Tectonic Stress Changes Research Articles

Evidence of Arctic methane emissions across the mid-Pleistocene

During the Pleistocene, Earth’s climate changed dramatically. The mid-Pleistocene transition (MPT; ~1.3–0.7 million years (Ma)) featured an important ice volume increase at both poles. The evolution of large Arctic ice sheets caused the sequestration of methane as free gas and hydrates in subseabed sediments. Ice volume changes, associated with variable pressures and temperatures, perturbed those giant reservoirs, causing methane leakages. Here, we present borehole data from the Arctic–Atlantic gateway region, providing foraminiferal stable carbon isotope and source-specific biomarker evidence that reveals three main seafloor leakage episodes that occurred prior to and across the mid-Pleistocene transition. By combining borehole data with hydrate stability modelling, we propose that tectonic stress changes associated with large ice volume early build-up and wastage during the mid-Pleistocene controlled episodic methane leakages from subsurface reservoirs. Our data indicate methane release, showing a potential scenario for vast Arctic areas storing methane that are now affected by ongoing ice volume decrease.

Tectonic stress changes related to plate spreading prior to the 2021 Fagradalsfjall eruption in SW Iceland

The Reykjanes Peninsula in SW Iceland is a part of the Mid-Atlantic plate boundary. It forms its transtensional segment with several volcanic and faulting systems. We focus on the 2017 seismicity that occurred in the central part of Reykjanes at the place of the Fagradalsfjall volcano prior to its eruption on March 19, 2021. We invert well-determined focal mechanisms of the 2017 seismicity and provide mapping of tectonic stress in space and time. Our results disclose heterogeneous stress field manifested by mix of shear, tensile and compressive fracturing. The prominent stress direction was in the azimuth of 120° ± 8°, which represents the overall extension related to rifting in the Reykjanes Peninsula. The activity initiated on the transform fault segment with predominantly shear strike-slip events. The non-shear fractures occurred later being associated with normal dip-slips and corresponding to the opening of volcanic fissures trending in the azimuth of 30–35°, perpendicular to the extension. The dip-slips were mainly located above an aseismic dike detected in the centre of the 2017 swarm. This dike represents a zone of crustal weakening during a preparatory phase of the future 2021 Fagradalsfjall volcanic eruption located at the same place. Moreover, we detected local variation of stress when the stress axes abruptly interchanged their directions in the individual stress domains. These stress changes are interpreted in a consequence of plate spreading and upcoming fluid flow during a preparatory phase of a rifting episode.

On the calculation of smoothing kernels for seismic parameter spatial mapping: methodology and examples

Abstract. Spatial mapping is one of the most useful methods to display information about the seismic parameters of a certain area. As in b-value time series, there is a certain arbitrariness regarding the function selected as smoothing kernel (which plays the same role as the window size in time series). We propose a new method for the calculation of the smoothing kernel as well as its parameters. Instead of using the spatial cell-event distance we study the distance between events (event-event distance) in order to calculate the smoothing function, as this distance distribution gives information about the event distribution and the seismic sources. We examine three different scenarios: two shallow seismicity settings and one deep seismicity catalog. The first one, Italy, allows calibration and showcasing of the method. The other two catalogs: the Lorca region (Spain) and Vrancea County (Romania) are examples of different function fits and data treatment. For these two scenarios, the prior to earthquake and after earthquake b-value maps depict tectonic stress changes related to the seismic settings (stress relief in Lorca and stress build-up zone shifting in Vrancea). This technique could enable operational earthquake forecasting (OEF) and tectonic source profiling given enough data in the time span considered.

The formation of the 8˚20’ N seamount chain, east pacific rise

Near-axis seamounts provide a unique setting to investigate three-dimensional mantle processes associated with the formation of new oceanic crust and lithosphere. Here, we investigate the characteristics and evolution of the 8˚20’N Seamount Chain, a lineament of seamounts that extends ~ 175 km west of the East Pacific Rise (EPR) axis, just north of the fracture zone of the Siqueiros Transform Fault. Shipboard gravity, magnetic, and bathymetric data acquired in 2016 are utilized to constrain models of seamount emplacement and evolution. Geophysical observations indicate that these seamounts formed during four distinct episodes of volcanism coinciding with changes in regional plate motion that are also reflected in the development of intra-transform spreading centers (ITSCs) along the Siqueiros transform fault (Fornari et al. 1989; Pockalny et al. 1997). Although volcanism is divided into distinct segments, the magnetic data indicate continuous volcanic construction over long portions of the chain. Crustal thickness variations along the chain up to 0.75 km increase eastward, inferred from gravity measurements, suggest that plate reorganization has considerably impacted melt distribution in the area surrounding the Siqueiros-EPR ridge transform intersection. This appears to have resulted in increased volcanism and the formation of the 8˚20’N Seamounts. These findings indicate that melting processes in the mantle and subsequently the formation of new oceanic crust and lithosphere are highly sensitive to tectonic stress changes in the vicinity of fast-spreading transform fault offsets.

