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1

A detailed analysis of microseismicity in Samos and Kusadasi (Eastern Aegean Sea) areas

Tan O., Papadimitriou E. E., Pabuccu Z., Karakostas V., Yoruk A., Leptokaropoulos K.

Acta Geophysica

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2014

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Vol. 62, no. 6

1283--1309

EN

A detailed investigation of microseismicity and fault plane solutions are used to determine the current tectonic activity of the prominent zone of seismicity near Samos Island and Kusadasi Bay. The activation of fault populations in this complex strike-slip and normal faulting system was investigated by using several thousand accurate earthquake locations obtained by applying a double-difference location method and waveform cross-correlation, appropriate for areas with relatively small seismogenic structures. The fault plane solutions, determined by both moment tensor waveform inversions and P-wave first motion polarities, reveal a clear NS trending extension direction, for strike slip, oblique normal and normal faults. The geometry of each segment is quite simple and indicates planar dislocations gently dipping with an average dip of 40-45°, maintaining a constant dip through the entire seismogenic layer, down to 15 km depth.

2

Statistical properties of aftershock rate decay: Implications for the assessment of continuing activity

Adamaki A, Papadimitriou E.E., Tsaklidis G.M., Karakostas V.

Acta Geophysica

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2011

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Vol. 59, no. 4

748-769

EN

Aftershock rates seem to follow a power law decay, but the assessment of the aftershock frequency immediately after an earthquake, as well as during the evolution of a seismic excitation remains a demand for the imminent seismic hazard. The purpose of this work is to study the temporal distribution of triggered earthquakes in short time scales following a strong event, and thus a multiple seismic sequence was chosen for this purpose. Statistical models are applied to the 1981 Corinth Gulf sequence, comprising three strong (M = 6.7, M = 6.5, and M = 6.3) events between 24 February and 4 March. The non-homogeneous Poisson process outperforms the simple Poisson process in order to model the aftershock sequence, whereas the Weibull process is more appropriate to capture the features of the short-term behavior, but not the most proper for describing the seismicity in long term. The aftershock data defines a smooth curve of the declining rate and a long-tail theoretical model is more appropriate to fit the data than a rapidly declining exponential function, as supported by the quantitative results derived from the survival function. An autoregressive model is also applied to the seismic sequence, shedding more light on the stationarity of the time series.

3

Seismic hazard assessment in central Ionian Islands area (Greece) based on stress release models

Votsi I., Tsaklidis G.M., Papadimitriou E.E.

Acta Geophysica

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2011

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Vol. 59, no. 4

701-727

EN

The long-term probabilistic seismic hazard of central Ionian Islands (Greece) is studied through the application of stress release models. In order to identify statistically distinct regions, the study area is divided into two subareas, namely Kefalonia and Lefkada, on the basis of seismotectonic properties. Previous results evidenced the existence of stress transfer and interaction between the Kefalonia and Lefkada fault segments. For the consideration of stress transfer and interaction, the linked stress release model is applied. A new model is proposed, where the hazard rate function in terms of X(t) has the form of the Weibull distribution. The fitted models are evaluated through residual analysis and the best of them is selected through the Akaike information criterion. Based on AIC, the results demonstrate that the simple stress release model fits the Ionian data better than the non-homogeneous Poisson and the Weibull models. Finally, the thinning simulation method is applied in order to produce simulated data and proceed to forecasting.

4

Multi-disciplinary research on geo- and man-made hazards. Preface to the topical Issue

Papadimitriou E.E., Inan S.

Acta Geophysica

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2010

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Vol. 58, no. 5

717-718

5

Fault complexity associated with the 14 August 2003 Mw6.2 Lefkada, Greece, aftershock sequence

Karakostas V.G., Papadimitriou E.E.

