Analysis of seismic reflection data as a tool for the seismotectonic assessment of a low activity intraplate basin – the Lower Tagus Valley (Portugal)

Cabral, João; Moniz, Catarina; Ribeiro, Paulo; Terrinha, Pedro; Matias, L.

doi:10.1023/b:jose.0000005722.23106.8d

Cited by 51 publications

(82 citation statements)

References 12 publications

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“…2000 m of Tertiary sediments consisting of alluvial fan deposits of Eocene-Oligocene age 200-400 m thick, overlain by Miocene fluvial and shallow marine sediments showing a variable width that surpasses 1000 m in depocenters. Fluvial sands and gravels of fini-Zanclean to Piazencian age, generally less than 100 m thick, unconformably overlie the Miocene deposits (Cabral et al 2003, Carvalho 2003, Carvalho et al 2016, Pais et al 2012, Rasmussen et al 1998. The culminating surface of the Pliocene sedimentation is still preserved as a plateau in some areas of the LTB, reaching an altitude of ca.…”

Section: Seismotectonic Settingmentioning

confidence: 99%

“…The Azambuja fault is another NNE-SSW trending structure located in the LTV (Figure 2) exhibiting geomorphic and structural evidence of Pliocene to Quaternary activity (Cabral 1995, Cabral et al 2003. This fault is evident in seismic reflection lines, showing steep thrust geometry downthrowing to the east the Cenozoic sediments of the LTB.…”

Section: Seismotectonic Settingmentioning

confidence: 99%

“…It later evolved to a transpressive foredeep basin during the Miocene, under a NNW-SSE to NW-SE compression that caused tectonic inversion of the extensional Mesozoic Lusitanian Basin (LB) located to the W (Fonseca 1989, Ribeiro et al 1990, Cabral 1995, Rasmussen et al 1998, Cabral et al 2003, Carvalho 2003, Carvalho et al 2016 (Figure 2).…”

Section: Seismotectonic Settingmentioning

confidence: 99%

“…These are linked by WNW-ESE to NW-SE faults also accommodating significant vertical offsets, which together constrain a few Neogene depocentres and structural highs in the basin. (Fonseca 1989, Rasmussen et al 1998, Cabral et al 2003, Carvalho 2003, Carvalho et al 2016.…”

Section: Seismotectonic Settingmentioning

confidence: 99%

“…50 km (Figure 2). It was generated in the Mesozoic as a normal fault zone of the LB (e.g., Rasmussen et al 1998, Kullberg 2000, Carvalho et al2005, and was later tectonically inverted, moving with oblique reverse-left lateral slip since the Neogene (Ribeiro et al 1990, Cabral et al 2003, Carvalho et al 20062008;. It outcrops north of Lisbon as a steep east-verging reverse fault placing Jurassic rocks of the LB, at the west, over Miocene deposits of Tortonian age, at the east.…”

Section: Seismotectonic Settingmentioning

confidence: 99%

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Los terremotos del Bajo Valle del Tajo (Portugal): Lisboa 26 de Enero de 1531 y Benavente 23 de Abril de 1909

2017

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Abstract. The Lower Tagus Valley (LTV) has been the source of several local earthquakes that affected the region of Lisbon, in the central part of Portugal. In spite of absence of strong earthquakes during the last 100 years, past events have produced large damage in this area. We present the state of the art concerning the last two major earthquakes, which occurred in 1531 and 1909. The effects of both events are described, based on coeval reports already interpreted by several authors. The source parameters determined by different authors are also presented. The characterization of the seismogenic potential of the LTV is very important to better estimate the seismic hazard and risk of the region of Lisbon and Tagus Valley.

