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This study relocates the seismicity in NE Aegean during the period 2011–2017 using data recorded by the Hellenic Unified Seismic Network (HUSN) in order to elucidate the relationship between seismicity and active faults in this area. P- and S-phase travel times of well-recorded events were first inverted in order to derive a minimum 1D velocity model with station delays using VELEST. Absolute locations of 4450 events were obtained by use of the nonlinear probabilistic algorithm NLLOC and the newly derived velocity model. Precise relative locations with horizontal and vertical uncertainties that do not exceed 1.2 km were calculated for 3354 events using the double-difference algorithm. The relocated seismicity delineates active faults to the south of Lesvos island, at the tip of Biga peninsula in Turkey and along the parallel strands of strike-slip faults that accommodate the westward motion of Anatolia. The comparison of the seismicity distribution with known active faults and the regional stress field shows that the strike-slip faults represent either principal shear zones, or Riedel shears oriented obliquely to the minimum stress axes. Normal faults are oriented almost perpendicular to the direction of the minimum stress axes in accordance with the transtensional deformation model. The seismogenic layer thickness derived from the depth distribution of relocated seismicity was found to be in the range of 14.8–15.8 km. By combining this thickness with geometrical characteristics of active faults and with a relationship that connects moment magnitude with rupture area, it is possible to estimate expected magnitudes of earthquakes. These magnitudes range from 6.3 to 7.2 depending on the rupture scenario that is considered for each fault. Of particular concern are the faults of Agia Paraskevi in Lesvos and Mastichochoria in Chios island that traverse densely populated areas and can produce large events with magnitudes from 6.4 to 6.9. Very little seismicity can be observed along these faults in the past 7 years, which may indicate either that they are creeping, or that they are locked and accumulate strain energy.

In this paper, high-resolution map of the Gutenberg–Richter b-value and seismic moment-release are provided for the Iranian Plateau using the unified and homogeneous part of the seismicity record of the region (January 1995–July 2016). We use these parameters as stressmeters and qualitatively explore their correlations with the GPS velocity field, strain rate, faulting mechanism, attenuation, and structure of the region. Our goal is to reveal the correlations and anomalous patterns that can help to better understand the seismotectonics and the state of present-day crustal stress within the region. A negative correlation between b-value and seismic moment release as well as convergence rates is found. Correlation between geodetic measurements and seismic observations might indicate the existence of a strong mechanical coupling between the basement and the sediment cover across Zagros. High geodetic strain rates east of the Hormuz strait, southern central Alborz, and along the north Tabriz fault correspond to low b-value anomalies at these areas. A strong low b-value anomaly is observed at the major tectonic discontinuity between the Zagros continental collision and the oceanic Makran subduction.

Nearly 20 years after the Mw = 6.0 Athens (Greece) earthquake of 7 September 1999, a significant Mw = 5.1 event struck on 19 July 2019 in roughly the same epicentral region, south of Mt Parnitha, ∼20 km NW of the Athens metropolitan area. In this work, we present a seismotectonic study of the 2019 sequence and investigate its relation with the 1999 aftershock zone and fault geometry. We also take advantage of this opportunity to re-examine the 1999 sequence, using modern cross-correlation and double-difference relocation tools. Waveforms recorded by stations of temporary local networks that were installed at a common site in both case studies are taken into account to identify strongly correlated earthquakes, in terms of waveform similarity, that may indicate a significant degree of resemblance in their source parameters. Our results indicate that the 2019 sequence partially overlaps the western segment of the 1999 aftershock zone. A spatial gap in the middle of that zone, attributed to a high coseismic slip patch during the 1999 mainshock, is still present in 2019, while an isolated cluster of the eastern segment was also reactivated. The relocated hypocenters of both sequences are distributed on nearly coinciding planes that strike ∼N113°-118 °E and dip 48−55° towards SSW, apparently offset by 1−2 km at seismogenic depths, though this difference is attributed to location biases. Their updip extensions outcrop at Mt Parnitha, 1−3 km north of the mapped Fili fault segments or their westwards extension. The 2019 sequence is considered to have occurred at the same structure as the western group of the 1999 aftershocks, which is likely a blind fault.

There is a difference in the seismogenic zonation used for seismic hazard assessment of ordinary buildings and that considered for critical facilities, because different levels of exceedence probability are taken into account. Consequently, in the second case tectonic structures with a low, or very low, likelihood of activation also need attention. The key factor in seismogenic zonation for seismic hazard assessment is investigated here considering some seismically undocumented faults of the northern Adriatic Sea area. Seismic hazard is evaluated for two constructions located around Trieste and close to the sea: an ordinary building and a critical facility. The results clearly show that the two constructions should be designed with quite a different level of expected ground motion in mind. Part of the difference, in the computation of the critical facility, is determined by the introduction of some faults without documented seismicity.

