Seismicity Variations in the Southern Aegean,Greece, Before and After the Large (M7.7) 1956 Amorgos Earthquake Due to Evolving Stress     

Eleftheria?PapadimitriouEmail author  Georgios?Sourlas  Vassilios?Karakostas 《Pure and Applied Geophysics》2005,162(5):783-804

The largest earthquake (M₀=4.9·10²⁷ dyn·cm) of the 20^th century in the territory of Greece occurred south of Amorgos Island, causing extensive destruction in the southern Aegean area. It occurred on an ENE–trending normal fault that is seated parallel to the Islands southern coastline. Changes in the rates of moderate–size earthquakes (M 5.0) that occurred before and after the Amorgos earthquake, within circular regions centered on its epicenter with radii of 100, 150 and 200 km, are investigated. The rate for moderate–size events just before the main shock appears to be considerably increased when compared to those of either preceding or subsequent periods. Further inspection reveals that more evident seismicity fluctuations are attributed to distances exceeding 100 km. These changes may be indicative of a broad region that is approaching a high stress state prior to an eventual large earthquake. Close to the main event, that is, within the 100–km radius, a remarkable quiescence period lasting about two decades before its occurrence was observed. Changes in seismicity are discussed in combination with static stress changes calculated by the application of the stress evolutionary model that takes into account the coseismic slip associated with the larger events (M 6.5) since the beginning of the 20^th century and the tectonic loading on the major faults in the study area. These larger events, as with the intermediate magnitude seismicity taking place at distances exceeding 100 km and which encircled the quiescent area observed during the last 22 years before the Amorgos earthquake, are well correlated with stress-enhanced areas in each stage of the evolutionary model.  相似文献   

A geographical information system managing geotechnical data for Athens (Greece) and its use for automated seismic microzonation   总被引：1，自引：1，他引：0  

A. A. Antoniou  A. G. Papadimitriou  G. Tsiambaos 《Natural Hazards》2008,47(3):369-395

This article presents a geographical information system (GIS) which manages geotechnical data obtained from detailed geotechnical surveys as well as from in situ observations in Athens, Greece. Thoroughly examined data from more than 2,000 exploratory boreholes and trial pits located in the wider area of Athens have been incorporated using a relational database system. From the analysis of these results, thematic maps are compiled to illustrate the distribution of engineering geological information (e.g. the depth of the “Athens schist” head). In addition, a methodology for an automated GIS-aided seismic microzonation study is outlined and is being employed taking into account the aforementioned geotechnical and engineering geological information, as well as existing seismological data to estimate the variability of seismic ground motion for the southern part of Athens.  相似文献   

The Mw6.7 12 October 2013 western Hellenic Arc main shock and its aftershock sequence: implications for the slab properties     

Eleftheria Papadimitriou  Vassilis Karakostas  Maria Mesimeri  Filippos Vallianatos 《International Journal of Earth Sciences》2016,105(7):2149-2160

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Forecasting seismicity rates in western Turkey as inferred from earthquake catalog and stressing history     

Konstantinos Leptokaropoulos  Eleftheria Papadimitriou  Beata Orlecka-Sikora  Vasileios Karakostas 《Natural Hazards》2014,73(3):1817-1842

The spatio-temporal variation in seismicity in western Turkey since the late 1970s is investigated through a rate/state model, which considers the stressing history to forecast the reference seismicity rate evolution. The basic catalog was divided according to specific criteria into four subsets, which correspond to areas exhibiting almost identical seismotectonic features. Completeness magnitude and reference seismicity rates are individually calculated for each subset. The forecasting periods are selected to be the inter-seismic time intervals between successive strong (M ≥ 5.8) earthquakes. The Coulomb stress changes associated with their coseismic slip are considered, along with the constant stressing rate to alter the rates of earthquake production. These rates are expressed by a probability density function and smoothed over the study area with different degrees of smoothing. The influence of the rate/state parameters in the model efficiency is explored by evaluating the Pearson linear correlation coefficient between simulated and observed earthquake occurrence rates along with its 95 % confidence limits. Application of different parameter values is attempted for the sensitivity of the calculated seismicity rates and their fit to the real data to be tested. Despite the ambiguities and the difficulties involved in the experimental parameter value determination, the results demonstrate that the present formulation and the available datasets are sufficient enough to contribute to seismic hazard assessment starting from a point such far back in time.  相似文献   

