Centroid Moment Tensor Catalog Research Articles

Earthquake source characterization by machine learning algorithms applied to acoustic signals

Underwater seismic events generate acoustic radiation (such as acoustic-gravity waves), that carries information about the source and can travel long distances before dissipating. Effective early warning, emergency response, and information dissemination for earthquakes and tsunamis require a rapid characterisation of the fault properties: geometry and dynamics. In this work, we analysed hydrophone recordings of 201 earthquakes, located in the Pacific and the Indian Ocean, by employing acoustic signal processing and classification methods. The analysis allows identifying the type of earthquake (i.e. slip type, magnitude) and provides near real-time estimation of the effective properties of the fault dynamics and geometry. The results were compared against values reported by the Harvard Global Centroid Moment Tensor catalog (gCMT), revealing statistical significance between the extracted acoustic properties used to feed machine learning algorithms and the predicted slip and magnitude values.

Investigating Time Dependent Stress Changes Globally Following Large Earthquakes (M≥7)

Triggered earthquakes can cause disproportionate damages depend on their magnitudes. In fact, there is a causal link between the spatial distribution of those events and the stress changes induced by the mainshock. Co-seismic stress loading is one of the key factors in determination of triggering mechanism. However, the time lags ranging hours to years and the stress diffusion over wider areas cannot be evaluated with the co-seismic process alone. In some cases, the stress interactions for long periods and larger areas can be attributed to post-seismic viscoelastic relaxations. In this study, M≥7 earthquakes from the Global Centroid Moment Tensor (GMCT) catalogue are modelled as dislocations to calculate shear stress changes on following earthquake nodal planes near enough to be triggered. The catalogue scanned for all other events (4.5<M<7) that occurred within ±2° from the centroid rupture planes. According to Omori law, which is one of the most reliable time predictable diagram of aftershock distributions, 10-year periods were used for the stress calculations. The events that had computed within ±0.01 to ±1 MPa stress change limits, considered as potential triggered events. The global co-seismic stress calculations show that 60.6% of the triggered events occurred in regions where the shear stress increased. The global stress change by incorporation viscous flow into co-seismic stress change were also tested. In this case, an increase in the rate of triggered events in both positive (15%) and negative (9%) shear stress areas were obtained. Despite the rate of triggered events has climbed significantly in both areas, only 2% of the changes have been computed globally. These rates are highly depending on fault mechanism across the plate boundaries. Thrust faults in the catalogue, for example, influence the stress distribution over broader regions and the dimension of fault ruptures. Therefore, thrust faults in the catalogue prevails the global statistics for both co-seismic and viscoelastic stress calculations. The results also demonstrate the significant effect of viscous flow, following large earthquakes, which cannot be neglected in stress interaction analysis.

A Testable Worldwide Earthquake Faulting Mechanism Model

Abstract In this article, we present a simple model to forecast global focal mechanisms. This model is based on a simple discrete counting distribution of the global centroid moment tensor catalog, and it also includes, using a Bayesian scheme, the a priori information from the Anderson theory of faulting. Our model is tested in hindcasting mode against independent data of global large earthquakes with Ms≥7. We obtained statistically significant good agreement between model and data using consistency test, demonstrating that this simple model can satisfactorily forecast focal mechanisms at the global scale. The defined testing procedure can be used to test the model in prospective mode against future events. These forecasts may inform short- to long-term hazard quantifications that require a finite source characterization, as well as real-time source inversion algorithms.

The Reliance of the Earthquake B-Value on Depth and Focal Mechanism

The earthquake size distribution (b-value) is a significant factor to recognize the seismic activity, seismotectonic, and seismic hazard assessment. In the current work, the connection of the b-constant value with the focal depth and mechanism was studied. The effect of the study scale (global, regional and local) on the dependence of b-value on the focal mechanisms was investigated. The database is quoted from the Global Centroid Moment Tensor catalog. The selected earthquakes are the shallow normal, reverse and strike-slip events. The completeness magnitude (Mc) is 5.3. The maximum likelihood method is utilized to compute the b-value. The obtained results show that the b-value is decreasing with depth to range 10-20 km, then increases to the depth of 40km. The turning point of b-value (increasing of b-value) locates at the depth of the transition brittle-ductile zone. Globally and regionally, low, moderate, and high b-values are associated with reverse, strike-slip, and normal focal mechanisms, respectively, while locally, the relation between b-values and focal mechanisms shows different association trends, such as low, moderate, and high b-values are associated with normal, strike-slip, and reverse focal mechanisms and so on.

