Prospectivity Mapping for Epithermal Deposits of Western Milos Using a Fuzzy Multi Criteria Evaluation Approach Parameterized by Airborne Hyperspectral Remote Sensing Data

A Mineral prospectivity mapping (MPM) approach using a GIS-based weighted linear combination implementation of a Multi-Criteria Evaluation approach utilising a fuzzy Analytical Hierarchy Process to elucidate expert knowledge has been implemented to analyse the spatial distribution of epithermal deposits on the Island of Milos, Greece and model their association with exploration evidence data with the aim of providing insights into the controls on ore deposition. An integrated field and Digital Airborne Imaging Spectrometer (DAIS) hyperspectral and thermal multispectral airborne remote sensing dataset supported by field mapping and laboratory analyses, has been utilised to resolve hydrothermal alteration and parameterise the MPM. This study has highlighted the intimate spatial relationship between topographic highs and locations with high grade silicified alteration at a number of locations. The ability of high spatial resolution multispectral Thermal InfraRed (TIR) remote sensing imagery, integrated with topographic data, to resolve these silicified topographic highs provides an additional tool in the exploration of epithermal deposits. The spatial relationships between silicified lithocaps, high-grade altered rocks, faulting and topographic highs were utilised in the development of the MPM model. A close association between the modelled results and the hydrothermal alteration mapped in the field supports the accuracy of this MPM approach.Funded by Natural Environment Research Council (NERC) GA/09f/139-RMS E355

Prospectivity mapping for high sulfidation epithermal porphyry deposits using an integrated compositional and topographic remote sensing dataset

The targeting and discovery of epithermal porphyry mineral deposits can be enhanced using a structured quantitative methodology to analyse the distribution of ore deposits and model their spatial association with exploration evidence providing improved understanding on the controls of ore deposition. A novel exploration tool integrating field and ASTER SWIR and TIR satellite imagery has been developed which provides an enhanced means of resolving surface expressions of the residual silica core of the lithocap. The alteration zones were clearly resolved by the remote sensing data and an intimate spatial relationship between high-grade altered rocks and topographic highs was identified at a number of locations. A Mineral Prospectivity Modelling (MPM) approach, parameterized by the results of the remote sensing study, using a GIS-based weighted linear combination implementation of a Multi-Criteria Evaluation approach and utilising a fuzzy Analytical Hierarchy Process to elucidate expert knowledge has been implemented to target high sulfidation epithermal porphyry deposits on the Island of Lesvos, Greece. The results from this integrated altitudinal-compositional modelling approach closely matched the hydrothermal alteration mapped in the field supporting the accuracy of this MPM approach.Leverhulme Trust NERC Field Spectroscopy Facilit

A 20-yr database (1997-2017) of co-seismic displacements from GPS recordings in the Aegean area and their scaling with Mw and hypocentral distance