The 2007 Talala,Saurashtra, western India earthquake sequence: Tectonic implications and seismicity triggering     

R.B.S. Yadav  E.E. Papadimitriou  V.G. Karakostas  D. Shanker  B.K. Rastogi  S. Chopra  A.P. Singh  Santosh Kumar 《Journal of Asian Earth Sciences》2011,40(1):303-314

A damaging and widely felt moderate (M_w 5.0) earthquake occurred in the Talala region of Saurashtra, Gujarat (western India) on November 6, 2007. The highly productive sequence comprised about 1300 micro earthquakes (M > 0.5) out of which 325 of M ? 1.5 that occurred during November 6, 2007–January 10, 2008 were precisely located. The spatial aftershock distribution revealed a NE–SW striking fault in accordance with the centroid moment tensor solution, which in turn implies left-lateral motion. The orientation and sense of shear are consistent with similarly orientated geological fault identified in the area from satellite imagery and field investigation.The aftershocks temporal decay, b-value of frequency–magnitude distribution, spatial fractal dimension, D, and slip ratio (ratio of the slip occurred on the primary fault to the total slip) were examined with the purpose to identify the properties of the sequence. The high b-value (1.18 ± 0.01) may be attributed to the paucity of the larger (M ? 4.0) aftershocks and reveals crustal heterogeneity and low stress regime. The high p-value (1.10 ± 0.39), implying fast decay rate of aftershocks, evidences high surface heat flux. A value of the spatial fractal dimension (D) equal to 2.21 ± 0.02 indicates random spatial distribution and source in a two-dimensional plane that is being filled-up by fractures. A slip ratio of 0.42 reveals that more slip occurred on secondary fault systems.The static Coulomb stress changes due to the coseismic slip of the main shock, enhanced off fault aftershock occurrence. The occurrence of a moderate earthquake (M_w 4.3) on October 5, 2008 inside a region of positive Coulomb stress changes supports the postulation on aftershock triggering. When the stress changes were resolved on a cross section including the stronger (M4.8) foreshock plane that is positioned adjacent to the main fault, it became evident that the activity continued there due to stress transfer from the main rupture.  相似文献   

Parametric investigation of lateral spreading of gently sloping liquefied ground     

Alexandros I. Valsamis  George D. Bouckovalas  Achilleas G. Papadimitriou 《Soil Dynamics and Earthquake Engineering》2010

This paper investigates the main parameters affecting the anticipated maximum surface displacements due to earthquake-induced lateral spreading of mildly sloping ground. The main tool used for this purpose is a numerical methodology employing a bounding surface plasticity model implemented in a finite difference code, which has been thoroughly validated against 16 published centrifuge lateral spreading experiments. This study shows that important problem parameters are the mean ground (surface) acceleration, the duration of strong shaking following the onset of liquefaction, the corrected SPT blowcount, the depth to the sliding plane, the inclination of the ground surface and the fines content of the liquefied soil layers. A new approximate multi-variable relation is proposed for the estimation of ground surface displacements due to lateral spreading in gently sloping ground, which includes the foregoing parameters. The form of the relation builds upon sliding block theory, but its final formulation is based on statistical analysis of the input data and the results from 120 parametric analyses performed with the validated numerical methodology. Comparison of the predictions of the proposed relation for ground surface displacement against pertinent field data (from 256 case histories) and centrifuge test measurements shows satisfactory accuracy. Furthermore, the variation of lateral displacements with depth is explored and distinct displacement patterns are proposed for uniform, 2-layer and 4-layer ground profiles.  相似文献   

Impact of tidal mixing with different scales of bottom roughness on the general circulation     

Exarchou  Eleftheria  von Storch  Jin Song  Jungclaus  Johann H. 《Ocean Dynamics》2012,62(10):1545-1563

