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This study analyzed the Democratic People's Republic of Korea's (DPRK) fourth (DPRK4, 6 January 2016 MW 4.49) and sixth (DPRK6, 7 September 2017 MW 5.2) declared nuclear tests, employing a joint seismic and Interferometric Synthetic Aperture Radar (InSAR) inversion to improve understanding of these events and enhance moment tensor (MT) inversion capabilities. The recent efforts have focused on employing seismic waveform and InSAR geodetic deformation data separately to analyze these and the previous nuclear tests (e.g., Chiang et al., 2018; Myers et al., 2018; Wang et al., 2018). Building upon our previous work (Chi-Durán et al., 2021), we performed a joint regional waveform, first-motion (FM) polarity, and surface displacement inversion, which demonstrated improved source-type discrimination, a revised MT solution with reduced scalar moment uncertainty, and an independently constrained location. In this article, we build on the previous results for DPRK6 by including an analysis using a four-layered velocity model with free-surface topography to compute the near-source static deformation Green's functions. The model consists of a 50 m basalt layer (VP = 2.07km/s, VS = 1.2km/s), a 250 m stratified volcanic deposit layer (VP = 1.73km/s VS = 1km/s), a 700 m weathered granodiorite layer (VP = 2.5km/s, VS = 1.3km/s) and a granodiorite half-space (VP = 5.35km/s, VS = 3.09km/s). The half-space shares the velocity of the regional MDJ2 velocity model (Ford et al., 2010), which has proven effective for waveform inversion in the region. This model considers the range of reported values for various lithologies and weathering effects. Our findings show that using the layered velocity model enhances the recovery of source location and depth for both the explosions by improving fits and reducing uncertainties. The joint inversion also improves source-type discrimination and better constrains the scalar seismic moment necessary for downstream yield estimation. [ABSTRACT FROM AUTHOR]

There has been considerable discussion as to how to assess when non-double-couple (NDC) components of seismic moment tensors represent real source processes. We explore this question by comparing moment tensors (MTs) of earthquakes in three global catalogs, which use different inversion procedures. Their NDC components are only weakly correlated between catalogs, suggesting that they are largely artifacts of the inversion. A monotonic decrease in the NDC components' standard deviation with magnitude indicates increased reliability of the NDC components for larger earthquakes. The standard deviation begins to decrease for large NDC components exceeding 60%, suggesting that they represent real source processes. Randomly generated NDC components with the same mean and standard deviation as in the MT catalogs only reproduce some of this decrease. Thus NDC components of large earthquakes and NDC components that exceed 60% are likely to represent real source processes.

Microseismic source mechanisms in underground mines can provide information about the rock mass response to mining. Conventional approaches to such studies rely upon moment tensor solutions that are susceptible to modeling assumptions and need reliable information about source locations and high-resolution velocity models. We propose the application of unsupervised clustering to group microseismic events into different classes directly from the waveform data such that the events in a specific class have similar source mechanisms. Our method has three main steps, first using spectral decomposition to separate the source terms from the path-receiver contributions in the observed amplitude spectra of events occurring in spatially dense clusters. Second, reducing the number of features from the source spectra using independent component analysis (ICA). Third, applying a Gaussian mixture model (GMM) to the reduced feature matrix to obtain event clusters. To test our method, we generate synthetic waveform data using the receiver network and the recorded microseismic event locations in an underground potash mine in Saskatchewan. Results show the ability of our method to separate events into different classes corresponding to differences in source mechanisms. Application to field data recorded in the mine during February 2021 successfully discriminates between blasts and microseismic events. The data recorded between 1 March and 30 June 2021 that contain microseismic events only are divided into two dominant classes. Using known moment tensors (MT) of some of these events for labeling, we interpret one of the two classes as having dominant double-couple mechanisms as compared to the other which most likely corresponds to the linear dipole-tensile mechanisms. Our method, combined with some expert knowledge such as MT of some larger magnitude events, can offer an assessment of source types of large microseismic populations as often encountered in induced seismicity. • A clustering approach is developed to group microseismic events based on source mechanisms. • The developed method works directly on three-component (3C) waveform data. • It can separate blasts from microseismicity and group events based on source types. [ABSTRACT FROM AUTHOR]