Tectonic Stress Changes Related to Plate Spreading During a Preparatory Phase of the 2021 Fagradalsfjall Eruption in Sw Iceland

Tectonic Stress Changes Related to Plate Spreading During a Preparatory Phase of the 2021 Fagradalsfjall Eruption in Sw Iceland

Detection of possible hydrological precursor anomalies using long short-term memory: A case study of the 1996 Lijiang earthquake

Historical data on underground fluid can be valuable for detecting potential hydrological precursors. Although different analysis methods have been employed, nonlinear dynamic fluctuations and the lack of auxiliary observations makes hydrological precursors difficult to identify. In this study, we investigated hydrological time series of data from six monitoring sites to identify possible precursors to the Lijiang earthquake. Two long short-term memory (LSTM) models were developed to simulate and forecast hydrological variations, with and without the use of auxiliary data. The results indicate that both models are useful and valid in forecasting short-term hydrological variations. The LSTM model developed using only historical data can provide good accuracy and validity in simulating and forecasting short-term hydrological variations when no auxiliary meteorological observations are available. The results show that observations made during seismically inactive periods can be better modeled than those made during active periods. Furthermore, the exponentially weighted moving average control chart was employed as a detector to identify anomalous signals. The results show that there was a false precursor in the time series from the six monitoring points (wells and springs). Hydrological anomalies at four of the wells occurred 1–6 months before the Lijiang earthquake and can be attributed to changes in tectonic stress. However, the anomalies at one of the other wells may be unrelated to this earthquake. An anomalous signal observed at a spring could not be related to earthquakes and may have been caused by other factors. This study shows that LSTM models are useful in detecting possible hydrological precursor anomalies.

The Outgoing Longwave Radiation Analysis of Medium and Strong Earthquakes

Two approaches are applied to outgoing longwave radiation (OLR) data to obtain abnormal changes before and after six earthquakes: the background field analysis (BFA) method, which focuses on statistically processing the increment of a radiation value to the multiyear average of the data; and the tidal force fluctuant analysis method, which abandons background data for many years by using the influence of tidal fluctuations to obtain incremental changes in radiation. The results demonstrate that the increase in OLR data identified via the BFA method was uncertain. In the time distribution, the occurrence time of anomalies is isolated and not continuous. In the spatial distribution, many OLR enhancement areas occurred multiple times in the nonseismic and remote seismic-related fault structure areas. In contrast, through the tidal force fluctuant analysis method a clear and consecutive OLR anomaly emerged in the seismogenic cycle of the tidal force. It corresponded with the tidal force through a unique evolution: increased-earthquake-shrink around the epicentre, consistent with the change in the law of thermal radiation during the rock-breaking process under stress, and clearly related to the earthquake's seismic tectonic stress change. It is proven that the tidal force of a celestial body may trigger an earthquake when the tectonic stress reaches its critical breaking point, and when the triggering action is a continuous rather than brief one-shot process. The in situ stress state is key. The OLR anomaly was the physical performance of underlying surface radiation from the change in seismic tectonic stress.

Detecting changes in long-period site responses after the M w 7.6 Chi-Chi earthquake, Taiwan, using strong motion records

Temporal changes in site effects are obtained using the HVSR (horizontal-to-vertical spectral ratio) method and strong motion records after the M w 7.6 Chi-Chi earthquake, Taiwan. Seismic data recorded between 1995 and 2010 are used, comprising 3,708 data from 15 stations adjacent to the Chelungpu fault. Temporal fluctuations are determined by analyzing the site effect variation using a time–frequency variation (TFV) diagram based on these seismic data. Stations adjacent to the fault show significant disturbances in the resonance frequency at 16–26 Hz. Station TCU129 shows a 40% drop in fundamental frequency after the main shock, and a gradual return to the original state over nine years. For stations located farther from the fault zone, sudden changes in tectonic stress play a dominant role in temporal changes to the HVSR. An impact analysis of the directional factor confirms our finding that the proximity of the fault to seismic stations has the most influence on data.

