A two-dimensional (2-D) cellular automata (CA) dynamic system constituted of cells-charges has been proposed for the simulation of the earthquake process. In this paper, the study is focused on the optimal parameterisation of the model... more
A two-dimensional (2-D) cellular automata (CA) dynamic system constituted of cells-charges has been proposed for the simulation of the earthquake process. In this paper, the study is focused on the optimal parameterisation of the model introducing the use of genetic algorithm (GA). The optimisation of the CA model parameterisation, by applying a standard GA, extends its ability to study various
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ABSTRACT Central Asia and its surroundings constitute a geodynamically complicated region, where almost all types of tectonic patterns can be observed. A triple junction, collision, and subduction zones, as well as extended fault systems... more
ABSTRACT Central Asia and its surroundings constitute a geodynamically complicated region, where almost all types of tectonic patterns can be observed. A triple junction, collision, and subduction zones, as well as extended fault systems of all types prevail in different parts of this region and compose one of the most interesting and complex geotectonic environments on Earth. This complicated setting is also associated with intense deformation, resulting in a large number of high seismicity zones, where numerous strong earthquakes occur, also extending, in some cases, to intermediate depths. Several previous studies have focused on specific seismotectonic zones in order to assess the active tectonic setting and the associated stress regime. We attempt to provide a unified but detailed picture of the stress field variability for the entire central Asia region, using the well-known inversion method proposed by Gephart and Forsyth (1984), modified in the present work on the basis of Fisher statistics. For this application, we employ a large number of focal mechanisms, spatially separated in 138 data groups. Τhe proposed modified algorithm (FD-BSM) examines the Fisher distribution of all possible stress principal axes solutions and select the one that: (a) shows the smallest angle variation from the Fisher mean in all three principal distributions and (b) minimizes the difference between the theoretical and observed slip vectors of the employed fault plane solution data. Synthetic tests and comparison of the corresponding results with real data show that, in cases where the stress regime is not clearly uniform or the number of available data is rather small, the models selected by the modified approach (FDBSM) are more robust and show better spatial coherence compared to the initial Gephart and Forsyth (1984) method or alternative techniques such as the method of Michael (1984, 1987) as adapted by Vavrycuk (2014).
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A new model is derived for the P and S velocity structure of the lithosphere continen- tal collision area of the Dalmatian, Albania and NW Greece coasts by the inversion of travel times of local events. The inversion technique applied is... more
A new model is derived for the P and S velocity structure of the lithosphere continen- tal collision area of the Dalmatian, Albania and NW Greece coasts by the inversion of travel times of local events. The inversion technique applied is non-linear with appro- priate three-dimensional ray tracing and preconditioning in order to reduce ray density effects on the results.
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ABSTRACT Two time-dependent seismicity models are tested by using recent reliable data of earthquakes generated in active regions of ten large areas (West Mediterranean, Aegean, Cyprus, Anatolia, Central Asia, Sumatra-Java, Japan, North... more
ABSTRACT Two time-dependent seismicity models are tested by using recent reliable data of earthquakes generated in active regions of ten large areas (West Mediterranean, Aegean, Cyprus, Anatolia, Central Asia, Sumatra-Java, Japan, North Pacific, California, South America) of the continental fracture system. The first one, called TIMAPR (Time and Magnitude Predictable Regional) model is based on interevent times of strong mainshocks (M=6.3-9.0) generated in circular seismogenic regions (networks of faults). The second, called D-AS (Decelerating-Accelerating Seismicity) model, is based on triggering of a mainshock by its preshocks. Tests of Decelerating–Accelerating precursory seismicity against synthetic catalogues with spatiotemporal clustering verify the validity of the D-AS model. Backward tests of both models showed that: a) every strong shallow mainshock is preceded by a decelerating and an accelerating preshock sequence within well-defined time, space and magnitude windows, allowing its intermediate-term prediction by the D-AS model, and b) in each circular seismogenic region the mainshocks show quasi-periodic behavior with interevent times following the TIMAPR model which is also applied to predict the mainshock. Forward tests of both models indicate candidate regions for the generation of strong mainshocks during the next decade (2013-2022 or so). Estimated (predicted) values of their basic focal parameters (time, magnitude, epicenter) and their uncertainties are given to objectively define the predicting ability of the joint application of the two models.
