Observations on the Stress Related Variations of Soil Radon Concentration in the Gulf of Corinth, Greece

Our observations indicate a characteristic pattern in the long-term variation of soil radon concentrations, which seems to be consistent with the expected variation of regional stress in relation to seismicity. However, it seems that the major changes in radon level begin before the rock rapture, i.e. before the earthquake occurs. These conclusions have emerged after long-term observations with continuous and thorough real-time gamma-radiation monitoring in the seismically active area of the Gulf of Corinth, Greece. The recordings acquired close to a hot spring were of very high quality, implying that the deep hydraulic flow can possibly play a key role in the pre-earthquake variation of radon level. We were able to observe outstanding examples of radon level variations before significant seismic events in the Gulf of Corinth that cannot be attributed to other external factors such as atmospheric phenomena

Evidence for stability in coda Q associated with the Egion (central Greece) earthquake of 15 June 1995

Abstract One hundred seventy-two seismograms, recorded at one seismological station located close to the source region of the Egion (Ms = 6.2) 15 June 1995 earthquake, were used to measure values of Q from the decay of the earthquake coda. The collected data were compared between events that occurred before and after the main event. The analysis showed no significant temporal variation in the value of coda Q for the region.</jats:p

Evidence for stability in coda Q associated with the Egion (central Greece) earthquake of 15 June 1995

International audienceOne hundred seventy-two seismograms, recorded at one seismological station located close to the source region of the Egion (Ms = 6.2) 15 June 1995 earthquake, were used to measure values of Q from the decay of the earthquake coda. The collected data were compared between events that occurred before and after the main event. The analysis showed no significant temporal variation in the value of coda Q for the region

Shallow attenuation in the west Corinth-Patras rift, Greece

International audienc

NOANET: A Continuously Operating GNSS Network for Solid-Earth Sciences in Greece

Abstract The NOANET network is a continuously operating high-rate Global Navigation Satellite System (GNSS) network in Greece whose primary role is to enhance and support geophysical research employing GNSS data. This network is operated by the Institute of Geodynamics of the National Observatory of Athens and currently (September 2020) consists of 26 stations, most of which are located close to major seismogenic structures of Greece to optimally measure tectonic and seismically induced motions. All NOANET receivers are configured to record and collect data with a sampling rate of 1 Hz, although some of them also collect data every 5 Hz on their ring buffer. The network is committed to free and open data sharing within the scientific community, and the collected data are made available via the NOANET data repository and distribution point for all interested parties with no limitations. Integrity, validity, and quality checks of the acquired data are performed using a variety of software tools along with in-house developed programs to supervise the network performance and detect ill-formed data and/or awkward station behavior. In addition, the conventional low-rate GNSS observation data of all NOANET stations are routinely processed on a daily basis to supervise their performance through their position time series. Since the beginning of its establishment, the NOANET network has recorded a variety of deformation signals, and a large number of published papers have used GNSS data from stations that are part of NOANET to constrain, model, and interpret the nature of the associated geophysical phenomena.</jats:p

High-resolution passive seismic tomography for 3D velocity, Poisson’s ratio<i>ν</i>, and P-wave quality<i>Q</i>_Pin the Delvina hydrocarbon field, southern Albania

We have studied using traveltimes of P- and S-waves and initial seismic-pulse rise-time measurements from natural microearthquakes to derive 3D P-wave velocity VPinformation (mostly structural) as well as P- and S-wave velocity VP/VSand P-wave quality factor QPinformation (mostly lithologic) in a known hydrocarbon field in southern Albania. During a 12-month monitoring period, 1860 microearthquakes were located at a 50-station seismic network and were used to obtain the above parameters. The data set included earthquakes with magnitudes ranging from –0.1 to 3.0 R (Richter scale) and focal depths typically occurring between 2 and 10 km. Kohonen neural networks were implemented to facilitate the lithological classification of the passive seismic tomography (PST) results. The obtained results, which agreed with data from nearby wells, helped delineate the structure of the reservoir. Two subregions of the investigated area, one corresponding to an oil field and one to a gas field, were correlated with the PST results. This experiment showed that PST is a powerful new geophysical technique for exploring regions that present seismic penetration problems, difficult topographies, and complicated geologies, such as thrust-belt regions. The method is economical and environmentally friendly, and it can be used to investigate very large regions for the optimal design of planned 2D or 3D conventional geophysical surveys.</jats:p

Regional ground‐motion prediction equations for amplitude‐, frequency response‐, and duration‐based parameters for Greece

Although all of the main properties of a ground motion cannot be captured through a single parameter, a number of different engineering parameters has been proposed that are able to reflect either one or more ground‐motion characteristics concurrently. For many of these parameters, especially regarding Greece, there are relatively few or no predictive models. In this context, we present a set of new regionally‐calibrated equations for the prediction of the geometric mean of the horizontal components of 10 amplitude‐, frequency response‐, and duration‐based parameters for shallow crustal earthquakes. These equations supersede previous empirical relationships for Greece since their applicability range for magnitude, and epicentral distance has been extended down to Mw 4 and up to 200 km, respectively, the incorporation of a term accounting for anelastic attenuation has been investigated, while their development was based on a ground‐motion dataset spanning from 1973 to 2014. For all ground‐motion parameters, we provide alternative optimal equations relative to the availability of information on the different explanatory variables. In all velocity‐based and contrary to the acceleration‐based parameters, the anelastic attenuation coefficient was found statistically insignificant when it was combined with the geometric decay and the coefficient accounting for saturation with distance. In the regressions where the geometric decay coefficient simultaneously incorporated the contribution of anelastic attenuation, its increase was found to be much less considerable in the velocity‐based than in the acceleration‐based parameters, implying a stronger effect of anelastic attenuation on the parameters that are defined via the acceleration time history