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On September 27, 2003, the destructive Chuya (Altai) earthquake (magnitude 7.3), the strongest earthquake among those recorded in 1991–2022 in continental Russia, occurred near the southwestern border of the Chuya and Kurai basins in southeastern Altai. We have analyzed the seismic activity of this area and compiled the scheme of neotectonic stresses of the Chuya–Kurai Basin and adjacent structures. The modern and neotectonic stresses of southeastern Altai have been compared. The neotectonic stresses are retrieved using the structural-geomorphological method of shear stress reconstruction. It has been found that the orientation of the subhorizontal compression axis of the first rank changes from meridional to NNE and NE. The earthquake occurred in the region within which the largest faults of rank I (Kurai and Shapshal), SSW part of the prerecent Charysh–Terekta fault (we combine it at the neotectonic stage with the fault bounding the Chagan–Uzun block from the southeast in a common regional fault of rank I) were activated at the neotectonic stage in an setting of additional compression. A larger-scale stress field has been also reconstructed for the Chagan–Uzun rigid block that delineates the Chuya and Kurai basins. The neotectonic fault of the NW strike bounding the Chuya and Kurai basins from the southwest has been identified. The fault, we notionally called Bezymyannyi, is divided by smaller faults of SE orientation into three segments and is included in the large South Chuya fault zone. According to the data on strong earthquake focal mechanisms in the investigated region, a stable subhorizontal position of the compression axis has been established (as well as at the neotectonic stage). It is accepted that strong earthquakes occur in a compression setting. The mechanisms of earthquakes (mostly, aftershocks) related to the Chuya event indicate the concentration of thrust mechanisms within the Chagan–Uzun elevated block. This may be due to the ongoing uplift of the Chagan–Uzun block at the current stage. Along the Bezymyannyi fault, the earthquake focal mechanisms are mostly shear-type. This is the result of formation of a shear field under the shear displacement along the fault during the earthquake. Major seismic events occur mainly in a compression setting. Thus, the Chuya earthquake is caused by a subhorizontal compression setting (both regional and local), which is determined by comparing the neotectonic and modern stresses. [ABSTRACT FROM AUTHOR]

Based on the analysis and interpretation of gravity and magnetic field anomalies, we studiedthe peculiarities of fault tectonics, structural-tectonic structure (including salt dome tectonics) of the Transcarpathian trough. We identified signs of the manifestation of deep faults and other large structural-tectonic elements in anomalies of gravity and magnetic fields. We then traced these structural-tectonic units by comparing the morphology, intensity, dimensions, and directions of the typical anomalous zones in the gravitational and magnetic fields with the tectonic structure of the region. We used digital maps of gravitational and magnetic fields; averaging transforms and relief-shadow images, we mapped local gravimagnetic anomalies. Analysis of the spatial structure of the original gravimagnetic fields and their transforms and structural-tectonic maps yielded a reflection of large tectonic elements of fault tectonics, anticlinal and salt dome structures in the gravimagnetic fields. Based on gravimagnetic data, the tectonic structure of the Transcarpathian trough was clarified, and the boundaries of tectonic zones and microplates were traced. The zone of the Transcarpathian deep fault is identified as a tectonic zone traced by a band of intense local positive anomalies of the gravity field along the Flysch Carpathians to the border of the Marmarosh massif. It is limited by high gradients from the southwest and northeast and is a reflection of the Pieniny and Marmarosh rock zones. The zone of the Transcarpathian deep fault is considered a suture zone of the Inner and Flysch Carpathians. In the structure of the anomalous gravity field of the Transcarpathian trough, a number of local anomalies associated with salt stocks, as well as individual anomalies, expected to be connected to salt-bearing deposits, werefound. We confirmed the effectiveness of gravimagnetic methods in the geological conditions of the Transcarpathian trough to detect anticlinal structures, basement protrusions, which create favorable conditions for oil and gas traps in sedimentary strata. Interpreting anomalous gravimagnetic fields in combination with geological and tectonic materials is an important condition for the integral process of studying the geological and tectonic structure of the Earth’s crust in the Transcarpathian region.