Research on the changes of the tidal force and the air temperature in the atmosphere of Lushan (China) Ms7.0 earthquake

The cycle process of the tidal force of celestial body for Lushan M7.0 earthquake, occurred in Lushan county of Sichuan, China on April 20, 2013 was calculated. The earthquake occurred at the lowest point phase. It indicated that the type of seismogenic fault that the tide force acted on belonged to the thrust fault. According to the tidal cycle, the abnormal air temperature change was analyzed based on NCEP satellite data around the whole China before and after the earthquake. The result showed that the air temperature changed evidently with the tide force changing. In temporal, the change went through: initial air temperature rise → strength→ reaching abnormal peak→ gradually decline; in spatial, the abnormal area winded its way along the margin of the southern Qinghai-Tibet Plateau and went through: scattered→ conversion→ scattered procession. The procession was similar to the change procession of a rock breaking under the stress loading. This shows that the stress change of rock may cause the air temperature change in the atmosphere before and after earthquake. It indicated that the tidal force of celestial body could trigger the earthquake, when the tectonic stress reaches its critical broken point and the air temperature anomaly was proportional to the seismic tectonic stress change. It was useful to combine air temperature and tidal force in earthquake precursory.

The Sensitivity of the Loa/Unload Response Ratio and Critical Region Selection Before Large Earthquakes

Occurrence of a large earthquake could be predicted by anomalous temporal increase of the Load/Unload Response Ratio (LURR). Previous studies have indicated that the stress field that existed before a large earthquake may have a strong influence on the evaluation of LURR. In this paper, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. This algorithm is devised to increase the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. In the algorithm, we assess the stress change and identify the areas with increased Coulomb stress before an earthquake using a simple back-slip dislocation model of the event. Retrospective tests of this algorithm on some disastrous earthquakes that occurred in the Chinese mainland in recent years show remarkable enhancement of the LURR precursory anomalies. By using the hypothetical faults for the large earthquake prediction, we further illustrate that the new algorithm is more sensitive to detect future earthquake of a particular magnitude range and location than the circular region algorithm. Hence, where sufficient information of the regional fault tectonics is given, the Coulomb stress algorithm can be used to augment current LURR technique for seismic hazard estimation.

Comparison of dike intrusions in an incipient seafloor-spreading segment in Afar, Ethiopia: Seismicity perspectives

[1] Oceanic crust is accreted through the emplacement of dikes at spreading ridges, but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood. Between 2005 and 2009 the ∼70 km long Dabbahu-Manda Hararo rift segment in Ethiopia has experienced 14 large volume dike intrusions, 9 of which were recorded on temporary seismic arrays. A detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems. All of the migrating swarms of earthquakes started from a <5 km radius zone at the middle of the Dabbahu-Manda Hararo segment, and traveled northward and southward along the rift axis. Small magnitude earthquakes associated with the margins of the propagating dike tips are followed by the largest magnitude, primarily low-frequency earthquakes. The seismic moment distributions show >80% of energy is released during the propagation phase, with minimal seismic energy release after the dike propagation ceases. We interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip, coincident with the onset of low-frequency earthquakes. Dike lengths show no systematic reduction in length with time, suggesting that topographic loading and stress barriers influence dike length, as well as changes in tectonic stress. The propagation velocities of all the dikes follow a decaying exponential. Northward propagating dikes had faster average velocities than those that propagated southward, suggesting preconditioning by the 2005 megadike, or ongoing heating from a subcrustal magma source north of the midsegment.

Reply to `A Second Opinion on "Operational Earthquake Forecasting: Some Thoughts on Why and How," by Thomas H. Jordan and Lucile M. Jones,' by Stuart Crampin

In folklore, a “silver bullet” is an effective weapon against were-wolves and witches. In earthquake prediction, a silver bullet is a diagnostic precursor —a signal observed before an earthquake that indicates with high probability the location, time, and magnitude of the impending event (Jordan 2006). In his comment, Crampin (2010) claims that shear-wave splitting (SWS) observations provide a silver bullet. He asserts that seismology is thus capable of raising earthquake forecasting out of the low-probability environment to which we assigned it in our recent opinion piece (Jordan and Jones 2010). We find his arguments unconvincing. His conceptual basis is the notion that changes in shear-wave anisotropy are sensitive to changes in tectonic stress—a respectable hypothesis. But he burdens this concept with a thick pile of more dubious assumptions to somehow conclude that SWS observations can yield diagnostic precursors of large earthquakes. This is not the appropriate forum for a critical analysis of the prediction methodology he has advocated for several decades ( e.g. , Crampin et al. 1984). Suffice it to note that Crampin's …