We present a catalog of moment tensor (MT) solutions and moment magnitudes, Mw, for 119 shallow (h ≤ 40 km) earthquakes in Greece and its surrounding lands (34°N–42°N, 19°E–30°E) for the years 2006 and 2007, computed with the 1D Time-Domain Moment Tensor inversion method (TDMT_INV code of Dreger, 2003 ). Magnitudes range from 3.2 ≤ Mw ≤ 5.7. Green's functions (GF) have been pre-computed to build a library, for a number of velocity profiles applicable to the broader Aegean Sea region, to be used in the inversion of observed broad band waveforms (10–50 s). All MT solutions are the outcome of a long series of tests of different reported source locations and hypocenter depths. Quality factors have been assigned to each MT solution based on the number of stations used in the inversion and the goodness of fit between observed and synthetic waveforms. In general, the focal mechanisms are compatible with previous knowledge on the seismotectonics of the Aegean area. The new data provide evidence for strike-slip faulting along NW–SE trending structures at the lower part of Axios basin, close to the heavily industrialized, and presently subsiding, region of the city of Thessaloniki. Normal faulting along E–W trending planes is observed at the Strimon basin, and in Orfanou Gulf in northern Greece. A sequence of events in the east Aegean Sea close to the coastline with western Anatolia sheds light on an active structure bounding the north coastline of Psara–Chios Islands about 20–25 km in length exhibiting right lateral strike-slip faulting.

In view of an anomalous crust–mantle structure beneath the 2001 Bhuj earthquake region, double-difference relocations of 1402 aftershocks of the 2001 Bhuj earthquake were determined, using an improved 1D velocity model constructed from 3D velocity tomograms based on data from 10 to 58 three-component seismograph stations. This clearly delineated four major tectonic features: (i) south-dipping north Wagad fault (NWF), (ii and iii) south-dipping south Wagad faults 1 and 2 (SWF 1 , SWF 2 ), and (iv) a northeast dipping transverse fault (ITF), which is a new find. The relocated aftershocks correlate satisfactorily with the geologically mapped and inferred faults in the epicentral region. The relocated focal depths delineate a marked variation to the tune of 12 km in the brittle–ductile transition depths beneath the central aftershock zone that could be attributed to a lateral variation in crustal composition (more or less mafic) or in the level of fracturing across the fault zone. A fault intersection between the NWF and ITF has been clearly mapped in the 10–20 km depth range beneath the central aftershock zone. It is inferred that large intraplate stresses associated with the fault intersection, deepening of the brittle–ductile transition to a depth of 34 km due to the presence of mafic/ultramafic material in the crust–mantle transition zone, and the presence of aqueous fluids (released during the metamorphic process of eclogitisation of lower crustal olivine-rich rocks) and volatile CO 2 at the hypocentral depths, might have resulted in generating the 2001 Bhuj earthquake sequence covering the entire lower crust.

The project “Seismic Hazard Assessment for Almaty” has a main objective to improve existing seismic hazard maps for the region of northern Tien Shan and especially for the surroundings of Almaty and to generate a new geodynamic model of the region. In the first step a composite seismic catalogue for the northern Tien Shan region was created, which contains about 20,000 events and is representative for strong earthquakes for the period back to the year 500. For the period of instrumental observation 1911–2006 the catalogue contains data for earthquakes with a body wave magnitude larger than 4. For smaller events with magnitudes up to 2.2 the data are only available since 1980. The composite catalogue was created on the basis of several catalogues from the United States Geologic Survey (USGS), local catalogues from the Kazakh National Data Centre (KNDC) and the USSR earthquake catalogue. Due to the different magnitudes used in several catalogues a magnitude conversion was necessary. Event density maps were created to rate the seismicity in the region and to identify seismic sources. Subsurface fault geometries were constructed using tectonic model which uses fault parallel material flow and is constrained by GPS data. The fault geometry should improve the estimation of the expected seismic sources from seismic density maps. First analysis of the earthquake catalogue and the density maps has shown that nearly all large events are related to fault systems. Annual seismicity distribution maps suggest different processes as the cause for the seismic events. Apart from tectonics, also fluids play a major part in triggering of the earthquakes. Beneath the Issyk-Kul basin the absence of strong seismic activity suggests aseismic sliding at the flat ramp in a ductile crust part and low deformation within the stable Issyk-Kul micro-continent which underthrust the northern ranges of Tien Shan. First results suggest a new partition of the region in tectonic units, whose bounding faults are responsible for most of the seismic activity.