The current study deals with a parameterization of diapycnal diffusivity in an ocean model. The parameterization estimates the diapycnal diffusivity depending on the location of tidal-related energy dissipation over rough topography. The scheme requires a bottom roughness map that can be chosen depending on the scales of topographic features. Here, we implement the parameterization on an ocean general circulation model, and we examine the sensitivity of the modeled circulations to different spatial scales of the modeled bottom roughness. We compare three simulations that include the tidal mixing scheme using bottom roughness calculated at three different ranges of spatial scales, with the largest scale varying up to 200 km. Three main results are discussed. First, the dependence of the topographic spectra with depth, characterized by an increase in spectral energy over short length scales in the deep ocean, influences the vertical profile of the diffusivity. Second, the changes in diffusivities lead to different equilibrium solutions in the Atlantic meridional overturning circulation and bottom circulation. In particular, the lower cell of the Atlantic overturning and the bottom water transport in the Pacific Ocean are stronger for stronger diffusivities at the corresponding basins and depths, and the strongest when using the small-scale roughness map. Third, a comparison of the density fields of the three simulations with the density field of World Ocean Atlas dataset, from which the models are initialized, shows that among the simulations with three different roughness maps, the one using small-scale bottom roughness map has the smallest density bias.

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Spatio-temporal properties and evolution of the 2013 Aigion earthquake swarm (Corinth Gulf,Greece)     

M. Mesimeri  V. Karakostas  E. Papadimitriou  D. Schaff  G. Tsaklidis 《Journal of Seismology》2016,20(2):595-614

The 2013 Aigion earthquake swarm that took place in the west part of Corinth Gulf is investigated for revealing faulting and seismicity properties of the activated area. The activity started on May 21 and was appreciably intense in the next 3 months. The recordings of the Hellenic Unified Seismological Network (HUSN), which is adequately dense around the affected area, were used to accurately locate 1501 events. The double difference (hypoDD) technique was employed for the manually picked P and S phases along with differential times derived from waveform cross-correlation for improving location accuracy. The activated area with dimensions 6?×?2 km is located approximately 5 km SE of Aigion. Focal mechanisms of 77 events with M?≥?2.0 were determined from P wave first motions and used for the geometry identification of the ruptured segments. Spatio-temporal distribution of earthquakes revealed an eastward and westward hypocentral migration from the starting point suggesting the division of the seismic swarm into four major clusters. The hypocentral migration was corroborated by the Coulomb stress change calculation, indicating that four fault segments involved in the rupture process successively failed by stress change encouragement. Examination of fluid flow brought out that it cannot be unambiguously considered as the driving mechanism for the successive failures.  相似文献   

Precursors Revealed by the Multifractal Dimension Around Ordos Block,North China     

Qin Changyuan  Yin Jingyuan  Papadimitriou E.E.  An Weiping 《中国地震研究》2002,16(2):167-177

Seismicity around the Ordos Block in the northern part of China has been studied by the multifractal dimensions with the help of complete data set of earthquakes with M≥2.5 since 1977.Seven regions around this block have been examined whiere the eight large earthquakes with M≥6.0 for the complete data occurred.In oirder to display the temporal distribution of the correlation dimension D2,a moving window of fixed number of events is used in every of the seven regions.Except for two regions with less seismic activity,all other five regions have obviously been found to display sudden changes of the correlation dimension for the events with M≥4.5.  相似文献   

Plasticity model for sand under small and large cyclic strains: a multiaxial formulation   总被引：1，自引：0，他引：1  

Achilleas G. Papadimitriou  George D. Bouckovalas 《Soil Dynamics and Earthquake Engineering》2002,22(3):15

This paper presents the multiaxial formulation of a plasticity model for sand under cyclic shearing. The model adopts a kinematic hardening circular cone as the yield surface and three non-circular conical surfaces corresponding to the deviatoric stress ratios at phase transformation, peak strength and critical state. The shape of the non-circular surfaces is formulated in accordance with the experimentally established failure criteria, while their size is related to the value of the state parameter ψ. To simulate cyclic response under small and large shear strain amplitudes without a change in model parameters, it was found necessary to introduce: (a) a non-linear hysteretic (Ramberg–Osgood type) formulation for the strain rate of elastic states and (b) an empirical index of the effect of fabric evolution during shearing which scales the plastic modulus. This index is estimated in terms of a macroscopic second-order fabric tensor, which develops as a function of the plastic volumetric strain increment and the loading direction in the deviatoric plane. Comparison of simulations to pertinent data from 27 resonant column, cyclic triaxial and cyclic direct simple shear tests provide a measure for the overall accuracy of the model.  相似文献