Konstantinos Leptokaropoulos

A Homogeneous Earthquake Catalog for Western Turkey and Magnitude of Completeness Determination

Abstract A catalog for earthquakes that occurred in western Turkey during the period 1964–2010 is compiled for achieving homogeneity for magnitudes. Data are obtained from the International Seismological Center (ISC), where earthquake magnitudes are reported in different scales and come from a variety of sources. For establishing a common magnitude expression, namely an equivalent moment magnitude , new relations correlating the different magnitude scales with each other are derived from converting as many as possible of the magnitudes reported in the ISC bulletins. After magnitude conversions, the completeness magnitude M c is sought by modifying the goodness‐of‐fit method of Wiemer and Wyss (2000) to become more appropriate for datasets with smaller sample size and higher M c thresholds. The study region is divided into four smaller regions on the basis of spatial data homogeneity, while different periods of similar seismic network performance are recognized and tested to seek spatiotemporal variation of M c . The results derived in each case are compared with those yielded by the application of both the original goodness‐of‐fit and maximum curvature methods and are found to be quite similar, although there are still cases with a difference exceeding 0.3 magnitude units. The goodness‐of‐fit method is very sensitive in the selection of the desirable percentage of fitting a power law (90% or 95%), whereas the proposed modification makes it independent of this level selection, and performing better especially for datasets that include events before 1990, when higher completeness magnitudes are evident. Online Material: Earthquake catalog with equivalent moment magnitude for western Turkey.

Time-dependent seismic hazard in Bobrek coal mine, Poland, assuming different magnitude distribution estimations

The purpose of this study is to evaluate seismic hazard parameters in connection with the evolution of mining operations and seismic activity. The time-dependent hazard parameters to be estimated are activity rate, Gutenberg–Richter b-value, mean return period and exceedance probability of a prescribed magnitude for selected time windows related with the advance of the mining front. Four magnitude distribution estimation methods are applied and the results obtained from each one are compared with each other. Those approaches are maximum likelihood using the unbounded and upper bounded Gutenberg–Richter law and the non-parametric unbounded and non-parametric upper-bounded kernel estimation of magnitude distribution. The method is applied for seismicity occurred in the longwall mining of panel 3 in coal seam 503 in Bobrek colliery in Upper Silesia Coal Basin, Poland, during 2009–2010. Applications are performed in the recently established Web-Platform for Anthropogenic Seismicity Research, available at https://tcs.ah-epos.eu/.

Temporal static stress drop variations due to injection activity at The Geysers geothermal field, California

We use a high-quality data set from the NW part of The Geysers geothermal field to determine statistical significance of temporal static stress drop variations and their relation to injection rate changes. We use a group of 322 seismic events which occurred in the proximity of Prati-9 and Prati-29 injection wells to examine the influence of parameters such as moment magnitude, focal mechanism, hypocentral depth, and normalized hypocentral distances from open-hole sections of injection wells on static stress drop changes. Our results indicate that (1) static stress drop variations in time are statistically significant, (2) statistically significant static stress drop changes are inversely related to injection rate fluctuations. Therefore, it is highly expected that static stress drop of seismic events is influenced by pore pressure in underground fluid injection conditions and depends on the effective normal stress and strength of the medium.

Non-stationarity and internal correlations of the occurrence process of mining-induced seismic events

A point process, e.g., the seismic process, is potentially predictable when it is non-stationary, internally correlated or both. In this paper, an analysis of the occurrence process of mining-induced seismic events from Rudna copper mine in Poland is presented. Stationarity and internal correlation are investigated in complete seismic time series and segmentally in subseries demonstrating relatively stable seismicity rates. It is shown that the complete seismic series are non-stationary; however, most of their shorter subseries become stationary. In the stationary subseries, the distribution of interevent time is closer to the exponential distribution, which is characteristic for the Poisson process. However, in most of these subseries, the differences between the interevent time and Poisson distributions are still significant, revealing correlations among seismic events.

IS-EPOS: a platform for anthropogenic seismicity research

Research in the field of anthropogenic seismicity (AS) requires not only seismicity data but also data regarding the progress of the technological/production activities which is the origin of the induced or triggered seismic events. Such data are typically restricted and proprietary, and therefore, usually not available for independent researchers who wish to develop, perform and verify scientific research. The induced seismicity-European plate observing system (IS-EPOS) web portal offers to its user’s access to data, applications and documents in order to facilitate AS research. IS-EPOS web portal has been designed to serve as one of the main pillars of the Thematic Core Service—-Anthropogenic Hazards belonging to pan-European multidisciplinary research infrastructure created within the EPOS program. IS-EPOS platform is open for research community and general public according to its rules of access. The platform is operating since January 2016 and is now integrated in the EPOS Integrated Core Services. IS-EPOS e-platform promotes new opportunities to study and comprehend the dynamic and complex solid earth system by integrating the use of multidisciplinary data, data products, analysis models and online applications. The integration of existing and new national and transnational Research Infrastructures increases the access and use of multidisciplinary data recorded by the solid earth observing systems, acquired in laboratory experiments and/or produced by computational simulations. In this paper, we describe the structure and the main innovative characteristics implemented in IS-EPOS. The platform is open to accommodate data integrated within other research projects, and it is continuously being updated with improvements in existing features and implementations of new ones. An appendix at the end of the article provides a summary of acronyms and abbreviations in order to make the reader familiar with the terms used throughout the manuscript.

Time‐Dependent Earthquake Occurrence Rates along the Hellenic Arc

Seismicity rate changes in the Hellenic subduction zone (southern Aegean Sea) were studied by applying the Dieterich (1994) rate/state‐dependent friction model combined with static Coulomb stress changes (ΔCFF). The coseismic slip of the strongest earthquakes (with moment magnitude, M w≥6.0) was considered to contribute to the stress field evolution along with the continuous tectonic loading. Stress changes were calculated just after each strong event, and their influence was examined in connection with the smaller magnitude earthquake occurrence rates. Qualitative and quantitative comparison between the observed seismicity rates (smoothed by the means of a probability density function) and the expected ones, as they were forecasted by the rate/state model, were investigated for the interseismic periods (study periods) between subsequent strong earthquakes. The calculations aim to identify areas of expected increased seismicity rates as candidates to accommodate enhanced seismic activity. Results strongly depend on the determination (smoothing) of the unperturbed (reference) seismicity rates and data adequacy. Seismicity rate results were filtered by certain criteria and constraints, in an attempt to overcome model uncertainties (epicentral errors, rupture models, parameter values) and to provide reliable results for specific areas of major interest, that is, in areas with increased positive Coulomb stress changes values. The modeling approach resulted in satisfactory correlation between observed and synthetic seismicity rates and, in particular, the two strong ( M w≥6) earthquakes that occurred in 2013 are located in areas of increased expected seismicity rates.