Στην παρούσα εργασία περιγράφουμε και διαθέτουμε μία βάση εξήντα τεσσάρων (64) σεισμικών μετατοπίσεων από τις καταγραφές μόνιμων σταθμών GPS, κατά την εικοσαετή χρονική περίοδο 1997-2017. Οι μετατοπίσεις οφείλονται σε μεγάλους, επιφανειακούς σεισμούς στον Ελληνικό χώρο οι οποίοι προκάλεσαν επιφανειακές κινήσεις (της τάξεως χιλιοστών έως δεκάδων εκατοστών) ανιχνεύσιμες από δίκτυα GPS-GNSS. Στην βάση περιλαμβάνονται δεδομένα μόνιμης μετατόπισης για αποστάσεις μεταξύ 2-132 km από το υπόκεντρο και για 11 σεισμούς με μεγέθη ροπής μεταξύ 5.5≤Mw≤6.9. Αυτά τα δεδομένα είναι χρήσιμα σε γεωλόγους, σεισμολόγους και μηχανικούς επειδή συμβάλουν στην πληρέστερη κατανόηση της μηχανικής των διαρρήξεων, της κατανομής των επιφανειακών παραμορφώσεων μετά από μεγάλους σεισμούς αλλά και σε άλλες εφαρμογές σεισμικής μηχανικής. Επιπλέον, έγινε ανάλυση με πρώτη νόρμα (L1- norm) παλινδρόμησης της απόσβεσης της μόνιμης, οριζόντιας επιφανειακής μετατόπισης συναρτήσει του μεγέθους και υποκεντρικής απόστασης. Βρήκαμε ότι τα δεδομένα μας ταιριάζουν καλύτερα με μία γραμμική συμπεριφορά για αυτό το εύρος μεγεθών. Προτείνουμε δύο εμπειρικές σχέσεις για τον υπολογισμό του σεισμικού μεγέθους βάσει της εδαφικής μετατόπισης και της αποστάσεως από το υπόκεντρο, οι οποίες μπορούν να χρησιμοποιηθούν εφόσον είναι διαθέσιμες επιλύσεις σταθμών σε σχεδόν-πραγματικό χρόνο.We describe and make available a dataset of 64 data points of Global Positioning System (GPS) displacements for significant, shallow earthquakes in Greece during the period 1997-2017. The displacement data can be used by earthquake geologists, engineers and seismologists in an effort to better understand the faulting process, the rupture mechanics, the pattern of ground-motions, and in engineering applications. We include recordings from GNSS networks at near-source to regional distances (2–132 km) for 11 earthquakes between global CMT moment magnitudes (Mw) 5.5 and 6.9. We also model the magnitude scaling properties of peak ground horizontal displacements (PGD and PGD-S) for these events using L1-norm minimisation regression. Our data indicate an almost linear attenuation of seismic strain with distance for this range of seismic magnitudes. We developed a set of relationships based on PGD (in cm) and distance to hypocentre R (in km), which may be used for the rapid estimation of the earthquake magnitude in near real-time.MwPGD = [LOG(PGD) + 8.2849]/(1.6810 – 0.2453LOGR)MwPGD-S = [LOG(PGD-S) + 8.0839]/(1.6793 – 0.2447LOGR

Temporal and spatial earthquake clustering revealed through comparison of millennial strain-rates from ³⁶Cl cosmogenic exposure dating and decadal GPS strain-rate

To assess whether continental extension and seismic hazard are spatially-localized on single faults or spread over wide regions containing multiple active faults, we investigated temporal and spatial slip-rate variability over many millennia using in-situ 36Cl cosmogenic exposure dating for active normal faults near Athens, Greece. We study a ~ NNE-SSW transect, sub-parallel to the extensional strain direction, constrained by two permanent GPS stations located at each end of the transect and arranged normal to the fault strikes. We sampled 3 of the 7 seven normal faults that exist between the GPS sites for 36Cl analyses. Results from Bayesian inference of the measured 36Cl data implies that some faults slip relatively-rapidly for a few millennia accompanied by relative quiescence on faults across strike, defining out-of-phase fault activity. Assuming that the decadal strain-rate derived from GPS applies over many millennia, slip on a single fault can accommodate ~ 30–75% of the regional strain-rate for a few millennia. Our results imply that only a fraction of the total number of Holocene active faults slip over timescales of a few millennia, so continental deformation and seismic hazard are localized on specific faults and over a length-scale shorter than the spacing of the present GPS network over this time-scale. Thus, (1) the identification of clustered fault activity is vital for probabilistic seismic hazard assessments, and (2) a combination of dense geodetic observations and palaeoseismology is needed to identify the precise location and width of actively deforming zones over specific time periods

Sub- and super-shear ruptures during the 2023 Mw 7.8 and Mw 7.6 earthquake doublet in SE Türkiye

An earthquake doublet (Mw 7.8 and Mw 7.6) occurred on the East Anatolian Fault Zone (EAFZ) on February 6th, 2023. The events produced significant ground motions and caused major impacts to life and infrastructure throughout SE Türkiye and NW Syria. Here we show the results of earthquake relocations of the first 11 days of aftershocks and rupture models for both events inferred from the kinematic inversion of HR-GNSS and strong motion data considering a multi-fault, 3D geometry. We find that the first event nucleated on a previously unmapped fault before transitioning to the East Anatolian Fault (EAF) rupturing for ~350 km and that the second event ruptured the Sürgü fault for ~160 km. Maximum rupture speeds were estimated to be 3.2 km/s for the Mw 7.8 event. For the Mw 7.6 earthquake, we find super-shear rupture at 4.8 km/s westward but sub-shear eastward rupture at 2.8 km/s. Peak slip for both events were as large as ~8m and ~6m, respectively

Ground Deformation and Seismic Fault Model of the M6.4 Durres (Albania) Nov. 26, 2019 Earthquake, Based on GNSS/INSAR Observations