The strong ground motions (GMs) recorded by strong motion networks are significant to increase the accuracy of seismic damage assessment. However, the influence of sensor density on seismic damage assessment remains unclarified. Therefore, a workflow is proposed in this study to quantitatively analyze the influence of sensor density on seismic damage assessment. The scenario-based earthquake simulation method is first used to provide the time history of GM at each location as the ground truth of the analysis. Subsequently, a GM prediction method, namely the interpolation method, is adopted to predict GMs at locations without sensors using measuring data from the limited sensors. Finally, the building scale and region scale seismic damage under different sensor densities are compared to quantitatively analyze the influence of sensor density on seismic damage assessment. A detailed case study for Zeytinburnu District, Istanbul, Turkey, is performed to demonstrate the proposed methods. The findings of this study can provide an important reference for seismic damage assessment and the deployment of strong motion networks. [ABSTRACT FROM AUTHOR]

A seismic network of ten three-component broadband seismographs was deployed in and around Hyderabad city during September–October 2020, which enabled us to record a rare lower-crustal cratonic earthquake of Mw 3.9 that occurred on 25 July 2021 (23:31:01.1) at 35 km depth below the region about 140 km south of Hyderabad city. Utilizing broadband waveforms from this network, we model source parameters and moment tensor solution of this rare event using simultaneous inversion of S-wave spectra and ISOLA software, respectively. The average corner frequency, seismic moment, moment magnitude, stress drop, and source radius are 3.87 Hz, 7.14E + 14 N-m, 3.8, 3.92 MPa, and 229 m, respectively. The modelled mean crustal Q varies from 506 (at VKB) to 4136 (at NLG), with an average of 2182 ± 1178, suggesting lower crustal attenuation below the Hyderabad region. We perform a deviatoric moment tensor inversion of multiple point sources on the band-passed (0.04–0.1 Hz) displacement traces of the Hyderabad event. The best fit is obtained at 35 km centroid depth, with a moment magnitude of 3.9, and a normal dip-slip mechanism with a minor strike-slip component with strike of 169°, dip of 65°, and rake of −113°. The P-axis orients N42°E, which is parallel to the direction of the absolute plate motion direction of the Indian Plate, while the T-axis orients E–W. The occurrence of this earthquake could be attributed to the sudden movement on the almost-vertical plane in the viscous lower crust due to high fluid pore pressure resulting from the presence of CO2-rich mantle fluids. [ABSTRACT FROM AUTHOR]

This paper provides an approximate analysis of quadrilateral slabs having various cases of aspect ratios and boundary conditions based on actual two-way action. Nine slabs with different boundary conditions, each having 11 aspect ratios were analyzed using SAP2000 software, thereafter, robustly validated against mathematical solutions. In this article, the hydrostatic point phenomenon was established as a reference point for identifying the slabs with actual two-way action and as a growth reference for other cases. This allows for the use of growth models for the hydrostatic and deviatoric moment tensors. The innovative selection of the extreme positive point moment facilitates the introduction of materials nonlinearity into the design. The plate shorter dimension was used for moment normalization in both directions to preserve the directional influence of the dimensions and to isolate the hydrostatic phenomenon. Through starting at a point of hydrostatic phenomenon occurrence and via fixing one of the plate's dimensions and extending the other (for any boundary conditions), the extreme point's Mohr circle develops from the hydrostatic point phenomenon as a growth in the hydrostatic component and drastic growth in the deviatoric component. Subsequently, the largest principal moment develops a higher magnitude as the aspect ratio increases. Furthermore, the non-identical boundary conditions on two perpendicular directions result in a deviation of the two-way action. [ABSTRACT FROM AUTHOR]

