SubSpread : an integrated approach to understand the signature, mechanics and controls of subaqueous spreading

Subaqueous spreading is a widespread type of mass movement, which involves extensional displacement along a gliding plane and the deformation of the failing layer into a sequence of ridges and troughs. Spreading has been poorly investigated, nonetheless it poses hazard to offshore infrastructures. SubSpread is a new project that will investigate the mechanics of the spreading failure and its geological controls in the subaqueous environment. The first objective of SubSpread is to identify the topographic and sedimentary signature of subaqueous environment. We have compiled a global database of subaqueous and subaerial spreads that includes information on physiography, geomorphology, sedimentology and geotechnical properties, where available. A preliminary analysis of the database reveals that spreading morphologies occur on both passive and active margins, especially in the headwall area of translational retrogressive slides. Potential causes of spreading include seismic loading (also glacially induced), sediment loading, and increased pore pressure generated by migration of fluid or gas. The latter may induce loss of shear strength and the formation of a weak layer, particularly in gentle open slopes. Information compiled in this database will also be used to develop a numerical model that can better understand the mechanics and rheological aspects of submarine spreading, focusing on the role played by pore pressure generation. The Tuaheni slide complex in the Hikurangi Margin of New Zealand is being used as a case-study in view of the wealth of geophysical and sedimentological data that are available. The final part of the SubSpread project will test whether the morphometric and sedimentological signature of spreading can provide information on past seismicity. In this case, the test site will be Lake Tekapo in the South Island of New Zealand.peer-reviewe

Lessons learned from liquefaction of the Canterbury Earthquake Sequence (2010-2011) to inform paleoliquefaction studies

Liquefaction affects late Holocene, loose packed and water saturated sediment subjected to cyclical shear stress. Liquefaction features in the geological record are important off-fault markers that inform about the occurrence of moderate to large earthquakes (> 5 Mw). The study of contemporary liquefaction features provides a better understanding of where to find past (paleo) liquefaction features, which, if identified and dated, can provide information on the occurrence, magnitude and timing of past earthquakes. This is particularly important in areas with blind active faults. The extensive liquefaction caused by the 2010-2011 Canterbury Earthquake Sequence (CES) gave the geoscience community the opportunity to study the liquefaction process in different settings (alluvial, coastal and estuarine), investigating different aspects (e.g. geospatial correlation with landforms, thresholds for peak ground acceleration, resilience of infrastructures), and to collect a wealth geospatial dataset in the broad region of the Canterbury Plains. The research presented in this dissertation examines the sedimentary architecture of two environments, the alluvial and coastal settings, affected by liquefaction during the CES. The novel aim of this study is to investigate how landform and subsurface sedimentary architecture influence liquefaction and its surface manifestation, to provide knowledge for locating studies of paleoliquefaction in future. Two study cases documented in the alluvial setting showed that liquefaction features affected a crevasse splay and point bar ridges. However, the liquefaction source layer was linked to paleochannel floor deposits below the crevasse splay in the first case, and to the point bar deposits themselves in the second case. This research documents liquefaction features in the coastal dune system of the Canterbury Plains in detail for the first time. In the coastal dune setting the liquefiable layer is near the surface. The pore water pressure is vented easily because the coastal dune soil profile is entirely composed of non-cohesive, very well sorted sandy sediment that weakly resists disturbance from fluidised sediment under pressure. As a consequence, the liquefied flow does not need to find a specific crack through which the sediment is vented at the surface; instead, the liquefied sand finds many closely spaced conduits to vent its excess of pore water pressure. Therefore, in the coastal dune setting it is rare to observe discrete dikes (as they are defined in the alluvial setting), instead A horizon delamination (splitting) and blistering (near surface sills) are more common. The differences in styles of surface venting lead to contrasts in patterns of ejecta in the two environments. Whereas the alluvial environment is characterised by coalesced sand blows forming lineations, the coastal dune environment hosts apparently randomly distributed isolated sand blows often associated with collapse features. Amongst the techniques tested for the first time to investigate liquefaction features are: 3D GPR, which improved the accuracy of the trenching even six years after the liquefaction events; thin section analysis to investigate sediment fabric, which helped to discriminate liquefied sediment from its host sediment, and modern from paleoliquefaction features; a Random Forest classification based on the CES liquefaction map, which was used to test relationships between surface manifestation of liquefaction and topographic parameters. The results from this research will be used to target new study sites for future paleoliquefaction research and thus will improve the earthquake hazard assessment across New Zealand

