Anastasia Kiratzi | Aristotle University of Thessaloniki (original) (raw)

Publications by Anastasia Kiratzi

Encyclopedia of Earthquake Engineering, 2015

Remote Sensing

The active collision of the Apulian continental lithosphere with the Eurasian plate characterizes... more The active collision of the Apulian continental lithosphere with the Eurasian plate characterizes the tectonics of the Epirus region in northwestern Greece, invoking crustal shortening. Epirus has not experienced any strong earthquakes during the instrumental era and thus there is no detailed knowledge of the way the active deformation is being expressed. In March 2020, a moderate size (Mw 5.8) earthquake sequence occurred close to the Kanallaki village in Epirus. The mainshock and major aftershock focal mechanisms are compatible with reverse faulting, on NNW-ESE trending nodal planes. We measure the coseismic surface deformation using radar interferometry and investigate the possible fault geometries based on seismic waveforms and InSAR data. Slip distribution models provide good fits to both nodal planes and cannot resolve the fault plane ambiguity. The results indicate two slip episodes for a 337° N plane dipping 37° to the east and a single slip patch for a 137° N plane dipping ...

Tectonophysics, 2012

Efpalio earthquake sequence provides some key elements to enhance our view on the western Corinth... more Efpalio earthquake sequence provides some key elements to enhance our view on the western Corinth Gulf tectonics. The sequence lasted almost six months, and included two Mw > 5 strong events, both exhibiting normal faulting along~E-W trending planes. This paper attempts to construct a unified seismotectonic model of the sequence jointly interpreting earthquake locations, moment-tensors and slip inversions in terms of the possible activated fault planes. Previous studies have connected the prevailing microseismic activity to a major low-angle, north-dipping structure under the Corinth Gulf and the Efpalio sequence favors such a general trend. Moreover, it clearly shows the significance of the shallow activity, so far less recognized, and possibly connected to the relatively steep faults outcropping on the northern coast. The first 18 January 2010 Mw > 5 event had almost no on-fault aftershocks and most likely it occurred on a 55°south-dipping nodal plane. The early off-fault aftershocks formed two clusters roughly E-W trending, both of which are connected with normal faulting. Cross-sections revealed that the northernmost cluster is connected with a north-dipping structure, where the second 22 January 2010 Mw > 5 event occurred. In addition, the very shallow parts of the faults (b 4 km) were mainly aseismic, probably due to their creeping behavior. Interestingly, both clusters, at their western and eastern ends, are bounded by NE-SW trending strike-slip faults, a pattern previously observed in normal-faulting structures in Greece. This observation further invokes the role of transfer faults in the western termination of Corinth Gulf, which provide the link with regional structures, such as the Trichonis and Rion-Patras fault systems. Most of all the 2010 Efpalio sequence enhanced the complex mechanical interactions within the Corinth Gulf fault network, with many earthquake generating cluster centers, an observation which has strong implications for the seismic hazard of this densely populated region.

Tectonophysics, 2006

This article was originally published in a journal published by Elsevier, and the attached copy i... more This article was originally published in a journal published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues that you know, and providing a copy to your institution's administrator.

Journal of Geophysical Research: Solid Earth, 2001

Seismic anisotropy, deduced from SKS splitting measured at 25 stations installed in the Aegean, d... more Seismic anisotropy, deduced from SKS splitting measured at 25 stations installed in the Aegean, does not show a homogeneous pattern. It is not restricted to the North Anatolian Fault but is distributed over a region several hundreds kilometers wide. Little anisotropy is observed in continental Greece or along the Hellenic arc; however, significant anisotropy is observed in the north Aegean Sea. Large values of delay times suggest that anisotropy is due to a long path within the upper mantle and to strong intrinsic anisotropy. Our results, both in fast polarization directions and in values of delay time, do not support the idea that anisotropy is associated with inherited tectonic fabric nor are they consistent with the present-day Aegean motion relative to an absolute frame. In contrast, the direction of fast polarization and the magnitude of delay times correlate well with the present-day strain rate observed at the surface deduced from both geodetic measurements and seismicity. This anisotropy is not horizontally restricted to major surface faults but is spread over a wide region.