On November 15, 2019, a sequence of small/micro earthquakes struck specific area near an oil production field in the northern part of the State of Kuwait. Generally, the phenomenon of the earthquakes swarming is rarely occurring in Kuwait. More than 56 earthquakes were monitored by the Kuwait National Seismic Network (KNSN) where the magnitudes of the earthquakes ranged between 0.8 and 4.1, and their recorded continued for two consecutive days. In this respect, we conducted a modern geophysical analysis (e.g. waveform-fitting, spectral analysis and faulting focal mechanism) to identify the nature and origin of these earthquakes. The values of moment tensors, double-couple (DC) and non-double-couple components signature, stress drop, and stress ratios are fundamentally calculated, in addition to detailed knowledge of the structural setting of the region where earthquake swarming occurred were also used to distinguish and estimate natural and anthropogenic components percentages of theses earthquakes. The results obtained indicated that these earthquakes sequence has an equivalent anthropogenic to tectonic component, meaning that it occurred as a result of oil extraction, but also occurred on pre-existing faults. [ABSTRACT FROM AUTHOR]

Intermediate‐depth seismicity beneath the Hindu Kush may reveal the Earth's best example of a stretching blob of mantle lithosphere sinking through the asthenosphere. Seismically, this region is the Earth's most active at intermediate depths (70–300 km). Fault plane solutions show nearly vertical stretching of the region in which the earthquakes occur, and a summation of seismic moment tensors implies that on average material at a depth of 300 km moves downward at ~40 mm/year relative to the overlying crust. As shown by Kufner et al. (2017, https://doi.org/10.1016/j.epsl.2016.12.043) and Zhan and Kanamori (2016, https://doi.org/10.1002/2016GL069603), the central part of the zone stretches so rapidly that this rate there is ~100 mm/year, much faster than the present‐day convergence rate of ~15 mm/year at the surface and across the Hindu Kush. The pattern of stretching, with maximum strain rates in the middle depths of the intermediate‐depth range, resembles that beneath the southeastern Carpathians, where Lorinczi and Houseman (2009, https://doi.org/10.1016/j.tecto.2008.05.024) have shown that seismicity is consistent with a blob of mantle lithosphere stretching rapidly and sinking into the asthenosphere, though more slowly than occurs beneath the Hindu Kush. Key Points: Intermediate‐depth seismicity beneath the Hindu Kush suggests rapid stretching and sinking of mantle lithosphereThis region shows removal of mantle lithosphere in action, better than anywhere [ABSTRACT FROM AUTHOR]

• It is improper to determine the failure nature of macro-crack by using the proportion of micro-cracks (tensile ⧹ shear). • Moment tensor inversion can indicate the forces applied on failure sources and distinguish the nature of primary and secondary cracks. • The failure modes of secondary cracks are complicated, changing from shear to tensile as the cracks propagate. Cracking processes have been extensively studied in brittle rock and rock-like materials. For a better understanding of failure processes, moment tensor is used to distinguish the nature of primary cracks and secondary cracks in a single-flaw-contained specimen based on the bonded-particle model, which can indicate the force applying on the failure source. The results reveal that the primary cracks solely consist of micro-tensile cracks and the failure nature is tensile, while the secondary cracks are composed of both micro-shear cracks and micro-tensile cracks and the failure mechanisms are complicated. The failure mechanisms of acoustic emission (AE) events of the first part of secondary cracks, which initiate from the tips of the pre-existing flaw, are mainly "implosional" and "shear", implying that the unbalance forces applied on the failure source are predominately implosional and shear components after breakage. As the secondary cracks propagate farther, the failure nature of AE event changes to "tensile" mode finally. [ABSTRACT FROM AUTHOR]

