Seismicity

Probabilistic methods to evaluate the seismic vulnerability of reinforced concrete (RC)frames are largely used in the context of performance based design and assessment, often de-scribing the structural response using global engineering demand parameters (EDPs) such as theinterstory drift. While such EDPs are able to synthetically describe the structural behavior, theuse of intermediate or local parameters of RC frames without seismic detailing can enable a morerealistic and thorough description of failure mechanisms for structural vulnerability. This study proposes an optimized methodology for the probabilistic evaluation of seismic demand of low ductility RC frames by exploring a range of intermediate, local and global EDPs, identifying ap-propriate regression models and comparing performances of different ground motion intensity measures used in the probabilistic analysis. Moreover, a probabilistic methodology for assessing the vulnerability of buildings retrofitted by means of dissipative braces is proposed. The method-ology use local EDP in order to develop single component and system fragility curves before andafter the retrofit. The proposed approach allows to highlight the possible changes in the mostsignificant collapse modalities before and after the retrofit and to evaluate the effectiveness of theretrofit by taking into account the probabilistic properties of the seismic behavior of the consid-ered systems. A benchmark 2-dimensional reinforced concrete frame with low ductility capacity isconsidered as case study. The frame is designed for gravity-loads only and does not comply with modern anti-seismic code requirements. It is retrofitted by introducing elasto-plastic dissipativebraces designed for different levels of their target base-shear capacity, following a design methodinvolving the pushover analysis of the bare frame. The obtained results show the effectiveness of the use of component level vulnerability evaluation of low ductility frames, and the effectivenessof the methodology in describing the changes in the performance due to retrofit. The proposedmethodology also allows testing the effectiveness of this simplified criterion employed for the de-sign of braces.

Thrust fault ruptures during earthquakes do not often propagate down to the brittle-ductile transition. Lithological variations control the behavior and depth of regional basal thrusts and decollement planes. Thrust fronts may be discontinuous along strike, limiting the dimension of single coseismic ruptures. These factors control the maximum expected magnitude in one region. This is the case of Italy where the convergence of few millimeter per year in the Apennines accretionary prism and along the retrobelt of the Alps generates compressional earthquakes with moderate to strong magnitudes. Here, using geological and geophysical data, we first compile a map of the undulated active basal thrust decollement for Italy that occurs from 1 to 17-km depth. Then, we verify the relationship between the length of seismogenic ruptures in thrust faults (Lf) and the maximum depth of thrust faulting (z max) of related earthquakes and find that their ratio (Lf/z max) ranges between 2 and 4. Finally, we compute the potential seismogenic volume and estimate the maximum magnitude using an empirical relationship that multiplies the decollement depth and the Lf/z max ratio. Maximum calculated magnitude is 6.7 ± 0.37 (depending on Lf/z max and fault dip angle), consistent with the largest magnitude of thrust-related earthquakes recorded in Italy (6.5-7.0). Lower magnitudes are predicted in the Ionian Seas at the external front of the Apennines where smaller crustal volumes are involved, whereas higher magnitudes are expected in the southern Po Basin, the western Adriatic Sea, Sicily offshore, and the Southern Alps where the decollement is deeper and the brittle volumes are far greater. Plain Language Summary Earthquakes are due to different kinds of crustal fault ruptures, and the observed magnitude depends on the rupture dimension, hence on the involved brittle volume. Those related to thrust faults generate magnitudes lower than expected if the decollement is shallow, whereas the magnitudes increase where the decollement is deeper. This is the case of Italy where many factors can explain the moderate to strong (M 5-7) observed magnitudes recorded so far in the contractional areas of the country: (i) the slow convergence rate (few millimeters per year) observed for the Apennines and Alps; (ii) the thrusts do not cut down the entire seismogenic crust; and that (iii) thrusts are undulated and segmented along strike, limiting the dimension of the fault rupture. We compile a map of the thrust decollement depth for Italy that is situated between 1-17 km. Then, we quantify the along-strike discontinuity, verifying the ratio between thrusts length and faulting depth of related earthquakes. Finally, we estimate the maximum expected magnitude for the study area. Calculated magnitudes are consistent with those occurred for thrust-related earthquakes in Italy, pointing to the importance of knowing the depth and the lateral continuity of faults to correctly assess the seismic potential of a region.