Why do continental normal fault earthquakes have smaller maximum magnitudes?

Continental normal fault earthquakes have been reported to have smaller maximum magnitudes (Mmax) than continental earthquakes with other fault geometries. This difference has significant implications for understanding seismic hazards in extensional regions. Using the Global Centroid Moment Tensor (GCMT) catalog, we examine how Mmax varies with fault geometry in continental regions, whether these trends are robust, and potential physical reasons for the smaller magnitudes of continental normal fault earthquakes.We find that the largest continental normal fault earthquakes are in the low Mw 7 range whereas other fault geometries can reach ~Mw 8. The continental normal fault earthquake magnitude-frequency distribution has a lower corner magnitude (a parameterization of Mmax) than other fault geometries. The observed smaller continental normal fault Mmax is not an artifact of classification criteria or catalog length. Probability calculations indicate that the GCMT catalog is long enough to capture differences in Mmax due to fault geometry. Additionally, our analysis indicates that neither fault length nor width is limiting the size of continental normal fault earthquakes. Fault complexity can limit rupture extent, but it is likely not the primary reason for the smaller continental normal fault Mmax.Rather, lithosphere yield stress (strength) appears to be the main factor controlling Mmax. In extension, lithosphere is weaker, failing at lower yield stresses than in compression. Although this yield stress difference is consistent with smaller continental normal fault earthquakes, it appears inconsistent with the occurrence of large oceanic normal fault earthquakes. However, the largest oceanic normal fault earthquakes occur near subduction zones where the lithosphere is bending. Laboratory studies indicate that bending lithosphere likely has a higher yield stress than lithosphere in pure extension, which may allow for larger oceanic normal fault earthquakes. Therefore, yield stress—rather than fault geometry alone—appears to be the key factor limiting an earthquake's maximum magnitude.

Estimated Seismic Source Parameters for 2019 Magnitude 7.6 Papua New Guinea Earthquake

On 14 May 2019, a major (Mw 7.6) earthquake struck eastern Papua New Guinea, causing a tsunami warning that was later canceled. The last major rupture in the region was a 2000 Mw 8.0 event, which resulted in massive horizontal land movements of up to several meters and a series of aftershocks with primarily thrust mechanisms, and caused a damaging tsunami. Seismic methods for characterizing the source process were applied. Vertical components of the long-period P-waves from 35 stations of the Global Seismic Network with even azimuthal coverage were adopted in the inversions. First, the focal mechanism solution was retrieved after the earthquake. From the inverted results as well as aftershock distribution, the causative fault of the great PNG earthquake was confirmed to be a fault of strike = 316°, dip = 84°, and rake = 0°, indicating that the earthquake was a left-lateral strike-slip event. Then, to clearly understand the spatiotemporal evolutionary process of the source rupture of the earthquake, far-field body wave data were collected, and the source rupture process of this earthquake was studied using the finite fault inversion method. A finite-fault model was estabished with length and width of 152 and 32 km, respectively, and we set the initial seismic source parameters referring to the center of the focal mechanism solution. This was estimated by the focal mechanism solutions of defferent studies referring to different focal mechanism solutions. We found that the focal mechanism solution determined by Global Centroid Moment Tensor Catalog was not appropriate. Inversion results indicated that the seismic moment was 3.63 × 1020 Nm (Mw 7.6), and the source duration was ~ 40 s. The rupture propagated mainly toward the northwest in an asymmetrical bilateral mode, with a maximum slip of ~ 13.2 m, and a large-scale slip patch strongly ruptured to the surface. The study of Coulomb stress changes suggested that the PNG earthquake may trigger a thrust-type rupture in the New Britain Trench, which has the potential to trigger a tsunami.