Journal of Geophysical Research: Solid Earth, 2000

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Journal of Seismology, 2002

Instrumental magnitudes in Greece have been reported as: a) Mmagnitudes based on the records of t... more Instrumental magnitudes in Greece have been reported as: a) Mmagnitudes based on the records of the Wiechert or Mainka seismographs,b) MLGR magnitudes based on the records of the Wood-Anderson(WA) seismographs (To = 0.8 sec, Veffective ~ 1000) or othershort period seismographs calibrated against WA records and,c) MLSM magnitudes based on strong motion records(accelerograms). Comparison of such magnitudes with momentmagnitudes, Mw,

Bulletin of the Geological Society of Greece, 2004

Evia Island (Greece) lies in a transition zone from strike-slip faulting in the east, due to the ... more Evia Island (Greece) lies in a transition zone from strike-slip faulting in the east, due to the strands of the North Anatolian Fault (NAF) that enter to the Aegean Sea, to normal faulting in the west along central Greece. In June 2003 a series of moderate events occurred in central Evia whose source parameters are investigated. These earthquakes caused serious damage to almost 20 residencies mainly in the town of Psachna. The sequence could be identified as an earthquake swarm with earthquake magnitudes in the range of 3 < M < 4.9. We used the Ρ and S arrivals at the stations of the National Seismic Network to relocate the events using the double-difference algorithm. All Ρ and S phase pickings were made by us using the broad band records from the network operated by the Geodynamic Institute of Athens. The relocated epicenters define a pronounced ENE- WSW zone, parallel to the high topography of the area. All depths are shallow from 1 to 8 Km. Regional waveform modeling was a...

Pure and Applied Geophysics PAGEOPH, 1985

A data set of nineteen, mainly shallow, moderate to large earthquakes, which occurred in the Aege... more A data set of nineteen, mainly shallow, moderate to large earthquakes, which occurred in the Aegean and the surrounding area, has been used to derive empirical relations for kinematic fault parameters. Thus the relations between seismic moment M0 and magnitude Ms and mb and between Mo and Ms and fault dimensions S and L have been determined. From these relations and theoretical ones it was deduced that earthquakes in the Aegean and the surrounding events, chiefly interplate, are characterized by low average stress drop values. Values of Aa ranging from 1 to 30 bar are consistent with the data. It was also found that, in general terms, most of the data obey the geometrical similarity condition L = 2w, where L is the fault length measured along the strike and w is its width measured along the dip. For strike-slip faults, however, the condition L = 4w seems to hold.

Tectonophysics, 2008

We investigate the properties of the April 2007 earthquake swarm (Mw 5.2) which occurred at the v... more We investigate the properties of the April 2007 earthquake swarm (Mw 5.2) which occurred at the vicinity of Lake Trichonis (western Greece). First we relocated the earthquakes, using P-and S-wave arrivals to the stations of the Hellenic Unified Seismic Network (HUSN), and then we applied moment tensor inversion to regional broad-band waveforms to obtain the focal mechanisms of the strongest events of the 2007 swarm. The relocated epicentres, cluster along the eastern banks of the lake, and follow a distinct NNW-ESE trend. The previous strong sequence close to Lake Trichonis occurred in June-December 1975. We applied teleseismic body waveform inversion, to obtain the focal mechanism solution of the strongest earthquake of this sequence, i.e. the 31 December 1975 (Mw 6.0) event. Our results indicate that: a) the 31 December 1975 Mw 6.0 event was produced by a NW-SE normal fault, dipping to the NE, with considerable sinistral strike-slip component; we relocated its epicentre: i) using phase data reported to ISC and its coordinates are 38.486°N, 21.661°E; ii) using the available macroseismic data, and the coordinates of the macroseismic epicentre are 38.49°N, 21.63°E, close to the strongly affected village of Kato Makrinou; b) the earthquakes of the 2007 swarm indicate a NNW-SSE strike for the activated main structure, parallel to the eastern banks of Lake Trichonis, dipping to the NE and characterized by mainly normal faulting, occasionally combined with sinistral strike-slip component. The 2007 earthquake swarm did not rupture the well documented E-W striking Trichonis normal fault that bounds the southern flank of the lake, but on the contrary it is due to rupture of a NW-SE normal fault that strikes at a ∼45°angle to the Trichonis fault. The leftlateral component of faulting is mapped for the first time to the north of the Gulf of Patras which was previously regarded as the boundary for strike-slip motions in western Greece. This result signifies the importance of further investigations to unravel in detail the tectonics of this region.

