Dominikos Vamvakaris - Academia.edu (original) (raw)

Papers by Dominikos Vamvakaris

In the present work we study the effect of the spatiotemporal distribution of seismicity on the e... more In the present work we study the effect of the spatiotemporal distribution of seismicity on the estimation of seismic hazard using both time-independent and time-dependent seismicity models, by employing a simple model for prediction of mainshocks. The estimation procedure is based on a Monte-Carlo procedure to create synthetic catalogues which have specific characteristics regarding their spatiotemporal and magnitude seismicity distributions. These catalogues are used to estimate the statistical distribution of the ground motion parameters for several sites of interest, by performing computations directly on all earthquakes of each catalogue. The computations are performed for S. Aegean, both for time-independent (Poisson time distribution), as well as time-dependent models for mainshocks. The results show significant differentiations regarding the seismic hazard levels between the different models, verifying the significance of performing computations for time-dependent hazard.

A study of the microearthquake activity observed at the Kaniani-Parnassos mines has performed in ... more A study of the microearthquake activity observed at the Kaniani-Parnassos mines has performed in order to determine the origin of the several "unknown" shocks observed at the area of the mine. Preliminary analysis of the recordings indicated that the shocks were of tectonic origin. A portable network of three accelerographs (located inside the mine -no absolute time) and five three-component digital seismographs (located in surface locations on top of the mine -absolute time available) were installed for a period of nine months. The analysis of impulsive, high frequency (>20 Hz), short duration (2-3 sec) recordings, showed that the observed seismicity is of very local scale, located at a specific section of the mine. The microseismic activity exhibited a very strong time-correlation with the exploitation level, as this is revealed from the very significant variation of the earthquake rate of occurrence after the start of the operation of the mine, as well as the clear c...

Natural Hazards and Earth System Sciences Discussions, 2013

ABSTRACT In the present work we present an effort to define a new seismic zonation model of area ... more ABSTRACT In the present work we present an effort to define a new seismic zonation model of area type sources for the broader Aegean area, which can be readily used for seismic hazard assessment. The definition of this model is based not only on seismicity information but incorporates all available seismotectonic and neotectonic information available for the study area, in an attempt to define zones which show not only a rather homogeneous seismicity release but also exhibit similar active faulting characteristics. For this reason, all available seismological information such as fault plane solutions and the corresponding kinematic axes have been incorporated in the analysis, as well as information about active tectonics, such as seismic and active faults. Moreover, various morphotectonic features (e.g. relief, coastline) were also considered. Finally, a revised seismic catalogue is employed and earthquake epicentres since historical times (550 BC-2008) are considered, in order to define areas of common seismotectonic characteristics, that could constitute a discrete seismic zone. A new revised model of 113 earthquake seismic zones of shallow earthquakes for the broader Aegean area is finally proposed. Using the proposed zonation model, a detailed study is performed for the catalogue completeness for the recent instrumental period. Using the defined completeness information, seismicity parameters (such as G-R values) for the 113 new seismic zones have been calculated, and their spatial distribution was also examined. The spatial variation of the obtained b values shows an excellent correlation with the geotectonic setting in the area, in good agreement with previous studies. Moreover, a quantitative estimation of seismicity is performed in terms of the mean return period, Tm, of large (M ≥ 6.0) earthquakes, as well as the most frequent maximum magnitude, Mt, for a typical time period (T = 50 yr), revealing significant spatial variations of seismicity levels within the study area. The new proposed seismic zonation model and its parameters can be readily employed for seismic hazard assessment for the broader Aegean area.