Tectono-Geomorphic Analysis in Low Relief, Low Tectonic Activity Areas: Case Study of the Temiskaming Region in the Western Quebec Seismic Zone (WQSZ), Eastern Canada

We designed a workflow to investigate areas of potential neotectonic deformation, making use of well-developed techniques, but applied to a site characterized by low relief and low or moderate tectonic activity. In this pilot study, we targeted the Temiskaming Graben, in Eastern Canada, where recent and ongoing geophysical and sedimentological investigations have revealed recent activity along this ancient structure. The dataset compiled for this experimental study covers an area of nearly 147 square km across the provinces of Ontario and Quebec. For efficiency in terms of computational resources, we first performed cluster analysis on knickpoint location, identifying seven areas with a high density of disruptions along river profiles. We then performed more detailed morphometric analysis at 30 m resolution, identifying knickpoints along river profiles, calculating the hypsometric integral across the landscape with a moving window, and mapping and comparing lineaments with known structural features. The results of our workflow showed that these three techniques can be efficiently combined for neotectonic analysis, and the synergistic approach strengthens the reliability and accuracy of our results. Our research extends the application of morphometric analysis, commonly used for exploring areas with intense tectonism and high topography, to areas that are characterized by low relief and low or moderate tectonic activity. The new areas identified with the workflow proposed in this research require ground-truthing through mapping and shallow geophysical investigations

Tectono-Geomorphic Analysis in Low Relief, Low Tectonic Activity Areas: Case Study of the Temiskaming Region in the Western Quebec Seismic Zone (WQSZ), Eastern Canada

We designed a workflow to investigate areas of potential neotectonic deformation, making use of well-developed techniques, but applied to a site characterized by low relief and low or moderate tectonic activity. In this pilot study, we targeted the Temiskaming Graben, in Eastern Canada, where recent and ongoing geophysical and sedimentological investigations have revealed recent activity along this ancient structure. The dataset compiled for this experimental study covers an area of nearly 147 square km across the provinces of Ontario and Quebec. For efficiency in terms of computational resources, we first performed cluster analysis on knickpoint location, identifying seven areas with a high density of disruptions along river profiles. We then performed more detailed morphometric analysis at 30 m resolution, identifying knickpoints along river profiles, calculating the hypsometric integral across the landscape with a moving window, and mapping and comparing lineaments with known structural features. The results of our workflow showed that these three techniques can be efficiently combined for neotectonic analysis, and the synergistic approach strengthens the reliability and accuracy of our results. Our research extends the application of morphometric analysis, commonly used for exploring areas with intense tectonism and high topography, to areas that are characterized by low relief and low or moderate tectonic activity. The new areas identified with the workflow proposed in this research require ground-truthing through mapping and shallow geophysical investigations

Continuous thermosalinograph oceanography along RV MARIA S. MERIAN cruise MSM103

Underway temperature and salinity data was collected along the cruise track with two autonomous measurement systems. Usually, the systems are changed after 6 hours. While temperature is taken at the water inlet in about 6.5 m depth, salinity is estimated within the interior measurement container from conductivity and interior temperature. Salinity was calibrated independently for both measurement containers (MCs). No correction was done for temperature. For details to all processing steps see Data Processing Report

A global review of subaqueous spreading and its morphological and sedimentological characteristics: A database for highlighting the current state of the art

