1,721,018 research outputs found
Detailed seismotectonic investigation of the broader Aegean region using digital seismological data
No full textThe present PhD thesis focuses on the characteristics of the natural processes taking place at the source of the earthquakes through the study of the focal mechanisms, the slip distribution and the characteristics of the earthquake sequences of the broader Aegean region. In Chapter 1 a review of the current kinematic models for the broader Aegean region is presented along with information regarding the physical characteristics of the crust and uppermost mantle. In this chapter also the velocity vectors derived from GPS campaigns from various authors are combined in addition to the slip vectors calculated from the focal mechanism of strong earthquakes for which the fault plane is known. In Chapter 2 the theory of the Moment Tensor is presented, together with the methods for its decomposition and information regarding the inversion process. The process of the construction of Green's function is analyzed, different velocity models are presented and tested and follows a discussion regarding the uncertainties of the inversion procedure. Chapter 3 includes the results of the epicenter and focal mechanism analysis of the seismic sequences of Skyros (2001), Vartholomio (2002), Psaxnon (2003), Saros (2003), Lefkada (2003), Loutron-Alexandroupolis (2004) and of the Sigaçik Gulf in Turkey (2005). In the current chapter the "quick focal mechanism" determination from the Geophysical Laboratory is presented along with a preliminary comparison of the results with those of International Seismological Institutes. -330- In Chapter 4 the inversion method for the calculation of the slip distribution on the fault plane using teleseismic data is presented. The method has been applied to the earthquakes: Montenegro mainshock (1979), Montenegro largest aftershock (1979), Lefkada (2003), Sigaçik (2005), Kythera (2006). Also it was performed a detailed sensitivity analysis of the inversion method in order to reveal its uncertainties and resolution. In this chapter the effect of directivity of the earthquakes is also analyzed, the Empirical Green's Function method and the inversion of the Source Time Function for the retrieval of the slip on the fault plane. Chapter 5 describes the way towards a realistic calculation of the ground motion from slip distribution models. Examples from the Montenegro events and Lefkada mainshock are presented and a discussion on the quality of the results is made. Chapter 6 hosts the conclusions of the present dissertation and a discussion of the geotectonic characteristics of the Aegean region
Definition of Seismogenic Faults by Combining Seismological, Geological and Geophysical Data: Case Studies From the Aegean Sea Area
No full textGeological 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 1999 Athens earthquake forms a characteristic example, where combination of seismological, geological and interferometric data was required to accurately locate the seismogenic fault. Proposed hypocenter locations of this earthquake differ as much as 16 km in the horizontal direction and 22 km in depth. The different sets of hypocenter parameters were tested through forward calculations of the surface displacement field, taking into account the distribution of slip during this earthquake, and the resulting fields were compared to interferometric and geological data to determine the best source model. Another example of the effectiveness of the combined geological, geophysical and seismological data sets is the recent determination of the western continuation of the Ganos Fault (Turkey) that ruptured in 1912, within the Gulf of Saros, in northeastern Aegean Sea. Until recently, geological observations supported the theory that the continuation of the Ganos Fault in the Gulf of Saros coincides with the fault along the northern coasts of the Gelibolu peninsula. Nevertheless, the combination of geological information with recent geophysical and seismological data tends to cancel this theory and rather supports that the western continuation of the Ganos fault is located close to the northern border of the Saros depression. These combined studies introduce new data for future seismic hazard studies in the broader area
Investigation of ground movements induced by water withdrawal via cluster-analysis applied to InSAR data
No full textRemote sensing methods (InSAR) provide advanced methodologies for detecting and precisely measuring ground deformations (GD) of anthropogenic origin like trend and seasonal aquifer-system response to exploitation and recharge.
We developed an algorithm that relies on the decomposition and clustering analysis of time series of GD to characterize the deformative behavior over a specific area due to anthropogenic activities related to water production. The vertical movements for monitoring points (MP) derived from InSAR measurements were decomposed into their seasonal (S) and trend (T) components. S is suitable for analyzing seasonal behavior of GD induced by oscillatory phenomena like aquifer withdrawal for agricultural purposes and seasonal rainfall recharges. T is more useful for measuring the impact of anthropogenic activities with a more linear and continuous behavior in time. Subsequently, the cluster analysis groups for all the MPs, which are grouped according to their similarities in S or T components, allows to define and quantify the deformative behavior of the system and the areal extent of the phenomenon.
We applied this method to different areas in Emilia-Romagna in northern Italy characterized by strong superposition between groundwater production and other anthropogenic activities such as gas /storage. We focused on identifying different behaviors of the time series related to the different activities. We compared the results form cluster analysis with ancillary info such as: water well positions, amount of fluid production, rainfall precipitation, the structural geology and the land use maps of the studied areas comparing the different seasonal behaviors related to those attributes. The analysis of the trend and seasonal component allowed us to verify our results and the reliability of this method with data from literature.