The Kos-Bodrum 20 July 2017 Mw6.6 earthquake ruptured an E-W normal fault dipping ~50° to the sou... more The Kos-Bodrum 20 July 2017 Mw6.6 earthquake ruptured an E-W normal fault dipping ~50° to the south. It caused destruction mainly in monumental structures in the city of Kos. We examine the source and rupture properties that shaped the near-fault ground motions. A key factor controlling the level of ground motions is the dip angle of the fault (between 30° to 60° in published mechanisms), alongside the dip polarity (to the north or to the south). The preferred slip model has two major asperities, with peak slip ~1.6m, located west and east of the hypocenter. The rupture propagated predominantly bilateral at a speed of 2.8 km/s. The ShakeMap shows an E-W spatial extension, in the mid-distance between the cities of Bodrum and Kos. The near-fault unique NS velocity time-series at Bodrum station, which is the fault normal direction, shows a late pulse, that is to say not at the beginning of the record, of period ~0.7s. In the absence of strong motion records in the city of Kos, we selected two near-fault horizontal time-series from the 2016 Norcia earthquake in Italy, as representative for the postulated bedrock motions. Adopting the preferred soil-profile and properties of Psycharis and Taflampas (2017) we perform 1D site response analysis, using the Bodrum and Norcia horizontal records as bedrock input motions, to estimate the surface motions. From all spectral comparisons, we conclude that the mainshock was characterized by enriched spectral ordinates for spectral periods >0.6s up to 2s, and that the effect of the soil in Kos city, is significant in this range.

Bulletin of Earthquake Engineering, 2021

The 30 October 2020 Samos earthquake (Mw 7.0) ruptured an east-west striking, north dipping norma... more The 30 October 2020 Samos earthquake (Mw 7.0) ruptured an east-west striking, north dipping normal fault located offshore the northern coast of Samos Island, previously inferred from the bathymetry and regional tectonics. This fault, reported in the faultdatabases as the North Samos and/or Kaystrios Fault, ruptured with almost pure dip-slip motion, in a region where both active extension and strike-slip deformation coexist. Historical information for the area confirms that similar ~ Mw7 events had also occurred in the broader Samos area, though none of the recent (last ~ 300 years) mainshocks appears to have ruptured the same fault. The spatial and temporal distribution of relocated aftershocks indicates triggering of nearby strike-slip and normal fault segments, situated in the areas where static stress has increased due to the mainshock generation. The relocated aftershocks and the slip model indicate that the sequence ruptured the upper crust (mainly the depth range 3-15 km). The top of the rupture plane nearly reached the sea bottom, located at a depth of < 1 km. Slip is confined in mainly two asperities, both located up-dip from the hypocenter and at shallow depths. The average displacement is ~ 1 m and the peak slip is ~ 3.5 m for a shear modulus of 3.2e10 N/m 2. While it is difficult to constrain the rupture velocity in the inversions, the model suggests a slow rupture speed of the order of 2.2 km/s. The resolved source duration is ~ 16 s, compatible with the ~ 32 km length of the fault that ruptured.