The Antarctic Ice Sheet has experienced large ice volume changes during the late Pleistocene glacial cycles. However, the exact amount and areas of mass change are difficult to establish, as both glaciological reconstructions and climate models rely on relatively sparse data sets, when compared to Northern Hemisphere data. We assess the potential contributions to present-day crustal motions and seismicity from glacially-induced ice mass changes. Three different scenarios for the late-Pleistocene ice-sheet distributions are considered. The viscoelastic response of the bedrock is computed for two earth models, a model with radially varying mantle viscosity only, and a model with three-dimensional viscosity variations based on a recent seismic tomographical study. In the latter model, East Antarctica is underlain by a stiff cratonic root, while the upper mantle underneath West Antarctica is weak. Our predicted present-day crustal motions depend strongly on the ice model chosen, with vertical motions focused on areas of former late Pleistocene ice domes. The horizontal motions are greatly affected by the earth rheology, as the horizontal flow pattern is controlled by the flow from the stiff East Antarctic cratonic root to the weaker West Antarctic mantle. Glacially-induced changes in fault stability margin are positive over much of Antarctica, indicating a seismically quiet state due to the large present-day ice sheet. At the site of the 1998 Balleny Island Earthquake ( M w = 8.1 ), the stresses are relatively small by comparison, and interestingly become more prone to stress failure, when a three-dimensional earth model is assumed.

Source parameters for 40 earthquakes with epicentres in the Aegean Sea and the surrounding lands have been determined using P and SH body waveform inversion of digital waveforms from the Global Seismograph Network (GSN). These results are combined with 145 previous solutions, 41 of which were determined by first motion polarities and 104 by waveform modelling. Thus, a new updated database of source parameters for earthquakes for the period 1953–1999 is available. These fault plane solutions confirm our previous knowledge about the seismotectonics of the Aegean Sea and the surrounding lands. They also provide strong evidence that the western part of the Peloponnese (Gulf of Patras to Gulf of Kyparissia) is mainly deforming by strike-slip faulting, parallel in strike to the Cephalonia Fault and are in favour of the models that suggest a connection of the North Anatolian Fault (NAF) zone with the transform zone of the Ionian Islands. The sedimentary arc (inner part of the Hellenic trench) is deforming by normal faulting with the T-axes trending ∼E–W. We did not determine any fault plane solutions at the eastern part of the Hellenic arc indicating pure strike-slip motions as expected from the presence of the Pliny and Strabo trenches. However, we did determine solutions that indicate normal faulting combined with a considerable strike-slip component. In the central Aegean Sea the newly determined focal mechanisms support the conclusion that the area, extending from the eastern coasts of Evia up to the coasts of Turkey, is exhibiting a clear strike-slip character. Thus, the effect of the propagating tip of the North Anatolian fault into the Aegean is very clearly pronounced. The focal mechanisms in the back-arc Aegean area confirm the existence of normal faulting with T-axes trending NNE–SSW in western Anatolia and NNW–SSE in Greece. A zone showing NNE–SSW extension that runs parallel to Northern Aegean branch of the NAF zone up to the Corinth Gulf is depicted from the mechanisms of few earthquakes.

GPS observations were carried out in three networks beginning in 1994 and repeated once a year to the present. Analysis of the repeated GPS campaigns from the three networks revealed horizontal movements at the level of 10–15 mm/a. Main characteristics of the seismotectonics of Egypt are investigated based on the geodetic results and the recently recorded seismic activity from 1900 to 2000. Accordingly, Egypt may be divided into eight seismic zones.

The centroid-moment tensor solutions of more than 300 earthquakes that occurred in the Himalayas and its vicinity regions during the period of 1977–1996 are examined. The resultant seismic moment tensor components of these earthquakes are estimated. The Burmese arc region shows prominent east–west compression and north–south extension with very little vertical extension. Northeast India and Pamir–Hindu Kush regions show prominent vertical extension and east–west compression. The Indian plate is subducting eastward beneath the northeast India and Burmese arc regions. The overriding Burmese arc has overthrust horizontally with the underthrusting Indian plate at a depth of 20–80 km and below 80 km depth, it has merged with the Indian plate making “Y” shape structure and as a result the aseismic zone has been formed in the region lying between 26°N–28°N and 91.5°E–94°E at a depth of 10–50 km. Similarly, the Indian plate is underthrusting in the western side beneath the Pamir–Hindu Kush region and the overriding Eurasian plate has overthrust it to form a “Y” shape structure at a depth of 10–40 km and below 60 km depth, it has merged with the Indian plate and both the plates are subducting below 60–260 km depth. Further south, the overriding Eurasian plate has come in contact with the Indian plate at a depth of 20–60 km beneath northwest India and Pakistan regions with left lateral strike slip motion.