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Section: Seismotectonic Settingmentioning

confidence: 99%

Section: Seismotectonic Settingmentioning

confidence: 99%

Section: Seismotectonic Settingmentioning

confidence: 99%

Section: Seismotectonic Settingmentioning

confidence: 99%

Section: Seismotectonic Settingmentioning

confidence: 99%

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Los terremotos del Bajo Valle del Tajo (Portugal): Lisboa 26 de Enero de 1531 y Benavente 23 de Abril de 1909

2017

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Floodplain Sediments of the Tagus River, Portugal: Assessing Avulsion, Channel Migration and Human Impact

Azevêdo

Ramos-Pereira

Ramos

et al. 2007

Sedimentary Processes, Environments and Basins

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A study of the Tagus River floodplain (Portugal) has been carried out using a variety of methods including sedimentological, geochemical and geochronological analyses, as well as geomorphological and hydrological studies, performed in order to characterize the flood sediments and the dynamics of the river during the Holocene. Until the 19th century, the Tagus was an anastomosed river, with multiple channels separated by large areas of floodplain; today, it is a single channel river with alternate bars, mainly as a result of anthropogenic modification. In order to study its behaviour during the Holocene, four cores ranging in length from 3.70 to 8.04 m were obtained from the floodplain and 232 samples were analysed. Detailed textural analysis was necessary owing to the lack of preservation of sedimentary structures in the cores. The sediments of the present-day geomorphological elements of the floodplain (bars, natural levees, crevasse-splay deposits, flood basin and abandoned channels) were also studied in order to compare their textural characteristics with those of the cored samples. Both the present analogues and core sediments were well discriminated using mean diameter versus standard deviation and average mean diameter versus average mud percentage graphical correlations. The textural parameters defined (sand/mud ratio, mean, standard deviation, skewness) and particularly the interparameter correlations, together with 12 14 C numerical ages of organic matter obtained, allowed the evaluation of: (i) sedimentological changes in the floodplain (channel migration, avulsion and crevasse-splay development); and (ii) the chronological evolution of the different energetic environments of the floodplain for the past 4 kyr. These approaches permitted the determination of sedimentation rates for the different alluvial plain environments. The highest sedimentation rates occurred in the flood basin and channelfill domains, with values ranging from 2.2 mm yr −1 to 4.7 mm yr −1 and the lowest in the channel (0.3 mm yr −1 ). Values from 0.8 to 1.6 mm yr −1 were recorded in sedimentary environments proximal to the channel, where several crevasse-splay episodes have been recognized. In the period common to the four cores, i.e. the past 4000 yr, the sedimentation rates decreased towards the present. In spite of increasing human intervention in the hydrographic basin during this time, the increasing aridity of the climate is considered to have outweighed the sediment availability, which resulted in a decreasing sedimentation rate.

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Signature of fault zone deformation in near‐surface soil visible in shear wave seismic reflections

Ghose

Carvalho

Loureiro

2013

Geophysical Research Letters

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Small‐throw seismogenic fault segments hidden in the Holocene sediments are crucial but difficult targets in seismic exploration. We report here the detection of the deformation pattern and a concealed fault segment in the unconsolidated sediments at Vila Franca Xira, Portugal, through identification in shear wave reflection data of multiple signatures of ductile deformation associated with faulting. We find step‐like changes in the stacking velocity along a shallow subsoil layer boundary, indicating synsedimentary faulting. We also recognize a consistent distortion in the moveout of the reflection events in the raw shear wave data. Synthetic modeling of seismic data helps in interpreting these observations and identifying backscattered energy from a steeply dipping shallow fault zone. Prior to this finding, there was no evidence for Holocene activity of this fault, although the fault is considered to be the most probable source for the disastrous 1531 earthquake.

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Analysis of seismic reflection data as a tool for the seismotectonic assessment of a low activity intraplate basin – the Lower Tagus Valley (Portugal)

Cited by 51 publications

References 12 publications

Los terremotos del Bajo Valle del Tajo (Portugal): Lisboa 26 de Enero de 1531 y Benavente 23 de Abril de 1909

Los terremotos del Bajo Valle del Tajo (Portugal): Lisboa 26 de Enero de 1531 y Benavente 23 de Abril de 1909

Floodplain Sediments of the Tagus River, Portugal: Assessing Avulsion, Channel Migration and Human Impact

Signature of fault zone deformation in near‐surface soil visible in shear wave seismic reflections

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