Critical sensitivity of load/unload response ratio and stress accumulation before large earthquakes: example of the 2008 Mw7.9 Wenchuan earthquake

The Load/Unload Response Ratio (LURR) method is often defined as the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to earth tide induced Coulomb Failure Stress change on optimally oriented faults. According to the method, anomalous increase in the time series of LURR usually occurs prior to occurrence of a large earthquake. Previous studies have indicated that the stress field that existed before a large earthquake has strong influence on the evaluation of LURR. In order to augment the sensitivity of LURR in measuring the criticality of stress accumulation before an earthquake, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. Coulomb stress change before the hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. Retrospective test of this new algorithm on the 2008 Mw7.9 Wenchuan earthquake shows remarkable enhancement of the LURR precursory anomaly. To illustrate the variation of LURR time series associated with our choice of identified areas with increased Coulomb stress before the earthquake, we calculate the spatial distributions of LURR within a circular region of 700 km radius centered at epicenter of the event. Comparing the spatial LURR distributions of different periods, the change of LURR within the Coulomb stress increase areas looks more prominent than the others: it remains at a low level for most of the time and markedly increases few years before the quake. This result further shows the validity of the Coulomb stress algorithm. Unlike circular regions, areas of increased Coulomb stress with anomalously increased LURR values before a large earthquake could provide a relatively more precise estimation of the criticality of the ensuing event.

Increasing critical sensitivity of the Load/Unload Response Ratio before large earthquakes with identified stress accumulation pattern

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.

Source Process of the Chi-Chi Earthquake: A Joint Inversion of Strong Motion Data and Global Positioning System Data with a Multifault Model

The Chi-Chi, Taiwan, earthquake of 21 September 1999 was a large thrust earthquake that caused disastrous damage. The surface fracture trace runs along the Chelungpu fault, which strikes N5� E along most of the faulting area but turns to the northeast while approaching its northern end. It finally presents a horsetaillike faulting system and bends to an east-northeast direction at the northern end. Both strong-motion and Global Positioning System (GPS) data recorded large displace- ments in the northern part. In this study, we use a multifault model to simulate the observed large strong-motion and GPS data. The results of the joint inversion reveal that in the southern part, slip occurred mainly in the shallow portion, reaching a maximum about 20 m on the ENE fault, where the rupture propagated to the deep part of the fault. There was obviously slip vector rotation from south to north, such that the slip on the branched fault plane was almost purely reverse faulting. The seismic moment, a total of 2.7 10 20 N m, was released in less than 40 sec during the mainshock. Aftershocks occurred mainly in areas where little or no slip occurred. Slip vector rotation can be explained by the complexity of regional tectonic stress. Changes in tectonic stress at the northern end of the fault inhibited the northward propagation of the rupture and favored the rupturing of the ENE fault.

Analytical and numerical solutions for alternative overpressuring processes: Application to the Callovo‐Oxfordian sedimentary sequence in the Paris basin, France

Previous studies that made use of basin models have shown that the normal geological evolution of the Paris basin does not generate the observed, albeit weak, excess pressures in some shale layers of the basin. Other processes that may have created the overpressures, currently neglected in such models, are investigated here. Terms accounting for osmotic effects and tectonic stress changes are successively added to the diffusivity equation. The effect of changes in outcrop boundary conditions is also calculated with a pseudo‐two‐dimensional analytical solution. These solutions are applied to the Callovo‐Oxfordian shale formation in the eastern part of the Paris basin, France. It is shown that a long‐term transient osmotic effect starting in the Tertiary could explain in part the observed excess pressures in the Callovo‐Oxfordian shale assuming effective diffusion coefficients of 1–5 × 10−12 m2 s−1 in line with the measurements and a pore radius b around 20 Å for the shales. However, because of the uncertainty on the value of the shale pore radius, additional head measurements and osmotic experiments on samples should be made to fully establish the possibility of an osmotic process. Our study also shows that recent changes in hydrodynamic boundary conditions could also explain excess pressure distribution in this shale layer. It is plausible that a combination of the two processes could best explain the distribution and intensity of the “overpressures.” Tectonic stress changes do not appear to be important; it is shown that for such processes, to maintain high pressures, strong and recent increase in tectonic compressive stress would be required.

