Seafloor Elevation Research Articles

Impact of Hurricane Irma on coral reef sediment redistribution at Looe Key Reef, Florida, USA

Abstract. Understanding event-driven sediment transport in coral reef environments is essential to assessing impacts on reef species, habitats, restoration, and mitigation, yet a global knowledge gap remains due to limited quantitative studies. Hurricane Irma made landfall in the Lower Florida Keys with sustained 209 km h−1 winds and waves greater than 8 m on 10 September 2017, directly impacting the Florida Reef Tract (FRT) and providing an opportunity to perform a unique comprehensive, quantitative assessment of its impact on coral reef structure and sediment redistribution. We used lidar and multibeam derived digital elevation models (DEMs) collected before and after the passing of Hurricane Irma over a 15.98 km2 area along the lower FRT including Looe Key Reef to quantify changes in seafloor elevation, volume, and structure due to storm impacts. Elevation change was calculated at over 4 million point locations across 10 habitat types within this study area for two time periods using data collected (1) approximately 1 year before the passing of Irma and 3 to 6 months following the storm's impact as well as (2) 3 to 6 months after and up to 16.5 months after the storm. Elevation change data were then used to generate triangulated irregular network (TIN) models in ArcMap to calculate changes in seafloor volume during each time period. Our results indicate that Hurricane Irma was primarily a depositional event that increased mean seafloor elevation and volume at this study site by 0.34 m and up to 5.4 Mm3, respectively. Sediment was transported primarily west-southwest (WSW) and downslope, modifying geomorphic seafloor features including the migration of sand waves and rubble fields, formation of scour marks in shallow seagrass habitats, and burial of seagrass and coral-dominated habitats. Approximately 16.5 months after Hurricane Irma (during a 13-month period between 2017 and 2019), net erosion was observed across all habitats with mean elevation change of −0.15 m and net volume change up to −2.46 Mm3. Rates of elevation change during this post-storm period were 1 to 2 orders of magnitude greater than decadal and multi-decadal rates of change in the same location, and changes showed erosion of approximately 50 % of sediment deposited during the storm event as seafloor sediment distribution began to re-equilibrate to non-storm sea-state conditions. Our results suggest that higher-resolution elevation change data collected over seasonal and annual time periods could enhance characterization and understanding of short-term and long-term rates and processes of seafloor change.

Detecting changes in seafloor elevation in sandy coastal environments using low-cost opensource tooling

Knowledge of sediment erosion and deposition can be useful for a variety of engineering, marine science, and environmental applications, but collecting detailed time-series measurements of the sediment–water interface can be challenging, particularly in coastal marine environments. We developed economical and open-source sediment level loggers to record sediment–water interface time-series data with accuracy up to 1 cm. The logger is composed of a programmable Circuit-Python (or Arduino) microcontroller and “breakout boards” that attach to a specially designed printed circuit board (PCB) and an array of evenly spaced photoresistors enclosed in a robust waterproof housing. These instruments were paired with temperature sensors in a study off the coast of Charleston, SC in the South Atlantic Bight where heat was used as a tracer to detect the flow of porewater in the permeable coastal sediments. This approach requires accurate knowledge of the depth of temperature sensors relative to the sediment–water interface. In this application, improved knowledge of the elevation of the sediment–water interface elevation data from the sediment level loggers reduced average root mean squared errors in modeling submarine groundwater discharge by as much as 25 %. The sediment level loggers can be easily installed, withstand long deployment times, and provide long-term recording abilities suitable for a range of environments.

Transition from the Continental Margin of Kamchatka to the Island Arc of the Kurile Islands: Features of Volcanism, Crustal Deformation and Geophysical Parameters of the Slab

Abstract—Magmatism manifestations in the transition zone from the continental margin of Kamchatka to the Kurile island arc and some geophysical parameters of the subducted oceanic plate of the Northwestern Pacific are considered. The presence of the Miocene coastal volcanic (Pribrezhny) complex at the base of the South Kamchatka volcanic belt contributes to intense crustal processes causing caldera-forming eruptions in the Holocene. The Northern Kuriles are characterized by initiation of areal volcanism associated with crustal fault zones. Anomalous is the absence of volcanism on Shumshu Island proximal to Kamchatka. Seismic tomography data reveal a high seismic velocity anomaly below it, which can explain this phenomenon. Based on the presented data an assumption is made about existence of a seafloor elevation on the slab, whose submergence led to disintegration of the melting regions responsible for generation of volcanism.

Estimating Earthquake-Induced Tsunami Height Probabilities without Sampling

Given a distribution of earthquake-induced seafloor elevations, we present a method to compute the probability of the resulting tsunamis reaching a certain size on shore. Instead of sampling, the proposed method relies on optimization to compute the most likely fault slips that result in a seafloor deformation inducing a large tsunami wave. We model tsunamis induced by bathymetry change using the shallow water equations on an idealized slice through the sea. The earthquake slip model is based on a sum of multivariate log-normal distributions, and follows the Gutenberg-Richter law for seismic moment magnitudes ranging from 7 to 9. For a model problem inspired by the Tohoku-Oki 2011 earthquake and tsunami, we quantify annual probabilities of differently sized tsunami waves. Our method also identifies the most effective tsunami mechanisms. These mechanisms have smoothly varying fault slip patches that lead to an expansive but moderately large bathymetry change. The resulting tsunami waves are compressed as they approach shore and reach close-to-vertical leading wave edge close to shore.