New Updated Classification of Shallow Earthquakes Based on Faulting Style

Earthquakes occur on faults and create new faults. They also occur on normal, reverse and strike-slip faults. The aim of this work is to suggest a new unified classification of Shallow depth earthquakes based on the faulting styles, and to characterize each class. The characterization criteria include the maximum magnitude, focal depth, b-constant value, return period and relations between magnitude, focal depth and dip of fault plane. Global Centroid Moment Tensor (GCMT) catalog is the source of the used data. This catalog covers the period from Jan.1976 to Dec. 2017. We selected only the shallow (depth less than 70kms) pure, normal, strike-slip and reverse earthquakes (magnitude ≥ 5) and excluded the oblique earthquakes. The majority of normal and strike-slip earthquakes occurred in the upper crust, while the reverse earthquakes occurred throughout the thickness of the crust. The main trend for the derived b-values for the three classes was: b normal fault>bstrike-slip fault>breverse fault. The mean return period for the normal earthquake was longer than that of the strike-slip earthquakes, while the reverse earthquakes had the shortest period. The obtained results report the relationship between the magnitude and focal depth of the normal earthquakes. A negative significant correlation between the magnitude and dip class for the normal and reverse earthquakes is reported. Negative and positive correlation relations between the focal depth and dip class were recorded for normal and reverse earthquakes, respectively. The suggested classification of earthquakes provides significant information to understand seismicity, seismtectonics, and seismic hazard analysis.

Spatial variation in the present-day stress field and tectonic regime of Northeast Tibet from moment tensor solutions of local earthquake data

SUMMARYFocal mechanism solutions and their predicted stress pattern can be used to investigate tectonic deformation in seismically active zones and contribute to understanding and constraining the kinematic patterns of the outward growth and uplift of the Tibetan Plateau. Herein, we determined the focal mechanisms of 398 earthquakes in Northeast Tibet recorded by the China National Seismic Network (CNSN) by using the cut-and-paste method. The results show that the earthquakes predominately exhibited thrust and strike-slip faulting mechanisms with very few normal events. We then combined the derived focal mechanisms with global centroid moment tensor (GCMT) catalogue solutions and previously published solutions to predict the regional distribution of the stress field through a damped linear inversion. The inversion results show that most of region is dominated by a thrust faulting regime. From the southern East Kunlun fault in the west to the northern Qilian Mountains along the Altyn Tagh fault (ATF), the maximum compression axis rotates slightly clockwise; farther to the south of the Haiyuan fault in the east, there is an evident clockwise rotation of the maximum compression axis, especially at the eastern end of the Haiyuan fault. In the Qilian Mountains, the axis of the compressive stress orientation approximately trends NE–SW, which does not markedly differ from the direction of India–Eurasia convergence, emphasizing the importance of the compressive stress in reflecting the remote effects of this continental collision. The overall spatial pattern of the principal stress axes is closely consistent with the GPS-derived horizontal surface velocity. A comparison of the stress and strain rate fields demonstrated that the orientations of the crustal stress axes and the surface strain axes were almost identical, which indicates that a diffuse model is more suitable for describing the tectonic characteristics of Northeast Tibet. Additionally, the compressive stress orientation rotated to ENE–WSW in the northern Qilian Mountains along the ATF and to ENE–WSW or E–W along the eastern part of the Haiyuan fault and its adjacent area to the south, highlighting the occurrence of strain partitioning along large left-lateral strike-slip faults or the lateral variation of crustal strength across these faults. Combining geodetic, geological and seismological results, we suggest that a hybrid model incorporating both the diffuse model associated with shortening and thickening of the upper crust and the asthenospheric flow model accounting for the low-velocity zone in the middle-lower crust may reflect the primary mode of crustal deformation in Northeast Tibet.

