scholarly journals Neotectonics of Graciosa island (Azores): a contribution to seismic hazard assessment of a volcanic area in a complex geodynamic setting

2014 ◽  
Vol 56 (6) ◽  
Author(s):  
Ana Hipólito ◽  
José Madeira ◽  
Rita Carmo ◽  
João Luís Gaspar
Keyword(s):  
Stress Field ◽  
Seismic Hazard ◽  
Plate Boundary ◽  
Seismic Hazard Assessment ◽  
Middle Pleistocene ◽  
Geodynamic Setting ◽  
Tectonic Deformation ◽  
Volcanic Area ◽  
Stress Regime ◽  
Regional Stress

<p class="MsoNormal" style="margin: 0cm 0cm 0pt; text-align: justify; line-height: 150%;">Graciosa is a mid-Pleistocene to Holocene volcanic island that lies in a complex plate boundary between the North American, Eurasian, and Nubian plates. Large fault scarps displace the oldest (Middle Pleistocene) volcanic units, but in the younger areas recent volcanism (Holocene to Upper Pleistocene) conceals the surface expression of faulting, limiting neotectonic observations. The large displacement accumulated by the older volcanic units when compared with the younger formations suggests a variability of deformation rates and the possibility of alternating periods of higher and lower tectonic deformation rates; this would increase the recurrence interval of surface rupturing earthquakes. Nevertheless, in historical times a few destructive earthquakes affected the island attesting for its seismic hazard. Regarding the structural data, two main fault systems, incompatible with a single stress field, were identified at Graciosa Island. Thus, it is proposed that the region is affected by two alternating stress fields. The stress field #1 corresponds to the regional stress regime proposed by several authors for the interplate shear zone that constitutes the Azorean segment of the Eurasia-Nubia plate boundary. It is suggested that the stress field #2 will act when the area under the influence of the regional stress field #1 narrows as a result of variations in the differential spreading rates north and south of Azores. The islands closer to the edge of the sheared region will temporarily come under the influence of a different (external) stress field (stress field #2). Such data support the concept that, in the Azores, the Eurasia-Nubia boundary corresponds to a complex and wide deformation zone, variable in time.</p>

scholarly journals Groundwater extraction-induced seismicity around Delhi region, India

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Deepak K. Tiwari ◽  
Birendra Jha ◽  
Bhaskar Kundu ◽  
Vineet K. Gahalaut ◽  
Naresh K. Vissa
Keyword(s):  
Plate Boundary ◽  
Mechanical Analysis ◽  
Tectonic Deformation ◽  
Ganga Basin ◽  
Stress Regime ◽  
Seismicity Rate ◽  
Basement Faults ◽  
Moderate Seismicity ◽  
Decadal Scale ◽  
Anthropogenic Seismicity

AbstractThe non-tectonic deformation, either of natural or anthropogenic origin, may influence the earthquake occurrence process and seismicity rate along the plate-boundary or ‘stable’ plate-interiors domains. The low magnitude but moderate seismicity rate of Delhi region on the stable plate-interiors domains of India, exhibits significant variation both in short-term at annual seasonal scale and in long-term at decadal scale. It correlates with the anthropogenic groundwater pumping for the extensive irrigation, urban activities, and seasonally controlled hydrological loading cycle of Indo-Ganga Basin hosted freshwater aquifers. Our coupled hydro-mechanical simulation and poro-mechanical analysis of basement fault stability suggest that the combined aquifer contraction and basement rock expansion act together to modulate the effective stress regime and anthropogenic seismicity on the basement faults in Delhi region.

scholarly journals When probabilistic seismic hazard climbs volcanoes: the Mt. Etna case, Italy – Part 1: Model components for sources parameterization

2017 ◽  
Vol 17 (11) ◽  
pp. 1981-1998 ◽  
Author(s):  
Raffaele Azzaro ◽  
Graziella Barberi ◽  
Salvatore D'Amico ◽  
Bruno Pace ◽  
Laura Peruzza ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Hazard Assessment ◽  
Seismic Hazard Assessment ◽  
Point Sources ◽  
Volcanic Complex ◽  
Probabilistic Seismic Hazard ◽  
Volcanic Area ◽  
High Quality ◽  
Mt Etna ◽  
Model Components