The Gulf of Aqaba is one of the most active places around Egypt, with several earthquake sequences having occurred there through ancient and modern times. In the last century, four earthquake sequences took place in the gulf (1983, 1990, 1993, and 1995). Recently, on 27 June 2015, a sequence of 96 earthquakes with local magnitudes ranging from 0.7 to 5.2 was recorded by the Egyptian National Seismological Network (ENSN). On 16 May 2016, another earthquake sequence started and continued for several consecutive days, with 95 events with local magnitudes ranging from 1.6 to 5.5 being centered south of the 27 June 2015 sequence. In this paper, we analyse the complete waveform and polarity data set of both earthquake sequences to determine their focal mechanisms and to update our knowledge of the stress field in the Gulf of Aqaba. Through the results obtained, we conclude that, the Gulf of Aqaba is affected by a primary structure of a left-lateral strike-slip fault with a minor normal component in most segments. Our study also infers the presence of a secondary structure, which is indicated to be a right-lateral strike-slip with a minor reverse component. [ABSTRACT FROM AUTHOR]

We present the revised Time Domain Moment Tensor (TDMT) catalogue for earthquakes with M_L larger than 3.6 of the first month of the ongoing Amatrice seismic sequence (August 24th - September 25th). Most of the retrieved focal mechanisms show NNW–SSE striking normal faults in agreement with the main NE-SW extensional deformation of Central Apennines. We also report a preliminary finite fault model analysis performed on the larger aftershock of this period of the sequence (M_w 5.4) and discuss the obtained results in the framework of aftershocks distribution.

In this study, a three-dimensional model was established to study the failure mechanism of granite after thermal treatment. Firstly, the evolution of micro-cracks and thermal stress in the sample was quantitatively analyzed, and the evolution of acoustic emission events under different stress levels was discussed. Then, combined with moment tensor inversion, the influence of temperature on the failure type of acoustic emission source was determined. The results show that: (1) High temperature increases the anisotropy of rock, and the thermal stress leads to the development of micro-cracks; (2) At 25 °C ∼ 450 °C, the magnitude of acoustic emission events is concentrated in −5.83 ∼ 4.23, and it in this temperature range is characterized of high damage intensity and high release energy. Above 450 °C, the magnitude is concentrated in −5.33 ∼ 6.23, b value changes in 2.1 ∼ 4.11, the development of micro-cracks becomes disordered. There is a negative exponential relationship between acoustic emission events and the number of micro-cracks; (3) The distribution of acoustic emission source types obtained from 2D and 3D models is consistent, the b value obtained by the 2D model is larger than that of the 3D model, which overestimates the temperature damage to the sample's mechanical properties. • The evolution of micro-cracks and thermal stress is quantitatively analyzed. • The failure mechanism of granite is studied based on moment tensor inversion. • The evolution of acoustic emission failure sources under the temperature is revealed. [ABSTRACT FROM AUTHOR]

The ensemble average diffusion propagator (EAP) obtained from diffusion MRI (dMRI) data captures important structural properties of the underlying tissue. As such, it is imperative to derive an accurate estimate of the EAP from the acquired diffusion data. In this work, we propose a novel method for estimating the EAP by representing the diffusion signal as a linear combination of directional radial basis functions scattered in q-space. In particular, we focus on a special case of anisotropic Gaussian basis functions and derive analytical expressions for the diffusion orientation distribution function (ODF), the return-to-origin probability (RTOP), and mean-squared-displacement (MSD). A significant advantage of the proposed method is that the second and the fourth order moment tensors of the EAP can be computed explicitly. This allows for computing several novel scalar indices (from the moment tensors) such as mean-fourth-order-displacement (MFD) and generalized kurtosis (GK)—which is a generalization of the mean kurtosis measure used in diffusion kurtosis imaging. Additionally, we also propose novel scalar indices computed from the signal in q-space, called the q-space mean-squared-displacement (QMSD) and the q-space mean-fourth-order-displacement (QMFD), which are sensitive to short diffusion time scales. We validate our method extensively on data obtained from a physical phantom with known crossing angle as well as on in-vivo human brain data. Our experiments demonstrate the robustness of our method for different combinations of b-values and number of gradient directions. [ABSTRACT FROM AUTHOR]