A Model for Visual Assessment of Fault Plane Solutions and Active Tectonics Analysis Using the Global Centroid Moment Tensor Catalog

In this study, individual fault plane solutions are developed using various methods to improve the understanding of active tectonics on a regional scale. The comparative analysis of a focal mechanism solution (FMS) has not elicited the attention of researchers. Therefore, this study aims (1) to visually analyze the fault plane solution for 20 local faults that are responsible for all the earthquakes that occurred using visualization techniques such as: fault parameters, the linked Bingham method, the ad hoc pressure (P) axis and tension (T) axis method, and the moment tensor method; (2) to identify the best method for FMS; and (3) to understand the active tectonics of a fault population. A comparative analysis of the models is systematically documented to improve the understanding of the methods. An analysis of the overall fault mechanism is conducted for the analytic determination of fault movement using fault population data from the Global Centroid Moment Tensor catalog. The approach used in this work is a newly designed method for analyzing the reliability of various techniques for fault mechanism and overall fault movement research. Findings show that for the fault mechanism analysis, the P and T axes method and the moment tensor method are better than the fault plane solution from the fault parameters and the linked Bingham method based on the input parameters, output information, model outfit, and accuracy. The moment tensor method is one of the best approaches for analyzing fault mechanism because the errors in the nine components used as input data for the modeling are negligible. Meanwhile, the P and T axes method is one of the best techniques for the overall analysis of fault movement. P and T dihedral analysis using Kamb contouring is modeled. It indicates that the overall mechanisms of compression and dilation are features at the NW–SE and E–W directions, respectively. This comprehensive and consistent analysis of the fault mechanism provides an overview of the seismotectonic settings in Sabah, Malaysia.

The focal depths of the 2008 Panzhihua earthquake sequence and the stress field in the source region

Focal depths of the 2008 MS6.1 Panzhihua earthquake sequence and tectonic stress field in the source area are investigated. Source depths of 24 earthquakes in Panzhihua earthquake sequence with a magnitude M≥3.0 were determined using the seismic depth phase sPL; additionally, the focal depths of 232 earthquakes were measured by fitting the three-component waveforms of the P and S waves. The source depth of the main shock is ~12 km. The majority of the aftershocks with magnitude M≥3.0 occurred in the brittle upper crust at the depths range of 12–18 km. Further, the Source mechanisms of the 232 events around the Panzhihua earthquake source area were determined, and the results show that the earthquakes have predominantly strike-slip mechanisms in the Dianzhong Block, but display complexity of the focal mechanisms outside and near the boundary of the Dianzhong block. The 232 earthquake mechanisms from this study are combined with the solutions from the Global Centroid Moment Tensor (GCMT) catalog to derive 2D stress field. The inversion results show that the Dianzhong block is predominantly under a strike slip faulting regime and the direction of the maximum principal compression σ1 is northwest-southeast (NW-SE)-trending. The distribution is coincide with GPS velocity field. However, orientations of principal stress axes as well as the faulting types change outside and near the Dianzhong block. The results show that the tectonic stress field in the study area is predominantly controlled by the southeast (SE)-trending horizontal movement and clockwise rotation of the Dianzhong block as a result of the eastward movement of eastern Tibetan meeting the old and rigid South China block (SCB). The Panzhihua earthquake ruptured at ~12 km depth where the tectonic stress regime is under the SE-direction horizontal compression and the NE-direction horizontal extension.

Impact of The 2004 Sumatra-Andaman Earthquake to The Stress Heterogeneity and Seismicity Pattern in Nothern Sumatra, Indonesia