The close vicinity of the Burmese subduction zone to the Himalayan collision zone across northeast India produces complex tectonics giving rise to a high level of seismicity. Using the hypocentral data of shallow earthquakes (h≤70 km) for the period 1897–1995, a large number of focal mechanism solutions and other geophysical data in correlation with major morphotectonic features in the Burmese arc and the adjoining areas, we identified 12 broad seismogenic zones of relatively homogeneous deformation. Crustal deformation rates have been determined for each one of these sources based on summation of moment tensors. The results indicate that along the Kopili–Bomdila fault zone in eastern Himalaya, the deformation is taken up as a compression of 0.12±0.01 mm/yr along N16° and an extension of 0.05±0.004 mm/yr along N104° direction. The deformation velocities show a NS compression of 18.9±2.5 mm/yr and an EW extension of 17.1±2.2 mm/yr in the Shillong Plateau region, while a compression of 5.4±2.8 mm/yr along N33° is observed in the Tripura fold belt and the Bengal basin region. The vertical component in the Shillong Plateau shows crustal thickening of 2.4±0.3 mm/yr. The deformation velocities in Indo–Burman ranges show a compression of 0.19±0.02 mm/yr along N11° and an extension of 0.17±0.01 mm/yr along N101° in the Naga hills region, a compression of 3.3±0.4 mm/yr along N20° and an extension of 3.1±0.36 mm/yr along N110° in the Chin hills region and a compression of 0.21±0.3 mm/yr in N20° and an extension of 0.18±0.03 mm/yr along N110° in the Arakan–Yoma region. The dominance of strike-slip motions with the P axis oriented on an average along N17° indicate that the Burma platelet may be getting dragged along with the Indian plate and the motion of these two together is accommodated along the Sagaing fault. The velocities estimated along Sagaing transform fault in the back-arc region suggest that the deformation is taken up as an extension of29.5±4.7 mm/yr along N344° and a compression of 12.4±1.9 mm/yr along N74° in the northern part of the fault zone, and a compression of 17.4±2.3 mm/yr along N71° and an extension of 59.8±8.0 mm/yr along N341° in the southern part of the fault zone. The average shear motion of about 13.7 mm/yr is observed along the Sagaing fault. The deformation observed in the southern part of the syntaxis zone along the Mishmi thrust indicate a compression of 0.63±0.08 mm/yr in N58° and an extension of 0.6±0.07 mm/yr in N328° direction. The region of Shan Plateau, west of Red River fault, shows a compression of 17.7±2.6 mm/yr along N36° and an extension of 16.1±2.4 mm/yr along N126°.

This study puts forward a segmentation model applied to active faults with the aim of assessing seismic hazard in the Central Apennines. The model, whose reliability had been ascertained during the 1997 Umbria–Marche earthquake sequence, also implies a review of the key terms used in the analysis of active faults and points out the need for a specific procedure in geological analysis for seismic hazard evaluation. Earthquake events which occurred in the Central Apennines in the past decades show that several surface faults can be activated throughout a single seismic event. As a result, the segmentation model proposed herein is based on the fact that surface faults are, on the whole, the superficial manifestation of a single deep seismogenic structure. Therefore, this model is based on the possibility to recognize similar geological, structural, historical, geometrical and rheological features at the surface, in order to infer the main properties of the fault zone at depth. Eventually, on the grounds of the specific features of the fault array, one may assess the geometry, kinematics, slip-rate and size of the deep seismogenic structure, i.e., all the required parameters to evaluate the seismic potential of the area.

