L'IMMAGINE SISMICA NELLE STRUTTURE CROSTALI DELLA PROVINCIA GEOTERMICA TOSCANA E LE PROPRIETA' PETROFISICHE DELLE ROCCE

2004/2005La tesi della dottoranda Umberta Tinivella ha avuto come obiettivo principale lo studio delle relazioni tra i dati sismici a riflessione e la caratterizzazione delle proprietà petrofisiche delle rocce e dei fluidi intrappolati all'interno dello spazio poroso, con particolare riguardo al regime della pressione dei pori. Per questo motivo, sono state utilizzate metodologie di analisi dei dati non standard, quali l'Amplitude Versus Offset (AVO) e l'analisi dei common image gathers (CIO) per determinare il campo di velocità delle onde P e S. Per quest'ultimo punto, sono state utilizzate migrazioni pre-stack in tempo e in profondità. Inoltre, sono stati considerati modelli teorici per meglio interpretare i risultati ottenuti. Tale procedura è stata applicata a· tre linee sismiche a riflessione, acquisite all'interno del progetto CROP (CROP 18A, 18B e 03) e localizzate in Toscana, per caratterizzare le proprietà delle rocce all'interno del campo geotermico presente nell'area, e in particolare il principale marker dell'area e cioè l'orizzonte K. L'elaborato della candidata si concentra principalmente sulla descrizione delle tecniche non convenzionali utilizzate per la caratterizzazione petrofisica, quali l'AVO, la teoria di Biot che descrive la relazione tra le velocità di propagazione delle onde sismiche P .e S e il regime anomalo della pressione dei pori, e la descrizione dell'anisotropia. Quest'ultimo punto è stato necessario in quanto l'analisi dei campi di velocità delle diverse linee hanno evidenziato una anisotropia nella crosta inferiore. Per quanto riguarda l'AVO, generalmente utilizzato per caratterizzare la fase fluida, è stato eseguito uno studio per meglio rappresentare e interpretare i risultati, cioè le sezioni di riflettività. In particolare, i cross-plot sono stati molto utili per identificare i canali preferenziali di risalita di magmi e fluidi dalla crosta profonda, mentre i rapporti tra le riflettività sono stati utilizzati per meglio interpretare le sezioni sismiche. Inoltre, i risultati AVO sono stati utili per comprendere la natura delle principali riflessioni. Infatti, grazie a questo tipo di analisi è possibile associare le riflessioni o a contrasti litologici o a variazioni nel contenuto di fluidi nei pori. Con il presente studio è stato quindi possibile integrare risultati di analisi diverse dei dati sismici a riflessione, quali le migrazioni, le analisi di velocità, le sezioni con la riflettività, i modelli teorici delle velocità in funzione della pressione dei pori e le analisi sui dati di pozzo. Si è ottenuto un modello finale coerente dell'area investigata all'interno della Provincia Geotermica Toscana. La dottoranda ha partecipato a numerosi incontri e workshops organizzati presso l'Università di Siena da parte del coordinatore e delle unità operative del progetto COFIN2000-Relazione fra struttura della crosta continentale e risorse geotermiche nella Toscana Meridionale ed ha avuto modo di seguire l'acquisizione e il controllo di qualità di rilievi sismici 3D nell'area di Larderello, eseguiti dalla DGS per conto dell'ENEL-Green Power. Parte dei risultati ottenuti sono stati presentati a congressi nazionali e internazionali. Di seguito sono riportati i dettagli degli abstracts del gruppo che ha lavorato su questi argomenti. L'asterisco indica che il lavoro è stato presentato dalla dottoranda.XVIII Ciclo1967Versione digitalizzata della tesi di dottorato cartacea

Gas Hydrates in Antarctica

Few potential distributing areas of gas hydrates have been recognized in literature in Antarctica: the South Shetland continental margin, the Weddell Sea, the Ross Sea continental margin and the Wilkes Land continental margin. The most studied part of Antarctica from gas hydrate point of view is the South Shetland margin, where an important gas hydrate reservoir was well studied with the main purpose to determine the relationship between hydrate stability and environment effects, including climate change. In fact, the climate signals are particularly amplified in transition zones such as the peri-Antarctic regions, suggesting that the monitoring of hydrate system is desirable in order to detect potential hydrate dissociation as predicted by recent modeling offshore Antarctic Peninsula. The main seismic indicator of the gas hydrate presence, the bottom simulating reflector, was recorded in few parts of Antarctica, but in some cases it was associated to opal A/CT transition. The other areas need further studies and measurements in order to confirm or refuse the gas hydrate presence

The potential response of the hydrate reservoir in the South Shetland Margin, Antarctic Peninsula, to ocean warming over the 21st century