Sumatra Island is a highly seismic active region due to its close location to the convergent zone between the Indo-Australian and Eurasian plates, and the existence of the Great Sumatran Fault (GSF). These conditions caused the island of Sumatra suffered from hundreds of earthquakes with Mw > 4 per year. Particularly, a 9.0 Mw Sumatra-Andaman 2004 earthquake occured in northern Sumatra which changed the in-situ stress and seismicity pattern. In such case, quantifying the tectonic stress perturbation prior and after 2004 Sumatra-Andaman earthquake is becoming key issue in assessing the seismic hazard. To invert the in-situ stress information in Sumatra, first we identify the fault plane from its auxiliary plane in the focal mechanism solutions using the fault instability criterion. There are 354 focal mechanisms data of earthquake with Mw > 5 and focal depths < 250 km along northern Sumatra Island from 1976 to 2010. This catalogue was compiled by combining the data from Global Centroid Moment Tensor (GCMT) catalogue and the International Seismological Centre (ISC) bulletin. We then divided the focal mechanism catalogue into two parts, i.e. prior and after Sumatra-Andaman 2004 earthquake. An iterative joint inversion is then implemented to estimate the in-situ stress orientation and its magnitude ratio. The in-situ principal stress orientation and magnitude ratio obtained from this study will be used to build a Sumatran stress map and its correlation with the seismicity pattern variations in the region. Our results produce remarkable changes of maximum principal stress orientation after 2004 megathrust earthquakes along the region. As the seismic hazard potential is controlled by stress concentration, the obtained results from this study could also be used further for seismic hazard mitigation in northern Sumatra.

Estimation of the Seismic Moment Rate from an Incomplete Seismicity Catalog, in the Context of the InSight Mission to Mars

We evaluate methods to estimate the global seismic moment rate of a planet from the k >= 1 largest events observed during a limited and possibly short-time span, as can be expected, for example, for lander missions to Mars. The feasibility of the approach is demonstrated with a temporary broadband seismometer that was recording in the Mojave desert, California, for 86 days in 2014, and by application to the Global Centroid Moment Tensor (CMT) catalog, subsets thereof, and a catalog of stable continental regions seismicity. From the largest event observed at Goldstone alone (M-w approximate to 7.9), we estimate the Earth's global moment rate to be 1.03 x 10(22) N . m/yr, whereas an estimation based on the 10 strongest events yields a rate of 5.79 x 10(21) N . m/yr. Summation of 42 yr of Global CMT solutions results in an average of 7.61 x 10(21) N . m/yr. In general, a 2 yr interval of Global CMT solutions is sufficient to estimate the Earth's annual moment rate to within a factor of 5 or better. A series of numerical experiments with more than 560 million synthetic catalogs based on the tapered Gutenberg-Richter distribution shows that the estimation is rather insensitive against an unknown slope of the distribution, and that bias and variance of the estimator depend on the ratio between moment rate and corner moment of the size frequency distribution. Moment rates of published Mars models differ by a factor of 1000 or more. Tests with simulated catalogs show that it will be possible to reject some of these models with data returned by NASA's InSight mission after two years of nominal mission life time.

Modern crustal seismicity in the northern Andean Precordillera, Argentina

The Precordillera in the Andean backarc region of Argentina has a long record of large and damaging earthquakes in the last century. Its northern part is not well known seismically neither its style of deformation. In this work we study modern crustal seismicity occurring in the same epicentral area of the historical 1894 earthquake. That earthquake caused deaths and severe damage even at large distances of about 500 km. Because of the unavailability of instrumental records to study this large earthquake, not many details of its seismic source are known. Our study involves broadband and short period seismic data from modern seismicity to characterise the same epicentral area. We used seismic records from the permanent Argentine network (INPRES) and from two temporary broadband experiments (CHARGE and SIEMBRA). We determine 44 seismic locations and their focal depths which are in the range between 10 and 30 km and magnitudes 1.2 ≤ M ≤ 4. In addition, we obtain 33 focal mechanism solutions for some of these earthquakes using P-wave first motions and amplitude ratios between P and S waves; for the same region, five more moderate earthquakes have been ever observed globally and reported by the Global Centroid Moment Tensor catalogue in the last 55 years. We note that epicentres are mainly distributed in the southern sector of the study region, with a relatively greater concentration in the foothills of the Frontal Andes Cordillera. Focal mechanisms show mainly reverse, and in less proportion strike-slip solutions. Overall these results agree with compression and shortening in an east-west orientation of the Andean northern Precordilleran backarc region.

