquakes. Most tidally triggered precursors before large earthquakes are found in subduction zones. We examined tidal triggering of earthquakes near the intracontinental Gaoligong Shear Zone, which is also a geothermally active region. We observed statistically significant correlations between tidally induced stresses and earthquake times, which only appeared approximately two years before the 2011 Tengchong Mw 5.1 and 5.0 earthquakes. The Schuster spectrum shows two peaks at ∼0.5 and ∼1.0 days related to the tidal period. The tidal phase distribution in the pre-mainshock time period shows that most earthquakes occur during phases of positive tidal shear stress and dilatancy strain. Our findings provide a typical case of tidal triggering of earthquake precursors in a continental setting. The stress state can be inferred using the Gutenberg–Richter b value, which characterizes the relative proportion between small and large earthquakes and correlates negatively with differential stress. We investigated the temporal changes of the b value and found that it retains a long-term low value but has a prominent short-term decline prior to mainshocks. The coincidence of low Schuster probability ps with a low b value suggests that the crustal medium is near a critical state, making it more sensitive to external perturbations. The results of epidemic-type aftershock sequence (ETAS) modelling revealed that the seismic activity is affected by not only cascading earthquake triggering but also external forcing. Taking the collective results of the Schuster test, b value, ETAS modelling, and other evidence, we suggest that tidal triggering of earthquakes is likely when the fault is in a near-critical stress state, and geothermal fluid may play an important role in the triggering mechanism.

Magnetotelluric evidence of fluid-related seismicity beneath the Chuxiong Basin, SE Tibetan Plateau

Fluids play an important role in intracontinental seismicity and have become an important issue in solid earth sciences. In this study, we present evidence of fluid-related seismicity on the southeastern Tibetan Plateau. A sequence of large earthquakes (Ms > 6.0) occurred in the Dayao and Yao'an areas within the Chuxiong Basin from 2000 to 2009, where no obvious traces of active faults at the surface indicate the source fault of these earthquakes. To reveal the deep earthquake structure and the mechanism of these earthquakes, we carried out two magnetotelluric (MT) profiles that intersected in the epicentral region. The three-dimensional (3-D) inversion method was used to provide a more realistic electrical resistivity model since phase tensor analysis showed 3-D features. The electrical structures along the two profiles showed similar characteristics: lower crustal conductors underlie the upper crustal resistive zone, the resistive zone may correspond to a crystalline basement, and the lower crustal conductors were interpreted as aqueous fluid-related and water-derived partial melting. Earthquakes were distributed mainly in the upper crustal resistive zone but not in the underlying conductive zones, which indicated that fluid migration into the upper crust may have contributed to triggering earthquakes in this area.

Precambrian Crystalline Basement Properties From Pressure History Matching and Implications for Induced Seismicity in the US Midcontinent

AbstractInjection‐induced seismicity across the US midcontinent has almost exclusively occurred in the crystalline basement that underlies the Arbuckle Group aquifer and its equivalents, the primary wastewater disposal zone in this region. However, the properties of the basement are not well known. Newly compiled data, from Class I wells in Kansas, provide a unique record of pressures in the Arbuckle and an opportunity to constrain the reservoir‐scale properties of the basement such as permeability, diffusivity, and specific storage. Constraints on these parameters are critical for modeling fluid flow and pressures across the entire Arbuckle‐basement system, and are necessary for accurate evaluation and prediction of injection‐induced earthquakes. Here, we present a detailed, three‐dimensional geological and pressure history‐matched numerical model for the Arbuckle and basement, based on data from >400 wells covering a large region in south‐central Kansas, where injection‐induced seismicity has been concentrated since 2014. Simulations of dynamic data from 319 wells indicate that Arbuckle pressures have increased by 1.1 MPa in high injection rate areas and an overpressure of <0.1 MPa may be the cause of seismicity in the basement. Pressure‐history matching also yields the likely range in porosity (0.3%–7%), permeability (0.1–0.7 mD), and diffusivity (0.004–0.07 m2/s) for the basement. The resulting estimates suggest reservoir‐scale properties of the basement are enhanced by faults and fractures. Importantly, the diffusivities determined in this study are lower than estimates derived from Kansas earthquake triggering fronts, and suggest that such seismicity‐based techniques may have limitations, particularly where space‐time patterns between injection and seismicity are complex.