Purpose. Studying the tectonic features of the structure of the earth’s crust of Kryvyi Rih-Kremenchuk suture zone to clarify the nature of the origin of seismic events in the Kryvbas. Methodology. To analyze and generalize the data on the Kryvbas seismicity with reference to large-scale geological and tectonic maps of exploration work. To study its tectonic structure based on geological, geophysical studies and drilling of Kryvyi Rih superdeep well. Findings. In the period 2011–2021, about 1,200 seismic events were recorded on the territory of Kryvbas, the majority of which had a minor magnitude ≥ 2.0. Among them there were identified 13 powerful industrial explosions from mb = 2.7–3.5 and 20 earthquakes of tectonic origin with mb = 2.1–4.5. Powerful explosions in mines predominantly induce earthquakes. In recent years, local earthquakes began to occur in tectonic fault zones outside the ore mining area, which indicates a change in the elastic-deformation state of the geological environment. The analysis of the attributes of local earthquakes and their locations suggests that Kryvyi Rih tectonic system and the entire eastern flank of the earth’s crust of the West Inhulets-Kryvyi Rih-Kremenchuk suture zone are geodynamically active structures, where the processes of thrust and shear tectonics are also observed on a recent geological time scale. Originality. A detailed analysis of the earthquakes shows that some of them occur at significant depths in the zones of tectonic faults outside of Kryvbas. At the same time, faults in separate directions are activated, where brittle deformations and viscousplastic formations are manifested in the past geological time. The location of local earthquakes made it possible to single out two sections and five linear zones of seismic activity in the region. Practical value. Based on the results from this research it is possible to create an applied model of the tectonic section of the earth’s crust to solve the problems of evolution and geodynamics of the lithosphere of the Ukrainian shield, mountain geology and to optimize mining. The identified faults of active inherited development are important in determining the development paths for quarries and mines in Kryvbas. [ABSTRACT FROM AUTHOR]

A set of tectonophysical methods has been applied to reconstruct the neotectonic stresses of the southeastern Altai Mountains within the Chuya–Kurai depression and its framing structures. It is suggested that at the neotectonic stage, the tectonic structures of the Altai Mountains underwent a transformation of geodynamic conditions—a situation of sublatitudinal horizontal compression with predominant reverse-fault and transpressional movements along faults that existed up to the Neogene was replaced by horizontal shear conditions with a NNE and NE subhorizontal compression axis and WNW and NW extension axis. With such a stress field, the dominant NW-trending faults in this territory are mainly characterized by dextral strike-slip displacements, and NE-trending faults, by sinistral. Submeridionally trending faults that formed at the neotectonic stage show clear signs of extensional structures. A feature of the faults of the Chuya–Kurai depression according to these studies is a fairly small number of megafractures (indicators of shear displacements) in shear zones. This indicates dominant reverse-fault and transpressional movements over large disjunctive structures in the region in the Paleozoic and Mesozoic versus neotectonic shear movements. The results of the research are of practical importance in studying the regional seismicity. [ABSTRACT FROM AUTHOR]

A density modeling of the north-western shelf of the Black Sea along 31°20’ E was carried out. According to its results, a complex block structure of the area is determined, which is closely connected with the history of its development. Signs of Baikal tectonic activation of the southern edge of the pre-Riphean Eastern European platform, as well as the adjacent part of the Scythian plate have been revealed. Areas formed during the Hercynian and Cimmerian epochs of tectogenesis have been identified within the Scythian plate. At the base of the Karkinit Trough, two areas of reduced crust resulting from riftogenesis with varying degrees of intensity of basification have been established. Two ancient volcanos of ryolite composition were found on the basement surface on the northern slope of the Kalamit swell. It is highly probable that the Gamburtsev uplift is an eastern extension of the Gubkin swell. According to the structure and value of the calculated densities, it is established that the Gamburtsev uplift is a «blind» mud volcano, which was formed during the second stage of the late Cimmerian cycle and was active throughout the Cretaceous period. A detailed analysis of the deep structure and fault tectonics of the local structures of the sedimentary cover in the intersection of the profile and the area of gas seeps was carried out. It was found that the Flangova, Partizanska and Hamburtseva structures are more promising for hydrocarbon accumulation. The hydrocarbon potential of the Ushakov structure (H-41) is questionable, because structurally and tectonically it is analogous to the Delphin structure, which was deemed unproductive based on drilling results. The area of gas seeps was found to be confined to a mantle fault, which separates two blocks with distinctly different structures and Meso-Cenozoic evolution of the Earth’s crust. It is proposed to conduct a detailed seismic survey in this area in order to identify local structures in the sedimentary cover, promising for hydrocarbons.

