Geohazard Assessment Research Articles

Deep-sea geohazards in the South China Sea

Various geological processes and features that might inflict hazards identified in the South China Sea by using new technologies and methods. These features include submarine landslides, pockmark fields, shallow free gas, gas hydrates, mud diapirs and earthquake tsunami, which are widely distributed in the continental slope and reefal islands of the South China Sea. Although the study and assessment of geohazards in the South China Sea came into operation only recently, advances in various aspects are evolving at full speed to comply with National Marine Strategy and ‘the Belt and Road’ Policy. The characteristics of geohazards in deep-water seafloor of the South China Sea are summarized based on new scientific advances. This progress is aimed to aid ongoing deep-water drilling activities and decrease geological risks in ocean development.

In-situ stress distribution and coalbed methane reservoir permeability in the Linxing area, eastern Ordos Basin, China

Understanding the distribution of in-situ stresses is extremely important in a wide range of fields such as oil and gas exploration and development, CO2 sequestration, borehole stability, and stress-related geohazards assessment. In the present study, the in-situ stress distribution in the Linxing area of eastern Ordos Basin, China, was analyzed based on well tested parameters. The maximum horizontal principal stress (SHmax), minimum horizontal principal stress (Shmin), and vertical stress (Sv) were calculated, and they were linearly correlated with burial depth. In general, two types of in-situ stress fields were determined in the Linxing area: (i) the in-situ stress state followed the relation Sv>SHmax>Shmin in shallow layers with burial depths of less than about 940 m, indicating a normal faulting stress regime; (ii) the SHmax magnitude increased conspicuously and was greater than the Sv magnitude in deep layers with depths more than about 940 m, and the in-situ stress state followed the relation SHmax>Sv>Shmin, demonstrating a strike-slip faulting stress regime. The horizontal differential stress (SHmax–Shmin) increased with burial depth, indicating that wellbore instability may be a potentially significant problem when drilling deep vertical wells. The lateral stress coefficient ranged from 0.73 to 1.08 with an average of 0.93 in the Linxing area. The coalbed methane (CBM) reservoir permeability was also analyzed. No obvious exponential relationship was found between coal permeability and effective in-situ stress magnitude. Coal permeability was relatively high under a larger effective in-situ stress magnitude. Multiple factors, including fracture development, contribute to the variation of CBM reservoir permeability in the Linxing area of eastern Ordos Basin.

How virtual reality can help visualise and assess geohazards

ABSTRACTGeohazard research requires extensive spatiotemporal understanding based on an adequate multi-scale representation of modelling results. The most commonly applied representation basis for collected data is still the one of a 2D plane, typically a map. Digital maps of spatial data can be visualised and processed by using Geographic Information Systems. It is far less common to use 3D geomodels for the analysis and visualisation of spatial data. For the visualisation of both spatial and temporal hazard components, there are no standardised tools. We claim that a full geohazard assessment is only possible inside a new type of geoscientific and technological environment that is at the same time multi-dimensional, spatiotemporal, integrated, fully interactive (tele-)immersive, and collaborative. Surface and subsurface processes are interacting at various scales that are difficult to be overviewed at once. Virtual Reality (VR) technology could provide an attractive solution to overcome the multi-dimensional and spatiotemporal obstacles. The review of geoscientific applications using VR technology developed by multiple teams around the world shows that some solutions have already been developed many years ago, but widespread use was not possible. This is clearly changing now and soon we will see if VR can contribute to a better understanding of geo-processes.

InSAR data for geohazard assessment in UNESCO World Heritage sites: state-of-the-art and perspectives in the Copernicus era