Iranian regional centroid moment tensor catalog: Solutions for 2012–2017

In 2012, the installation of broadband seismic stations in Iran allowed the beginning of the moment tensor project of Iranian earthquakes by the Iranian Seismological Center (IRSC). In a period of five years, 194 moment tensors with 3.7 ≤ MW ≤ 7.6 were computed based on analysis of seismograms recorded at local and regional distances. Included in the catalog are the moment tensors of 83 events, not modeled by GCMT. A reasonable consistency exists between the mechanisms of common events in the two catalogs. The average moment magnitude difference is 0.1 and the Kagan angle is below 20° for 61% of the earthquakes. The P, B and T axes difference is up to 15°. The moment tensor catalog of Iran shows a decrease of the magnitude of completeness by 0.3 after this study. The number of accepted solutions as a fraction of attempts of the project, with the average of 55%, increased from 40% in 2012 to 68% in 2016, due to the expansions of the seismic networks in Iran. The dataset includes earthquakes from all seismic zones in Iran with the dominance of thrust faulting. The calculated depths in this study are consistent with the subregion seismotectonic conditions of Iran. The information on seven earthquakes with MW 6.0+ and 53 events with 5.0 ≤ Mw < 6.0 is also included, and relation to regional faults and reasons of the large/small damaging effects are discussed. Considering the expansion of the broadband seismic stations in Iran, the future development of IRSC moment tensor project should concentrate more on determining the mechanisms of minor events, especially in the regions with no larger earthquakes.

Earth tidal stress as an earthquake trigger prior to the Wenchuan earthquake, Sichuan, China

Cyclic stress variations in the crust of the earth are caused by the earth tide. Although these stress variations are small in comparison to tectonic stress, tidal stress rates are often larger than those of tectonic stress accumulation. Thus, tidal stress could be considered as one of the possible triggers for an earthquake. Many scientific studies have been conducted to examine the correlation between the earth tide and earthquake occurrence. In this study, the shear and normal stresses caused by the earth tide on the focal fault plane of the Wenchuan earthquake, Sichuan, China, are calculated using the focal mechanism solution published by the Global Centroid Moment Tensor catalog and the Preliminary Reference Earth Model. We analyzed how the tidal stresses on the fault plane changed when the Wenchuan earthquake occurred. The Schuster’s test was applied to define correlations between earthquakes occurring around the epicenter area before the Wenchuan earthquake and stresses caused by the daily earth tide. A P -value was calculated and used to quantify the statistical significance of the evidence. Earthquake data used in this study were obtained from the China Earthquake Networks Center, China Earthquake Administration. The temporal variation and spatial distribution of the P -value, indicating the significance of the test, were investigated. The obtained results show that the daily tidal stress was in favor of slip of the focal fault when the Wenchuan earthquake occurred. For earthquakes ( M L≥2.7) that occurred in the study area, the P -value began to drop in June 2007, approaching the lowest value (0.85%) very close to the occurrence time of the M S8.0 Wenchuan main shock. Most of low- P -value ( P -value situated in the near northeast of the epicenter can be found prior to the Wenchuan earthquake from the spatial distribution of P -value in the Longmenshan Fault. It can be concluded from the above-mentioned results that significant correlations between earthquakes occurring around the epicenter area and the daily tide existed prior to the Wenchuan earthquake. These tide-triggered earthquakes were in the south part of the rupture zone of the Wenchuan earthquake, northeast of the epicenter. Therefore, tidally triggered earthquakes occurred around the epicenter area prior to the Wenchuan earthquake.

Natural Time and Nowcasting Earthquakes: Are Large Global Earthquakes Temporally Clustered?