Abstract. Rapid loss estimation after potentially damaging earthquakes is critical for effective emergency response
and public information. A methodology and software package,
ELER-Earthquake Loss Estimation Routine, for rapid
estimation of earthquake shaking and losses throughout the
Euro-Mediterranean region was developed under the Joint
Research Activity-3 (JRA3) of the EC FP6 Project entitled
“Network of Research Infrastructures for European
Seismology-NERIES”. Recently, a new version (v2.0) of
ELER software has been released. The multi-level methodology
developed is capable of incorporating regional variability
and uncertainty originating from ground motion predictions,
fault finiteness, site modifications, inventory of physical
and social elements subjected to earthquake hazard and
the associated vulnerability relationships. Although primarily
intended for quasi real-time estimation of earthquake
shaking and losses, the routine is also equally capable of incorporating
scenario-based earthquake loss assessments.
This paper introduces the urban earthquake loss assessment
module (Level 2) of the ELER software which makes
use of the most detailed inventory databases of physical and
social elements at risk in combination with the analytical vulnerability
relationships and building damage-related casualty
vulnerability models for the estimation of building damage
and casualty distributions, respectively. Spectral capacitybased
loss assessment methodology and its vital components
are presented. The analysis methods of the Level 2 module,
i.e. Capacity Spectrum Method (ATC-40, 1996), Modified
Acceleration-Displacement Response Spectrum Method
(FEMA 440, 2005), Reduction Factor Method (Fajfar, 2000)
and Coefficient Method (ASCE 41-06, 2006), are applied to
the selected building types for validation and verification purposes. The damage estimates are compared to the results
obtained from the other studies available in the literature,
i.e. SELENA v4.0 (Molina et al., 2008) and ATC-55 (Yang,
2005). An urban loss assessment exercise for a scenario
earthquake for the city of Istanbul is conducted and physical
and social losses are presented. Damage to the urban
environment is compared to the results obtained from similar
software, i.e. KOERILoss (KOERI, 2002) and DBELA
(Crowley et al., 2004). The European rapid loss estimation
tool is expected to help enable effective emergency response,
on both local and global level, as well as public information

The relative contribution of tectonic and kinematic processes to seismic behaviour of mountain belts is still controversial. To understand the partitioning between these processes we developed a model that simulates both tectonic and seismic processes in a continental collision setting. These 2D seismo-thermo-mechanical (STM) models obtain a Gutenberg–Richter frequency–magnitude distribution due to spontaneous events occurring throughout the orogen. Our simulations suggest that both the corresponding slope (b value) and maximum earthquake magnitude (Mw max) correlate linearly with plate convergence rate. By analyzing 1D rheological profiles and isotherm depths we demonstrate that plate convergence rate controls the brittle strength through a rheological feedback with temperature and strain rate. Faster convergence leads to cooler temperatures and also results in more larger seismogenic domains, thereby increasing both Mw max and the relative number of large earthquakes (decreasing b value). This mechanism also predicts a more seismogenic lower crust, which is confirmed by a transition from uni-to bi-modal hypocentre depth distributions in our models. This transition and a linear relation between convergence rate and b value and Mw max is supported by our comparison of earthquakes recorded across the Alps, Apennines, Zagros and Himalaya. These results imply that deformation in the Alps occurs in a more ductile manner compared to the Himalayas, thereby reducing its seismic hazard. Furthermore, a second set of experiments with higher temperature and different orogenic architecture shows the same linear relation with convergence rate, suggesting that large-scale tectonic structure plays a subordinate role. We thus propose that plate convergence rate, which also controls the average differential stress of the orogen and its linear relation to the b value, is the first-order parameter controlling seismic hazard of mountain belts.

article A survey of published scientific literature was undertaken to identify and catalog observed earthquake pre- cursors. The earthquake precursors selected for analysis included electric and magnetic fields, gas emissions, groundwater level changes, temperature changes, surface deformations, and seismicity. For each of these precursors, the published scientific literature was searched to document the statistics of each reported earth- quake precursor (spatial extent, time, duration, amplitude, signal/noise ratio), to analyze dependence of the observable for each precursor on earthquake magnitude, and to explore proposed physical models to explain eachearthquakeprecursor.Somegeneralcharacteristics wereobservedfortheseprecursoryphenomena.First, the largest amplitude precursory anomalies tend to occur before the largest magnitude earthquakes. Also, the number of precursory anomalies tends to increase the closer in time to the occurrence of the earthquake. Finally,theprecursoryanoma...