In the South Shetland Margin (SSM), Antarctic Peninsula, a bottom-simulating reflector indicates the presence of hydrate between ca. 500 and 3000 m water depth (mwd). The cold seabed temperatures allow hydrate stability at shallower water depths. During the past five decades, the Antarctic Peninsula has been warming up faster than any other part of the Southern Hemisphere, and long-term ocean warming could affect the stability of the SSM hydrate reservoir at shallow waters. Here, we model the transient response of the SSM hydrate reservoir between 375 and 450 mwd to ocean warming for the period 1958–2100. For the period 1958–2010, seabed temperatures are given by oceanographic measurements in the area, and for 2010–2100 by two temperature scenarios represented by the observed trends for the periods 1960–2010 (0.0034°C y−1) and 1980–2010 (0.023°C y−1). Our results show no hydrate-sourced methane emissions for an ocean warming rate at the seabed of 0.0034 °C y−1. For a rate of 0.023°C y−1, emissions start in 2028 at 375 mwd and extend to 442 mwd at an average rate of about 0.91 mwd y−1, releasing ca. 1.13×103 mol y−1 of methane per metre along the margin by 2100. These emissions originate from dissociation at the top of the hydrate layer, a physical process that steady-state modelling cannot represent. Our results are speculative on account of the lack of direct evidence of a shallow water hydrate reservoir, but they illustrate that the SSM is a key area to observe the effects of ocean warming-induced hydrate dissociation in the coming decades

Gas Hydrate and Free Gas Concentrations in Two Sites inside the Chilean Margin (Itata and Valdivia Offshores)

Two sectors, Itata and Valdivia, which are located in the Chilean margin were analysed by using seismic data with the main purpose to characterize the gas hydrate concentration. Strong lateral velocity variations are recognised, showing a maximum value in Valdivia offshore (2380 ms−1 above the BSR) and a minimum value in the Itata offshore (1380 m·s−1 below the BSR). In both of the sectors, the maximum hydrate concentration reaches 17% of total volume, while the maximum free gas concentration is located Valdivia offshore (0.6% of total volume) in correspondence of an uplift sector. In the Itata offshore, the geothermal gradient that is estimated is variable and ranges from 32 °C·km−1 to 87 °C·km−1, while in Valdivia offshore it is uniform and about 35 °C·km−1. When considering both sites, the highest hydrate concentration is located in the accretionary prism (Valdivia offshore) and highest free gas concentration is distributed upwards, which may be considered as a natural pathway for lateral fluid migration. The results that are presented here contribute to the global knowledge of the relationship between hydrate/free gas presence and tectonic features, such as faults and folds, and furnishes a piece of the regional hydrate potentiality Chile offshore

Gas hydrate and free gas estimation from seismic analysis offshore Chiloé island (Chile)

In this study one seismic section offshore Chiloé Island was analyzed to better define the seismic character of the hydrate-bearing sediments. The velocity analysis was used to estimate the gas-phase concentration and relate it to the geological features. The velocity model allowed us to recognize two important layers that characterize hydrate- and free gas-bearing sediments above and below the BSR respectively: one located above the BSR, characterized by high velocity (1,800-2,200 m/s) and a second one, below the BSR, characterized by low velocity (1,600-1,700 m/s). A weak reflector at about 100 m below the BSR marks the base of the second layer. AVO analysis and offset stack sections confirming that the reflector interpreted as BGR is related to free gas presence in the pore space. The velocity field is affected by lateral variation, showing maximum (above the BSR) and minimum (below the BSR) values in the sector. Here, the highest gas hydrate and free gas concentrations were calculated, obtaining 9.5% and 0.5% of total volume respectively. A variable BSR depth (from 300 to 600 mbsf) can be justified supposing a variable geothermal gradient (from 25 to 45 °C/km)