In the past years there has been a growing demand for precise earthquake locations for seismicity, tectonics and seismic hazard studies. Recently this has become possible because of the development of sophisticated location algorithms, as... more
In the past years there has been a growing demand for precise earthquake locations for seismicity, tectonics and seismic hazard studies. Recently this has become possible because of the development of sophisticated location algorithms, as well as hardware resources. This is expected to lead to a better insight of seismicity in the near future. A well-known technique, which has been
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Physical processes in the earth's lithosphere compose a nonlinear complex system. Earthquake generation is part of this process. Till now, several computational geophysical models have been proposed in order to tackle complex problems... more
Physical processes in the earth's lithosphere compose a nonlinear complex system. Earthquake generation is part of this process. Till now, several computational geophysical models have been proposed in order to tackle complex problems associated with proper ...
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The structure of the area of the Mygdonia Basin has been extensively studied during the last decade and its seismic potential is sufficient to produce an adequate set of seismic phase data. This makes the broader Mygdonia Basin area an... more
The structure of the area of the Mygdonia Basin has been extensively studied during the last decade and its seismic potential is sufficient to produce an adequate set of seismic phase data. This makes the broader Mygdonia Basin area an appropriate "test-site" for developing and testing new techniques regarding regional-local scale seismic tomography. In the present work, the P- and S-wave velocity structure of the broader area of the Mygdonia Basin is studied by the inversion of traveltimes of earthquakes. The main objective is to produce a more detailed velocity model of the structure of the area, using a technique based on double differences. The quality of the results of seismic tomography depends, among other factors, on the errors in the locations of the earthquakes used. To reduce these errors, the double difference earthquake location algorithm can be used to relocate the earthquakes before introducing them in travel-time tomography. Using a local-scale 1-D and prel...
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... Three different data sets were used in the present work to accurately define the Wadati–Benioffzone of the Hellenic arc (Appendix A). The first one consists of earthquakes recorded at local seismological networks which were installed... more
... Three different data sets were used in the present work to accurately define the Wadati–Benioffzone of the Hellenic arc (Appendix A). The first one consists of earthquakes recorded at local seismological networks which were installed and operated in the southern Aegean area ...
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This paper presents an extensive simulation tool based on a Cellular Automata (CA) system that models fundamental seismic characteristics of a region. The CA-based dynamic model consists of cells-charges and it is used for the simulation... more
This paper presents an extensive simulation tool based on a Cellular Automata (CA) system that models fundamental seismic characteristics of a region. The CA-based dynamic model consists of cells-charges and it is used for the simulation of the earthquake process. The simulation tool has remarkably accelerated the response of the model by incorporating principles of the High Performance Computing (HPC). Extensive programming features of parallel computing have been applied, thus improving its processing effectiveness. The tool implements an enhanced (or hyper-) 2-dimensional version of the proposed CA model. Regional characteristics that depend on the seismic background of the area under study are assigned to the model with the application of a user-friendly software environment. The model is evaluated with real data that correspond to a circular region around Skyros Island, Greece, for different time periods, as for example one of 45years (1901–1945). The enhanced 2-dimensional version of the model incorporates all principal characteristics of the 2-dimensional one, also including groups of CA cells that interact with others, located to a considerable distance in an attempt to simulate long-range interaction. The advanced simulation tool has been thoroughly evaluated. Several measurements have been made for different critical states, as well as for various cascade (earthquake) sizes, cell activities and different neighbourhood sizes. Simulation results qualitatively approach the Gutenberg–Richter (GR) scaling law and reveal fundamental characteristics of the system.