Highlights • Subaqueous spreading occurs on gently inclined surfaces (<3°). • Gliding planes could be clays or sandy materials undergoing loss of strength. • It is documented on some of the largest marine landslides. • SubSpread Database includes 32 case studies. • Contourite and glaciogenic deposits represent often the slipping surfaces. Abstract Subaqueous spreading, a type of extensional mass transport that is characterized by a ridge and trough morphology, has been documented globally but is poorly understood. Subaqueous spreading is observed on gently inclined surfaces (typically <3°) when sediment bodies experience a sudden reduction of shear strength along their basal plane during clay softening or liquefaction of sands or silty sand sediment. Historically, spreading has been associated with very large landslides, but many unknown aspects of these mass movements have yet to be clarified. Does spreading influences the large catastrophic failure? What are the sedimentological and morphological aspects that contribute in initiating this process? These are some of the research questions that spurred the present work. Here, we introduce a database that incorporates information from thirty-two case studies, and use this to provide key insights into the sedimentary and morphological aspects of subaqueous spreading that will assist in the identification of spreading elsewhere. We find that subaqueous spreading is most common along passive glacial margins, but is also observed along active margins. The occurrence of contourites interlayered with glaciogenic deposits is, in most cases, associated with landslides (or landslide complexes) with spreading morphology. The database shows that seismic loading is commonly suggested to be the dominant trigger mechanism, although more geotechnical observations and modelling analysis would be needed to support this conclusion. We compare subaqueous spreading with terrestrial spreading, in particular to earthquake-related lateral spreading and clay landslides. We find that subaqueous spreading shares the same driving processes and potentially also some of the trigger mechanisms that are associated with the terrestrial spreading cases. Future work will be required to address the association between spreading and its occurrence on some of the largest landslides on Earth, its development mechanism, and its potential hazard implications

Sedimentary features influencing the occurrence and spatial variability of seismites (late Messinian, Gargano Promontory, southern Italy)

Seventeen layers characterized by soft-sediment deformation structures (SSDS) were identified within the "calcari di Fiumicello", an upper Messinian (Miocene) stratigraphic unit (30 m thick), cropping out in the northern sector of the Gargano Promontory (Apulia, southern Italy). Facies analysis was performed on the whole outcrop and detailed sedimentological investigations were carried out on the deformed beds, in order to interpret the deformation mechanism, the driving mechanism and the possible trigger agent. Deformed layers occur in some thin-bedded ooidal limestones, skeletal calcarenite, as well as in some pebble-size conglomerate, alternated with marls, deposited in a protected embayment or barrier-island-lagoon system, possibly characterized by high salinity, and tidal influx. SSDS can be classified as load- and slump/slide structures. The continuous exposures allow us to follow a single deformed layer along tens of meters, hence several types of lateral variations were observed that can be summarized as follows: (1) SSDS disappear within a few meters (with a decreasing pattern of their deformation or in an abrupt way); (2) deformed layers laterally change in thickness and morphology; and (3) a single deformed bed can laterally correspond to two deformed beds. Most of the soft sediment deformation features were identified as liquefaction and/or fluidization features related to seismic shocks (seismites). Seismites are often used as an indicator of seismic events, especially along small outcrops, trench excavation and core analysis. This study highlights the value of the sedimentological analysis for paleoseismic investigations, with the aim of improving criteria for identifying seismites in the sedimentary record, and their suitability as marker of seismic events

A field survey of soil pH and extractable aluminium in the Ashburton Lakes Catchment, New Zealand

Soil extractable aluminium (Al) concentrations have a strong impact on the establishment, growth and persistence of pasture legumes. A survey of 21 soil profiles in the Ashburton Lakes catchment was conducted to determine the key factors driving extractable Al concentrations. The mean Al (0.02 M CaCl₂) concentration was 7.8 mg/kg with the highest values in the top 50 cm of the soil profile. However, there was considerable variation among sites. Landform age, rainfall and depth were all important variables for extractable Al (but R² was low), while landform type was not. The highest Al concentrations in the 20 cm depth zone were found at the wettest sites in the catchment where rainfall was ≥ 1266 mm and where pH was lowest. Farmers in this catchment could use this knowledge to determine which areas of their farms are most susceptible to elevated Al concentrations and at what depth. This would assist in determining which areas could be targeted for development and which are unsuitable