Evidence for a developing plate boundary in the western Mediterranean

Acknowledgements The authors acknowledge support from the Spanish Ministry of Economy and Competitiveness through the Complementary Action ESF TopoEurope TOPOMED (CGL2008- 03474-E/BTE) and national project EVENT (CGL2006-12861-C02-02). L.G.P. was funded by the Spanish Ministry of Education, Culture and Sport through the FPU fellowship AP2012-1579 and a Short-Term Scientific Mission (COST-STSM-ECOST-STSM-ES1301- 180814-045667) inside the COST Action ES1301. This study benefited from a Marie Skłodowska-Curie Individual Fellowship to L.G.P. (H2020-MSCA-IF-2017 796013), the project “MORPHOMED” (PID2019-107138RB-I00) funded by MCIN/SRA (State Research Agency/10.13039/501100011033), FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades/Projects (B-RNM-305-UGR18, A-RNM-508-UGR20 and P18-RT-3632), and acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S) and C.R.R. project PID2019-109559RB-I00 of the Spanish “Ministerio de Ciencia e Innovación”.We thank the reviewers (JoaoDuarte and anonymous) for their insightful comments. This work has been carried out within Grup de Recerca Consolidat de la Generalitat de Catalunya “Barcelona Center for Subsurface Imaging” (2017 SGR 1662).Additional information Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41467-022-31895-z.The current diffuse-strain model of the collision between Africa and Eurasia in the western Mediterranean predicts a broad region with deformation distributed among numerous faults and moderate-magnitude seismicity. However, the model is untested because most deformation occurs underwater, at poorly characterized faults of undetermined slip. Here we assess the diffuse-strain model analysing two active offshore fault systems associated with the most prominent seafloor relief in the region. We use pre-stack depth migrated seismic images to estimate, for the first time, the total Plio-Holocene slip of the right-lateral Yusuf and reverse Alboran Ridge structurally linked fault system. We show that kinematic restoration of deformational structures predicts a slip of 16 ± 4.7 km for the Alboran Ridge Fault and a minimum of 12 km for the Yusuf Fault. Thus, this fault system forms a well-defined narrow plate boundary that has absorbed most of the 24 ± 5 km Plio-Holocene Africa-Eurasia convergence and represents an underappreciated hazard.MCIN Projects A-RNM-508-UGR20, B-RNM-305-UGR18, P18-RT-3632H2020 Marie Skłodowska-Curie Actions H2020-MSCA-IF-2017 796013, PID2019-107138RB-I00Society for Research on AdolescenceGeneralitat de Catalunya 2017 SGR 1662Ministerio de Educación, Cultura y Deporte AP2012-1579, COST-STSM-ECOST-STSM-ES1301-180814-045667, ES1301 MECDMinisterio de Economía y CompetitividadMinisterio de Ciencia e InnovaciónSevero Ochoa Centre of Excellence CEX2019-000928-S, PID2019-109559RB-I0

Enclosure acoustics considerations for the study of the effect of noise on fish

Comunicación presentada en el 54º Congreso Español de Acústica – TECNIACÚSTICA 2023, Cuenca, 18-20 de octubre de 2023.El estudio del comportamiento de los peces resulta extremadamente complicado en un entorno de libertad, especialmente si hablamos de su exposición a diferentes fuentes sonoras. Por este motivo, de las investigaciones en marcha son llevadas a cabo en el seno de un laboratorio, bien en peceras o bien en tanques, teniendo así un entorno controlado donde monitorizar continuamente el comportamiento de las muestras. Sin embargo, un recinto confinado difiere considerablemente de un espacio abierto. Mientras que un pez en libertad estará sometido por norma general a un campo sonoro libre, cuando hablamos de un recinto cerrado las condiciones cambian notablemente.Studying the behaviour of fish is extremely difficult in a free environment, especially when it comes to their exposure to different sound sources. For this reason, existing research is carried out in a laboratory, either in fish tanks or in tanks, thus having a controlled environment in which the behaviour of the samples can be continuously monitored. However, a confined enclosure differs considerably from an open space. While a fish in the wild will generally be subjected to a free sound field, when we talk about an enclosed area the conditions change markedly.This research was financed by the European Union Next Generation EU and FEDER funds under the projects PCI2022-135081-2 and PID2021-127426OB-C22 of the Ministry of Science and Innovation of Spain, respectively

A cold seep triggered by a hot ridge subduction

The Chile Triple Junction, where the hot active spreading centre of the Chile Rise system subducts beneath the South American plate, offers a unique opportunity to understand the influence of the anomalous thermal regime on an otherwise cold continental margin. Integrated analysis of various geophysical and geological datasets, such as bathymetry, heat flow measured directly by thermal probes and calculated from gas hydrate distribution limits, thermal conductivities, and piston cores, have improved the knowledge about the hydrogeological system. In addition, rock dredging has evidenced the volcanism associated with ridge subduction. Here, we argue that the localized high heat flow over the toe of the accretionary prism results from fluid advection promoted by pressure-driven discharge (i.e., dewatering/discharge caused by horizontal compression of accreted sediments) as reported previously. However, by computing the new heat flow values with legacy data in the study area, we raise the assumption that these anomalous heat flow values are also promoted by the eastern flank of the currently subducting Chile Rise. Part of the rift axis is located just below the toe of the wedge, where active deformation and vigorous fluid advection are most intense, enhanced by the proximity of the young volcanic chain. Our results provide valuable information to current and future studies related to hydrothermal circulation, seismicity, volcanism, gas hydrate stability, and fluid venting in this natural laboratory