Protection of natural and cultural heritage is encompassed by the United Nations’ 2030 Agenda for Sustainable Development and is among the innovative applications and services of the European Union’s Earth Observation programme Copernicus. We are currently witnessing an increasing exploitation of Interferometric Synthetic Aperture Radar (InSAR) methods to assess geohazards affecting cultural heritage. This paper offers the first data mining exercise to identify InSAR geoinformation that is digitally available and/or published and that spatially includes one or more cultural, natural and mixed UNESCO World Heritage Site (WHS). The exercise focused on the 45 countries of geographical Europe, Turkey, Israel and the Russian Federation, and their 445 WHS of Outstanding Universal Value. We built a database of academic and grey literature collated via a Boolean search of the ISI Web of Science catalogue and systematic skim-reading to a total number of 280 publications as of the end of 2016. Over 460 InSAR open access digital datasets were also analysed. We found clusters of WHS covered by InSAR data in Italy, the Netherlands, western Germany, eastern Spain, Greece and the UK that match with the geographic distribution of InSAR expertise and geohazard hotspots. The existing stock of InSAR geoinformation already provides an overall WHS coverage of 36%, with similar proportion of available data for ‘urban’ (40%) and ‘rural’ (34%) WHS. The sites with the highest number of publications are historic city centres (e.g. Amsterdam, Athens, Barcelona, Lisbon, Paris, Rome), as well as Permanent Geohazard Supersites (e.g. Mt. Etna, Naples, Istanbul), where the impact of natural and/or anthropogenic processes is well known. First generation SAR data (mainly ERS-1/2) predominate in the literature with over 15 new publications/year since 2002, whilst second and third generation data show less pronounced rates since 2007 and 2014, respectively. The current engagement level of end-users appears still limited (less than 1% of publications involve heritage stakeholders), and a shared guidance on the use of InSAR for heritage practitioners does not exist yet. Towards the development of Copernicus’ services and applications in support of cultural heritage preservation and management, our analysis contributes to: outline the existing capabilities; focus on requirements for bespoke InSAR-derived products and services; and consider possible implementation scenarios both in emergency and ordinary circumstances.

Reprint of Unexpected fast rate of morphological evolution of geologically-active continental margins during Quaternary: Examples from selected areas in the Italian seas

In the last few decades, seafloor imagery systems have drastically changed our vision of a mostly regular and depositional marine landscape, evidencing how erosive and mass-wasting processes are widespread in the marine environments, with particular reference to geologically-active areas. Most of the previous studies have focused on the characterization of these features, whereas a very few ones have tried to estimate what is the extent and order of magnitude of erosion rates in these areas. In this paper, we show several examples from some of the most geologically-active margins off Southern Italy aimed to a) quantify the spatial extent of such processes, b) better understand the role of submarine erosion in the morphogenesis of the coastal sector, and c) try to roughly estimate the order of magnitude of erosion rates in these areas. The results are impressive, with mass-wasting features widespread from coast down to −2600, affecting from the 52% up to 97% of the whole continental slope. Because of the narrow or totally lacking shelves in these areas, mass-wasting processes often occur close to the coast and match embayment of the coast, so indicating a key role in the morphogenesis of coastal sector, with significant implication on the related geohazard. Finally, based on a morphological approach integrated by available stratigraphic constraints we have roughly estimated average erosion rates in these areas, ranging from (at least) some mm/year to a few cm/year, i.e., some hundreds of meters up to kilometers eroded in each eustatic cycle. Despite the large uncertainties of these estimates as well as their spatial and temporal variability in response to regional and local factors, the obtained values are very high and they should be considered for future model of margin evolution, source-to-sink computation and marine/coastal geohazard assessment.

Direct monitoring of active geohazards: emerging geophysical tools for deep‐water assessments

ABSTRACTSeafloor networks of cables, pipelines, and other infrastructure underpin our daily lives, providing communication links, information, and energy supplies. Despite their global importance, these networks are vulnerable to damage by a number of natural seafloor hazards, including landslides, turbidity currents, fluid flow, and scour. Conventional geophysical techniques, such as high‐resolution reflection seismic and side‐scan sonar, are commonly employed in geohazard assessments. These conventional tools provide essential information for route planning and design; however, such surveys provide only indirect evidence of past processes and do not observe or measure the geohazard itself. As such, many numerical‐based impact models lack field‐scale calibration, and much uncertainty exists about the triggers, nature, and frequency of deep‐water geohazards. Recent advances in technology now enable a step change in their understanding through direct monitoring. We outline some emerging monitoring tools and how they can quantify key parameters for deep‐water geohazard assessment. Repeat seafloor surveys in dynamic areas show that solely relying on evidence from past deposits can lead to an under‐representation of the geohazard events. Acoustic Doppler current profiling provides new insights into the structure of turbidity currents, whereas instrumented mobile sensors record the nature of movement at the base of those flows for the first time. Existing and bespoke cabled networks enable high bandwidth, low power, and distributed measurements of parameters such as strain across large areas of seafloor. These techniques provide valuable new measurements that will improve geohazard assessments and should be deployed in a complementary manner alongside conventional geophysical tools.