Long-period magnetotelluric soundings were carried out in the eastern part of the Fore-Sudetic Monocline in central Europe to determine the deep geoelectrical structure. It is an important area in the contact zone of the Palaeozoic terranes of Western Europe and the Proterozoic East European Craton. The research area includes the Dolsk fault zone and the Odra fault zone, which are essential geological boundaries of a regional nature separating crustal blocks of various origins. There were conducted 51 soundings on the quasi-regular mesh 150 km in SE and 225 km in NE. The research region is highly urbanized, and hence some of the data were strongly disturbed. Careful processing of data was required, and sometimes measurements had to be repeated at other locations. The collected data allow constructing 3-D models of the electrical conductivity distribution. A parallel version of the ModEM 3-D inversion code was used for modelling. The information contained in each used transfer function was also examined by performing a separate inversion of these functions. The obtained resistivity distribution models confirm the Dolsk and Odra faults' location as postulated previously by geologists. They also show that these very deep faults are reaching the lower crust. However, they do not clearly state how far the contemporary lowering of the Baltica reaches under cover of younger Palaeozoic sediments. [ABSTRACT FROM AUTHOR]

This paper is concerned with spatial relationships between seismic zones in the eastern Priamurye region (М ≥ 5) on the one hand and, on the other, regional faults and zones of hidden faults as indicated by axes of gravity and magnetic anomalies. The seismoactive zones where М ≥ 5 earthquakes occurred are mostly confined to regional faults, while there are two cases where no such relationship has been detected. Seismic zones are observed both at intersections of regional faults and at intersections of regional faults with hidden faults of different rank. The seismic zones comprise inclined and subvertical deep-seated faults as identified by deep seismic sounding (DSS), the earthquake converted wave method (ECWM), and magnetotelluric sounding (MTS) surveys. The seismoactive zones were studied by geophysical techniques to identify indication of fluid saturation, as follows: the seismoactive faults frequently control low velocity and low resistivity inhomogeneities in the Earth's crust and upper mantle; some seismoactive faults have displaced the Moho interface; there are dome-shaped flexures of crustal interfaces and of the Moho interface; and the crust is found to contain numerous conversion interfaces. The deep occurrence of seismoactive faults and the indications of fluid saturation suggest that the seismoactive faults in the eastern Priamurye region provide supply of fluids from the mantle to the crust. [ABSTRACT FROM AUTHOR]