Bulletin of the Geological Society of Greece

We carry out a probabilistic seismic hazard assessment (PSHA) for Lesvos Island, in the northeast... more We carry out a probabilistic seismic hazard assessment (PSHA) for Lesvos Island, in the northeastern Aegean Sea. Being the most populated island in the northern Aegean Sea and hosting the capital of the prefecture, its seismic potential has significant social-economic meaning. For the seismic hazard estimation, the newest version of the R-CRISIS module, which has high efficiency and flexibility in model selection, is used. We incorporate into the calculations eight (8) ground motion prediction equations (GMPEs). The measures used are peak ground acceleration, (PGA), peak ground velocity, (PGV), and spectral acceleration, (SA), at T=0.2 sec representative of the building stock. We calculate hazard curves for selected sites on the island, sampling the southern and northern parts: Mytilene, the capital, the village of Vrisa, Mithymna and Sigri. Hazard maps are also presented in terms of all three intensity measures, for a mean return period of 475 years (or 10% probability of exceedanc...

Pure Appl Geophys, 2003

The empirical Green's functions technique is applied to simulate strong ground motion records fro... more The empirical Green's functions technique is applied to simulate strong ground motion records from the September 7, 1999, Athens earthquake. Information on the fault parameters from previous independent studies has been used and several scenarios were examined, in regard to the location of the starting point of the rupture, by comparing the synthetic records with the corresponding observed ones, through a residual function and a correlation function. The results show that the rupture started at the deepest, $4-5 km, part of the fault from its western edge. This hypocenter was then used, in combination with the initial fault model, to stochastically simulate the strong ground motion during the Athens main shock, in terms of peak-ground acceleration at hard rock. The results show that directivity might have significantly contributed to the destructiveness of this earthquake at specific parts of the Athens Metropolitan area.

Pure and Applied Geophysics, Dec 1, 1991

The rates and configuration of seismic deformation in the North Aegean trough-North Anatolian fau... more The rates and configuration of seismic deformation in the North Aegean trough-North Anatolian fault are determined from the moment tensor mechanisms of the earthquakes that occurred within this region. The analysis is based on KOSTROV'S (1974) formulation. The fault plane solutions of the earthquakes of the period 1913-1983 with Ms > 6.0 are used. The focal mechanism of some of the past events (before 1960) is assumed, based on the present knowledge of the seismotectonics as well as on the macroseismic records of the area studied. The analysis showed that the deformation of the northern Aegean is dominated by EW contraction (at a rate of about 15 mm/yr) which is relieved by NS extension (at a rate of about 9 mm/yr). It was also shown that the northern part of North Anatolia (north of 39.7~ parallel) undergoes contraction in the EW direction (at a rate of about 9 mm/yr) and NS extension as the dominant mode of deformation (at a rate of about 5 mm/yr). It may be stated therefore, that the pattern of deformation of the northern Aegean and the northern part of North Anatolian fault is controlled by the NS extension the Aegean is undergoing as a whole, and the dextral strike-slip motion of the North Anatolian fault. The southern part of North Anatolia is undergoing crustal thinning at a rate of 2.3 mm/yr, NS extension (at a rate of 5 mm/yr) as well as EW extension (at a rate of 4 mm/yr), which are consistent with the occurrence of major normal faulting and justify the separation of North Anatolia into two separate subareas.

Abstract We investigate the rupture process of the 14 February 2008, M6. 7 earthquake sequence th... more Abstract We investigate the rupture process of the 14 February 2008, M6. 7 earthquake sequence that occurred offshore the westernmost tip of the Peloponnese peninsula in southern Greece. The sequence occurred close to the western boundary of the subducting African lithosphere with the overlying Aegean crust. Three were the strongest events of the sequence: 14 Feb 2008 M6. 7 depth 30 km, low-angle (10o) thrust, its strongest aftershock on the same day and two hours later of M6. 1 depth 33km, again low angle thrust and on ...

Agu Fall Meeting Abstracts, Dec 1, 2004

Abstract Geological and geophysical data are often combined with seismological observations to de... more Abstract Geological and geophysical data are often combined with seismological observations to define faults that are related to past, as well as recent catastrophic earthquakes. Such a combination of information from different disciplines is rather required in areas such as the Aegean, where the sparseness of permanent seismological networks on one hand, and the high seismotectonic complexity on the other hand, pose constraints on the efficient definition of seismogenic sources by using seismological methods alone. The ...