The main goal of this study is to provide moment tensor solutions for small and moderate earthquakes of the Matese seismic sequence in southern Italy for the period of December 2013–January 2014. We estimate the focal mechanisms of 31 earthquakes with local magnitudes related to the Matese earthquake seismic sequence (December 2013–January 2014) in Southern-Central Italy which are recorded by the broadband stations of the Italian National Seismic Network and the Mediterranean Very Broadband Seismographic Network (MedNet) run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The solutions show that normal faulting is the prevailing style of seismic deformation in agreement with the local faults mapped out in the area. Comparisons with already published solutions and with seismological and geological information available allowed us to properly interpret the moment tensor solutions in the frame of the seismic sequence evolution and also to furnish additional information about less energetic seismic phases. Focal data were inverted to obtain the seismogenic stress in the study area. The results are compatible with the major tectonic domain of the area. [ABSTRACT FROM AUTHOR]

• We compute seismic moment tensors of nine events recorded by InSight on Mars. • Our inversion methodology relies on body waves, secondary phases and surface waves. • Seven seismic events are supposed to be linked to the activity of Cerberus fossae. • Two seismic events are possibly related to the planet thermal contraction. Since early 2019, the InSight mission has proven that Mars is seismically active, with more than 900 seismic events recorded. Among them, several events have characteristics close to terrestrial tectonic earthquakes. Most of these events are located on the major graben system of Cerberus fossae and, a little further north, on the secondary system of Grjotá Valles. In this study, we invert the seismic moment tensors for nine of these tectonic marsquakes characterized by high quality data. Seven of them are located on Cerberus fossae/Grjotá Valles and two of them are located near the Martian dichotomy. The moment tensors allow us to interpret the nature and depth of the seismic sources at the origin of these events. In our approach, we invert the P and S body waveforms, the PP, SS, PPP and SSS secondary phase maximum amplitudes and we look for solutions with surface waves weaker than the Martian noise. From our results on moment tensors, we determine that all our events have been triggered at moderate depths of 15–36 km. We deduce that the seven events located on Cerberus fossae have geometries similar to the fractures and are generated by tectonics. This activity is supposed to result from the reactivation of previous faults and fractures, which would have been initially induced by the propagation of volcanic dikes at depth. The two dichotomy events are due to deep compressive fracturing of the Martian lowlands. They are therefore triggered by the planetary thermal contraction. Our results are in strong agreement with recent studies on the event depths and on the previous moment tensors calculated for two events. [ABSTRACT FROM AUTHOR]

We study acoustic emissions (AEs) associated with shear and tensile failures around a horizontal borehole in a sandstone sample subjected to triaxial stress. The aim is to relate the AE event rate to macroscopic observations of sample deformation and the percentage of isotropic and deviatoric components of the seismic moment tensors to the expected failure mechanisms. The horizontal hole interferes with the applied load and forms a strongly spatially dependent anisotropic stress field, focusing the crack initiation into both shear and tensile failures. The recorded AEs follows reasonably well existing damage models, but the elastic solution of hoop stress does not represent the onset of failure around the borehole. The focal mechanisms correlate with the orientation of macroscopic fractures in the sample. Events close to the borehole show a higher fraction of isotropic percentage in moment tensors compared to events occurring in the macroscopic fracture featuring higher double-couple percentages. The inhomogeneous stress field due to the borehole and the stress induced damage is strongly affecting the axial and radial velocities which in turn affect the waveforms of the recorded AEs and the resulting moment tensors. The VP/VS ratio obtained from the ratio of isotropic to compensated linear vector dipole components of the moment tensors is close to that obtained from ultrasonic velocity measurements. [ABSTRACT FROM AUTHOR]