Assessment of Tsunami-related Geohazard Assessment for Coasts of Hersek Peninsula and Gulf of İzmit

Tsunamis are one of
 the most dreadful natural disasters; they could cause abysmal damage to all
 kind of lives in the hinterland within instantly. It is a major right-lateral
 moving fault that runs along the tectonic boundary between the Eurasian Plate
 to the north and the Anatolian Plate to the south. The western segment of the North
 Anatolian Fault splits into three main branches. The northern one of NAF is
 generally subdivided in several subsegments that have been the source of
 frequent large historical earthquakes. The Sea of Marmara coasts is located on
 the western extension of the NAFZ which is one of the most important active
 faults with strike-slip characteristics, which are not likely to generate
 tsunami. However, in the light of tsunami catalogs based on historical
 documents, it is possible to say that Sea of Marmara has tsunamigenic potential.
 The İstanbul shorelines, Gemlik Bay, Kapıdağ N-NE shores, Gelibolu, Hersek
 Peinsula and Gulf of İzmit are one of the most significant geohazards in Sea of
 Marmara due to the tsunami effect.

Reconstructed seismic and tsunami scenarios of the 1905 Calabria earthquake (SE Tyrrhenian sea) as a tool for geohazard assessment

Italy is one of the most seismically active regions in the central Mediterranean and one of the countries with the longest record of historical earthquakes in the world. Over the last decades the scientific community has recognised the value of historical data when used to constrain modelling tools in hazard analyses. This is the case of the destructive 1905 Calabria (South Italy) earthquake, followed by a tsunami and by many secondary effects on the environment observed both inland and offshore. Recently acquired geophysical data allowed to identify an active normal fault, named Sant'Eufemia Fault, located nearshore in the Sant'Eufemia Gulf (SE Tyrrhenian sea), considered the most probable seismogenic source of the 1905 earthquake and capable to trigger future events.In this paper we perform a scenario-based deterministic analysis for an earthquake resulting from the rupture of the Sant'Eufemia fault (SEF) and a preliminary potential risk analysis. After defining source parameters compatible with the 1905 earthquake (ca. 40km fault length and ca. 2.3m slip, Mw 6.9), KF-analysis and tsunami simulations are carried out and modelling results are compared against historical available data. The obtained results allow one to border areas in central Calabria that are most exposed to geohazard deriving from the analyzed fault. Some of these areas happen to be zones with intense economic/touristic and urban development, which calls for the need to integrate the ongoing development plans with adequate programs of risk mitigation and prevention.

Contourite identification along Italian margins: The case of the Portofino drift (Ligurian Sea)

A brief review of the published evidence of current deposits around Italy is the occasion to test the robustness of matching bottom current velocity models and seafloor morphologies to identify contourite drifts not yet documented. We present the result of the regional hydrodynamic model MARS3D in the Northern Tyrrhenian and Ligurian Sea with horizontal resolution of 1.2 km and 60 levels with focus on bottom current: data are integrated over summer and winter 2013 as representative of low and high intensity current conditions.The Eastern Ligurian margin is impacted by the Levantine Intermediate Water (LIW) with modeled mean velocity of bottom current up to 20 cm s−1 in winter 2013 and calculated bottom shear stress exceeding 0.2 N m−2 in water depth of 400–800 m. By crossing this information with seafloor morphology and geometry of seismic reflections, we identify a sediment drift formerly overlooked at ca 1000 m water depth. The Portofino separated mounded drift has a maximum thickness of at least 150 m and occurs in an area of mean current velocity minimum. Independent evidence to support the interpretation include bottom current modelling, seafloor morphology, seismic reflection geometry and sediment core facies. The adjacent areas impacted by stronger bottom currents present features likely resulted from bottom current erosion such as a marine terrace and elongated pockmarks.Compared to former interpretation of seafloor morphology in the study area, our results have an impact on the assessment of marine geohazards: submarine landslides offshore Portofino are small in size and coexist with sediment erosion and preferential accumulation features (sediment drifts) originated by current-dominated sedimentary processes. Furthermore, our results propel a more general discussion about contourite identification in the Italian seas and possible implications.