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ABSTRACT We examined the seismic activity which preceded six strong mainshocks that occurred in the Aegean (M = 6.4–6.9, 33–43° N, 19–28° E) and two strong mainshocks that occurred in California (M = 6.5–7.1, 32–41° N, 115–125° W) during... more
ABSTRACT We examined the seismic activity which preceded six strong mainshocks that occurred in the Aegean (M = 6.4–6.9, 33–43° N, 19–28° E) and two strong mainshocks that occurred in California (M = 6.5–7.1, 32–41° N, 115–125° W) during 1995–2010. We find that each of these eight mainshocks has been preceded by a pronounced decelerating and an equally easily identifiable accelerating seismic sequence with the time to the mainshock. The two preshock sequences of each mainshock occurred in separate space, time, and magnitude windows. In all eight cases, very low decelerating seismicity, as well as very low accelerating seismicity, is observed around the actual epicenter of the ensuing mainshock. Statistical tests on the observed measures of decelerating, q d, and accelerating, q a, seismicity against similar measures calculated using synthetic catalogs with spatiotemporal clustering based on the ETAS model show that there is an almost zero probability for each one of the two preshock sequences which preceded each of the eight mainshocks to be random. These results support the notion that every strong shallow mainshock is preceded by a decelerating and an accelerating seismic sequence with predictive properties for the ensuing mainshock.
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Accelerating strain energy released by the generation of intermediate magnitude preshocks in a broad (critical) region, and decelerating energy released in a narrower (seismogenic) region, is considered as a distinct premonitory pattern... more
Accelerating strain energy released by the generation of intermediate magnitude preshocks in a broad (critical) region, and decelerating energy released in a narrower (seismogenic) region, is considered as a distinct premonitory pattern useful in research for intermediate-term earthquake prediction. Accelerating seismicity in the broad region is satisfactorily interpreted by the critical earthquake model and decelerating seismicity in the narrower region
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Accelerating seismic crustal deformation due to the occurrence of intermediate magnitude earthquakes leading to the generation of a mainshock is considered as a critical phenomenon. This hypothesis is tested by the use of a large data... more
Accelerating seismic crustal deformation due to the occurrence of intermediate magnitude earthquakes leading to the generation of a mainshock is considered as a critical phenomenon. This hypothesis is tested by the use of a large data sample concerning different seismotectonic environments (Aegean area, Italy, Anatolia and Japan). Elliptical critical regions for a large number of strong mainshocks have been identified by applying a power-law relation between the cumulative Benioff strain and the time to the mainshock rupture. Empirical relations between the parameters of this model previously suggested by various authors have been further improved by the use of this large sample of data. Moreover, it is shown that the logarithm of the equivalent circle radius of the critical region scales not only with the magnitude of the ensuing mainshock but also with the average seismicity level of the study area, similar to the logarithm of the duration of the preshock (accelerated deformation)...
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ABSTRACT The seismicity of western Macedonia is examined in the present paper. On the basis of historical information as well as on instrumental data it is found that this area is characterized by low seismicity. The focal region of the... more
ABSTRACT The seismicity of western Macedonia is examined in the present paper. On the basis of historical information as well as on instrumental data it is found that this area is characterized by low seismicity. The focal region of the Grevena-Kozani 1995 earthquake exhibits the highest seismicity in terms of probabilities for the generation of strong (Ms ≥ 6.0) earthquakes in a period of fifty years. Two other regions with relatively high seismicity were also distinguished (west of Edessa and around Prespes lakes). Accurate determination of focal parameters of all earthquakes occurred in the area during October 1975-April 1995, by the use of a 3-D crustal model shows that the seismic activity is related to the graben structures of the studied area. Finally, evidence is presented that the triggering of the 1995 earthquake may be related to the impoundment of the Polyfytos artificial lake.
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... Ionian islands), called NAB in the pre-sent paper, where dextral strike-slip ruptures dominate. ... The distribution of the time lag between each of the postshocks and the preceding ... which is the first evidence that major Marmara... more
... Ionian islands), called NAB in the pre-sent paper, where dextral strike-slip ruptures dominate. ... The distribution of the time lag between each of the postshocks and the preceding ... which is the first evidence that major Marmara Sea earthquakes trigger strong earthquakes in the ...
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... 1981). Recent detailed investigation of accelerating preshock sequences in broad critical regions (Papazachos & Papazachos 2000, 2001; Papa-zachos et al. ... 1986; Dewey 1988), despite the fact that no generally... more
... 1981). Recent detailed investigation of accelerating preshock sequences in broad critical regions (Papazachos & Papazachos 2000, 2001; Papa-zachos et al. ... 1986; Dewey 1988), despite the fact that no generally accepted model for the extension mechanism exists. ...