1,721,086 research outputs found
Palaeoseismological investigations of Aegean-type active faults.
No full textPalaeoseismological studies carried out in the Aegean Region during the past decade or so, mainly from faults lying in mainland Greece, are reconsidered and their results re-evaluated. We focus on active normal faults and particularly on the principal seismotectonic parameters, such as the coseismic displacement associated to past events and the length of the seismogenic structures. Based on new both field observations and existing data and following few assumptions, we attempt to calculate the maximum seismic moment possibly associated to past earthquakes and documented from palaeoseismological studies. These seismic moments are compared with those estimated from historical earthquakes for which both maximum vertical displacement and surface rupture length are known. Similarities and differences of the two datasets are discussed, showing that palaeoseismologically-calculated magnitudes and displacements per event appear to be systematically underestimated in the Aegean Region as well as their seismic potential. For selected faults, we also obtained reliable values of the recurrence interval of moderate to large earthquakes and estimates of the slip-rate. Differences in these parameters are attributed to the different geotectonic settings
Magnitude versus faults' surface parameters: quantitative relationships from the Aegean Region.
No full textField trip to Western Macedonia and Thessaly
No full textRecent and active tectonics in Western Macedonia and Thessaly. The Kozani Grevena earthquake of May 1995
Magnitude versus faults' surface parameters: quantitative relationships from the Aegean
No full textHistorical and seismotectonic data from the broader Aegean Region have been collected and all possible information relative to ground deformation associated to earthquakes that hit the area have been re-evaluated. All events associated to co-seismic surface faulting have been selected and further investigated, while geomorphologic and geological criteria have been used to recognise and characterise the seismogenic faults associated to these ‘morphogenic earthquakes’ (sensu Caputo, 1993). In particular, in order to perform seismic hazard analyses, we compiled a list of all earthquakes where the surface rupture length (SRL), the maximum vertical displacement (MVD) or the average displacement (AD) is available. We thus obtained reliable values of these source parameters for 36 earthquakes, of which 26 occurred during the 20th century, 6 in the 19th century and the three remaining earlier. Magnitude versus SRL and MVD have been compiled for estimating empirical relationships. The calculated regression equations are: Ms = 0.90·log(SRL) + 5.48 and Ms = 0.59·log(MVD) + 6.75, showing good correlation coefficients equal to 0.84 and 0.82, respectively. Co-seismic fault rupture lengths and especially maximum displacements in the Aegean Region have systematically lower values than the same parameters world-wide, but are similar to those of the Eastern Mediterranean-Middle East region. The envelopes of our diagrams are also calculated and discussed for estimating the worst-case scenario. Furthermore, for all investigated seismogenic structures, based on several geological criteria, we measured the 'geological' fault length (GFL), that is the total length of the neotectonic faults showing cumulative recent activity. We then compared SRL with GFL and their ratio shows a clear bimodal distribution with a major peak at 0.8-1.0, indicating that about 50% of the investigated earthquakes ruptured almost the entire fault length, while a second peak around the value of 0.5, is clearly related to a segmentation process of longer neotectonic structures. Further implications of this distribution are also discussed. Eventually, from the distribution of GFL versus magnitude we also infer an important geological threshold for the occurrence of ‘morphogenic earthquakes’ at about 5.5 degrees
The North Aegean Region: a Tectonic Paradox?
No full textIn the past two decades, several publications have been presented concerning the recent and active fault geometry, kinematics and geodynamics of the Aegean Region and particularly of the northern sector. Data and results are often contradictory and because of the complexity of the area most hypotheses and models should be carefully considered.
The right-lateral movement of the North Anatolia Fault continues into some branches of the North Aegean fault system. There, strike-slip motion along NE-SW trending faults coexists with dip-slip E-W trending faults in the frame of an extensional regime related to N-S crustal stretching.
