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Τις τελευταίες δεκαετίες, η αυξανόμενη πρόοδος στην επεξεργασία των δορυφορικών δεδομένων για την αξιοποίησή τους στον εντοπισμό πιθανών θέσεων υδροθερμικών εξαλλοιώσεων και παρουσίας ορυκτών πόρων έχει αποτελέσει αντικείμενο εντατικής έρευνας. Στην παρούσα εργασία, παρουσιάζουμε τα αποτελέσματα μιας μελέτης που συνδυάζει εργαστηριακές αναλύσεις και επεξεργασία δορυφορικών δεδομένων για την ορυκτολογική εξέταση ζώνης εξαλλοίωσης από την διείσδυση γρανιτοειδούς που εντοπίστηκε στην επιφάνεια της νησίδας «Κουτάλα» στην περιοχή της Λαυρεωτικής. Στόχος είναι η διερεύνηση της δυνατότητας των δορυφορικών δεδομένων Sentinel-2 και WorldView-3 VNIR στην ανίχνευση και χαρτογράφηση ορυκτών εξαλλοίωσης που ευρέθησαν κατά τις εργαστηριακές αναλύσεις δειγμάτων τα οποία πιθανώς να συνδέονται με Fe-Mn μετάλλευμα. Για τον σκοπό αυτό, εφαρμόστηκαν δύο μέθοδοι, φασματοσκοπία ανάκλασης και φασματικοί δείκτες. Στην πρώτη μέθοδο, συλλέγονται οι φασματικές υπογραφές όλων των ορυκτών που εντοπίστηκαν στην περιοχή από φασματικές βιβλιοθήκες. Κατόπιν εφαρμόζεται μετασχηματισμός των τιμών ανακλαστικότητας με την αφαίρεση του συνεχούς. Στη συνέχεια, αναζητώνται οι απορροφήσεις που χαρακτηρίζουν αποκλειστικά το κάθε ορυκτό για τον κάθε αισθητήρα. Ο αισθητήρας του οποίου τα φασματικά κανάλια μπορούν και ανιχνεύουν τα περισσότερα ορυκτά εξαλλοίωσης επιλέγεται για την χαρτογράφησή τους. Η δεύτερη μέθοδος αφορά στον υπολογισμό και παραγωγή χαρτών φασματικών δεικτών, όταν υπάρχουν τα απαραίτητα κανάλια. Ο δείκτης που ανιχνεύει τρισθενή σίδηρο υπολογίζεται και στους δύο δορυφορικούς αισθητήρες. Ο δισθενής σίδηρος και ο δείκτης εξαλλοίωσης υπολογίζονται μόνο με τα δεδομένα Sentinel-2 λόγω των δύο καναλιών που διαθέτει στο μικροκυματικό υπέρυθρο. Τα αποτελέσματα της μελέτης δείχνουν ότι οι εργαστηριακές μετρήσεις και η επεξεργασία των δορυφορικών δεδομένων συμφωνούν και είναι συμπληρωματικές. Τα δορυφορικά δεδομένα παρέχουν πληροφορία ως προς την χωρική κατανομή των ορυκτών πάνω στο νησί. Συγκεκριμένα, προκύπτει ότι τα δεδομένα WorldView-3 VNIR, ανιχνεύουν μόνο την παρουσία γκαιτίτη και Mn_οξειδίων/υδροξειδίων. Αντίθετα, τα δεδομένα Sentinel-2 φαίνεται ότι είναι ικανά να ανιχνεύσουν (ι) την εξαλλοίωση καθώς και (ιι) όλα τα ορυκτά που συνδέονται με πιθανή παρουσία Fe-Mn μεταλλεύματος, είτε έχουν τρισθενή είτε δισθενή σίδηρο στη σύστασή τους. Οι χάρτες που προκύπτουν δείχνουν ότι υπάρχει, σε διαφορετικό βαθμό, σημαντική εξαλλοίωση σε όλη την επιφάνεια του νησιού η οποία συνδέεται με την μαγματική διείσδυση. Ωστόσο, η εξαλλοίωση είναι πιο ισχυρή στο ανατολικό τμήμα της νησίδας όπου παρατηρείται και η επαφή σχιστολίθων/γρανιτοειδούς. Με την παρούσα μελέτη, για πρώτη φορά στη νησίδα (ι) γίνεται ανίχνευση και χαρτογράφηση ορυκτών που συνδέονται με πιθανή παρουσία Fe-Mn μεταλλεύματος και (ιι) παράγονται χάρτες ορυκτών εξαλλοίωσης οι οποίοι παρέχουν πληροφορία τόσο για την χωρική κατανομή των ορυκτών στην επιφάνεια όσο και έμμεσες εκτιμήσεις του βαθμού παρουσίας τους., During the last decades, the rapid progress of remote sensing data processing for their utilization in detecting locations of possible sites linked to hydrothermal alteration and ores has gained increasing attention due to significant time and cost savings. In this study, we present the findings of a joint remote sensing and laboratory examination of a mineralization zone induced by a granitoid intrusion onshore the islet of “Koutala”, in Lavreotiki, central Greece. Our objective is to investigate the potential of Sentinel-2 and WorldView-3 VNIR satellite data to detect and map oxidized ore zones and alteration minerals that are detected from laboratory analysis of samples and could be linked to Fe-Mn mineralization. Two approaches are followed, namely reflectance spectroscopy and spectral indices. In reflectance spectroscopy, the spectral signatures of all minerals detected in the study area are retrieved from spectral libraries. The signatures are resampled to Sentinel-2 and to WorldView-3 VNIR spectral bands. Continuum-removal is then applied and the diagnostic absorption features of each mineral are detected for each spectral band configuration. The dataset with the best spectral configuration for mineral detection is then used for the production of mineral maps using the corresponding satellite image. The second approach involves the calculation of spectral indices, namely ferric, ferrous iron and hydroxyl-bearing alteration, on reflectance spectra. The ferric iron index is applied to both satellite datasets while the two other indices require the use of SWIR bands and therefore, they can be only calculated on Sentinel-2 data. All results show that laboratory and satellite data analyses results are consistent and complementary. WorldView-3 VNIR data seem to be sensitive only to the ferric and manganese phase. Sentinel-2 data seem to be capable to detect and map all alteration minerals that are potentially linked to Fe-Mn ore, including both ferric and ferrous phases. The mineral absorption and spectral indices maps show that in the investigated area, there is significant mineralization related to the granitoid intrusion. Hydrothermal alteration is observed on the entire surface of the islet but it seems to be stronger at the eastern part of the islet where the granitoid/schist contact is located. It is the first time that (i) minerals linked to a potential Fe-Mn ore are detected on the islet and (b) the corresponding alteration mineral maps are produced from satellite data, revealing their spatial distribution and providing indirect estimations of the degree of their presence.