Faint Echo Extraction from ALB Waveforms Using a Point Cloud Semantic Segmentation Model

As an active remote sensing technology, airborne LIDAR can work at all times while emitting specific wavelengths of laser light that can penetrate seawater. Airborne LIDAR bathymetry (ALB) records an object’s full return waveform, including the water surface, water column, seafloor, and the objects on it. Due to the seawater’s absorption and scattering and the seafloor’s reflectivity effect, the seafloor’s amplitude of seafloor echoes varies greatly. Seafloor echoes with low signal-to-noise ratios are not easily detected using waveform processing methods, which can lead to insufficient seafloor topography depth and incomplete seafloor topography coverage. To extract faint seafloor echoes, we proposed a depth extraction method based on the PointConv deep learning model, called FWConv. The method assumed that spatially adjacent echoes were correlated. We converted all the spatially adjacent multi-frame waveforms into a point cloud. Each point represented a bin value in the waveform, and the points’ properties contained spatial coordinates and the amplitude in the waveform. In the semantic segmentation of these point clouds using deep learning models, we considered not only each centroid’s amplitude, but also its neighboring points’ distance and amplitude. This enriched the centroids’ features and allowed the model to better discriminate between background noise and seafloor echoes. The results showed that FWConv could extract faint seafloor echoes in the experimental area and was not easily affected by noise, and that the correctness reached 99.82%. The number of point clouds increased by 158%, and the seafloor elevation accuracy reached 0.20 m concerning the multibeam echo sounder data.

Benthic macrohabitat classification and Madracis spp. coral patch distribution in a deep-sea marine protected area of Colombia

Corales de Profundidad National Natural Park (CPNNP), at the central Colombian Caribbean margin, has an extension of 142.195 ha with depths ranging from 34 to 1,234 m. The CPNNP’s essential ecological value isMadracisspp. as potential structure-forming deep-water coral; this work represents the first footages of these unique habitats for the Colombian Caribbean. In 11 sectors, remote video surveys are conducted, based on a detailed digital elevation model. From these sectors, four cover mesophotic zones (46–169m depth), and seven cover aphotic zones (up to 354m depth). After still images’ description and interpretation, a guide was generated with nine types of macrohabitats surrounding the coral formations of the CPNNP: soft substrate (mud/sand), soft substrate/rubble/rock with solitary corals, coral and shell rubble, rock/ledges with attached fauna, rugged stones with attached fauna, hard substrate with attached fauna, sandstone with attached fauna, soft substrate with burrows, and pockmark with attached fauna. Video transect analysis confirms the occurrence ofMadracisspp., with coral patches as the main framework builder of the CPNNP. These patches comprise many clumped 50 to 80 cm high coral colonies that developed over slow slopes, with seafloor elevations between 107 and 233 m and textured soils of soft and not very compact ridges, associated with the macrohabitat sandstone with attached fauna. This information is being used for the management and monitoring of this unique protected area.

Sediment accretion in a lower-energetic location during two consecutive cold fronts

ABSTRACT During the passage of two consecutive atmospheric cold fronts that migrated eastward along the northern Gulf of Mexico, currents, waves, and seafloor elevation were observed from instrumentation attached to a metal structure called ‘quadpod’ at the 7.5 m bathymetric contour off the coast of Panama City, Florida. During the passage of the first front, significant wave height (Hs) increased from 0.15 m to 1.2 m, and seafloor elevation relative to the quadpod increased by up to 5 cm at the quadpod location. During the passage of the second front, Hs peaked at 2 m, and seafloor elevation increased by up to 15 cm over 24 h. The increase in the seafloor elevation is consistent with the burial of surrogate munitions observed with sonar imagery and with sediment accretion from a Delft3D simulation. The model predicts cross-shore seafloor changes with erosion nearshore and accretion offshore, starting at approximately 250 m from the coast. The seafloor elevation increase is attributed to sediment accretion driven by wave forcing. The results of this study have important implications for morphological changes and object burial during a period of front-driven waves in the northern Gulf of Mexico, which is typically a lower energetic environment.