Abstract. The volcanic region of Mt. Etna (Sicily, Italy) represents a perfect lab for testing innovative approaches to seismic hazard assessment. This is largely due to the long record of historical and recent observations of seismic and tectonic phenomena, the high quality of various geophysical monitoring and particularly the rapid geodynamics clearly demonstrate some seismotectonic processes. We present here the model components and the procedures adopted for defining seismic sources to be used in a new generation of probabilistic seismic hazard assessment (PSHA), the first results and maps of which are presented in a companion paper, Peruzza et al. (2017). The sources include, with increasing complexity, seismic zones, individual faults and gridded point sources that are obtained by integrating geological field data with long and short earthquake datasets (the historical macroseismic catalogue, which covers about 3 centuries, and a high-quality instrumental location database for the last decades). The analysis of the frequency–magnitude distribution identifies two main fault systems within the volcanic complex featuring different seismic rates that are controlled essentially by volcano-tectonic processes. We discuss the variability of the mean occurrence times of major earthquakes along the main Etnean faults by using an historical approach and a purely geologic method. We derive a magnitude–size scaling relationship specifically for this volcanic area, which has been implemented into a recently developed software tool – FiSH (Pace et al., 2016) – that we use to calculate the characteristic magnitudes and the related mean recurrence times expected for each fault. Results suggest that for the Mt. Etna area, the traditional assumptions of uniform and Poissonian seismicity can be relaxed; a time-dependent fault-based modeling, joined with a 3-D imaging of volcano-tectonic sources depicted by the recent instrumental seismicity, can therefore be implemented in PSHA maps. They can be relevant for the retrofitting of the existing building stock and for driving risk reduction interventions. These analyses do not account for regional M  >  6 seismogenic sources which dominate the hazard over long return times (≥ 500 years).

The sources of lithospheric tectonic stresses

1991 ◽  
Vol 337 (1645) ◽  
pp. 73-81 ◽  
Keyword(s):  
Stress Field ◽  
Lower Mantle ◽  
Large Scale ◽  
Plate Boundary ◽  
Vertical Stress ◽  
Viscous Drag ◽  
Tectonic Deformation ◽  
Tectonic Stresses ◽  
Deep Mantle

The stresses associated with large-scale tectonic deformation have three possible origins: (1) plate-boundary forces counterbalanced by viscous drag beneath the plates; (2) density heterogeneities situated within the plates (say at depths shallower than 200 km); (3) mass heterogeneities in the deep mantle. The first two are shown to be equally important for the understanding of the stress field. No topography (no vertical stress) seems to be associated with lower-mantle mass anomalies. This is most compatible with a two-layer convective mantle where the lower-mantle mass anomalies, mechanically decoupled from the lithosphere, are unable to induce tectonic stresses.

scholarly journals Neotectonic analysis, active stress field and active faults seismic hazard assessment in Western Crete

2017 ◽  
Vol 47 (2) ◽  
pp. 582 ◽  
Author(s):  
D. Mountrakis ◽  
A. Kilias ◽  
A. Pavlaki ◽  
C. Fassoulas ◽  
E. Thomaidou ◽  
...  
Keyword(s):  
Stress Field ◽  
Seismic Hazard ◽  
Hazard Assessment ◽  
Hazard Analysis ◽  
Active Faults ◽  
Seismic Hazard Assessment ◽  
Fault Zones ◽  
Extension Phase ◽  
Fault System ◽  
Normal Faults

Within the framework of this study the complicated fault system of Western Crete was napped in detail and its kinematic and dynamic setting was analysed in order to distinguish 13 major active and possible active fault zones, the seismic potential of which was assessed. Moreover, kinematic data and striations were used to estimate the corresponding stress field geometry. Two stress phases were recognized: 1st the N-S extension phase (D1) in Mid-Upper Miocene to Lower Pliocene times forming E-W normal faults that bound the Neogene basins; 2nd the E-W extension phase (D2) in Late Pliocene-recent times forming N-S trending active normal faults. Smaller, mainly NE-SW trending faults, with significant strike-slip component, indicate a kinematic compatibility to the D2 phase, acting as transfer faults between larger N-S fault zones. The faults were incorporated in a detailed seismic hazard analysis together with the available seismological data, involving both probabilistic and deterministic approaches, for seismic hazard assessment of several selected sites (municipalities).

scholarly journals When probabilistic seismic hazard climbs volcanoes: the Mt Etna case, Italy. Part I: model components for sources parametrization