On March 3, 2021 a Mw=6.3 shallow earthquake occurred in the mountainous region of Damasi, about 20 km to the northwest of Larisa, Thessaly, central Greece, in a region of active crustal extension but of low strain. This event was followed by a Mw=6.0 shallow earthquake on March 4, 2021 about 12 km to the northwest, inside the sedimentary basin of the Titarisios river. On March 12, 2021 a third event of Mw=5.6 occurred 7 km further towards NNW, near the NW edge of the basin. All events show normal-slip kinematics as indicated by the moment tensor solutions, with minor strike-slip components. Because of the shallow depth of the events it was possible to map the surface deformation using InSAR. The preliminary results from InSAR show three main lobes of subsidence, partially overlapping. The deformation pattern indicates the activation of three normal faults, previously unknown in this part of Thessaly. The earthquakes generated numerous secondary phenomena with vast areas of alluvial deposits exhibiting spectacular liquefaction features. No tectonic ruptures were found in the cases of events 2 and 3, however a series of sporadic, NW-SE striking surface breaks were found on the mountains north of village Zarko that are aligned with the vanishing gradient of the interferometric phase of the 1st event. &nbsp

On the 3rd and 4th of March 2021, two strong earthquakes of M6.3 and M6.0, respectively occurred at Thessaly, Central Greece. During extensive field survey and mapping, accompanied by UAV aerial surveys, following the strong earthquakes, numerous (more than 400 cases) liquefaction-related features were identified, including sand blows and craters, fissures and lateral spreading cracks/ruptures along the Pinios and Titarisios river banks. A rapid documentation of these features was important, as most of these features were going to be erased or smoothed by the ploughing season that is ongoing in the area.

Here we present the results of a kinematic slip model of the 2020 Mw 6.7 Doğanyol-Sivrice, Turkey Earthquake, the most important event in the last 50 years on the East Anatolian Fault zone. Our slip model is constrained by two Sentinel-1 interferograms and by 5 three-component high-rate GNSS recordings close to the earthquake source. We find that most of the slip occurs predominantly in three regions, two of them at between 2 and 10 km depth and a deeper slip region extending down to 20 km depth. We also relocate the first two weeks of aftershocks and find a distribution of events that agrees with these slip features. The HR-GNSS recordings suggest a strongly unilateral rupture with the effects of a directivity pulse clearly seen in the waveforms and in the measure peak ground velocities. The slip model supports rupture propagation from northeast to southwest at a relatively slow speed of 2.2 km/s and a total source duration of ~20s. In the absence of near-source seismic stations, space geodetic data provide the best constraint on the spatial distribution of slip and on its time evolution.