Soft-sediment deformation structures in the Late Messinian Abu Madi Formation, onshore Nile Delta, Egypt : triggers and tectonostratigraphic implications

The Upper Messinian Abu Madi Formation of the Nile Delta constitutes sediments deposited during the final stage of the Messinian salinity crisis (MSC). Several levels of soft-sediment deformation structures (SSDS) were observed in the transgressive heterolithic fluvial fades deposited adjacent to the deep-seated faults. The most common deformation features include diapiric structures, intraformational lithoclastic breccia, small-scale normal faults, skimp folds, and liquefied beds. Such association of SSDS typically resembles those described elsewhere as generated by a complex interplay of gravity-driven and seismically induced liquefaction processes. The pore pressure measurements revealed high pore fluid density similar to 9.1 ppg equivalent density values which reflect a mild pressure disequilibrium in Abu Madi sediments. Pressure disequilibration is observed all over the studied section of the Abu Madi Formation and is not only restricted to the fluvial channel sandstones deposited during rapid loading. Therefore, allogenic seismic activity has been proposed as the main trigger for pressure disequilibrium and the development of SSDS in the Abu Madi Formation. The heterolithic nature of the Abu Madi sediments as well as the scarcity of bioturbation provides the favourable conditions for the preservation of the seismically induced deformation. The lateral variation in thickness suggests deposition of the Abu Madi Formation during periods of active subsidence which promotes the generation of the SSDS. Late MSC tectonism likely controlled the evolution and sedimentary facies variability of the Abu Madi canyon-infill system, and therefore the distribution of Abu Madi facies varies significantly over very short distances. Abu Madi SSDS follows the spatial distribution observed in other "lago-mare" deposits (e.g., Foes Formation and SE Spain), characterized by spatial variability and vertical rhythmic alternation between deformed and non-deformed layers. Accordingly, regional tectonic instability in the circum-Mediterranean margins during the late stage of the MSC is proposed

Detailed pattern analysis of liquefaction surface ejection in an alluvial setting: Lessons from the Canterbury earthquake sequence

The 2010 -2011 Canterbury earthquake sequence has provided an opportunity to study how liquefaction correlates with different sedimentary environments. Our results demonstrate that liquefaction surface manifestation at two sites in a floodplain setting was mainly located on highertopographic areas such as crevasse splays or scroll bars ridges. However, in the crevasse splay the potential liquefiable layer we identified was part of a channel fill sequence within an abandoned meander partially buried by the crevasse splay. In an inner meander setting, the source layers of the liquefied sands is associated with sediments that form the scroll bar itself. Our study focuses on liquefaction in the alluvial environment along the Halswell River (Greenpark, 5 km South-West from Lincoln). We aim to establish a correlation between landforms affected from liquefaction and their sediment architecture. The first site (Hardwick) is an old river channel overlaid by a crevasse splay deposit, and the second site (Marchand) is an inner meander belt; both were severely affected by liquefaction during the Darfield and Christchurch earthquakes. At each site we: (1) mapped the distribution of liquefaction and alluvial geomorphic features with DEMs derived from LIDAR; (2) undertook Ground Penetrating Radar surveys; (3) dug several trenches to expose the surficial stratigraphy and liquefaction features; and (4) retrieved 18 m of core sediments to look for the liquefiable layers. We also collected samples for radiocarbon, microscopic sediment fabric and grain size analysis. Nine seismic cone penetration tests were also carried out to at least 12 m to reveal the geotechnical properties and explore the sediment architecture of the deeper sediments. The lessons learned about the influence sediment architecture on the patterns of liquefaction during the Canterbury sequence will be applied in future paleoliquefaction studies , helping to improve assessments of liquefaction potential and seismic hazard across the country