The results of this work enable us to quantify and isolate the effects of water production on GD from other anthropogenic effects
The instability of the MW and ML comparison for earthquakes in Greece for the period 1969 to 2007
No full textInternational audienceWe use 576 earthquakes of magnitude, , 3.3 to 6.8 that occurred within the region 33° N–42.5° N, 19° E–30° E in the time period 1969 to 2007 to investigate the stability of the relation between moment magnitude, , and local magnitude, , for earthquakes in Greece and the surrounding regions. We compare to as reported in the monthly bulletins of the National Observatory of Athens (NOA) and to as reported in the bulletins of the Seismological Station of the Aristotle University of Thessaloniki. All earthquakes have been analyzed through regional or teleseismic waveform inversion, to obtain , and have measured maximum trace amplitudes on the Wood–Anderson seismograph in Athens, which has been in operation since 1964. We show that the Athens Wood–Anderson seismograph performance has changed through time, affecting the computed by NOA by at least 0.1 magnitude units. Specifically, since the beginning of 1996, its east–west component has been recording systematically much larger amplitudes compared to the north–south component. From the comparison between and reported by Thessaloniki, we also show that the performance of the sensors has changed several times through time, affecting the calculated 's. We propose scaling relations to convert the values reported from the two centers to . The procedures followed here can be applied to other regions as well to examine the stability of magnitude calculations through time
Earthquake ground motion scenarios in urban areas: the case of the city of Thessaloniki (Northern Greece)
No full textPreliminary statistical analysis of borehole and geological data from the Po plain
Full text linkThe Po Plain area in the north of Italy can be considered a natural geological and geophysical
laboratory due to its complex geological evolution, particularly from the Miocene to today. Much
of our understanding about the subsurface of the Po Plain is due to the large amount of data collected during the period of hydrocarbon exploration in Italy. In total more than 7000 wells have
been drilled and thousands of km of seismic acquisition lines have been acquired. Furthermore,
the study of the natural gas fields contributed with additional data facilitating the creation of
detailed structural and stratigraphic models of the subsurface. The majority of the “original” data,
including well logs, seismic and geological profiles existed in paper format thus posing challenges
for their integration into modern models where digital data are incorporated to achieve a sound
description of the subsoil. Livani et al. (2023) have collected and digitized a large number of
“original” data and subsequently used them to recreate the overall subsurface architecture of the
Po plain and extract the physical properties of the main geological units. In this study, we use the
results of the work of Livani et al. and we perform a preliminary statistical analysis on them. We
explore relationships between rock density and geological formations, we compare log data (GR,
sonic) with lithologies and we investigate the lithological content for each of geological formations. Ultimately, we compare some of our results with previously published research
Multidisciplinary investigation of the natural and anthropogenic ground movements in the Po Plain (Northern Italy) using geological and satellite data
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Fully Integrated Hydrocarbon Reservoir Studies: Myth or Reality?
Full text linkAbstract: Problem statement: In the petroleum industry and especially during reservoir studies, data coming from different disciplines must be combined in order to generate a model that is representative of the reservoir being studied and can be used for defining the most viable development strategy of the field from both an economic and technical standpoint. Each of these disciplines represents an independent piece of a puzzle that is solved by professionals from various scientific fields who have different educational backgrounds. Integration among geophysics, geology, fluid dynamics and geomechanics is truly essential, but requires specific approaches and procedures for generating and calibrating a reservoir model capable of dealing with all and each of these aspects. Approach: Independent workflows were examined for each of the disciplines involved so as to highlight unavoidable interdependencies between static, dynamic and geomechanical models, even when the goal is to tackle each issue separately. Then, the traditional working method was compared to the integrated approach that supports the generation and calibration of models based on data and interpretation results from all the disciplines involved in the entire project. Results: The Construction of a reservoir model should be regarded as a dynamic process, subject to repeated updates as new data is made available and by frequent modifications when inconsistencies are found between the understanding that different specialists have of the same system. This approach has exhibited great advantages in terms of improvement in the quality and flexibility of the model, reduction of working time and generation of a single final model that can be adapted or used for any kind of simulation problem. Conclusion: An integrated approach is necessary for reservoir modeling purposes. Modern reservoir studies should be designed accordingly to permit the full integration of static, dynamic and geomechanical data into a single reservoir model. Integration is always beneficial, even though there still remains a misconception that it is not needed at all times. For this reason, it is recommended that an effort is made to set up a model capable to handle all aspects of a reservoir study each time a new field study is undertaken, even when it is not envisioned that all aspects might be of interest in the future
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