Based on a 2 year seismic record from a local network, we characterize the deformation of the seismogenic crust of the Pamir in the northwestern part of the India-Asia collision zone. We located more than 6000 upper crustal earthquakes in a regional 3-D velocity model. For 132 of these events, we determined source mechanisms, mostly through full waveform moment tensor inversion of locally and regionally recorded seismograms. We also produced a new and comprehensive neotectonic map of the Pamir, which we relate to the seismic deformation. Along Pamir's northern margin, where GPS measurements show significant shortening, we find thrust and dextral strike-slip faulting along west to northwest trending planes, indicating slip partitioning between northward thrusting and westward extrusion. An active, north-northeast trending, sinistral transtensional fault system dissects the Pamir's interior, connecting the lakes Karakul and Sarez, and extends by distributed faulting into the Hindu Kush of Afghanistan. East of this lineament, the Pamir moves northward en bloc, showing little seismicity and internal deformation. The western Pamir exhibits a higher amount of seismic deformation; sinistral strike-slip faulting on northeast trending or conjugate planes and normal faulting indicate east-west extension and north-south shortening. We explain this deformation pattern by the gravitational collapse of the western Pamir Plateau margin and the lateral extrusion of Pamir rocks into the Tajik-Afghan depression, where it causes thin-skinned shortening of basin sediments above an evaporitic décollement. Superposition of Pamir's bulk northward movement and collapse and westward extrusion of its western flank causes the gradual change of surface velocity orientations from north-northwest to due west observed by GPS geodesy. The distributed shear deformation of the western Pamir and the activation of the Sarez-Karakul fault system may ultimately be caused by the northeastward propagation of India's western transform margin into Asia, thereby linking deformation in the Pamir all the way to the Chaman fault in the south in Afghanistan. [ABSTRACT FROM AUTHOR]

We investigate the seismicity occurred in the Po area, in the period July 2011-June 1012, by means of moment tensor and we use our set of revised focal mechanisms - computed for M> 3.7 earthquakes - to evaluate Coulomb elastic stress changes in order to detect potential intermediate-distance faults interaction, and the main features of this complex structural system.

Abstract: We apply a method for retrieving accurate moment tensors in the acoustic emission (AE) experiments based on the joint inversion of a family of AE events for their moment tensors and for the sensor amplifications including coupling effects between sensors and a specimen. The accuracy and efficiency of the method is tested on AEs recorded during three different temporal stages of a triaxial compression experiment on a cylindrical Bentheim sandstone specimen. The results show improved quality of the moment tensors indicated by significantly lower root-mean-square residuals between observed and predicted amplitudes. The approach is particularly suitable for detailed studies of the source parameters of AE events, to obtain accurate focal mechanisms and seismic moment tensors and for detecting fracturing regime of microcracks. [Copyright &y& Elsevier]

Abstract: The determination of source parameters and full moment tensors in mines is a difficult task, especially, when the velocity model of the mining environment is complex and strongly heterogeneous. The heterogeneities in the velocity model are usually caused by the presence of ore bodies, host rocks, tunnel systems and large excavations due to mining activity. The mined-out cavities introduce strong velocity contrasts in the model, cause multiple scattering of waves and result in a complex wave field with long coda waves. We have analysed five blasts and five induced microseismic events recorded at the Pyhäsalmi ore mine, Finland, and suggest a strategy of successfully inverting for the seismic moment tensors. We compute accurate locations using an eikonal solver and perform the time-domain moment tensor inversion from full waveforms using a generalized linear inversion. Green''s functions are computed using a 3-D finite difference visco-elastic code capable of reproducing complex interactions of waves and structures. To suppress the sensitivity of the inversion to inaccuracies of locations and the velocity model, we analyse the data in the frequency range from 30 to 80Hz. The analysis of blasts and microseismic events proves that the moment tensor inversion is successful. The moment tensors of blasts display a high percentage of positive isotropic components. However, the presence of minor shear faulting triggered during blasting cannot be excluded. On the other hand, the moment tensors of microseismic events display significant negative isotropic and compensated linear vector dipole components. This indicates that the predominant mechanism of the events is probably related to the collapse of rock due to mining activity. [Copyright &y& Elsevier]