The publication presents stress determinations from geological and kinematical indicators of tectonic stress fields, varying in ranks, for the Kola Peninsula. The objective is to determine possible mechanisms of formation of recent structures in the eastern segment of the Baltic shield and to forecast seismogenic and technogenic hazard of fracturing.The study is focused on the Kovdor and Khibin Paleozoic alkaline-ultrabasic blocks. Tectonic stresses are reconstructed by M.V. Gzovsky’s method [1954; 1975] based on identification of conjugated shear systems. Neotectonic stresses are studied by the kinematic method [Gushchenko, 1979] on the basis of measurements of tectonic displacment vectors from slickensides (Figure 2). Local stress data processed by the method for determination of general stress fields provide for reconstruction of main normal stresses which are arbitrarily considered as regional stresses [Sim, 1980; 2000]. This study uses the method of bandpattern distribution of fracturing in fault zones [Danilovich, 1961] which determines the main displacement line on the fault plane.The study of the Zhelezny mining site (Kovdor block, Figures 3 and 4) revealed that elements of fractures of two different ages (centroclinal fractures of the prototectonic genesis and fractures of later tectonic activation) are spatially overlapping due to rock collapse and lacking stability of benches. Numerous inversions and changes of kinematics of relative displacements were reviewed. It was observed that the southeastern wall of the quarry collapsed due to local extension (Fig. 6Band Photos 1 and 2), and a large fault, i.e. a prototectonic fracture, was dipping towards the quarry. Based on the analyses of local stresses at various points of the quarry (Table 1), two ‘regional’ stress fields can be revealed (Figures 7 and 8). The first paleostess field was associated with reverse faults of the WNW subhorizontal axis of compression and the steeply dipping axis of extension. The second field was related to shear faults; its axis of compression maintained the WNW orientation, while the extension axis was reoriented, and the axis of extension attained submeridional position and a less steep dip. The second field is younger as suggested by traces of two displacements identified on several planes, the youngest of which are shears.From the analysis of measurements taken at 273 planes with striations, it is evident that striations are distributed in a bandshape pattern. The band of fractures is coincident with the plane of the transition axis of the young ‘regional field (Figure 9); main maximums of density of the planes with striations are symmetrically scattered in a fanlike pattern from the axis of compression and extension of this field. Generally, the striations reflect traces of younger displacements, and their consistency with the axes of the young field supports our conclusions on age relationships between the two ‘regional’ fields. Four major stages of deformation of the Kovdor block under study are distinguished by analyses of the tectonic stresses (Figure 10).Within the limits of the Khibin block, 14 local states of stresses are reconstructed for three mining sites (Table 2, Figure 11). At the Central mining site, reindexation of local axis of compression and extension in the fault wings give evidence of the fault activity during the neotectonic stage (Figure 13). The ‘regional’ stress field of the Khibin block is associated with a reserve fault with lowangle NNW orientation of the axis of compression (Figure 14). The tectonophysical studies conducted at the mining sites of the Kola Peninsula give grounds to conclude that activity of faults, which positions are different at the mining sites, is variable, depending on orientations of the faults against the youngest ‘regional’ main stress. From sets of indicators, a relative age of the revealed ‘regional’ fields of stresses is accepted as neotectonic and recent.For the segments of the Kovdor block under study, four phases of deformation are distinguished, including two early phases revealed by structural indicators, and two last phases revealed from orientations of the axes of the main stresses in the reconstructed ‘regional’ fields. The reverse field of stresses of Deformation Phase 3 (which is a more ancient ‘regional’ field according to reconstructed tectonic stresses) at the Kovdor block and the reversefault field at the mining sites of the Khibin block may reflect a phase of brittle deformation of the rocks after the blocks were exposed to the day surface. Since then the deformation mechanisms might have been determined by two factors which controlled subhorizontal compression: residual gravity stresses in considerably eroded magmatic bodies as ‘recollections’ of being subject to constraint environment at depth [Rebetsky, 2008], and the impact of rifting in the Northern Atlantics. The fact that the neotectonic ‘regional’ stress field of the Kovdor block is fully similar to that of the Central Karelia (Figure 1) give grounds to conclude that the mechanism of deformation of the block under study might have been controlled by both factors. The Khibin block has a lopolithic shape which gradually converts into a centraltype conic structure with depth. It should thus be squeezed upward by the impact of horizontal compression of any genesis, as evidenced by the subvertical extension axis of the general field of the Khibin area and the recent topography as the highest mountains of the Kola Peninsula are located in the block under study.

