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Papazachos, Costas
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- PublicationOpen AccessOn the validity of the regional time and magnitude predictable model in China(1999-10)
; ; ; ; ;Qin, C.; Laboratory of Geophysics, University of Thessaloniki, Greece ;Papadimitriou, E. E.; Laboratory of Geophysics, University of Thessaloniki, Greece ;Papazachos, B. C.; Laboratory of Geophysics, University of Thessaloniki, Greece ;Karakaisis, G. F.; Laboratory of Geophysics, University of Thessaloniki, Greece; ; ; A simplified form of the "regional time and magnitude predictable model" gives the time interval, T, between two successive mainshocks in a region and the magnitude, Mf, of the following mainshock by the relations: logT=cMP+a; Mf=CMp+A, where Mp is the magnitude of the preceding mainshock, a, A are constants which depend on the minimum considered mainshock and on the region's tectonic loading (moment rate). The physical meaning of the model is that the larger the magnitude of the preceding main shock, Mp, the longer the time, T, will be till the occurrence of the next one and the smaller its magnitude, Mf. This means that parameters c and C are positive and negative, respectively, when the model has been found valid for a certain area. In order to examine if the above model is appropriate to describe the seismicity behavior in the area of China, a detailed inspection was carried out aiming to show if the estimated values of parameters c and C favor the model. The results show that c tends to the global value 0.33, obtained by Papazachos and Papadimitriou (1997), and that C tends to be within the range [-0.30, -0.23]. The results, which favored the model, greatly outnumber those that do not follow it, the latter being concentrated around the boundaries of the seismically active regions. It is concluded that the results, which favor the model, obviously dominate the whole territory of China.183 189 - PublicationOpen AccessPrecursory accelerated Benioff strain in the Aegean area(2001-04)
; ; ;Papazachos, C.; Geophysical Laboratory, University of Thessaloniki, Greece ;Papazachos, B.; Geophysical Laboratory, University of Thessaloniki, Greece; Accelerating seismic crustal deformation due to the occurrence of intermediate magnitude earthquakes leading to the generation of a mainshock has recently been considered a critical phenomenon. This hypothesis is tested by the use of a large data sample concerning the Aegean area. Elliptical critical regions for fifty-two strong mainshocks, which have occurred in the Aegean area since 1930, have been identified by applying a power-law relation between the cumulative Benioff strain and the time to the main rupture. Empirical relations between the parameters of this model have been further improved by the use of a large data sample. The spatial distribution of preshocks with respect to the mainshock is examined and its tectonic significance is pointed out. The possibility of using the results of this work to predict the epicentre, magnitude and time of ensuing mainshocks are discussed and further work towards this goal is suggested.157 655 - PublicationOpen AccessMonitoring of the geomagnetic and geoelectric field in two regions of Greece for the detection of earthquake precursors(1997-03)
; ; ; ; ; ;Vargemezis, G.; Geophysical Laboratory, University of Thessaloniki, Greece ;Zlotnicki, J.; Laboratoire de Geophysique d'Orleans, France ;Tsokas, G.; Geophysical Laboratory, University of Thessaloniki, Greece ;Papazachos, B. C.; Geophysical Laboratory, University of Thessaloniki, Greece ;Papadimitriou, E. E.; Geophysical Laboratory, University of Thessaloniki, Greece; ; ; ; Two magnetotelluric stations have been installed in the South-Eastern Thessaly basin (Central Greece), which have recorded the geomagnetic and geoelectric fields since 1993. The aim is to detect long lasting abnormal changes of the geoelectric field which may be due to impending earthquakes. The geoelectric recordings were checked against the climatic changes such as temperature changes and precipitation and no correlation was observed. Ten anomalies were observed with characteristics similar to seismoelectric signals which have been reported in the literature and thus we can assume that these changes constitute precursory phenomena. The duration of these signals varies from several days to a few weeks. Some of them keep on developing until the occurrence of an earthquake, and others appear like transient changes several days before. The high seismicity of the area where the stations are located creates difficulties in the correlation of the signals with certain shocks.155 141 - PublicationOpen AccessLarge seismic faults in the Hellenic arc(1996-10)