If we take into account the geodynamic environment of the region, several mechanical problems arise. To the east, the Aegea is compressed by the westward convergence of Anatolia, while to the south and west along the Hellenic Arc, a hemyradial compression occurs due to subduction. Moreover, the North Anatolia-North Aegean Trough fault system resembles a restraining bend. To the contrary, the whole area is affected by pure extension and local transtension, along the NE-SW trending structures, Accordingly, the major paradox of the area and especially in the western sector (fault termination?) is the occurrence of extension where compression should areally, or at least locally, predominate
Earthquake Geology: methods and applications
No full textEarthquakes are complex natural phenomena that can be studied from different perspectives and using a variety of methods. Prior to the 20th century, the study of earthquakes (literally Seismology) was done by geologists, but when the seismograph was invented, field geologists were progressively set aside and the investigation of seismic events became an exclusive matter of seismologists, which conversely mainly focused on the seismic waves and the physics of the source, generally omitting to investigate the geological aspects of the fault, which in reality is the causative structure of most earthquakes. Only during the second half of the 20th century, became clear that the exploitation of geological data and the use of geological methodologies in their broadest sense are crucial for investigating seismic events and in general the active tectonics of an area. Indeed, structural, stratigraphic, geomorphological and remote sensing techniques and methods, among others, represent the modern tools in Earthquake Geology researches. The major advantages of Earthquake Geology is to examine a larger time window than instrumental, historical and archaeoseismological studies can do. Not secondarily, Earthquake Geology is also capable of detecting and examining the cumulative effects of earthquakes occurred in an area over very long periods. Indeed, linear and areal morphogenic earthquakes leave on the earth's surface permanent features that contribute to shape the landscape. Accordingly, geological investigations can detect, measure and study such features even several years, centuries or millennia after they were formed by earthquakes. Additionally, with geological studies, crucial information can be obtained for regions where instrumental seismic records or detailed historical seismological information are not available, but where destructive earthquakes hhave been generated in the past and similar events may be generated in the future. Geological approaches to the investigation of past earthquakes are fundamental to contribute in determining or inferring important parameters for SHA analyses, including the mean slip-rate, the maximum expected magnitude and the return period for a given magnitude
The Greek Database of Seismogenic Sources (GreDaSS), version 2.0.0: A compilation of potential seismogenic sources (Mw>5.5) in the Aegean Region.
No full textThe Greek Database of Seismogenic Sources is a project devoted to provide Greek authorities of a complete and modern tool for improving the Seismic Hazard Assessmant (SHA) of the country. It also represents a valuable source of information for scientists who want to deal with earthquake scenarios and modelling, geodynamics, active deformation and many more.
GreDaSS is an open-file, continuously updatable, that can accommodate all proposals from multi-field researchers. As a GIS-based database, consists of several layers, both graphical and metadata ones, based on the general structure of the Italian DISS
Earthquake Geology: methods and application
No full textEarthquake Geology researches need an integrated, interdisciplinary approach with the contribution of Geomorphologists, Structural Geologists, Surveyors, Sedimentologists and Pedologists among other specialists. For specific case studies, the synergy with Seismologists, Historians, Engineers, Architects and Archaeologists would be fruitful and/or necessary.
A key aspect in Earthquake Geology investigations is the need of rigorous and transparent methodologies and not only empirical and qualitative interpretations. An implicit major target in following a quantitative approach is to provide results ready to be included in SHA analyses. As a matter of fact, the collected information and obtained results could be directly and straightforwardly exploited for this purpose only when converted into numbers representing, for example, the epicentral location, the magnitude or the date of an earthquake together with an estimate of their reliability.
With regard reliability of the results obtained with geological investigations, another crucial point that should be better focused on by Earthquake Geologists, is the need to evaluate the uncertainties in both original data and proposed interpretations and the operators should start giving ranges and numerical values of upper/lower boundaries of specific parameters. Due to the variety of the geological record possibly bearing information on past events and the diversity in methodological approaches, this is certainly not a simple task and it represents the future challange for Earthquake Geology investigations. The achievement of this goal will permit this discipline to make an important qualitative leap thus preventing to be considered "son of a minor God" during SHA analyses
Late Cainozoic geodynamic evolution of Thessaly and surroundings (Central-Northern Greece)
No full textIn the framework of the late Alpide deformation of Greece and of the recent and active extensional tectonism of the Aegean region, the geotectonic evolution of Thessaly region (Central-Northern Greece) has been examined based on quantitative and qualitative structural analysis and using stratigraphic, sedimentological, morphotectonic and seismological data. The geometry of the faults, their architecture and the knowledge of the stress pattern are used to explain some aspects of the tectonics and crustal dynamics of Thessaly and surroundings. The oldest compressional phases taken into account show a mean ENE-WSW direction of shortening and have been defined as late-Alpide (Early Aquitanian and Langhian). A later (Late Miocene-Pliocene) NE-SW extensional phase has been related to the Hellenic post-orogenic collapse which develops behind the collisional front between the Aegean (Eurasia) and African plates. This phenomenon diachronically migrates from the east (Central Macedonia, Thermaikos Basin) towards the west (Epirus, Albania) where it is still active. As a consequence of this second phase, the area forms a basin-and-range-like structure. The third and last phase (Middle Pleistocene-Present) is characterized by a N-S direction of extension and affects the whole Aegean region. It generates new E-W trending basins superimposed on the inherited ones thus giving as a final result, the complex blocky crustal pattern we can actually observe. The recent and active right-lateral strike-slip movements along the North Aegean Trough seem to stop in the Sporades Basin and do not affect the uppermost crust of mainland Greece. A further WNW-ESE directed extension observed occasionally in Central and Northern Greece could be explained as local events or as block-related deformation
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