The western part of the Bohemian Massif hosts an intersection of two regional fault zones, the SW-NE trending Ohře/Eger Graben and the NNW-SSE trending Mariánské Lázně Fault, which has been reactivated several times in the geological history and controlled the formation of the Tertiary Cheb Basin. The broader area of the Cheb Basin is also related to permanent seismic activity of ML 3+ earthquake swarms. The Eastern Marginal Fault of the Cheb Basin (northern segment of the Mariánské Lázně Fault) separates the basin sediments and underlying granites in the SW from the Krušné Hory/Erzgebirge Mts. crystalline unit in the NE. We describe a detailed geophysical survey targeted to locating the Eastern Marginal Fault and determining its geometry in the depth. The survey was conducted at the Kopanina site near the Nový Kostel focal zone, which shows the strongest seismic activity of the whole Western Bohemia earthquake swarm region. Complex geophysical survey included gravimetry, electrical resistivity tomography, audiomagnetotellurics and seismic refraction. We found that the rocks within the Eastern Marginal Fault show low resistivity, low seismic velocity and density, which indicates their deep fracturing, weathering and higher water content. The dip of the fault in shallow depths is about 60° towards SW. At greater depths, the slope turns to subvertical with dip angle of about 80°. Results of geoelectrical methods show blocky fabric of the Cheb Basin and deep weathering of the granite bedrock, which is consistent with geologic models based on borehole surveys. [ABSTRACT FROM AUTHOR]

Based on the analytical study of V. G. Chuvardinsky’s monographs on the revision of the generally accepted glacial theory, the authors of the review concluded that there was convincing evidence of a fault-tectonic origin of ‘ice-exaration’ relief of the Baltic Shield. Developed by Chuvardinsky, a radically new methodology of boulder prospecting of ore deposits not only refuted the old glacial theory, but also led to the discovery of copper-nickel deposits, a new apatite alkaline massif, promising manifestation of copper-nickel ore, platinum group metals, native gold, chromite and other mineral resources. A thorough drilling of ice sheets in Greenland and Antarctica for the international project determined the absence of boulder material over the entire thickness of the ice, only pulverulent and fine particles (mainly volcanic ash) were found in the ice. Bottom ice layers are immobilised, their function is preservation of the geological surface. V. G. Chuvardinsky far outstripped western and Russian scientists in the field of Earth Sciences. His field studies on the Baltic Shield not only refuted the mighty glacial theory, but also created and substantiated a new geological concept instead. Professor V. Z. Negrutsa was quite right when he wrote in his review on Chuvardinsky’s work (journal Geomorfologiya, 2003, no. 1), ‘Evidence of Chuvardinsky about tectonic origin of geological and geomorphological features traditionally associated with the Quaternary glaciation is so obvious and reproducible both by field observations and by geological modeling that is presented irrefutable and undeniable in its essence’. In general, assessing the scientific significance of V. G. Chuvardinsky’s works, it can be stated that his work would have done honour to research institutes of geological and geographical orientation according to the level of study of the geological material and the value of his field studies. His books present the material for several doctoral theses. Radiocarbon dating of fossil organic residues excluded continental glaciation of Fennoscandia as well as Eurasian plains. The glacial theory is hopelessly outdated but now it is continuing its leadership functioning.

Highlights: [•] The classical Mid-Cretaceous tectonic űcrisisƇ of Tunisia is actually mainly of Albian age. [•] Synsedimentary deformations increased throughout the Early to Middle Albian. [•] Extensional deformation preceded and triggered halokinetic movements. [•] This Albian tectonics was related to the opening of the equatorial Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Geodynamic activity in the area of West Bohemia is typified by the occurrence of earthquake swarms, Quaternary volcanism and high flux of mantle-derived CO. The highest swarm activity occurs beneath the eastern edge of the Cheb basin, which is delineated by the NW-SE trending morphologically pronounced Mariánské Lázně Fault (MLF) controlling the formation of the basin. The previous trenching survey across the MLF zone has identified several fault strands with possible Quaternary activity. In this paper we present the results of the geophysical survey focused to trace the faults signatures in geophysical sections and to build an image of near surface tectonics. The method of electric resistivity tomography (ERT) along two profiles parallel to the trench identified a strong resistivity contrast between the bodies of sandy gravels in the middle and conductive clayey sands to the west and weathered crystalline basement to the east. The 2-D ground penetration radar (GPR) sections show direct correlation of reflections with lithological boundaries identified in the trench. As expected, the GPR signal amplitudes increase with the resistivities found in the ERT sections. Two of the four faults identified in the trench are indicated in the resistivity and GPR sections. A 3-D GPR measurement has identified a spot of high amplitudes elongated parallel to the MLF trend, which coincides with the high resistivity body. To improve the signal-to-noise ratio of the time slices we stacked the GPR time slices within vertically homogeneous blocks. This provided a contrast image of the sand-gravel body including its boundaries in three dimensions. The detailed analysis of the 3-D GPR cube revealed additional fault that limits the highly reflective sands and appears to be offset by another younger fault. Our results suggest a complex fault pattern in the studied area, which deserves a further study. [ABSTRACT FROM AUTHOR]