; ;Papazachos, B. S.; Geophysical Laboratory, University of Thessaloniki, Thessaloniki, GreeceUsing information concerning reliable fault plane solutions, spatial distribution of strong earthquakes (Ms³ 6.0) as well as sea bottom and coastal topography, properties of the seismic faults (orientation, dimension, type of faulting) were determined in seven shallow (h < 40 km) seismogenic regions along the convex part of thc Hellenic arc (Hellenic trench) and in four seismogenic regions of intermediate depth earthquakes (h = 40-100 km) along the concave part of this arc. Except for the northwesternmost part of the Hellenic trench, where the strike-slip Cephalonia transform fault dominates, all other faults along this trench are low angle thrust faults. III thc western part of the trench (Zante-west Crete) faults strike NW-SE and dip NE, while in its eastern part (east Crete-Rhodos) faults strike WNW-ESE and dip NNE. Such system of faulting can be attributed to an overthrust of the Aegean lithosphere on the eastern Mediterranean lithosphere. The longest of these faults (L = 300 km) is that which produced the largest known shallow earthquake in the Mediterranean area (21 July 365, Ms = 8.3) which is located near the southwestern coast of Crete. The second longest such fault (L = l 70 km) is that which produced a large earthquake (December 1303, Ms = 8.0) in the easternmost part of the trench (east of Rhodos island). Both earthquakes were associated with gigantic tsunamis which caused extensive damage in the coast of many Eastern Mediterranean countries. Seismic faults of the intermediate depth earthquakes in the shallow part of the Benioff zone (h = 40- 100 km) are of strike-slip type, with a thrust component. The orientations of these faults vary along the concave part of the arc in accordance with a subduction of remnants of all old lithospheric slab from the convex side (Mediterranean) to the concave side (Aegean) of thc Hellenic arc. The longest of these faults (L = 220 km) is that which produced the largest known intermediate depth earthquake in the whole Mediterranean area (12 October 1856, M = 8.2) north of Crete. The second longest such fault (L = 160 km) produced a large earthquake (26 June 1926, M = 8.0) in the easternmost part of the concave part of the arc (near Rhodos). Both earthquakes caused very serious damage in several Eastern Mediterranean countries but were not associated with tsunamis.349 3912 - PublicationRestrictedGeochemical and isotopic changes in the fumarolic and submerged gas discharges during the 2011–2012 unrest at Santorini caldera (Greece)(2013)
; ; ; ; ; ; ; ; ; ;Tassi, F.; Department of Earth Sciences, University of Florence,Italy ;Vaselli, O.; Department of Earth Sciences, University of Florence,Italy ;Papazachos, C. B.; Geophysical Laboratory, Aristotle University of Thessaloniki, ;Giannini, L.; Department of Earth Sciences, University of Florence,Italy ;Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Vougioukalakis, G. E.; IGME—Institute for Geology and Mineral Exploration, ;Karagianni, E.; Geophysical Laboratory, Aristotle University of Thessaloniki, ;Vamvakaris, D.; Geophysical Laboratory, Aristotle University of Thessaloniki, ;Panagiotopoulos, D.; Geophysical Laboratory, Aristotle University of Thessaloniki,; ; ; ; ; ; ; ; Abstract A geochemical survey of fumarolic and submerged gases from fluid discharges located in the Nea Kameni and Palea Kameni islets (Santorini Island, Greece) was carried out before, during, and after the unrest related to the anomalously high seismic and ground deformation activity that affected this volcanic system since January 2011. Our data show that from May 2011 to February 2012, the Nea Kameni fumaroles showed a significant increase of H2 concentrations. After this period, an abrupt decrease in the H2 contents, accompanied by decreasing seismic events, was recorded. A similar temporal pattern was shown by the F−, Cl−, SO4 2−, and NH4 + concentrations in the fumarolic condensates. During the sharp increase of H2 concentrations, when values up to 158 mmol/ mol were measured, the δ13C–CO2 values, which prior to January 2011 were consistent with a dominant CO2 thermometamorphic source, have shown a significant decrease, suggesting an increase of mantle CO2 contribution. Light hydrocarbons, including CH4, which are controlled by chemical reactions kinetically slower than H2 production from H2O dissociation, displayed a sharp increase in March 2012, under enhanced reducing conditions caused by the high H2 concentrations of May 2011–February 2012. The general increase in light hydrocarbons continued up to July 2012, notwithstanding the contemporaneous H2 decrease. The temporal patterns of CO2 concentrations and N2/Ar ratios increased similarly to that of H2, possibly due to sealing processes in the fumarolic conduits that diminished the contamination related to the entrance of atmospheric gases in the fumarolic conduits. The compositional evolution of the Nea Kameni fumaroles can be explained by a convective heat pulse from depth associated with the seismic activation of the NE–SW-oriented Kameni tectonic lineament, possibly triggered by either injection of new magma below Nea Kameni island, as apparently suggested by the evolution of the seismic and ground deformation activity, or increased permeability of the volcanic plumbing system resulting from the tectonic movements affecting the area. The results of the present study demonstrate that the geophysical and geochemical signals at Santorini are interrelated and may be precursory signals of renewed volcanic activity and encourage the development of interdisciplinary monitoring program to mitigate the volcanic risk in the most tourist-visited island of the Mediterranean Sea.462 66 - PublicationOpen AccessNon-linear arrival time tomography(1997-01)