The idea of an Intensity scale based on coseismic environmental effects started to ripe early in the'80s following the macroseismic surveys of strong earthquakes, in particular, for Italy, those occurred in 1976 (Friuli) and 1980 (Irpinia-Basilicata). In fact, during such surveys, it was often observed that intensity could not be reliably evaluated only based on damage to artefacts. This was specially true for sparsely populated areas and for the highest degrees, because it was extremely difficult to estimate damage above degree X. Environmental ...

We utilized the seismicity and the potential field data to study the tectonic deformation and to delineate the seismically active subsurface tectonic trends of El-Faiyum area. To accomplish these goals, we analyzed and interpreted the seismicity data, the reduced to pole total magnetic intensity, and the Bouguer anomaly maps. We also used the spatial distribution of the recent seismic events and the focal mechanism to outline the local seismic zones that control the seismicity of the study area and to determine the sense of the motion along the subsurface active faults. The focal mechanism of the recent seismic events and the interpreted subsurface tectonic faults from the potential field data reflect strike-slip movements with normal components along the subsurface active faults. The gravity and magnetic maps show a NE-SW regional trend with low gravity and magnetic values. The NE-SW regional trend extends across the whole area and could be related to the Pelusium Megashear fault. A NE-SW trend with high gravity and magnetic exists at the northern part and coincides with the Kattania Uplift and the basaltic flows in Gabal Qatrani area. The gravity and magnetic maps also reveal several local anomalies with different polarities, amplitudes, and extensions, which reflect anticlinal and synclinal structures on the basement surface. The seismotectonic map, generated by linking the basement structure map and the spatial distribution of the recent earthquake foci, reveals the dominant tectonic trends and the subsurface active faults.

Konsol olarak davranan bir istinat duvarı  arkasında  desteklenen  zeminin  duvar üzerinde  oluşturduğu
yatay  basınç  değerlerinin  zemin  derinliği  ile  sıfırdan  başlayarak  sabit  bir  değerde  doğrusal  olarak  arttığını
varsayan  yaklaşım  durağan  yükleme  koşullarında  ve  belirli  duvar  sehim  değerlerinin  duvar  derinliğince
sağlandığı  varsayımı  ile  geçerlidir.  Diğer  taraftan,  deprem  etkileri  altında  duvar  üzerinde  oluşan  dinamik
basınç  değerleri,  sıradan  istinat  duvarı  tasarım  yöntemlerinde  dikkate  alınmamakla  birlikte,  duvarın  şekil
değiştirmezlik (rijitlik) değerlerine göre değişebilmektedir. Bu çalışmada, zemin-duvar arayüzey etkileşimini
dikkate alarak kurgulanan bir sonlu elemanlar modeli üzerinden, duvarın farklı kesit özelliklerinden kaynaklı
şekil  değiştirmezlik  değerlerinin  yatay  ivme  altında  hareketlenen  zeminin  duvar  üzerinde  oluşturduğu
dinamik  yatay  basınç  üzerindeki  etkileri  ile  statik  durumda  aktif  ve  durağan  koşulların  duvar  boyunca
oluşumu irdelenecektir.