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2010. During this period, 407 earthquakes and 85 quarry blasts were detected and located in the region under consideration. With a total of only 19 events with M ≥ 2.5, the seismic activity in the year 2010 was below the average over the previous 35 years. The two most noteworthy earthquakes were the M 3.4 Barrhorn event near Sankt Niklaus (VS) and the M 3.0 event of Feldkirch, both of which produced shaking of intensity IV. [ABSTRACT FROM AUTHOR]

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Abstract: Almost 50,000 long period (LP) events were recorded at Mt. Etna from November 2003 to May 2006. We analysed these events, as well as very long period (VLP) events which were associated with some of them. During some intervals the spectral and wavefield features of LP events remained steady, with significant changes occurring between the intervals. Based on the times of the changes, we distinguish five different sub-periods. In particular, during sub-period III (June–November 2005) the wavefield at the stations nearest to the summit area was composed of P waves. Locations for 150 LP events occurring in sub-period III, determined using radial semblance, changed, at the same time as the events'' spectral features changed. It was during this sub-period that many of the LP events were associated with VLP events. Based on similarity of the waveforms, we distinguished two families of VLP events, with gradually evolving waveforms. The two families are located in slightly different places, but near the sources of the LP events. The change between the families occurred at the same time as the spectra of the LP events changed. Finally the source of the VLP events was investigated by performing complete waveform moment tensor inversion of stacks of the two families. Synthetic Green''s functions for the full moment tensor were calculated for a homogeneous half-space. For both families, the source region with the highest variance reduction lies approximately beneath the active craters, at 500m below the altitudes of the stations. The solutions for both families are very similar with sources that are between 60 and 70% isotropic. Attempts to determine deviatoric moment tensors produced consistently poorer fits. The remaining energy is poorly constrained and is likely to be noise. In conclusion, these results highlight changes in the LP and VLP events at Mt. Etna over time, and the causal relationship between them. [Copyright &y& Elsevier]

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Copyright of Swiss Journal of Geosciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: The INGV-Harvard European-Mediterranean Regional Centroid Moment Tensor (RCMT) Catalog collects solutions routinely computed since 1997 for earthquakes with moderate magnitude () in the Mediterranean region. The database represents an extension to smaller magnitudes of the Harvard global CMT catalog, based on analysis of seismograms recorded at regional distance, and modeling of intermediate period surface waves. The catalog includes about 600 events, 200 of which in the Italian region. This study extends the catalog back in time, for the Italian region, as long as made possible by available digital data – i.e. since 1977 – with the same analysis and inversion method used for current seismicity. As a result, we present here 65 new moment tensors, for years between 1977 and 1997. These solutions represent 45% of the total number of events analyzed, the existing seismograms being often too scarce to allow a stable solution. The new dataset includes events in many seismic zones where moderate seismicity had previously been scarcely documented, e.g., the Po Plain, the Central to Southern Apennines and the Adriatic Sea. The complete dataset, including previously determined RCMTs and CMTs, represents the seismic deformation in the Italian area during the last 25 years. [Copyright &y& Elsevier]