Mechanical stability of the Redbank Thrust Zone, Central Australia: Dynamic and rheological implications

Deep seismic reflection profiling and other studies indicate that the Moho has been significantly displaced by intracratonic deformation on the Redbank Thrust Zone in central Australia. A two‐dimensional finite‐element model of the thick‐skinned crustal structure of the Redbank Thrust Zone shows that the gravitational stresses generated by the distribution of crustal masses are in agreement with the tectonic and seismic quiescence of the area. Rock failure is concentrated in the downthrusted, and therefore Theologically weakened, crustal segments. Conversely, the upthrusted slices of lower crust and upper mantle undergo little deformation and no failure and thus constitute a mechanically strong whole‐crustal core. The presence of north‐south oriented intraplate stresses derived from far‐field plate boundary forces does not contribute to the inferred mechanical equilibrium of the crust in central Australia. The results may have implications for the mechanical stability of intracratonic thick‐skinned crustal structures elsewhere, and for the long‐term strength of continental lithosphere in general. The models, however, do predict the possibility of intraplate seismicity in response to small changes in tectonic stress, since parts of the crust are already at or close to the failure limit.

Tidal triggering of earthquake swarms at Kilauea Volcano, Hawaii

Between 1967 and 1983, four earthquake swarms occurred on Kilauea Volcano, Hawaii, with durations ranging from 68 to 156 hours. Plots of the number of events per hour show a remarkable modulation having diurnal and semidiurnal periodicities. We test the hypothesis that these fluctuations are tidally triggered. A correlogram showing the correlation coefficient between the swarm series and tidal strain oriented at 20° intervals and phase shifted at 1‐hour intervals gives the orientation and phase of the tidal strain most closely resembling the swarm plots. Maximum correlation occurs at different orientations and phases for three of the four swarms, which occur in tectonically different parts of the volcano. Two of the swarms which occur in the same region can be fit with a common tidal forcing function even though they occurred more than a year apart. The discrete Fourier transform of the swarm data shows a dominance of diurnal energy over semidiurnal energy, compared with the opposite dominance for the transform of the theoretical tidal function at the times of the swarms. We checked whether the diurnal dominance might be generated by cultural noise by raising the threshold magnitude of the earthquakes used without noticeably affecting the results. Also the phase of the correlation varies from swarm to swarm relative to local Hawaii time. Diurnal dominance remains not completely understood, but tidal influences appear to be the best explanation for the modulation of the activity. These observations limit the rate of tectonic stress change in the rift zones of Kilauea to less than the tidal stress rate.

Intermediate-term, pre-earthquake phenomena in California, 1975?1986, and preliminary forecast of seismicity for the next decade

Intermediate-term observations preceding earthquakes of magnitude 5.7 or greater in California from 1975 through 1986 suggest that: (1) The sudden appearance of earthquakes in a previously inactive area indicates an increased likelihood of a significant earthquake in that area for a period from days to years; (2) these larger earthquakes tend to occur towards the ends of creeping fault segments; (3) one large earthquake in a region increases the likelihood of a subsequent significant event in the adjacent area; and (4) marginal evidence for the occurrence of a regional deformation event suggests that such events increase the probability of earthquake occurrence throughout the entire area. A common element in many of these observed patterns appears to be the transmission and amplification of tectonic stress changes by the mechanism of fault creep, and suggests that surface fault creep is a sensitive indicator of changes in stress. The preceding critieria are used to construct a preliminary ‘forecast’ of the likely locations of significant earthquakes over the next decade.

Radon and helium anomalies in mud volcanoes from northern Apennines(Italy). A tool for earthquake prediction.

Rn-222 and total helium contained in saline waters and associated gaseous fluids from a series of mud volcanoes occurring along the northeastern border of the Apennine chain (northern Italy) have been determined as possible precursors of local earthquakes. Investigations spanned over about one year (May 1986-May 1987) during which a series of low- to medium-magnitude (M = 3-4.5) local earthquakes occurred with distinct focus. Spike-like Rn anomalies were almost systematically observed a short time (hours to few days) before and after the main shocks. These anomalies were frequently accompanied by slight but significant short-term changes in water chemistry. A unique very strong He anomaly was recorded in coincidence with a shock in an area very close to the focus. The significance of the observed short-term anomalies of Rn and hydrochemical parameters (chlorinity, alkaline earths content) is explained in terms of an upsetting of the equilibrium between two chemically distinct (pellicular and normal) connate waters in confined reservoirs. Pellicular water trapping radiogenic Rn would be abruptly liberated into normal connate water by a tectonic stress change. In most cases, helium seems to be insensitive to seismic events, this probably being due to the shallowness of the foci. The data confirm that mud volcanoes represent very sensitive natural systems for predicting local earthquakes.