Geophysical data from open sources are widely used as support of integrated analysis in regional geologic studies in seismically active areas, such as Mexico. High seismicity with repetitive earthquakes occurs in areas of the subduction zones formed during the tectonic evolution and correlates with geophysical anomalous fields. This paper investigates the correspondence between the geophysical, topographic and seismic setting of Mexico using Generic Mapping Tools (GMT) scripting toolset for data processing. The approach for automated mapping using GMT console and shell scripts is presented as an advanced cartographic method aimed to get insights into in the geology and geophysics of Mexico. The data were obtained from open source high-resolution datasets: GEBCO, EGM-2008, satellite-derived gravity, EMAG2 magnetic anomaly and IRIS seismic database. The correspondence between the geological and geophysical data of Mexico has been verified through the comparison between the thematic maps, regional distribution of gravity anomalies and locations of earthquakes. Seven new maps are performed on geologic, geophysical, topographic and seismic data. Seismic mapping is presented for the period of 2007-2021 demonstrating events with magnitude from 1.5 to 7.2. The impact of tectonic processes that formed Middle American Trench and active Trans-Mexican Volcanic Belt on high regional seismicity with intensive earthquakes is explored. The study finds that GMT is an effective tool for high-quality mapping and cartographic analysis. The IRIS data can be used for geologic analysis of Mexico.

Dados geofísicos de fontes abertas são amplamente usados como suporte de análise integrada em estudos geológicos regionais em áreas sismicamente ativas, como o México. Alta sismicidade com terremotos repetitivos ocorre em áreas das zonas de subducção formadas durante a evolução tectônica e se correlaciona com campos anômalos geofísicos. Este artigo investiga a correspondência entre o cenário geofísico, topográfico e sísmico do México usando o conjunto de ferramentas de script Generic Mapping Tools (GMT) para processamento de dados. A abordagem para mapeamento automatizado usando o GMT e scripts de shell é apresentada como um método cartográfico avançado com o objetivo de obter insights sobre a geologia e a geofísica do México. Os dados foram obtidos de conjuntos de dados de alta resolução de código aberto: GEBCO, EGM-2008, gravidade derivada de satélite, anomalia magnética EMAG2 e banco de dados sísmico IRIS. A correspondência entre os dados geológicos e geofísicos do México foi verificada através da comparação entre os mapas temáticos, distribuição regional de anomalias gravitacionais e localizações de terremotos. Sete novos mapas são realizados em dados geológicos, geofísicos, topográficos e sísmicos. O mapeamento sísmico é apresentado para o período de 2007-2021 demonstrando eventos com magnitude de 1,5 a 7,2. O impacto dos processos tectônicos que formaram a trincheira da América Central e o cinturão vulcânico transmexicano ativo na alta sismicidade regional com terremotos intensos é explorado. O estudo concluiu que o GMT é uma ferramenta eficaz para mapeamento e análise cartográfica de alta qualidade. Os dados IRIS podem ser usados para análises geológicas do México.

Landsat lineaments identified by Earth Satellite Corporation (EARTHSAT, 1997) can be groundtruthed across the Appalachian Basin of New York State (NYS). Both fracture intensification domains (FIDs) and faults are observed in outcrop along the lineaments. Confirmation of deep structure associated with the surface structure is provided by both well log analyses and seismic reflection data (primarily proprietary). Additional faults are proposed by comparing the lineament locations with gravity and magnetic data. The result is a web of basement faults that crisscross New York State. By overlaying epicenter locations on the fault/lineament maps, it is possible to observe the spatial correlation between seismic events and the faults. Every seismic event in the Appalachian Basin portion of NYS lies on or near a known or suspected fault. It thus appears that not only are there more faults than previously suspected in NYS, but also, many of these faults are seismically active.

This volume builds on presentations made at two thematic sessions on “The Active Tectonics of the Circum-Adriatic Region” at the EGU 2007 and 2008 General Assemblies in Vienna. In both sessions, contributions were invited from workers incorporating structural, geophysical, seismological, remote sensing, geodetic and thermochronological methods to better understand the crustal evolution and ongoing development of one of Europe's most interesting tectonic regions. The Adriatic region occupies a central position within the geodynamic framework of the Central Mediterranean. It is surrounded by actively deforming belts of diverse character including transpressional, contractional, strike-slip and extensional domains, collectively defining the structurally complex and kinematically varied boundaries of the Adria plate. Because many countries occupy the circum-Adriatic region, international collaborative research into the tectonic activity and associated natural hazards of the region is relevant and important to European society. In this context, the papers presented in this volume provide important new data that bear on various aspects of the active tectonics of the circum-Adriatic region. These contributions typically draw on multidisciplinary structural, geophysical and geochronological datasets to draw new conclusions concerning the spatial and temporal evolution of Adria's bounding deformation zones, especially the southeastern and southern Italian regions and NE Adriatic region. In this overview, we provide a state-of-the-art summary of different aspects of present-day Adria geodynamics to provide a common background for the individual contributions that follow.