Unexpected fast rate of morphological evolution of geologically-active continental margins during Quaternary: Examples from selected areas in the Italian seas

In the last few decades, seafloor imagery systems have drastically changed our vision of a mostly regular and depositional marine landscape, evidencing how erosive and mass-wasting processes are widespread in the marine environments, with particular reference to geologically-active areas. Most of the previous studies have focused on the characterization of these features, whereas a very few ones have tried to estimate what is the extent and order of magnitude of erosion rates in these areas. In this paper, we show several examples from some of the most geologically-active margins off Southern Italy aimed to a) quantify the spatial extent of such processes, b) better understand the role of submarine erosion in the morphogenesis of the coastal sector, and c) try to roughly estimate the order of magnitude of erosion rates in these areas. The results are impressive, with mass-wasting features widespread from coast down to −2600, affecting from the 52% up to 97% of the whole continental slope. Because of the narrow or totally lacking shelves in these areas, mass-wasting processes often occur close to the coast and match embayment of the coast, so indicating a key role in the morphogenesis of coastal sector, with significant implication on the related geohazard. Finally, based on a morphological approach integrated by available stratigraphic constraints we have roughly estimated average erosion rates in these areas, ranging from (at least) some mm/year to a few cm/year, i.e., some hundreds of meters up to kilometers eroded in each eustatic cycle. Despite the large uncertainties of these estimates as well as their spatial and temporal variability in response to regional and local factors, the obtained values are very high and they should be considered for future model of margin evolution, source-to-sink computation and marine/coastal geohazard assessment.

Geohazards assessment in longwall coal mining using monitored seismic events

Geohazards assessment in longwall coal mining using monitored seismic events

Geohazards assessment in longwall coal mining using monitored seismic events

Geohazards assessment in longwall coal mining using monitored seismic events

Identification and assessment of geohazards affecting pipelines and urban areas

The paper addresses methods and criteria of risk assessment associated with land subsidence threatening pipelines, buildings, and constructions. Currently, there are some practical issues relating to geohazards that should be taken into account while constructing a pipeline. The article provides comparison data on the effects of Spitak earthquake and the natural disaster in Neftegorsk in terms of geohazards impact on the pipeline systems. The suggested risk assessment procedure embraces a wide range of aspects: from soil properties to economic and management issues.

The role of mass-transport deposits and turbidites in shaping modern lacustrine deepwater channels

Subaquatic canyons are an important pathway for sediment transport into oceanic and lacustrine basins. Understanding the mechanisms governing their geomorphological evolution is a key to predict the sediment distribution patterns through these sediment conduits as well as to implement geo-hazard assessments. Submerged channels developed in large lacustrine basins offer a small-scale natural laboratory to understand the sedimentological processes operating in submarine channels. For this reason, a multidisciplinary research initiative -including time-lapse, high-resolution bathymetric surveys, innovative coring using submersibles, in situ geotechnical tests, and geophysical and sedimentological analyses-was applied to unravel the factors controlling the geomorphological evolution of the Rhone delta channels in Lake Geneva during the last decades. The morphology of the lacustrine Rhone Delta consists of a freshwater delta system deeply incised by nine canyons (C1C9). Geotechnical measurements in proximal areas and sediment cores retrieved in the distal fans at the end of each canyon revealed complex sediment dynamics. No turbidity current events have occurred in the easternmost canyons (C1C4) during the last decades while the western canyons sediment record (C5C9) indicated repeated flushing events during the 20th century. The main “active” canyon C8 has been dominated by turbidite activity on the canyon floor with frequent overspill events along the levees. A large 6.2 × 106 m3 Mass-Transport Deposit (MTD) that resembles a debrite in its upper section was found in the distal area of the active channel. The MTD was dated at 1998–2000 CE and most likely originated from proximal delta areas affected by frequent slope failures of the steep channel walls. In situ geotechnical tests on the modern proximal channel floor showed an unconsolidated soft top-layer that might have served as a low-friction surface favouring the MTD long run-out distance to the distal part of the channel. The MTD has had a major effect morphological evolution of the distal channel by filling the existing conduit, indirectly promoting the formation of a new channel. The role of MTD emplacement in subaquatic channels has important implications for hydrocarbon exploration as they control channel avulsion processes and the location of sand-prone deposits. This study gives a detailed insight on poorly investigated short-term sedimentological dynamics that affect the long-term evolution of turbidite systems and channel migration processes. This detailed model of a river-dominated deep-lacustrine depositional system can be used as an analog for similar modern and ancient deep-water systems.