This paper considers the geological structure, geodynamics, and seismicity of the Tan Lu-Okhotsk rift system, which includes the Bohai Wan, Liaohe, Khanka, Middle Amur, and Lower Amur basins. The basins have common regularities typical of rift zones but differ in the deep structure and physical parameters of their crust, in particular, in the distribution of the strength properties, which also affect the seismicity level. It was established that the level and type of seismicity in the rift system is mainly determined by the local geodynamic conditions. [ABSTRACT FROM AUTHOR]

Magnetic anomaly data are presented from a new helicopter-borne high-resolution aeromagnetic survey in southern McMurdo Sound. Anomaly data have been acquired at a common 305 m elevation above the McMurdo and southern McMurdo ice shelves and draped over the volcanic islands that pin them. The resulting anomaly patterns provide a significant advance in the understanding of the rift related geology beneath the floating ice shelves. More extensive Erebus Volcanic Province (McMurdo Volcanic Group) rocks are indicated along with a significant blanket of glaci-volcaniclastic sediment on the seafloor between the volcanic islands in southern McMurdo Sound. These glaci-volcaniclastic sediments are inferred to originate from former grounding of the southern McMurdo Ice Shelf as a marine ice sheet. A strong N–S fabric is also observed in the anomaly data suggesting that the rift structure observed in the Victoria Land basin persists to the south beneath the McMurdo and southern McMurdo ice shelves. W–N–W transfer faults identified within the Transantarctic Mountain rift flank to the west are not obvious in the aeromagnetic data set, implying that the ‘Discovery Accommodation Zone’ may be restricted to the region between a southward extension of the range bounding fault that marks the limit of the Victoria Land Basin and the right lateral offset in the Transantarctic Mountain front in southern Victoria Land. [ABSTRACT FROM AUTHOR]

We present here a detailed analysis of a seismic data set recorded by a dense seismological network installed over 6 months in the southeast of France. This experiment was set-up at the boundary between the Ligurian basin and the southern subalpine thrust belt (the Nice arc), which is a complex tectonic region that undergoes low to moderate seismicity. We recorded more than 500 microearthquakes, among which 348 occurred exactly in the centre of the network during a very active seismic sequence that lasted mainly over 2 months. We performed an absolute location of all of the events and calculated the magnitudes. Then we applied a cross-correlation technique to gather similar events and to relocate relatively few of them. This method revealed a very clear alignment of 19 events in a direction N120° oblique to the N20° general trend of seismicity. Focal mechanisms were determined for the four largest events and composite solutions for 32 smaller ones. Both the alignments of the earthquakes and the focal solutions revealed that two oblique segments of the fault were activated during the crisis. The main segment (8 km long) that was oriented NNE with a left-lateral strike slip movement is called the Blausasc fault. Taking into account the tectonic evolution and the relationships between surface structures and the distribution of earthquakes, and through a paleaoreconstruction of the tectonic evolution, we propose that the Blausasc fault is the hidden root of the Peille-Laghet fault, which has a mapped length of at least 15 km. The smaller segment (0.6 km long) that was activated during the crisis could be interpreted as an antithetic Riedel fracture. The active Blausasc fault is located in a densely populated zone, at only 10 km from the crowded cities of Monaco and Nice. It is thus particularly interesting to analyse it for hazard assessment. In the last section, we present a simulation that is aimed at predicting what the ground motion in the city of Nice would be like if an earthquake of magnitude 5.7 occurs on this fault. For this, we used the recordings of the largest event of the seismic sequence ( Ml= 3.2) and an empirical Green's function summation scheme to simulate the ground motion at two stations situated in urban environments. The values obtained show that especially on soft soil sites, the effects of such an earthquake would be considerable in the city of Nice. [ABSTRACT FROM AUTHOR]