Tehri Reservoir Operation Modulates Seasonal Elastic Crustal Deformation in the Himalaya

AbstractThe filling and emptying cycles of reservoir operations may change hydrological mass loading, leading to a flexural deformation of the crust that may compromise the infrastructure safety or trigger earthquakes. In this study, we investigate the seasonal crustal response of the Tehri reservoir in the Garhwal Himalaya, northern India, using interferometric synthetic aperture radar (InSAR), Global Positioning System, the Gravity Recovery and Climate Experiment, radar altimetry, and in‐situ water‐level measurements. Results show that the evolution of vertical ground deformation is modulated elastically by the reservoir operation, whereas the horizontal displacement measured near the reservoir exhibits a time lag of ∼65 days with respect to the vertical displacements and water‐level variations. The delayed deformation transients indicate that the reservoir loading/unloading cycles affect the near‐surface hydrology in its neighborhood. The broader distribution and higher amplitude of ground deformation during the loading periods revealed by the InSAR time series can be explained by water–rock interactions, which cause a decrease in the effective Young's modulus within the top 300‐m crustal layer. Our results demonstrate the potential of using space geodetic data to ensure a better understanding of the solid Earth response to regional hydrological changes.

Systematic Triggering of Large Earthquakes by Karst Water Recharge: Statistical Evidence in Northeastern Italy

It is known that surface water accumulation by natural or anthropic causes like precipitation and reservoir impoundment can trigger earthquakes. The phenomenon is amplified and sped up in karst areas, where fracture systems can store large quantities of water and facilitate its percolation to seismogenic depths, increasing both elastic stress and pore pressure on pre-existent faults. The present work explored the possibility that this mechanism had systematically triggered major earthquakes in northeastern Italy, where seismicity is concentrated along the pre-Alpine thrust belt, characterized by the alignment of a series of karst massifs. The time occurrence of damaging and destructive earthquakes (moment magnitude Mw between 4.8 and 6.4) since 1901 was compared with the evolution of the Palmer Drought Severity Index (PDSI), an index of soil moisture that summarizes precipitation and, through temperature, water evaporation. Statistical analysis based on the bivariate Ripley’s K-function shows a significant time correlation between earthquakes and the peaks of PDSI since 1934, with the two strongest earthquakes (1936 Alpago-Cansiglio earthquake and 1976 Friuli earthquake, Mw 6.1 and 6.4, respectively) placed by the two PDSI maxima. The analysis was extended back in time to the last millennium, showing a time correlation between the occurrence of destructive earthquakes (Mw ≥ 6.2) and the peaks of ice extension in the European Alps, assumed as a proxy for groundwater accumulation in the study area. This evidence presented herein coupled with geological characteristics of the area and recent observations on large crustal deformations induced by heavy precipitation suggests that, if PDSI is a valid ground water indicator, karst water recharge may play a role in triggering major earthquakes in northeastern Italy, also relating their occurrence to the large scale climate changes affecting precipitation and evaporation.

Atmospheric Pressure Anomalies over Earthquakes Epicenters

This article is an analysis of the anomalies in atmospheric pressure days before and during the occurrence of earthquakes. The research started from the review of scientific articles in which it has been proposed that atmospheric events generate or trigger seismicity, and that earthquakes alter the atmosphere. Therefore, the atmospheric pressure pattern in Costa Rica during earthquakes with a magnitude greater than or equal to 6.5 Mw, for the period 1950 – 2020, was studied in order to investigate a possible link between atmospheric events and underground processes of the planet. For this, atmospheric pressure anomaly maps were drawn in which the epicenter of the earthquakes was located. Among the results, it stands out that 64% of the epicenters occurred in areas where the pressure anomaly had a value close to or equal to zero. This could indicate, as other authors have suggested, that atmospheric pressure alters the cortical stress pattern, thus contributing to the triggering of earthquakes.