We use optical satellite data to map the co-seismic displacements for the Mw=7.5 strike-slip earthquake of 28 September 2018 in Palu, Sulawesi, Indonesia. This was a strike-slip faulting event at shallow depth that occurred within the interior of the Molucca Sea microplate, which is part of the Sunda tectonic plate. Using optical image correlation from Sentinel-2 and Planet imagery, we mapped the surface rupture extent of the earthquake and calculated the co-seismic offsets. Before- and after- the earthquake image acquisitions were analyzed using MicMac software and the MPIC-OPT service on the ESA Geohazards TEP platform. Our results include the mapping of a) the detailed trace of the ruptured fault at the southern part of the region (Palu segment) and b) a more complex deformation pattern at the northern part of the rupture. Analysis of the horizontal displacement field and sequential profiles across the fault also enabled mapping of the fault zone complexity, secondary faulting, fault zone width and large co-seismic gravitational phenomena. A mean displacement of 3-5 metres was calculated for a total earthquake rupture length of more than 140 km. Our results agree with the focal mechanism solution for the earthquake which indicates that the rupture occurred on a left-lateral, north-south striking fault. The significance of this event is also associated with the severity of the tsunami impact attributed to a strike slip fault. Further investigation is necessary to determine the source of the tsunami as primarily tectonic or due to another mechanism although a more complex mechanism is likely., Report submitted to EMSC on 19 October 2018 12:00 UTC

OVSICORI GPS instruments are noninertial and directly measure displacements with respect to a global reference frame, while inertial sensors are affected by systematic offsets—primarily tilting—that adversely impact integration to displacement. We study the magnitude scaling properties of peak ground displacement (PGD) from high-rate GPS networks at near-source to regional distances (~10–1000 km), from earthquakes between Mw6 and 9. We conclude that real-time GPS seismic waveforms can be used to rapidly determine magnitude, typically within the first minute of rupture initiation and in many cases before the rupture is complete. While slower than earthquake early warning methods that rely on the first few seconds of P wave arrival, our approach does not suffer from the saturation effects experienced with seismic sensors at large magnitudes. Rapid magnitude estimation is useful for generating rapid earthquake source models, tsunami prediction, and ground motion studies that require accurate information on long-period displacements. Los instrumentos GPS no son inerciales y miden directamente los desplazamientos con respecto a un marco de referencia global, mientras que los sensores inerciales se ven afectados por compensaciones sistemáticas, principalmente la inclinación, que impactan negativamente en la integración con el desplazamiento. Estudiamos las propiedades de escalamiento de magnitud del desplazamiento máximo del suelo (PGD) de redes GPS de alta velocidad en distancias cercanas a la fuente a distancias regionales (~ 10-1000 km), de terremotos entre Mw6 y 9. Concluimos que las formas de onda sísmica GPS en tiempo real se puede utilizar para determinar rápidamente la magnitud, por lo general dentro del primer minuto del inicio de la ruptura y en muchos casos antes de que se complete la ruptura. Si bien es más lento que los métodos de alerta temprana de terremotos que se basan en los primeros segundos de la llegada de la onda P, nuestro enfoque no sufre los efectos de saturación experimentados con los sensores sísmicos de grandes magnitudes. La estimación rápida de la magnitud es útil para generar modelos rápidos de fuentes de terremotos, predicción de tsunamis y estudios de movimiento del suelo que requieren información precisa sobre desplazamientos de períodos prolongados. Os instrumentos de GPS não são inerciais e medem diretamente os deslocamentos em relação a um referencial global, enquanto os sensores inerciais são afetados por deslocamentos sistemáticos - principalmente inclinação - que impactam negativamente a integração ao deslocamento. Nós estudamos as propriedades de escala de magnitude do deslocamento do solo de pico (PGD) de redes GPS de alta taxa na fonte próxima a distâncias regionais (~ 10–1000 km), de terremotos entre Mw6 e 9. Concluímos que formas de onda sísmica de GPS em tempo real pode ser usado para determinar rapidamente a magnitude, normalmente no primeiro minuto do início da ruptura e, em muitos casos, antes que a ruptura seja concluída. Embora mais lento do que os métodos de alerta precoce de terremoto que dependem dos primeiros segundos da chegada da onda P, nossa abordagem não sofre os efeitos de saturação experimentados com sensores sísmicos em grandes magnitudes. A estimativa rápida de magnitude é útil para gerar modelos rápidos de fontes de terremotos, previsão de tsunami e estudos de movimento do solo que requerem informações precisas sobre deslocamentos de longo período. University of California, United States University of Washington, United States Universidad de Chile, Chile Nanyang Technological University, Singapore Universidad Nacional, Costa Rica National Observatory of Athens, Greece Observatorio Vulcanológico y Sismológico de Costa Rica