; ; ;Papazachos, C. B.; Institute of Engineering Seismology and Earthquake Engineering (ITSAK), Foinikas, Thessaloniki, Greece ;Nolet, G.; Department of Geological and Geophysical Sciences, Princeton University, Princeton, USA; The use of 1D or pseudo- 3D ray tracing techniques in linearized tomographic problems leads to solutions for which it is difficult to assess the true resolution and error distribution. For this reason, we employ a revised 3D bending algorithm (Moser et al., 1992) and show that it can be used efficiently for a non-linear inversion in a stepwise scheme. Initial paths are determined from graph theory in order to avoid local minima in bending. The importance of 3D ray tracing in inversion studies and the limitations of the standard 1D approach are demonstrated through synthetic examples. The speed of the ray tracing and the simple scaling scheme allow for an implementation in large-scale tomographic problems.148 283 - PublicationOpen AccessSesame Project - Deliverable D20-04 - WP04 H/V Technique : Empirical Evaluation - Comparisons of Damage Distribution in Modern Urban Areas with Results from (H/V) Spectral Ratio(2004-07)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Bordoni, Paola; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Cara, Fabrizio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cultrera, Giovanna; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Dimitriu, Petros; ITSAK, Thessaloniki, Greece ;Di Giulio, Giuseppe; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Hatzidimitriou, Panagiotis; ITSAK/AUTH-Geolab, Thessaloniki, Greece ;Lenti, Luca; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Marra, Fabrizio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Marcellini, Alberto; CNR, Milan, Italy ;Milana, Giuliano; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Oliveira, Carlos; Inst. Superior Tecnico, Lisbon, Portugal ;Pagani, Marco; CNR, Milan, Italy ;Panou, Areti; ITSAK, Thessaloniki, Greece ;Papazachos, Costas; ITSAK/AUTH-Geolab, Thessaloniki, Greece ;Rovelli, Antonio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Savvaidis, Alexandros; ITSAK, Thessaloniki, Greece ;Senos, M. Luisa; Inst. Meteorology, Lisbon, Portugal ;Tento, Alberto; CNR, Milan, Italy ;Tertulliani, Andrea; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Teves-Costa, Paula; ICTE/UL, Lisbon, Portugal ;Theodoulidis, Nikos; ITSAK, Thessaloniki, Greece; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; In this Report comparisons of seismic damage distribution with the (H/V) spectral ratio results is attempted, under the framework of the SESAME Project (Site Effects Assessment Using Ambient Excitations, EC-RGD, Project No. EVG1-CT-2000-00026 SESAME), Task A (H/V technique), Work Package 04 (WP04– H/V Technique: Empirical Evaluation).239 127 - PublicationOpen AccessMicroearthquake study of the broader Thessaloniki area (Northern Greece)(2006-08)
; ; ; ; ; ; ;Paradisopoulou, P. M.; Department of Geophysics, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece ;Karakostas, V. G.; Department of Geophysics, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece ;Papadimitriou, E. E.; Department of Geophysics, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece ;Tranos, M. D.; Department of Geology, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece ;Papazachos, C. B.; Department of Geophysics, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece ;Karakaisis, G. F.; Department of Geophysics, School of Geology, Aristotle University of Thessaloniki, Thessaloniki, Greece; ;; ; ; A temporary network of twelve portable digital seismological stations was operated around the city of Thessaloniki (Northern Greece) for a period of 19 months (from July 2001 to April 2002 and from October 2002 to August 2003), providing data that enabled the study of the interconnection between microseismicity and active tectonics in the area. During the operation period 277 microearthquakes that were recorded in more than four stations were accurately located and 64 fault plane solutions were determined. Seismic activity is associated with ENE-WSW, E-W and ESE-WNW striking normal faults and is nearly confined to the first 15 km, thus defining the seismogenic layer in the study area. The mean orientation of the axis of maximum extension (T-axis) is NS to NNE-SSW, determined from fault plane solutions, in agreement with the regional extensional stress pattern, which strikes perpendicular to the orientation of the main WNW-ESE active faults of the area.200 368