The misfit angles between observed and theoretical slip directions are important in evaluating the reliability of the solution to a stress tensor inversion. The distance between stress tensors is also essential for evaluating the resolution of a method of separating stresses from heterogeneous fault-slip data. Here, we define ‘angular stress distance’ for this purpose. This new method has the attribute of improved distance measurements compared with existing methods. The value of angular stress distance is equivalent to a number of important properties. First, the distance between the correct and optimal stresses for a data set approximates the mean misfit angle. Secondly, when we evaluate the dispersion of reduced stress tensors obtained via a bootstrap or other resampling technique, the value of the dispersion evaluated with the mean distance of the tensors from the optimal solution is approximately equal to the noise level of the data. Thirdly, the distance is equal to the Lode angle difference of the stresses if they have common principal orientations. We demonstrate that stresses cannot share common principal axes if their distance is greater than a certain threshold value. The relationships among the distances that have been proposed for reduced stress tensors are also discussed. [ABSTRACT FROM AUTHOR]

We examine the expected elastic and inelastic strain accumulation and release across the transpressive Alpine Fault of New Zealand using a finite element model, which incorporates a frictional fault and material behaviour in the crust based on geophysical measurements and rock mechanics experiments. A zone of localized ductile creeping is predicted beneath the part of the fault that slips seismically. Localized creeping results from (a) thermal weakening along the fault ramp and (b) enhanced stresses due to interaction with the shallow, brittle fault above. The creeping zone controls the shorter-wavelength feature seen in the GPS-determined surface velocities. Using the model we show that: (1) seismic faulting loads the creeping shear zone elastically, transferring stress to the mid-crust, and enhancing creep localization in the lower crust; (2) seismic loading and additional thermal weakening, due to long-term advection and exhumation of rocks along the Alpine Fault, can explain the shallow depth and localization of creeping below the Alpine Fault several hundred years after an earthquake and (3) model surface velocities are in good agreement with present-day velocities determined from campaign GPS measurements. Model strain rates show a transient response after faulting that lasts for the first ca. 20 per cent of the interseismic period ( ca. 100 yr), with a gradual broadening in the surface velocity signal and almost constant strain rates thereafter until the next faulting event occurs. [ABSTRACT FROM AUTHOR]

Abstract: To estimate the deep structure of the southern part of the Nojima Fault, southwest Japan without the influence of near-surface structures, we analyzed the Love-wave-type fault-zone trapped waves (LTWs) recorded by a borehole seismometer at 1800m depth. We examined the polarization, dispersion, and dominant frequency of the wavetrain following the direct S-wave in each seismogram to identify the LTW. We selected eight candidates for typical LTWs from 462 records. Because the duration of the LTW increases with hypocentral distance, we infer that the low velocity fault-zone of the Nojima Fault continues towards the seismogenic depth. In addition, since the duration of the LTW increases nonlinearly with hypocentral distance, we infer that the S-wave velocity of the fault-zone increases with depth. The location of events showing the LTW indicates that the fault-zone dips to the southeast at 75° and continues to a depth of approximately 10km. We assumed a uniform low-velocity waveguide to estimate the average structure of the fault-zone. We estimated the average width, S-wave velocity, and Q s of the fault-zone by comparing an analytical solution of the LTW with measured data. The average width, S-wave velocity, and Q s of the fault-zone are 150 to 290m, 2.5 to 3.2km/s, and 40 to 90, respectively. Hence the fault-zone structure with a larger width and smaller velocity reduction than the fault-zone model estimated by previous surface observation is more suitable to represent the average fault-zone structure of the Nojima fault. The present study also indicated that the shallow layers and/or a shallow fault-zone structure drastically changes the characteristics of the LTW recorded at the surface, and therefore cause a discrepancy in the fault-zone model between the borehole observation and surface observation. [Copyright &y& Elsevier]

