Assessment, STrategy And Risk Reduction for Tsunamis in Europe

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Anomalous levels in the southern Portuguese continental shelf sedimentary record: potential evidence of the 1755 CE Lisbon Tsunami

Publication . Kümmerer, Vincent; Veiga-Pires, C.; Drago, Teresa

At present, knowledge about tsunami event deposits in outer shelf environments with water depths > 60 m is limited, although understanding of the involved processes as tsunami induced erosion of seafloor sediments and induced backwash currents are critical for tsunami hazard assessment. Both, incoming tsunami waves and generated backwash currents can leave signatures in the offshore sedimentary record. Preservation of tsunami imprints seems more likely in offshore deposits as in onshore deposits, which are in contrary more regarded. Thus, a multidisciplinary approach was conducted to detect probable imprints left by the 1755 Lisbon tsunami event in 3 cores from the southern Portuguese continental shelf with water depths > 57 m. Age model results, based on 14C and 210Pb ages, confirm the ages of the sediment to the 1755 Lisbon tsunami event. Other extreme events such as storms can be excluded trough hydrodynamic considerations. Implementing new high-resolution methodologies as the multivariate analyses of sand composition and microtextural features on quartz grain surfaces yielded more evidence for a tsunamigenic origin of previous detected high energy event layers in the studied core sections in the context of ASTARTE project, although no remarkable terrigenous signal is present. The heterogenous and mixing character of the probable 1755 Lisbon offshore tsunami deposits coupled with hydrodynamic considerations suggest, that subunits related to different tsunami wave incursions and backwash phases re unlikely to be preserved in similar environments as the study area. Also, spatial depositional differences of tsunami sediments were encountered in the study area by differences in mean grain size, sand composition, and simulated horizontal surface velocities. The new applied methodologies contribute paleo-tsunami layer identification and facilitate new studies on offshore tsunami deposits. While the southern Portuguese shelf seems to be a very good study area, we suggest for near future works to collect multiple cores aligned in transects for a better understanding of tsunami sedimentation dynamics

2019-12-04Master thesis

Open Access

Offshore 1755 CE Lisbon Tsunami deposit in the southern portuguese continental shelf

Publication . Kümmerer, Vincent; Drago, Teresa; Veiga-Pires, Cristina; Silva, Pedro; Lopes, Ana; Magalhães, Vitor; Roque, Cristina; Rodrigues, Ana Isabel; Terrinha, Pedro; Mena, Anxo; Francés, Guillermo; Kopf, Achim; Völker, David; Salgueiro, Emilia; Alberto, Ana; C. Lopes, Cristina; Costa, Pedro; Baptista, Maria Ana

The importance of tsunami hazard assessment is only possible if a complete dataset of events is available, allowing the determination of the recurrence intervals of the tsunamis adapted to local and regional conditions. One possible way to know these intervals is to study the offshore sedimentary record, looking for sediment remobilised and transported by the incoming tsunami waves and generated backwash currents. Even if these deposits are not of easy access (and not so well studied), the tsunami depositional signature has potential to be better preserved than those located onshore.

2020-03-23Conference object

Open Access

Multiproxy characterization of high energy layers in the nner continental shelf of Quarteira (Southern Portugal) - Preliminary results

Publication . Santos, Jacqueline; Drago, Teresa; Moura, Delminda; Magalhães, Vitor; Roque, Cristina; Silva, Pedro F.; Rodrigues, Ana Isabel; Terrinha, Pedro; Anxo, Mena; Francés, Guillermo; Lopes, Ana; Alberto, Ana; Baptista, Maria Ana

The occurrence of sedimentary layers indicating high energy events is common in the continental shelves sedimentary record. Their presence has been usually related either to tsunami waves or storm waves. In both cases, the identification of the transport mechanism requires a variety of proxies. This work presents the preliminary results of the analysis of a gravity core (MW-107) collected at ca. 57 m water depth in the inner continental shelf of Quarteira (Algarve) and aims to identify potential high energy events.

2022-07Conference object

Open Access

Exploring offshore sediment evidence of the 1755 CE Tsunami (Faro, Portugal): implications for the study of outer shelf Tsunami deposits

Publication . Kümmerer, Vincent; Drago, Teresa; C. Veiga-Pires, C.; Silva, Pedro F.; Magalhães, Vitor; Mena, Anxo; Lopes, Ana; Rodrigues, Ana Isabel; Schmidt, Sabine; Terrinha, Pedro; Baptista, Maria Ana

Outer shelf sedimentary records are promising for determining the recurrence intervals of tsunamis. However, compared to onshore deposits, offshore deposits are more difficult to access, and so far, studies of outer shelf tsunami deposits are scarce. Here, an example of studying these deposits is presented to infer implications for tsunami-related signatures in similar environments and potentially contribute to pre-historic tsunami event detections. A multidisciplinary approach was performed to detect the sedimentary imprints left by the 1755 CE tsunami in two cores, located in the southern Portuguese continental shelf at water depths of 58 and 91 m. Age models based on 14C and 210Pbxs allowed a probable correspondence with the 1755 CE tsunami event. A multi-proxy approach, including sand composition, grain-size, inorganic geochemistry, magnetic susceptibility, and microtextural features on quartz grain surfaces, yielded evidence for a tsunami depositional signature, although only a subtle terrestrial signal is present. A low contribution of terrestrial material to outer shelf tsunami deposits calls for methodologies that reveal sedimentary structures linked to tsunami event hydrodynamics. Finally, a change in general sedimentation after the tsunami event might have influenced the signature of the 1755 CE tsunami in the outer shelf environment.

2020Journal article

Open Access

New study on the 1941 Gloria Fault earthquake and tsunami

Publication . Baptista, Maria Ana; Miranda, Jorge Miguel; Batllo, Josep; Lisboa, Filipe; Luis, Joaquim; Macia, Ramon

The M similar to 8.3-8.4 25 November 1941 was one of the largest submarine strike-slip earthquakes ever recorded in the Northeast (NE) Atlantic basin. This event occurred along the Eurasia-Nubia plate boundary between the Azores and the Strait of Gibraltar. After the earthquake, the tide stations in the NE Atlantic recorded a small tsunami with maximum amplitudes of 40 cm peak to through in the Azores and Madeira islands. In this study, we present a re-evaluation of the earthquake epicentre location using seismological data not included in previous studies. We invert the tsunami travel times to obtain a preliminary tsunami source location using the backward ray tracing (BRT) technique. We invert the tsunami waveforms to infer the initial sea surface displacement using empirical Green's functions, without prior assumptions about the geometry of the source. The results of the BRT simulation locate the tsunami source quite close to the new epicentre. This fact suggests that the co-seismic deformation of the earthquake induced the tsunami. The waveform inversion of tsunami data favours the conclusion that the earthquake ruptured an approximately 160 km segment of the plate boundary, in the eastern section of the Gloria Fault between -20.249 and -18.630 degrees E. The results presented here contribute to the evaluation of tsunami hazard in the Northeast Atlantic basin.

2016-08Journal article

Open Access