The objective of this paper is to analyze the temporal clustering of large global earthquakes with respect to natural time, or interevent count, as opposed to regular clock time. To do this, we use two techniques: (1) nowcasting, a new method of statistically classifying seismicity and seismic risk, and (2) time series analysis of interevent counts. We chose the sequences of $$M_{\lambda } \ge 7.0$$ and $$M_{\lambda } \ge 8.0$$ earthquakes from the global centroid moment tensor (CMT) catalog from 2004 to 2016 for analysis. A significant number of these earthquakes will be aftershocks of the largest events, but no satisfactory method of declustering the aftershocks in clock time is available. A major advantage of using natural time is that it eliminates the need for declustering aftershocks. The event count we utilize is the number of small earthquakes that occur between large earthquakes. The small earthquake magnitude is chosen to be as small as possible, such that the catalog is still complete based on the Gutenberg-Richter statistics. For the CMT catalog, starting in 2004, we found the completeness magnitude to be $$M_{\sigma } \ge 5.1$$ . For the nowcasting method, the cumulative probability distribution of these interevent counts is obtained. We quantify the distribution using the exponent, $$\beta$$ , of the best fitting Weibull distribution; $$\beta = 1$$ for a random (exponential) distribution. We considered 197 earthquakes with $$M_{\lambda } \ge 7.0$$ and found $$\beta = 0.83 \pm 0.08$$ . We considered 15 earthquakes with $$M_{\lambda } \ge 8.0,$$ but this number was considered too small to generate a meaningful distribution. For comparison, we generated synthetic catalogs of earthquakes that occur randomly with the Gutenberg–Richter frequency–magnitude statistics. We considered a synthetic catalog of $$1.97 \times 10^5$$ $$M_{\lambda } \ge 7.0$$ earthquakes and found $$\beta = 0.99 \pm 0.01$$ . The random catalog converted to natural time was also random. We then generated $$1.5 \times 10^4$$ synthetic catalogs with 197 $$M_{\lambda } \ge 7.0$$ in each catalog and found the statistical range of $$\beta$$ values. The observed value of $$\beta = 0.83$$ for the CMT catalog corresponds to a p value of $$p=0.004$$ leading us to conclude that the interevent natural times in the CMT catalog are not random. For the time series analysis, we calculated the autocorrelation function for the sequence of natural time intervals between large global earthquakes and again compared with data from $$1.5 \times 10^4$$ synthetic catalogs of random data. In this case, the spread of autocorrelation values was much larger, so we concluded that this approach is insensitive to deviations from random behavior.

Global regionalized seismicity in view of Non-Extensive Statistical Physics

In the present work we study the distribution of Earth’s shallow seismicity on different seismic zones, as occurred from 1981 to 2011 and extracted from the Centroid Moment Tensor (CMT) catalog. Our analysis is based on the subdivision of the Earth’s surface into seismic zones that are homogeneous with regards to seismic activity and orientation of the predominant stress field. For this, we use the Flinn–Engdahl regionalization (FE) (Flinn and Engdahl, 1965), which consists of fifty seismic zones as modified by Lombardi and Marzocchi (2007). The latter authors grouped the 50 FE zones into larger tectonically homogeneous ones, utilizing the cumulative moment tensor method, resulting into thirty-nine seismic zones. In each one of these seismic zones we study the distribution of seismicity in terms of the frequency–magnitude distribution and the inter-event time distribution between successive earthquakes, a task that is essential for hazard assessments and to better understand the global and regional geodynamics. In our analysis we use non-extensive statistical physics (NESP), which seems to be one of the most adequate and promising methodological tools for analyzing complex systems, such as the Earth’s seismicity, introducing the q-exponential formulation as the expression of probability distribution function that maximizes the Sq entropy as defined by Tsallis, (1988). The qE parameter is significantly greater than one for all the seismic regions analyzed with value range from 1.294 to 1.504, indicating that magnitude correlations are particularly strong. Furthermore, the qT parameter shows some temporal correlations but variations with cut-off magnitude show greater temporal correlations when the smaller magnitude earthquakes are included. The qT for earthquakes with magnitude greater than 5 takes values from 1.043 to 1.353 and as we increase the cut-off magnitude to 5.5 and 6 the qT value ranges from 1.001 to 1.242 and from 1.001 to 1.181 respectively, presenting a significant decrease. Our findings support the ideas of universality within the Tsallis approach to describe Earth’s seismicity and present strong evidence ontemporal clustering and long-range correlations of seismicity in each of the tectonic zonesanalyzed.