Three-dimensional velocity structure of the upper crust was determined by inversion of P-waves travel time in the area of the Aliakmon river basin, where a strong earthquake of Ms = 6.6 occurred on May 13, 1995. The area is located at the northwestern part of the Greek mainland. To investigate the 3-D crustal velocity structure of the region, a two-step tomographic procedure has been applied. The data set consists of the travel time residuals of 366 very well located earthquakes, recorded by at least seven stations of a portable network, which was installed at the Kozani-Grevena broader region by the Institute of Geodynamics, immediately after the shock of 13 May, 1995. In order to improve the initial (reference) velocity model, before the inversion of the travel times, the “minimum 1-D” initial velocity model was obtained. The results show that at shallow depths low velocities are predominant in the whole region and there is no sharp horizontal velocity variation. The velocity at shallow depths seems to be affected from the surface geology. Despite the absence of large scale seismotectonics features in the region there is a remarkable vertical increase of the velocity below the depth of 15 Km, supporting the existence of a second order discontinuity in the crust of the region.

Three-dimensional tectonic movement with relation to gravity change is described elasto-visco-plastically and numerically with the total strain concept. With driving force acting either horizontally or vertically at depth, the relative gravity change to a reference point at ground surface is calculated and compared with gravity surveys and also levelling measurements before a main shock. For the case of gravity changed caused mainly by the horizontal driving-force, the gradient of gravity change ( Δg / Δh ) does not deviate very much from the Free-air gravity gradient (−3.08 μcal/cm), but for the case caused by upper mantle uplifting, together with a soft layer existing within the crust, the gradient deviates from this value a great deal, it is consistent with the geophysical and geodetical data monitored at ground surface during the 1976 Tangshan earthquake development. The abnormal relationship between the tectonic movement and the local gravity change is then controlled by both the nature of driving force and the geological structure, especially presence of a soft layer in the mid-crust. Such a localized gravity change due to tectonic stressing seems to be quite different from the regional gravity anomally and then could be used as a precursor phenomenon of a coming earthquake.

Slow seismotectonic movements along inclined deep fault planes under compressive horizontal stresses are supposed to be the principal mechanism controlling the structure and processes in island-arc systems. In order to treat the stress variations caused by this mechanism, a simple geomechanical model is investigated. We consider a shearing surface crack embedded in a homogeneous elastic half-space. The key element of the model is viscous interaction between the sides of the crack, the viscosity varying with depth. The model differs from the classical steady-state mode of subduction by nonstationary creep processes on deep faults and possibly by cyclical evolution of island-arc systems. The results of our numerical analysis are in good agreement with geological, geophysical and seismological data. (i) Vertical displacements of the free surface in the model fit well with the typical topography of a trench—arc-basement rise—back-arc basin system. (ii) The Benioff seismic zone is supposed to be formed due to the concentration of shear stresses near the fault plane. The characteristic patterns of seismicity, the fine geometry of Benioff zones, and their double-planed structure can be explained in terms of our model. (iii) A zone of considerable heat generation caused by viscous dissipation along the fault plane is found within a narrow area in the depth range 100–200 km. Moreover, the island-arc basement rise is characterized in the model by a relative tension of a few tens or even hundreds of bars, while at depths of 100–150 km below the surface, additional compression of the same order of magnitude acts. The magmatic plumbing system may be visualised as a “toothpaste tube” or a sponge filled with magma which is squeezed from the depths to the surface due to the redistribution of the tectonic stresses only. This can explain the physical origin of island-arc magmatism and the typical position of volcanic belts.

The system of stresses in the lithosphere (0–59 km) and upper asthenosphere (60–150 km) was analysed on the basis of focal-mechanism data for events of M > 5.0 in 1964–1982. The zoning was made considering types of faulting and predominant stress systems. Four uniformly-stressed zones have been identified within the lithosphere and two zones within the upper asthenosphere. The deep distribution of types of faulting and stresses shows the presence of a double seismic focal zone under Kamchatka. Schemes of seismotectonic-deformation (STD) rate-tensor components were dran separately for the lithospheric and asthenospheric layers. To this end, data on individual and averaged focal-mechanism solutions and regional seismic moment-energy class relationships were used. The average STD rate for the lithosphere is 10−9 yr−1, and for the upper asthenosphere 10−10 yr−1. Vertical and horizontal components of STD are of the same order.

The original historical data from surveys of the damage caused by the great Calabro-Messina earthquake are analyzed in detail. This analysis allows the macroseismic field to be reconstructed in a way more compatible with a modern scientific viewpoint, laying maximum importance on indications supplied by the MSK intensity scale. A geometrical model of the focus has been worked out, adopting in part the schemes proposed by Shebalin. This model, together with the macroseismic field parameters, is correlated with the regional structural parameters. Finally, in their quest for better knowledge of the regional seismotectonic pattern, the authors search for evidence of geodynamic consistency by analyzing a spatio-temporal period in the neighborhood of the event.