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Université de Savoie - France
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- PublicationRestrictedSedimentary impacts of recent moderate earthquakes from the shelves to the basin floor in the western Gulf of Corinth(2017)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ;In seismically active areas, long termrecords of large earthquakes are indispensable to constrain reccurence patterns of large earthquakes. In thewestern Corinth Rift, one of the most active areas in Europe in terms of seismicity, data about ancient earthquakes are still insufficient, despite historical records covering the last two millenia and several studies in onshore paleoseimology. In this paper, we test the use of offshore sediments from the Gulf of Corinth to identify sediment failures and tsunamis that have been triggered by historical earthquakes. Two shelves (40–100mdeep), one sub-basin (180m) and the basin floor (330m) have been sampled by short gravity cores. The coreswere analyzed in order to identify and characterize event deposits. The age control has been provided by 137Cs and 210Pb activity measurements showing that the cores represent 2 to 4 centuries of sedimentation. In each site, sandy event deposits are interbeded in the muddy, hemipelagic sedimentation. The age of event deposits has been compared to the record of historical earthquakes using newand publishedmacroseismic data. This comparison shows temporal coincidence of some event deposits and documented earthquakes with a macroseismic intensity ≥ VII in the area, e.g. in 1861 CE, 1888 CE and 1909 CE. In nearshore, shallow-water settings, the record of event deposits does not exactly fitwith the historical record of large earthquakes because too few event deposits are present. Thismay be due to the absence of sediment failures or to a lower preservation of the deposits in such settings. In the deepest site, in the basin floor, the correspondence is better: a sandy turbidite probably corresponds to each large earthquake since 1850 CE, except one aseismic sediment density flow that occurred at the end of the 20th century. Surprisingly, theMs=6.2, June 15, 1995 Aigion earthquake is only possibly recorded in one nearshore site on the Aigion Shelf, in the form of a tsunami back-wash flow deposit. This study showed that moderate earthquakes (M 5.8–6.5) can significantly impact marine sediments. Regarding the evaluation of seismic hazard in the area, the basin floor is proposed as a promising site for long term paleoseismology in the Gulf of Corinth, while shallower settings need to be considered more carefully.529 7 - PublicationRestrictedTrench investigation on the main strand of the Boconó fault in its central section, at Mesa del Caballo, Mérida Andes, Venezuela(2008)
; ; ; ; ; ; ; ; ;Audemard, F. A. M.; FUNVISIS - Caracas ;Ollarves, R.; FUNVISIS - Caracas ;Bechtold, M.; FUNVISIS - Caracas ;Diaz, G.; FUNVISIS - Caracas ;Beck, C.; Université de Savoie - France ;Carrillo, E.; Universidad Central de Venezuela ;Pantosti, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Diderix, H.; NMCP - The Netherlands; ; ; ; ; ; ; The Mesa del Caballo trench assessment confirms the Holocene activity of the main strand of the Boconó fault at the Apartaderos pull-apart basin. Fifteen earthquakes, of which fourteen have been radiocarbon dated, have been recognized, spanning the last 20,500 yr. Recurrence intervals of these ≥7 magnitude events are variable. The dominant mode of recurrence is 400–450 yr, and the second one is 900 yr. Eventually some events are 1400–1800 yr apart. We suspect that our seismic record may be incomplete. This could be easily justified by several conditions: most of the earthquake recognitions is based on open-crack filling and they superpose spatially (eventually masking or destroying older fills), trenching may miss some events because the fault is made of en echelon Riedel shears, and a short return period may lead to faint differences between paleosoils few hundreds years of age apart. This trench also images an older activity of the fault, as evidenced by plentiful earthquake-triggered liquefaction features, as well as slumping and rotational sliding. By comparing paleoseismic results between the Morro de Los Hoyos and Mesa del Caballo trenches, it appears that both fault strands bounding the Apartaderos pull-apart basin move simultaneously. Besides, the main strand also coseismically slips twice in between those common events. In other words, the seismic scenario could be that the northern strand recurs every 1200–1350 yr while the southern does every 400– 450 yr. This is also in agreement with a respective slip share of 25 and 75% of the 9–10 mm/yr average slip of the Boconó fault in the Mérida Andes central sector.333 30 - PublicationRestrictedMultiproxy record for the last 4500 years from Lake Shkodra (Albania/Montenegro)(2012)
; ; ; ; ; ; ; ; ; ; ;Zanchetta, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Van Welden, A.; Geological Survey of Norway (NGU), Trondheim, Norway ;Baneschi, I.; IGG-CNR sez. Pisa, Pisa, Italy ;Drysdale, R. N.; Department of Resource Management and Geography, University of Melbourne, Victoria, Australia ;Sadori, L.; Dipartimento di Biologia Ambientale, Università ‘La Sapienza’, Rome, Italy ;Roberts, N.; School of Geography, Earth and Environmental Sciences, University of Plymouth, UK ;Giardini, M.; Dipartimento di Biologia Ambientale, Università ‘La Sapienza’, Rome, Italy ;Beck, C.; Laboratoire de Géodynamique des Chaînes Alpines, Université de Savoie, Le Bourget du Lac, France ;Pascucci, V.; Dipartimento Scienze Botaniche, Ecologiche e Geologiche University of Sassari, Sassari, Italy ;Sulpizio, R.; Dipartimento Scienze della Terra e Geoambientali, University of Bari, Bari, Italy; ; ; ; ; ; ; ; ; A multi-proxy record is presented for approximately the last 4500 cal a BP from Lake Shkodra, Albania/Montenegro. Lithological analyses, C/N ratio and δ13C of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic. The δ18O record of bulk carbonate indicates the presence of two prominent wet periods: one at ca. 4300 cal a BP and one at ca. 2500–2000 cal a BP. The latter phase is also found in southern Spain and Central Italy, and represents a prominent event in the western and central Mediterranean. In the last 2000 years, four relatively wet intervals occurred between ca. 1800 and 1500 cal a BP (150–450 AD), 1350–1250 (600–700 AD), 1100–800 (850–1150 AD), and at ca. 90 cal a BP (1860 AD). Between ca. 4100 and 2500 cal a BP δ18O values are relatively high, with three prominent peaks indicating drier conditions at ca. 4100–4000 cal a BP, ca. 3500 and at ca. 3300 cal a BP. Four additional drier events are identified at 1850 (ca. 100 AD), 1400 (ca. 550 AD), 1150 (800 AD) and ca.750 cal a BP (1200 AD). The pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area, which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment. However, since ca. 900 cal a BP a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities. Copyright © 2012 John Wiley & Sons, Ltd.186 17