Characteristics of global strong earthquakes and their implications for the present-day stress pattern

Earthquakes occurred on the surface of the Earth contain comprehensive and abundant geodynamic connotations, and can serve as important sources for describing the present-day stress field and regime. An important advantage of the earthquake focal mechanism solution is the ability to obtain the stress pattern information at depth in the lithosphere. During the past several decades, an increasing number of focal mechanisms were available for estimating the present-day stress field and regime. In the present study, altogether 553 focal mechanism data ranging from the year 1976 to 2017 with Mw \(\ge \)7.0 were compiled in the Global/Harvard centroid moment tensor (CMT) catalogue, the characteristics of global strong earthquakes and the present-day stress pattern were analyzed based on these data. The majority of global strong earthquakes are located around the plate boundaries, shallow-focus, and thrust faulting (TF) regime. We grouped 518 of them into 12 regions (Boxes) based on their geographical proximity and tectonic setting. For each box, the present-day stress field and regime were obtained by formal stress inversion. The results indicated that the maximum horizontal principal stress direction was \(\sim \)N–S-trending in western North America continent and southwestern Indonesia, \(\sim \)NNE–SSW-trending in western Middle America and central Asia, \(\sim \)NE–SW in southeastern South America continent and northeastern Australia, \(\sim \)NEE–SWW-trending in western South America continent and southeastern Asia, \(\sim \)E–W-trending in southeastern Australia, and \(\sim \)NW–SE-trending in eastern Asia. The results can provide additional constraints to the driving forces and geodynamic models, allowing them to explain the current plate interactions and crustal tectonic complexities better.

Estimating the macroseismic parameters of earthquakes in eastern Iran

Macroseismic intensity values allow assessing the macroseismic parameters of earthquakes such as location, magnitude, and fault orientation. This information is particularly useful for historical earthquakes whose parameters were estimated with low accuracy.Eastern Iran (56°–62°E, 29.5°-35.5°N), which is characterized by several active faults, was selected for this study. Among all earthquakes occurred in this region, only 29 have some macroseismic information. Their intensity values were reported in various intensity scales. After collecting the descriptions, their intensity values were re-estimated in a uniform intensity scale. Thereafter, Boxer method was applied to estimate their corresponding macroseismic parameters.Boxer estimates of macroseismic parameters for instrumental earthquakes (after 1964) were found to be consistent with those published by Global Centroid Moment Tensor Catalog (GCMT). Therefore, this method was applied to estimate location, magnitude, source dimension, and orientation of these earthquakes with macroseismic description in the period 1066–2012. Macroseismic parameters seem to be more reliable than instrumental ones not only for historical earthquakes but also for instrumental earthquakes especially for the ones occurred before 1960. Therefore, as final results of this study we propose to use the macroseismically determined parameters in preparing a catalog for earthquakes before 1960.

Centroid moment tensor catalogue using a 3‐D continental scale Earth model: Application to earthquakes in Papua New Guinea and the Solomon Islands

AbstractAlthough both earthquake mechanism and 3‐D Earth structure contribute to the seismic wavefield, the latter is usually assumed to be layered in source studies, which may limit the quality of the source estimate. To overcome this limitation, we implement a method that takes advantage of a 3‐D heterogeneous Earth model, recently developed for the Australasian region. We calculate centroid moment tensors (CMTs) for earthquakes in Papua New Guinea (PNG) and the Solomon Islands. Our method is based on a library of Green's functions for each source‐station pair for selected Geoscience Australia and Global Seismic Network stations in the region, and distributed on a 3‐D grid covering the seismicity down to 50 km depth. For the calculation of Green's functions, we utilize a spectral‐element method for the solution of the seismic wave equation. Seismic moment tensors were calculated using least squares inversion, and the 3‐D location of the centroid is found by grid search. Through several synthetic tests, we confirm a trade‐off between the location and the correct input moment tensor components when using a 1‐D Earth model to invert synthetics produced in a 3‐D heterogeneous Earth. Our CMT catalogue for PNG in comparison to the global CMT shows a meaningful increase in the double‐couple percentage (up to 70%). Another significant difference that we observe is in the mechanism of events with depth shallower then 15 km and Mw &lt; 6, which contributes to accurate tectonic interpretation of the region.