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Copyright of Eclogae Geologicae Helvetiae is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Eclogae Geologicae Helvetiae is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We investigated moment tensors (MTs) of 70 events of the earthquake swarm which occurred in January 1997 in NW Bohemia. A refined location using the master-event procedure shows that all the foci clustered in a volume of less than 0.5 km3 comprising two compact clusters—the southern and northern ones. The results of single-source, absolute-moment tensor inversion of the P- and SH-peak amplitudes reveal two types of the source mechanisms, A and B in our denotation, which dominated in the swarm. Type A implies an oblique normal faulting with a nearly pure double-couple (DC) source. For the B type, an oblique-thrust faulting and a combined source [double-couple combined with the isotropic (ISO) and compensated linear-vector dipole (CLVD) components] are typical. Magnitudes of the non-double-couple components of MT appear unrelated to the ML magnitude of the event. The proximity of hypocentres of A and B events guarantees the non-double-couple source mechanisms of the B events not to be an artefact of a mismodelling of the medium. To exclude finiteness of the focus or station-site effects as possible causes of spurious non-double-couple components of MTs of the B events, the residuals of the peak amplitudes across the set of the B events were analysed and the jack-knife test was applied. The A and B events separate in time and space. Consequently, three major phases of swarm activity can be distinguished. In the first, only the southern cluster was active and A events prevailed, while B events dominated in the northern cluster in the third phase. Both A and B events occurred (the former in the southern cluster, the latter in the northern one) during the second phase. The initiation of the B events in the northern cluster are reflected in a pronounced increase in the non-double-couple components of the MTs, which points to tensile-source mechanisms as a consequence of a hypothesised fluid injection. [Copyright &y& Elsevier]

The Mediterranean region is seismically very active and undergoing rapid deformation. Earthquakes as strong as M≥6 are present, but relatively rare. On the other hand, moderate-magnitude seismicity (4.5) is widespread and, often, damaging. An improved knowedge of moderate-magnitude earthquakes can contribute significantly to a better understanding of active tectonics in the region. Harvard centroid-moment tensors (CMT) today represent the most widely used reference for reliable source mechanisms, but modelling seismic sources with the CMT technique for earthquakes with magnitude less than M≈5–5.5 is quite difficult. Since 1997, we are using an extension of the standard CMT algorithm to compute regional centroid-moment tensors (RCMT) for moderate-magnitude earthquakes (MW as low as 4.0), analyzing intermediate-period surface waves from regional and teleseismic seismograms. We routinely apply the algorithm to European–Mediterranean seismicity to produce a catalog of seismic moment tensors for events with magnitude between 4.5 and 5.5, which generally are not included in the Harvard CMT catalog. In this paper, we show the results for earthquakes that occurred between 1997 and 2000, consisting of 252 solutions, and we discuss the characteristics of the catalog and the areas where these new data are most relevant. [Copyright &y& Elsevier]

The 1976 Friuli seismic sequence is known for itscomplexity, with several unusually large aftershocksoccurring in the epicentral area. The source region, where the northeastern part of the Alpine chain meetsthe northern Dinaric chain, is characterized by a complexcompressional tectonic regime. Previous studies have not clearly identified which of the two main tectonic systems was activated, in part due to the limited precision of derived earthquake parameters, such as hypocentral coordinates and focal mechanisms. We review the locations for the 10 largest events of the sequence, including theSeptember 16, 1977 and April 18, 1979 earthquakes andwe compute their centroid moment tensors. Source parameters are calculated using intermediate period surfacewaves and the modification of the Harvard centroid-moment tensoralgorithm proposed by Arvidsson and Ekström (1998). A summary of all available geological, geodetic and seismological data show that most of the earthquakes may be associated with the Periadriatic overthrust and other related thrust faults. Based on their locations and focal mechanisms only two ofthe early aftershocks (May 7, 1976 and May 9, 1976) appear instead to have occurred on Dinaric structures. [ABSTRACT FROM AUTHOR]

In this paper, a new method is presented for 3D motion estimation by image region correspondences using stereo cameras. Under the weak perspectivity assumption, we first employ the moment tensor theory (Cyganski and Orr) to compute the monocular affine transformations relating images taken by the same camera at different time instants and the binocular affine transformations relating images taken by different cameras at the same time instant. We then show that 3D motion can be recovered from these 2D transformations. A space time fusion strategy is proposed to aim at robust results. No knowledge of point correspondences is required in the above processes and the computations involved are linear. To find corresponding image regions, new affine invariants, which show stronger invariance, are derived in term of tensor contraction theory. Experiments on real motion images are conducted to verify the proposed method. [ABSTRACT FROM AUTHOR]