An important task of seismic hazard assessment consists of estimating the rate of seismic moment release which is correlated to the rate of tectonic deformation and the seismic coupling. However, the estimations of deformation depend on the type of information utilized (e.g. geodetic, geological, seismic) and include large uncertainties. We therefore estimate the deformation rate in the Lower Rhine Embayment (LRE), Germany, using an integrated approach where the uncertainties have been systematically incorporated. On the basis of a new homogeneous earthquake catalogue we initially determine the frequency–magnitude distribution by statistical methods. In particular, we focus on an adequate estimation of the upper bound of the Gutenberg–Richter relation and demonstrate the importance of additional palaeoseismological information. The integration of seismological and geological information yields a probability distribution of the upper bound magnitude. Using this distribution together with the distribution of Gutenberg–Richteraandbvalues, we perform Monte Carlo simulations to derive the seismic moment release as a function of the observation time. The seismic moment release estimated from synthetic earthquake catalogues with short catalogue length is found to systematically underestimate the long-term moment rate which can be analytically determined. The moment release recorded in the LRE over the last 250 yr is found to be in good agreement with the probability distribution resulting from the Monte Carlo simulations. Furthermore, the long-term distribution is within its uncertainties consistent with the moment rate derived by geological measurements, indicating an almost complete seismic coupling in this region. By means of Kostrov's formula, we additionally calculate the full deformation rate tensor using the distribution of known focal mechanisms in LRE. Finally, we use the same approach to calculate the seismic moment and the deformation rate for two subsets of the catalogue corresponding to the east- and west-dipping faults, respectively. [ABSTRACT FROM AUTHOR]

The major bends of the San Andreas fault in California are associated with significant variations in the along-fault topography. The topography-induced perturbations in the intermediate principal stress may result in the rotation of the fault with respect to the maximum compression axis provided that the fault is non-vertical, and the slip is horizontal. The progressive fault rotation may produce additional topography via thrust faulting in the adjacent crust, resulting in a positive feedback. The observed rotation of the fault plane due to the along-fault variations in topography is used to infer the magnitude of the in situ differential stress. Our results suggest that the average differential stress in the upper crust around the San Andreas fault is of the order of 50 MPa, implying that the effective fault strength is about a factor of two lower than predictions based on Byerlee's law and the assumption of hydrostatic pore pressure. [ABSTRACT FROM AUTHOR]

In order to estimate the averaged fault zone structure, i.e. the width, shear wave velocity andQs of the Mozumi-Sukenobu fault, central Japan, we analysed the Love-wave-type fault zone trapped waves recorded by a seismic array deployed in a subsurface survey gallery. We selected the typical Love-wave-type trapped waves based on the characteristics of dispersion, amplitude, apparent velocity and the polarization of wave trains following the direct shear wave. We selected nine events showing typical Love-wave-type trapped waves from 154 earthquakes. Epicentres of the events were located along the surface trace of the Mozumi-Sukenobu fault. The nine events showing trapped waves were found to be located in a plane dipping to the south at an angle of approximately 75° to 85°. The duration of the fault zone trapped waves increase non-linearly with the increase of hypocentral distance. This result implies an increase in shear wave velocity of the fault zone with depth and/or horizontal distance from the array. In order to obtain averaged fault zone structure from hypocentre to receiver, we assumed fault zone structure to be a 2-D uniform low-velocity waveguide, and modelled the dispersion curve and the waveform of trapped waves using an analytical solution. The width, shear wave velocity andQs of the fault zone were estimated to be 160 to 400 m, 2.9 to 3.1 km s−1 and 60 to 90, respectively. The width of the fault zone estimated in this analysis is consistent with the width of the extent of fault zone at the survey gallery. We also conducted 3-D finite difference simulation (3-D FDM) on fault zone trapped waves using depth-dependent structure models referred to the 2-D averaged structure, indicating the possible depth-dependent structures. The 2-D modelling is useful as an initial guide to the 3-D imaging of a fault zone. [ABSTRACT FROM AUTHOR]