We examine the effect of time-dependent seismicity on seismic hazard using a revised synthetic ca... more We examine the effect of time-dependent seismicity on seismic hazard using a revised synthetic catalogue approach. The synthetic catalogues are generated using a crude Monte-Carlo approach, having specific characteristics regarding their spatiotemporal and magnitude distribution. Seismic hazard estimates are computed by direct computation of expected ground motions for each site of interest, using the complete dataset of each involved catalogue. The approach is initially validated using comparisons with conventional seismic hazard algorithms for timeindependent seismic hazard assessment. For this reason synthetic catalogues using a Poisson time distribution are used, adopting the spatial and magnitude seismicity distribution of a revised zonation model for the broader Aegean area. The results verify the applicability of the proposed approach, as well as its potential for improved estimates for complex seismotectonic settings (subduction zones, etc.). Furthermore, we demonstrate the possibility to stabilize the noise introduced into the hazard estimates from the random catalogue variability by introducing modified hazard estimates from the application of Gumbel's 1st-type extreme value distribution. As a second step catalogues with specific spatiotemporal characteristics are examined, where we assume that mainshocks above a certain cut-off magnitude (e.g. M>6.0) can be predicted, even with large space-time-magnitude uncertainties and significant false-alarm probabilities, while lower magnitude events are following a time-independent pattern. The proposed approach allows to quantitatively estimate the independent and combined effect of both prediction uncertainties and false-alarms on seismic hazard. The obtained results for the broader Aegean area suggest that even for relatively large prediction uncertainties and false alarm probabilities for mainshocks, a significant portion of the "real" seismic hazard is recovered, allowing the approximate identification of areas that will be mostly affected by the expected mainshocks, at least for the examined mainshock scenarios. This observation suggests that the consideration of even approximate mainshock prediction estimates may be practically useful for time-dependent hazard assessment

The Kastoria-Nestorion region, which belongs to the Tertiary MesoHellenic Trough (MHT), is a low ... more The Kastoria-Nestorion region, which belongs to the Tertiary MesoHellenic Trough (MHT), is a low relief NW-SE trending intermountainous basin filled with Tertiary molasse-type sedimentary rocks and nowadays drained by the Aliakmnonas River and its tributaries. In the present work, the large fault zones in the region and the general fault pattern are defined, mapped and described with the aid of satellite images. In addition, a large number of fault-slip data from the mesoscale exposed faults has been recorded, in order to better understand the faulting geometry and kinematics of the region. The stress-inversion analysis of these fault-slip data in comparison with earthquake faultplane solution information permits us to define the stress regimes imposed to the region from the Late Tertiary up to the present and to correlate them with the late orogenic and post-orogenic deformation of the Hellenic orogen. In particular, five stress regimes have been defined from which the former two (D1 and D2) are related to the late collisional processes between the Apulia and Eurasia plates, the next two events (D3 and D4) are related to the present-day Hellenic subduction zone, whereas the last D5 event which is the active deformation of the region appears as an intra-continental or intra-plate deformation more related with the Adria-Eurasia ongoing convergence rather with the Hellenic subduction zone.

Data of more than 150 temporary and permanent broadband seismological stations deployed in the Ae... more Data of more than 150 temporary and permanent broadband seismological stations deployed in the Aegean-Anatolian domain between May 2007 and May 2009 are grouped in the SIMBAAD (Seismic Imaging of the Mantle Across the Anatolian Domain) dataset. We compute noise cross-correlations between all station pairs on a 1.5-yr duration. We obtain more than 11.000 correlations for each component of the cross-correlation tensor. We apply a MFA (Multiple Filter Analysis) method to measure group velocity dispersion curves of Rayleigh waves on 4 components of the correlation tensor (ZZ, ZR, RZ, RR) and of Love waves on the TT component, both in positive and negative times. According to the theory, a noise cross-correlation converges to the Green function if noise sources are randomly distributed around the station pair. If this condition is fulfilled, the cross-correlation should be symmetrical in time. We compare group velocity measurements between positive and negative times to evaluate the conv...

In the Aegean-Anatolian domain, one of the key questions is the mantle structure between the Hell... more In the Aegean-Anatolian domain, one of the key questions is the mantle structure between the Hellenic arc and Eastern Anatolia. The SIMBAAD temporary seismic experiment was designed to address this question and image the diffuse boundary between the Aegean and Anatolian plates. Deployed during 2 years, the SIMBAAD experiment is a dense seismic broadband network over continental Greece, the Aegean, South Bulgaria and Western Turkey, arranged to fill-in the gaps between permanent broadband stations. The database includes continuous records of 146 true broadband (cut-off period >= 90s) seismic stations, both temporary and permanent, with a spacing of about 80km. This study uses records of 400 teleseismic events of magnitude >= 6. We present results of fundamental mode Rayleigh wave travel-time tomography in the entire region [20-40°E; 35-42°N]. We apply semi-automatic time-frequency filtering to encompass the amount of data and retrieve the fundamental mode Rayleigh waves. The ti...