We combined field mapping and structural analysis of Landsat imagery in order to identify active faults in the broader area of the Simitli graben and to the east towards the cities of Razlog and Bansko, in southwest Bulgaria. We mapped five large active fault segments with normal-slip kinematics and down-to-north displacement and three smaller, antithetic faults near Razlog. Our work suggests that: (a) present-day deformation in SW Bulgaria is extensional and is accommodated by seismic slip along E–W, NE–SW and WNW–ESE normal faults; (b) inversion of fault slip data shows a σ3 axis oriented 336–356 ◦ ; (c) the Krupnik fault comprises one earthquake segment with a general NE–SW strike and dip to the N–NW; its length is about 20 km so its earthquake potential is of the order of Mw = 6.7 ± 0.3; (d) as the 4 April, 1904 earthquake comprised two events, a static stress triggering hypothesis may apply, which is also compatible with the fault segmentation, geomorphology and the macroseismic reports. Source faults for the first event (10:02 a.m.) may have been either the 12 km long Gradevo fault or the 11 km long Elovitsa fault. We estimate a moment magnitude of 6.3 for this event. The first event triggered the second one (10:28 a.m.) on the Krupnik fault. © 2005 Elsevier Ltd. All rights reserved.

We study the tectonic deformation from the February 2017 shallow earthquake sequence onshore Biga Peninsula (NW Turkey, NE Aegean region). We use InSAR interferograms (Sentinel-1 satellites) to identify the seismic fault (striking N110°E) and seismological data (parametric data and Moment Tensor solutions from NOA and KOERI catalogues) so as to refine its geometry and kinematics using inversion techniques. Despite the moderate magnitudes of the main events of the sequence (5.0 ≤ Mw ≤ 5.2), the total surface deformation is 2.2 fringes (or maximum 6.2 cm along LOS) and it is well visible with InSAR because of the shallow depth of the four main events (6–8 km) and the good coherence of the signal phase. Our geodetic inversion showed that the fault has normal-slip kinematics, dimensions of 6 by 6 km (length, width) and dips at 45°. The InSAR data are fitted by a uniform slip of 28 cm. In addition, 429 earthquakes were relocated with the HypoDD software and the use of a 1-D velocity model. The dip-direction of the fault is not retrievable from InSAR, but a south-dipping plane is clear from seismology and the aftershocks distribution. The spatial distribution of relocated events indicates the activation of one fault with a rupture zone length of about 10 km, a result of the occurrence of off-fault aftershocks along strike the main rupture. A stress inversion using 20 focal mechanisms (M ≥ 3.6; NOA solutions) indicates that faulting accommodates a N196°E extension. It is confirmed that moderate (5.0 ≤ M ≤ 5.2) shallow events can be traced in InSAR studies and can produce surface displacements that provide useful data in fault inversion., Remote Sensing, 10 (7), ISSN:2072-4292

On March 3, 2021 a Mw=6.3 shallow earthquake occurred in the mountainous region of Damasi, about 20 km to the northwest of Larisa, Thessaly, central Greece, in a region of active crustal extension but of low strain. This event was followed by a Mw=6.0 shallow earthquake on March 4, 2021 about 12 km to the northwest, inside the sedimentary basin of the Titarisios river. On March 12, 2021 a third event of Mw=5.6 occurred 7 km further towards NNW, near the NW edge of the basin. All events show normal-slip kinematics as indicated by the moment tensor solutions, with minor strike-slip components. Because of the shallow depth of the events it was possible to map the surface deformation using InSAR. The preliminary results from InSAR show three main lobes of subsidence, partially overlapping. The deformation pattern indicates the activation of three normal faults, previously unknown in this part of Thessaly. The earthquakes generated numerous secondary phenomena with vast areas of alluvial deposits exhibiting spectacular liquefaction features. No tectonic ruptures were found in the cases of events 2 and 3, however a series of sporadic, NW-SE striking surface breaks were found on the mountains north of village Zarko that are aligned with the vanishing gradient of the interferometric phase of the 1st event., Partially funded by the joint research - industry project MIS-5070928, financed by the EU and the Greek Government