Surface-wave methods for anomaly detection

Perimeter-defense operations, geohazard assessment, and engineering characterization require the detection and localization of subsurface anomalies. Seismic waves incident upon these discontinuities generate a scattered wavefield. We have developed various surface-wave techniques, currently being fielded, that have consistently delivered accurate and precise results across a wide range of survey parameters and geographical locations. We use the multichannel analysis of surface waves approach to study the multimode Rayleigh wave, the backscatter analysis of surface waves (BASW) method to detect anomalies, 3D visualization for efficient seismic interpretation, BASW correlation for attribute analysis, and instantaneous-amplitude integration in the complex BASW method. Discrete linear moveout functions and [Formula: see text]-[Formula: see text] filter designs are optimized for BASW considering the fundamental and higher mode dispersion trends of the Rayleigh wave. Synthetic and field data were used to demonstrate multimode BASW and mode separation, which accentuated individual scatter events, and ultimately increased confidence in points of interest. Simple correlation algorithms between fundamental and higher-mode BASW data offer attribute analysis that limits the subjective interpretation of BASW images. Domain sorting and Hilbert transforms allow for 3D visualization and rapid interpretation of an anomaly’s wavefield phenomena within an amplitude cube. Furthermore, instantaneous-amplitude analysis can be incorporated into a more robust complex BASW method that forgives velocity-estimation inaccuracies, while requiring less rigorous preprocessing. Our investigations have suggested that a multifaceted surface-wave analysis provides a valuable tool for today’s geophysicists to fulfill anomaly-detection survey requirements.

Deep-water seamounts, a potential source of tsunami generated by landslides? The Hirondelle Seamount, NE Atlantic

Submarine mass failures represent one of the most significant marine geo-hazards. Their importance as a major contributor to tsunami generation and hazard has been recognized over the last 20–30years. This study investigates a newly mapped submarine landslide, the South Hirondelle Landslide (SHL), and its potential to generate a tsunami and to threat the surrounding coasts. The SHL is located 150km offshore South West Iberia, along the southern flank of the Hirondelle Seamount. Here, available swath bathymetry and one multichannel seismic profile show the presence of large, geometrically well constrained, deep-water landslide deposit of about 500km3 and its associated scar. The failure likely occurred in one single event and according to a detailed numerical modelling of the landslide dynamics and of the resulting water propagation the mass failure generated a mega-tsunami, with significant impact along the surrounding coastal areas of Iberia and Morocco. This result strongly supports the inclusion of tsunami induced by deep-water submarine landslides in the marine geo-hazard assessment of the North East Atlantic region.

A Review of Three Significant Geohazards in the Canadian Cordillera: the Case of River Floods, Debris Flows/Floods, and Debris/Rock Avalanches

Research into sudden-onset geohazards, such as river floods, debris flows/floods and debris/rock avalanches is prominent in literature on the Canadian Cordillera. The unresolved question is the relative importance of river floods, debris flows/floods and debris/rock avalanches over shorter and longer time scales and at smaller and larger spatial scales. River flooding is the costliest geohazard at regional scale and over century time scales but debris/rock avalanches are the deadliest at individual slope scale and over seasonal time scale. In terms of work done on the landscape, debris flows/floods are the most pervasive geohazard and have a huge influence on the long-term moulding of the landscape but figure less prominently in terms of fatalities and cost. Intensified land use, such as forestry, mining, agriculture and urbanization, is the primary reason for the increase in the cost of geohazards to society over the past three decades but climate change adds further uncertainties to the assessment of future geohazards.