Geophysical Journal International, 2012

Geological Society, London, Special Publications, 2006

Northern Greece is an intracontinental region behind the Hellenic subduction zone, with widesprea... more Northern Greece is an intracontinental region behind the Hellenic subduction zone, with widespread seismic activity (ranging from low to high), with strong destructive earthquakes of Mg6.0 in historical to recent times. Geological and seismological data indicate that recent seismic activity is mainly localized along large, inherited, fault zones, which have transected Northern Greece since Oligocene-Miocene times. The main active fault zones in Thrace, and Eastern and Central Macedonia strike approximately east-west, with lengths of 40-120 km. Fault segments strike WNW-ESE to ENE-WSW and range from 10 to 30 km in length. In Western Macedonia the main active fault zones strike NE-SW to ENE-WSW with lengths of 40-60 km and consist of 10-30 km segments. The region's strong earthquakes are usually associated with reactivation of these fault segments and are estimated at M=5.6-6.5. Focal mechanisms and fault-slip data from the fault zones indicate a change in the trend of extension axes from NNE-SSW in Eastern Macedonia-Thrace to NNW-SSE in Western Macedonia. Thus, neotectonic and seismological data suggest that variations in fault patterns, as determined from the large inherited fault zones transecting Northern Greece, are the major factor governing this change in the trend of maximum extension. This interpretation is consistent with the long-lived arcuate shape of the Hellenic subduction zone.

… 2010, held 2-7 May …, 2010

The question of the driving engine for the rapid displacement of Anatolia towards the W-SW is sti... more The question of the driving engine for the rapid displacement of Anatolia towards the W-SW is still open: push by the Arabian indenter, or pull by the retreat of the Hellenic slab? The hypothesis of a basal drag of Anatolia and Aegea by mantle flow related to slab retreat receives increasing attention. To better constrain mantle flow, we have mapped the azimuthal anisotropy of seismic velocity in a broad area including continental Greece, the Aegean Sea, Western Turkey and Southern Bulgaria. The splitting parameters of the core phases SKS and SKKS have been measured on records of the SIMBAAD temporary experiment and permanent broadband stations. The station coverage is rather dense (60-80 km) and homogeneous in the area [35-42°N; 20-34°E]. In W-Anatolia and the Aegean east of 24°E and north of 38°N, the anisotropy is fairly uniform, with N45 fast-velocity directions and an average time lag of 1s. In continental Greece west of 24°E, the anisotropy is weaker, with time lags smaller than 0.5s in average. In SW-Anatolia, the fast velocity directions are heterogeneous, with time lags of 0.7s in average. The anisotropy parameters measured in NW-Anatolia and N-Aegea (N45 and ∼1s) are very consistent with the results of similar studies conducted in North-Central Anatolia (NAF experiment) and in Eastern Anatolia (ETSE experiment). This observation of a very uniform pattern from Eastern Anatolia to the North of the Aegean strengthens the hypothesis of mantle anisotropy being due to mantle flow in the asthenosphere as a consequence of the fast retreat of the Hellenic slab. Deviations from this homogeneous pattern observed in continental Greece, S-Aegean and SW-Anatolia can also be explained by this model, for example with a slab tear beneath SW-Anatolia.

Bulletin of Volcanology, 2013

A geochemical survey of fumarolic and submerged gases from fluid discharges located in the Nea

Bulletin of the Seismological Society of America, 2009

On 8 January 2006, an intermediate-depth earthquake occurred at the western part of the Hellenic ... more On 8 January 2006, an intermediate-depth earthquake occurred at the western part of the Hellenic trench close to the island of Kythera (southern Greece). This is the first intermediate-depth earthquake in the broader Aegean area that has produced such an extensive set of useful recordings, as it was recorded by the main permanent seismological networks and numerous acceleration sensors operating in Greece, as well as by EGELADOS, a large-scale temporary amphibian broadband seismological network deployed in the southern Aegean area.