Abstract. High seismic activity in the Philippines originates from tectonic convergence related to surface and subsurface seismotectonic features. Based on earthquake data, the archipelago can be divided into the seismically-active Philippine Mobile Belt and the aseismic North Palawan Block. The latter represents a rifted continental fragment of the Eurasian margin that juxtaposed with the rest of island arc units in central Philippines. Earthquake hypocenter plots on planar and in vertical profiles show that the seismic events are associated with known seismotectonic features. In addition, data suggest that the collision zone between the North Palawan Block and the Philippine Mobile Belt is characterized by a decreased amount of hypocenters at > 100 km depths. Although field evidence favors the presence of a subducted slab or slabs beneath western central Philippines, these are difficult to image using the present seismicity distribution dataset.

Western Anatolia is one of the most seismically active continental regions in the world and much of it has been undergoing NS-directed extensional deformation since Early Miocene time. In a cooperative study, seismologists from Saint Louis University, USA and Dokuz Eylül University, Turkey, deployed five broad-band and 45 short-period seismic stations in western Anatolia between 2002 November and 2003 October. The present paper uses data collected by this network and the data from five permanent stations operated by the Kandilli Observatory and Earthquake Research Institute to map the hypocentral distribution of local earthquakes and to determine crustal structure of western Anatolia. We obtained a 1-D P-wave crustal velocity model using a generalized scheme for simultaneously obtaining earthquake locations and a crustal velocity model. Our velocity model is characterized by crustal velocities that are significantly lower than average continental values. The low velocities may be associated with high crustal temperatures, a high degree of fracture, or the presence of fluids at high pore pressure in the crust. We located 725 local earthquakes and classified them in three categories. We found that the level of seismic activity in western Anatolia is higher than previously reported. Station delays resulting from the inversion process correlate with near-surface geology and the thickness of sediments throughout the region. The hypocentral distribution of the events indicates that peak seismicity for the region occurs at depths of about 10 km.

Coulomb stress variations may trigger earthquakes, while the stress transfer process is not clear. In this paper, Coulomb stress changes are investigated for the sequences of strong earthquakes in the Caucasus region, which followed the 1988 M w 6.8 in Spitak, the 1991 M w 6.9 in Racha and the 2000 M w 6.2 in Baku. Our results show that the mainshocks induced variations in the stress field where most of the seismic events occurred. Coulomb stress increases 2 bars corresponding nearly to places of aftershocks, while the stress falls above 10 bars for Racha mainshock. The calculated Coulomb stress loaded about 5 bars at the end of rupture plane and the stress falls ~9 bars for Spitak mainshock. Our stress pattern shows a correlation within the areas of Coulomb stress caused by the combination of seismicity. Correlations between the coseismic Coulomb stress changes and the observed spatial patterns of the aftershocks created by the mainshock are illustrated by the stress variations over both optimally oriented and specified fault planes. An apparent correlation between the mainshock stress changes and the detected spatial pattern of the aftershocks is found, confirming the utility of the stress maps in constraining the expected locations of the forthcoming aftershocks and mitigating earthquake hazards.

Kashmir valley India is located in seismically
active Himalayan-Hindukush belt, which has been witnessed by the number of high magnitude earthquakes
during the past centuries. The presence of active seismogenic faults, soft alluvium and shallow groundwater levels
in the basin of the Kashmir valley signifies its detrimental
effect on the occurrences of future strong ground motions.
In view of severe damaging attitudes and frequent occurrences of earthquakes in the region the present paper
emphasizes attenuation model for seismic hazards zonation
to ensure the safe and comfortable expansion of settlements
and industrial establishments. For the purpose detailed
study was performed on the seismically deformed beds,
water-table conditions and past seismic activities of the
area around the valley. The results of study reveal the peak
ground acceleration (PGA) of 10, 5 and 2 % probabilities
of event in 50-year lifetime with probability of 2 % for
PGA = 0.652 (g), 5 % for PGA = 0.460 (g) and 10 % for
PGA = 0.372 (g) which varies with the different surface
and sub-surface conditions of the area