Acta Geophysica

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2010

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Vol. 58, no. 5

838-854

EN

The Mw6.2 Lefkada earthquake occurred on 14 August 2003 beneath the western coastline of Lefkada Island. The main shock was followed by an intense aftershock activity, which formed a narrow band extending over the western coast of the Island and the submarine area between Lefkada and Kefalonia Islands, whereas additional off fault aftershocks formed spatial clusters on the central and northwestern part of the Island. The aftershock spatial distribution revealed the activation of along-strike adjacent fault segment as well as of secondary faults close to the main rupture. The properties of the activated segments were illuminated by the precisely located aftershocks, fault plane solutions determination and the cross sections performed parallel and normal to their strike. The aftershock focal mechanisms exhibited mainly strike slip faulting throughout the activated area, although deviation of the dominant stress pattern is also observed. The results help to emphasize the importance of the identification of activated nearby fault segments possibly triggered by the main rupture. Because such segments are capable to produce moderate events causing appreciable damage, they should be viewed with caution in seismic hazard assessment in addition to the major regional faults.

6

Rupture model of the great AD 365 Crete earthquake in the southwestern part of the Hellenic Arc

Papadimitriou E. E., Karakostas V. G.

Acta Geophysica

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2008

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Vol. 56, no. 2

293-312

EN

An M8.3 earthquake struck the southwestern part of the Hellenic Arc, near the Island of Crete, in AD 365, generating a tsunami that affected almost the entire eastern Mediterranean region. Taking into account that the time history of seismic-ity in this region is fairly complete for such earthquakes in the historical catalog, which can be dated as back as the 5th century B.C., there is no indication that this segment of plate boundary has been fully ruptured again. The seismic hazard associated with this part of the Hellenic Arc necessitates the evaluation of the rupture characteristics of this great event. The constraint of the faulting geometry was initially achieved by using information from seismicity, and the focal mechanisms of earthquakes that occurred during the instrumental period. A rupture model for this great earthquake is constructed by assuming an elastic medium and calculating the theoretical surface displacements for various fault models that are matched with the observed surface deformation gleaned from historical reports. The resulted fault model concerns thrust faulting with a rupture length of 160 km and a seismic moment of 5.7×1028 dyn*cm, an average slip of 8.9 m and a corresponding moment magnitude equal to 8.4, in excellent agreement with the macroseismic estimation. The absence of such events recurrence is an indication of the lack of complete seismic coupling that is common in subduction zones, which is in accordance with the back arc spreading of the Aegean microplate and with previous results showing low coupling for extensional strain of the upper plate.

7

Application of the stress evolutionary model along the Xiaojiang fault zone in Yunnan Province, Southeast China

Paradisopoulou P.M., Garlaouni Ch.G., Jin X., Papadimitriou E.E., Karakostas V.G., Yang J.

Acta Geophysica

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2007

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Vol. 55, no. 4

577-593

EN

The Xiaojiang fault zone constitutes part of the major Xianshuihe¨CXiaojiang left lateral structure that bounds the rhombic-shaped block of Yunnan¨CSichuan to the east. Long strike slip fault zones that have repeatedly accommodated intense seismic activity, constitute a basic feature of southeast China. Known historical earthquakes to have struck the study area are the 1713 Xundian of M6.8, 1725 Wanshou mountain of M6.8, the 1733 Dongchuan of M7.8, and the strongest one, the 1833 Songming of M8.0. Although instrumental record did not report events of this magnitude class, the 18th century clustering as well as the 19th century large event prompted the investigation of stress transfer along this fault zone. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic half-space, and taking into account both the coseismic slip in strong (M ˇÝ 6.8) earthquakes and the slow tectonic stress buildup along the major fault segments. Geological and geodetic data are used to infer the geometry of these faults and long term slip rates on them, as well as for the fault segments that slipped. Evidence is presented that the strong historical events as well as the ones of smaller magnitude that occurred during the instrumental era, are located in areas where the static stress was enhanced. By extending the calculations up to present, possible sites for future strong events are identified.