We identify the source of the Mw = 6.4 earthquake that rocked north-central Albania on November 26, 2019 02:54 UTC. We use synthetic aperture radar interferograms tied to the time series of coordinates of two permanent Global Navigation Satellite System (GNSS) stations (DUR2 and TIR2). We model the source by inverting the displacement data. Assuming in our model a half-space elastic medium and uniform slip along a rectangular fault surface, we invert the 104 picked measurements on a couple of ascending and descending interferograms to calculate the parameters of the fault. All inversions made with different input parameters converge towards a stable and robust solution with root mean square (r.m.s.) residual of 5.4 mm, thus ~1/5 of a fringe. They reveal that the earthquake occurred deep in the crust on a low-angle fault (23°) dipping towards east with a centroid at 16.5 km depth. The best-fitting length and width of the fault are 22 and 13 km, and the reverse slip, 0.55 m. The seismic moment deduced from our model agrees with those of the published seismic moment tensors. This geometry is compatible with a blind thrust fault that may root on the main basal thrust, i.e., along the thrust front that separates Adria–Apulia from Eurasia. It is notable that there is a 123 ns yr−1 active shortening of the crust between the GNSS stations DUR2-TIR2 (equivalent to a shortening rate of 3.6 mm yr−1), and roughly in the east–west direction. Given this amount of strain the recurrence time of M6+ earthquakes along this fault should be of the order of 150 years

Multisegment ruptures and Vp / Vs variations during the 2020–2021 seismic crisis in western Corinth Gulf, Greece

International audienceSUMMARY On 2020 December 23, a seismic crisis initiated in the western Corinth Gulf offshore Marathias, lasted several months, and generated thousands of small magnitude earthquakes. The Gulf of Corinth is well known for earthquake swarm occurrence and short-lived burst-like earthquake sequences, mostly triggered by crustal fluids. Here, we perform a detailed seismic analysis aiming to identifying earthquake clusters within the seismic crisis and define their spatial and temporal characteristics. Thanks to the dense seismic station coverage in the area, operated by the Hellenic Unified Seismological Network and Corinth Rift Laboratory, we relocate shallow seismicity and compile a high-resolution earthquake catalogue containing ∼1400 earthquakes spanning the first two months of the seismic crisis. We identify 19 earthquake clusters by applying spatio-temporal criteria and define the geometry (strike and dip) using principal component analysis for 11 of them. Our results are consistent with moment tensor solutions computed for the largest earthquake in each cluster. A striking feature of the seismic activity is the west-towards-east migration with a notable increase in Vp/Vs values for each cluster and a slight increase of the dip angle for the identified fault segments. Furthermore, we find that each cluster contains several burst-like, short interevent time, repeating earthquakes, which could be related to aseismic slip or fluid migration. Overall, we show that the 2020–2021 seismic crisis consists of earthquake clusters that bifurcate between swarm-like and main shock–aftershock-like sequences and ruptured both north- and south-dipping high-angle fault segments. The 2020–2021 seismic activity is located between 5 to 8 km, shallower than the low angle north-dipping (∼10°) seismic zone which hosts long-lived repeating sequences at ∼9–10 km depth. This study supports a hypothesis that the low-angle north-dipping seismicity defines the brittle-ductile transition in the western Corinth Gulf, with seismic bursts occurring at shallower depths in the crust

Static stress transfer from the May 20, 2012, M 6.1 Emilia-Romagna (northern Italy) earthquake using a co-seismic slip distribution model

We model the static stress transfer for the May 2012 northern Italy earthquakes, assuming that failure of the crust occurs by shear. This allows the mechanics of the process to be approximated by the Okada (1992) expressions for displacement and strain fields due to a finite rectangular source in an elastic, homogeneous and isotropic half-space. The slip model of the May 20, 2012, earthquake was derived using empirical Green’s functions and a least-squares inversion scheme of source time functions computed from regional broadband seismological data. The derived model is then incorporated into the computation of Coulomb stress change (ΔCFF) to investigate the possibility that the May 20, 2012, M 6.1 event triggered the second earthquake that occurred on May 29, 2012 (M 5.9). We calculate the Coulomb stress changes for both: (a) optimally oriented planes to regional compression; and (b) planes of fixed orientation assuming that E-W striking, south-dipping thrust faults of the May 29, 2012, type of rupture was a candidate for failure. In both cases, we find that the triggering is promoted as the ΔCFF values in the hypocentral area of the May 29, 2012, earthquake are positive (between 0.61-0.74 bar).