We investigate the Mw 6.5 Norcia (Central Italy) earthquake by exploiting seismological data, DInSAR measurements, and a numerical modelling approach. In particular, we first retrieve the vertical component (uplift and subsidence) of the displacements affecting the hangingwall and the footwall blocks of the seismogenic faults identified, at depth, through the hypocenters distribution analysis. To do this, we combine the DInSAR measurements obtained from coseismic SAR data pairs collected by the ALOS-2 sensor from ascending and descending orbits. The achieved
vertical deformation map displays three main deformation patterns: (i) a major subsidence that reaches the maximum value of about 98 cm near the epicentral zones nearby the town of Norcia; (ii) two smaller uplift lobes that affect both the hangingwall (reaching maximum values of about 14 cm) and the footwall blocks (reaching maximum values of about 10 cm). Starting from this evidence, we compute the rock volumes affected by uplift and subsidence phenomena, highlighting that those
involved by the retrieved subsidence are characterized by significantly higher deformation values than those affected by uplift (about 14 times). In order to provide a possible interpretation of this volumetric asymmetry, we extend our analysis by applying a 2D numerical modelling approach based on the finite element method, implemented in a structural-mechanic framework, and exploiting the available geological and seismological data, and the ground deformation measurements retrieved from the multi-orbit ALOS-2 DInSAR analysis. In this case, we consider
two different scenarios: the first one based on a single SW-dipping fault, the latter on a main SW-dipping fault and an antithetic zone. In this context, the model characterized by the occurrence of an antithetic zone presents the retrieved best fit coseismic surface deformation pattern. This result allows us to interpret the subsidence and uplift phenomena caused by the Mw 6.5 Norcia earthquake as the result of the gravitational sliding of the hangingwall along the main fault plane and the frictional force acting in the opposite direction, consistently with the double couple fault plane
mechanism.

To investigate the characteristics of earthquake hazard parameters as a means of identifying different zones of seismicity, we have compiled a catalogue of about 1850 moderate to large-sized earthquakes with magnitudes m≥4.0 or greater in southern Turkey for the time period from 1900 to 1990. Several methods have been applied to the earthquake catalogue to assess seismic hazard. The study area is divided into 77 overlapping cells of 2° size. Theoretical calculations were made for the prediction of maximum magnitude, intensity, b-values, strain energy release and corresponding m3 and peak ground acceleration levels for a given period of time. The resultant seismic hazard for each parameter is depicted as a contour map to indicate lateral variations in areas of seismic source. A combination and evaluation of various hazard parameters resulted in more reasonable estimates of hazard. It is found that the most hazardous seismic zones are the Rhodes and Burdur zones where the level of peak ground acceleration reaches up to 280 cm s-2 for an average return period of 100 years.

The paper illustrates a probabilistic methodology for assessing the vulnerability of low-ductility reinforced concrete (RC) buildings retrofitted by dissipative braces. The aim is to highlight the most important parameters controlling the capacity of these systems and specific aspects concerning the response uncertainties. The proposed methodology is based on local engineering demand parameters (EDPs) for monitoring the seismic response and on the development of component and system fragility curves before and after the retrofit. Its capability is tested considering a RC frame designed for gravity-loads only retrofitted by elasto-plastic dissipative braces. The results show the effectiveness of the methodology in describing the changes in the response and in the failure modalities due to the retrofit. Moreover, the retrofit effectiveness is evaluated by introducing proper synthetic parameters describing the fragility curves and highlighting the importance of employing local rather than global EDPs in the seismic risk evaluation of low-ductility frames.