Different frequencies and triggers of canyon filling and flushing events in Nazaré Canyon, offshore Portugal

Submarine canyons are one of the most important pathways for sediment transport into ocean basins. For this reason, understanding canyon architecture and sedimentary processes has importance for sediment budgets, carbon cycling, and geohazard assessment. Despite increasing knowledge of turbidity current triggers, the down-canyon variability in turbidity current frequency within most canyon systems is not well constrained. New AMS radiocarbon chronologies from canyon sediment cores illustrate significant variability in turbidity current frequency within Nazaré Canyon through time. Generalised linear models and Cox proportional hazards models indicate a strong influence of global sea level on the frequency of turbidity currents that fill the canyon. Radiocarbon ages from basin sediment cores indicate that larger, canyon-flushing turbidity currents reaching the Iberian Abyssal Plain have a significantly longer average recurrence interval than turbidity currents that fill the canyon. The recurrence intervals of these canyon-flushing turbidity currents also appear to be unaffected by long-term changes in global sea level. Furthermore, canyon-flushing and canyon-filling have very different statistical distributions of recurrence intervals. This indicates that the factors triggering, and thus controlling the frequency of canyon-flushing and canyon-filling events are very different. Canyon-filling appears to be predominantly triggered by sediment instability during sea level lowstand, and by storm and nepheloid transport during the present day highstand. Canyon-flushing exhibits time-independent behaviour. This indicates that a temporally random process, signal shredding, or summation of non-random processes that cannot be discerned from a random signal, are triggering canyon flushing events.

What causes large submarine landslides on low gradient (<2°) continental slopes with slow (∼0.15 m/kyr) sediment accumulation?

AbstractSubmarine landslides can cause damaging tsunamis, the height of which scales up with the volume of the displaced mass. The largest underwater landslides are far bigger than any landslides on land, and these submarine megaslides tend to occur on open continental slopes with remarkably low gradients of less than 2°. For geohazard assessments it is essential to understand what preconditions and triggers slope failure on such low gradients. Previous work has suggested that generation of high excess pore pressure due to rapid sediment deposition plays a key role in such failures. However, submarine slope failure also occurs where sedimentation rates are low (<0.15 m/kyr), such as off northwest Africa. We use a fully coupled stress and fluid flow finite element model to test whether such low sedimentation rates can generate sufficient excess pore pressures to cause failure of a 2° slope. The sensitivity of overpressure generation and slope stability is assessed with respect to different sedimentation rates and patterns, sediment consolidation properties, and stratigraphic layer configurations. The simulations show that, in general, it is difficult to generate significant excess pore pressure if sediment accumulation is slow and the only pressure source. However, we identify a sediment compression behavior that can lead to submarine landslides in locations worldwide. Our results imply that compressibility is an important factor for the stability of low gradient continental slopes.

Soil geohazard mapping for improved asset management of UK local roads

Abstract. Unclassified roads comprise 60 % of the road network in the United Kingdom (UK). The resilience of this locally important network is declining. It is considered by the Institution of Civil Engineers to be "at risk" and is ranked 26th in the world. Many factors contribute to the degradation and ultimate failure of particular road sections. However, several UK local authorities have identified that in drought conditions, road sections founded upon shrink–swell susceptible clay soils undergo significant deterioration compared with sections on non-susceptible soils. This arises from the local road network having little, if any, structural foundations. Consequently, droughts in East Anglia have resulted in millions of pounds of damage, leading authorities to seek emergency governmental funding. This paper assesses the use of soil-related geohazard assessments in providing soil-informed maintenance strategies for the asset management of the locally important road network of the UK. A case study draws upon the UK administrative county of Lincolnshire, where road assessment data have been analysed against mapped clay-subsidence risk. This reveals a statistically significant relationship between road condition and susceptible clay soils. Furthermore, incorporation of UKCP09 future climate projections within the geohazard models has highlighted roads likely to be at future risk of clay-related subsidence.