2017 ◽  
Author(s):  
Raffaele Azzaro ◽  
Graziella Barberi ◽  
Salvatore D'Amico ◽  
Bruno Pace ◽  
Laura Peruzza ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Hazard Assessment ◽  
Seismic Hazard Assessment ◽  
Point Sources ◽  
Volcanic Complex ◽  
Probabilistic Seismic Hazard ◽  
Volcanic Area ◽  
High Quality ◽  
Mt Etna ◽  
Model Components

Abstract. The volcanic region of Mt Etna (Sicily, Italy) represents a perfect lab for testing innovative approaches to seismic hazard assessment, given the availability of a long record of historical and recent observations of seismic and tectonic phenomena, the high quality of various geophysical monitorings and especially because the very fast geodynamics clearly demonstrate some seismotectonic processes. We present here the model components and the procedures adopted for defining seismic sources to be used in a new generation of Probabilistic Seismic Hazard Assessment (PSHA) whose first results and maps are presented in a companion paper, Peruzza et al. (2017). The sources include, in a picture of increasing complexity, area seismic zones, individual faults and gridded point sources that are obtained by integrating geological field data with long and short earthquake datasets (the historical macroseismic catalogue that covers about three centuries, and a high-quality instrumental locations database for the last decades). The analysis of the frequency-magnitude distribution identifies two main fault systems within the volcanic complex featuring different seismic rates that are controlled essentially by volcano-tectonic processes. We discuss the variability of the mean occurrence times of major earthquakes along the main Etnean faults by using an historical approach and a purely geologic method. We derive a magnitude-size scaling relationship specific for this volcanic area, which was has been implemented into a recently developed software tool – FiSH, Pace et al. (2015) – which we use to calculate the characteristic magnitudes and the related mean recurrence times expected for each fault. Results suggest that for Mt Etna area, the traditional assumptions of uniform and Poissonian seismicity can be relaxed; a time-dependent fault-based modelling, joined with a 3D imaging of volcano-tectonic sources depicted by the recent instrumental seismicity, can be therefore implemented in PSHA maps. They can be relevant for the retrofitting of the existing building stock, and for driving risk reduction interventions. These analyses do not account regional M > 6 seismogenic sources which dominate the hazard at long exposure times (&amp;geq; 50 yrs).

scholarly journals The Volcanic Relief within the Kos-Nisyros-Tilos Tectonic Graben at the Eastern Edge of the Aegean Volcanic Arc, Greece and Geohazard Implications

Geosciences ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 231
Author(s):  
Paraskevi Nomikou ◽  
Pavlos Krassakis ◽  
Stavroula Kazana ◽  
Dimitrios Papanikolaou ◽  
Nikolaos Koukouzas
Keyword(s):  
Seismic Hazard ◽  
Ground Truth ◽  
Volcanic Field ◽  
Middle Pleistocene ◽  
Volcanic Area ◽  
African Plate ◽  
Volcanic Arc ◽  
Geophysical Surveys ◽  
Volcanic Debris

The active Kos-Nisyros-Tilos volcanic field is located in the eastern sector of the Aegean Volcanic Arc resulting from the subduction of the African plate beneath the Aegean plate. The volcanic activity is developed since Middle Pleistocene and it occurs within a tectonic graben with several volcanic outcrops both onshore and offshore. Data obtained from previous offshore geophysical surveys and ROV exploration, combined with geospatial techniques have been used to construct synthetic maps of the broader submarine area. The volcanic relief is analyzed from the base of the volcanic structures offshore to their summits onshore reaching 1373 m of height and their volumes have been computed with 24.26 km3 for Nisyros Island and a total volume of 54.42 km3 for the entire volcanic area. The volcanic structures are distinguished in: (1) volcanic cones at the islands of Nisyros (older strato-volcano), Pergousa, Yali and Strongyli, (2) volcanic domes at the islands of Pachia, East Kondeliousa and Nisyros (younger Prophitis Ilias domes), (3) submarine volcanic calderas (Avyssos and Kefalos). Submarine volcanic debris avalanches have been also described south of Nisyros and undulating features at the eastern Kefalos bay. Submarine canyons and channels are developed along the Kos southern margin contrary to the Tilos margin. Ground truth campaigns with submarine vessels and ROVs have verified the previous analysis in several submarine volcanic sites. The geohazards of the area comprise: (1) seismic hazard, both due to the activation of major marginal faults and minor intra-volcanic faults, (2) volcanic hazard, related to the recent volcanic structures and long term iconic eruptions related to the deep submarine calderas, (3) tsunami hazard, related to the seismic hazard as well as to the numerous unstable submarine slopes with potential of gravity sliding.

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