This study performs a reanalysis of the seismicity recorded during the 1996 Gjálp eruption that occurred at NW Vatnajökull, Iceland. The seismicity was recorded by the temporary HOTSPOT network consisting of 30 three-component broadband stations. In total 301 events were identified between 29 September and 12 October and their phases were manually picked. A velocity model was estimated from P-phase travel times by using VELEST. Events were first located using the algorithm NON-LINLOC in order to obtain absolute locations. Precise relative locations were obtained with HYPODD by utilizing catalog and cross-correlation differential travel times. Results show that events clustered first along the SW rim of the Bárðarbunga caldera and later along the Gjálp fissure, with most hypocentral depths located between 3 and 8 km. Waveforms of the 10 largest events that followed the Bárðarbunga earthquake were inverted in order to obtain moment tensors. For all events we found that the deviatoric moment tensor fits the data better than pure double-couple or full moment tensor solutions. Events along the Bárðarbunga caldera exhibited reverse focal mechanisms, while those at the Gjálp fissure exhibited mostly strike-slip faulting. Seismic velocity variations calculated using ambient noise interferometry, point to the possibility that a small subglacial eruption occurred at Bárðarbunga before the main earthquake. This removed melt from the magma chamber causing its roof to collapse, and also resulted in the lateral migration of magma towards the Gjálp fissure. The 2014-2015 Bárðarbunga-Holuhraun eruption shares common characteristics with the 1996 Gjálp eruption, although the size of the latter was much smaller.

Time domain moment tensor analysis of 145 earthquakes (M w 3.2 to 5.1), occurring during the period 2006e2014 in Gujarat region, has been performed. The events are mainly confined in the Kachchh area demarcated by the Island belt and Kachchh Mainland faults to its north and south, and two transverse faults to its east and west. Libraries of Green's functions were established using the 1D velocity model of Kachchh, Saurashtra and Mainland Gujarat. Green's functions and broadband displacement waveforms filtered at low frequency (0.5e0.8 Hz) were inverted to determine the moment tensor solutions. The estimated solutions were rigorously tested through number of iterations at different source depths for finding reliable source locations. The identified heterogeneous nature of the stress fields in the Kachchh area allowed us to divide this into four Zones 1e4. The stress inversion results indicate that the Zone 1 is dominated with radial compression, Zone 2 with strike-slip compression, and Zones 3 and 4 with strike-slip extensions. The analysis further shows that the epicentral region of 2001 M W 7.7 Bhuj mainshock, located at the junction of Zones 2, 3 and 4, was associated with predominant compressional stress and strike-slip motion along ~ NNE-SSW striking fault on the western margin of the Wagad uplift. Other tectonically active parts of Gujarat (e.g. Jamnagar, Talala and Mainland) show earthquake activities are dominantly associated with strike-slip extension/compression faulting. Stress inversion analysis shows that the maximum compressive stress axes (s 1) are vertical for both the Jamnagar and Talala regions and horizontal for the Mainland Gujarat. These stress regimes are distinctly different from those of the Kachchh region.

Keywords: comb fractures calcite veins fault–fluid interaction fluid inclusions carbonate faults seismicity The extensional Val Roveto Fault, which is the longest exhumed potentially-seismogenic structure of central Apennines, Italy, is examined to constrain earthquake-related fluid circulation and fluid sources within shallow carbonate-hosted faults. The study focuses on fault-related comb and slip-parallel veins that are calcite-filled and cut through the principal surface of the Val Roveto Fault. We observe multiple crack-and-seal events characterized by several veining episodes, probably related to different slip increments along the fault plane. We show that vein calcite precipitated in Late Pleistocene time below the present-day outcrop level at a maximum depth of ∼350 m and temperatures between 32 and 64 • C from meteoric-derived fluids modified by reactions with crustal rocks and with a mantle contribution (up to ∼39%). The observed warm temperatures are not compatible with a shallow (≤∼350 m) precipitation depth, which, in this region, is dominated by circulation of cold meteoric water and/or shallow groundwater. Based on structural–geochemical data, we propose that deep-seated crust–mantle-derived warm fluids were squeezed upward during earthquakes and were hence responsible for calcite precipitation at shallow depths in co-seismic comb and slip-parallel fractures. As comb-and slip-parallel veins are rather common, particularly along seismogenic extensional faults, we suggest that further studies are necessary to test whether these veins are often of co-seismic origin. If so, they may become a unique and irreplaceable tool to unravel the seismic history of hazardous active faults.