Improving ESRI ArcGIS Performance of Coastal and Seafloor Analyses with the Python Multiprocessing Module

Zieg, J. and Zawada, D.G., 2021. Improving ESRI ArcGIS performance of coastal and seafloor analyses with the Python multiprocessing module. Journal of Coastal Research, 37(6), 1288–1293. Coconut Creek (Florida), ISSN 0749-0208. Coastal research frequently involves the use of a GIS to analyze large areas for changes in response to major weather events, human action, and other factors. The GIS workflows used to conduct these analyses can be complex and sometimes require multiple days to complete. Long runtimes often exist even on modern high-powered workstations if the GIS software does not use parallel computing techniques, which prevents it from fully utilizing the capabilities of multicore processors. If a GIS application supports a programming interface that allows geoprocessing tools to be called from an external program, then GIS workflows can use parallel functionality embedded in that programming language to divide the load of a large workflow among multiple child processes. In ArcMap and ArcGIS Pro, this technique can be implemented by using the Python programming interface and the multiprocessing module in Python to run geoprocessing tools in child processes. This method was used in the Seafloor Elevation Change Analysis Tool (SECAT), a Python script written for ArcMap and ArcGIS Pro that calculates changes in seafloor elevation over time using two different digital elevation models. Running SECAT with between one and eight child processes on two different datasets improved execution times by at least a factor of 2.4. These results demonstrate that using the Python multiprocessing module can significantly accelerate a variety of time-consuming workflows.

A semi-empirical scheme for bathymetric mapping in shallow water by ICESat-2 and Sentinel-2: A case study in the South China Sea

To derive shallow water bathymetry for coastal areas, a common approach is to deploy a scanning airborne bathymetric light detection and ranging (LiDAR) system or a shipborne echosounder for ground surveys. However, recent advancements in satellite remote sensing, including the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) offer new tools for generating satellite derived bathymetry (SDB). The key payload onboard ICESat-2 is the Advanced Topographic Laser Altimeter System (ATLAS), a micro-pulse, photon-counting LiDAR system, simultaneously emitting six separate 532 nm beams at 10 kHz pulse rate. However, despite its high resolution, the major limitation for bathymetry is that ICESat-2 only provides along-track height profiles, leaving observation gaps between the parallel ground tracks. Merging ICESat-2 observations with optical multispectral imagery, as demonstrated herein, provides an effective solution for deriving a full scene of water depth in light of the spectral attenuation behavior.This study aims to combine ICESat-2 and Sentinel-2 optical data to derive shallow water bathymetry (depth <20 m) at six islands and reefs in the South China Sea. ICESat-2 ATL03 point clouds of georeferenced photons are first filtered to determine the seafloor elevation along the ground track. Results indicate a root-mean-square error (RMSE) of 0.26–0.61 m as compared with independent observations from an airborne LiDAR campaign. Next, three semi-empirical functions, namely the Modified Linear/Polynomial/Exponential Ratio Models with its kernel formed by the log ratio between Sentinel-2′s green and blue bands, are used to fit the spectral data with ICESat-2 height profiles. After water depth mapping using the trained model, independent ICESat-2 point clouds are used to validate the Sentinel-2 derived bathymetry. The RMSE values of the three models using the weighted average of multiple images for these six islands are within 0.50–0.90 m in 0–15 m deep. We also demonstrate that a synthesis of satellite laser altimetry and optical remote sensing can produce SDB results that potentially meet the requirement of category C in Zones of Confidence (ZOC) of the Electronic Navigational Chart (ENC) in 0–8 m deep. It is foreseen that ICESat-2 will be a helpful tool for mapping coastal and shallow waters around the world especially where bathymetric data are unavailable.

Seafloor Geodesy From Repeated Multibeam Bathymetric Surveys: Application to Seafloor Displacement Caused by the 2011 Tohoku-Oki Earthquake

Repeated multibeam bathymetric surveys played an important role for understanding the distribution of coseismic seafloor displacement caused by the March 11, 2011 Mw 9.0 Tohoku-oki earthquake. After the earthquake, we collected bathymetric data along the same tracks obtained before the earthquake. The selected tracks were crossing the trench and extending from the landward to seaward trench slopes. We examined the seafloor displacement on the landward relative to the seaward by means of the difference in bathymetry before and after the earthquake. The multibeam bathymetric survey has the advantage of areal coverage. The repeated surveys clarified the areal distribution of the coseismic seafloor displacement. In the main rupture area, very large seafloor displacement was observed. Sharp bathymetric change at the trench axis provided solid evidence that the fault slip on the shallowest part of the megathrust reached the trench axis and peaked at the trench axis. The very large displacement is limited to the particular area. Smaller seafloor displacements were observed in the area tens of kilometers away from the main rupture area. We present methods and results of the repeated multibeam bathymetric surveys and an application to the seafloor displacement caused by the 2011 Tohoku-oki earthquake in the northern Japan Trench. Less than several meters in seafloor vertical displacements and less than 20 m in seafloor horizontal displacement were estimated in the northern Japan Trench. The estimated smaller displacements are comparable in magnitude to error of the seafloor displacement observation from our bathymetric survey. Nevertheless, three adjacent survey tracks showed coherent relative differences in seafloor elevation, which suggests the relative difference enables us to discuss the along-track variation in seafloor displacement in the area. However, our survey was affected by uncertainties of roll and pitch biases and sound velocity errors. Well-prepared repeated multibeam bathymetric survey for the purpose of seafloor geodesy could lead to a higher resolution and more accurate result. Repeated acquisition of high resolution and accuracy bathymetric data using state-of-the-art technology will be important to quantitative discussion of the seafloor displacements caused by even smaller magnitude earthquakes and tsunamis.

紀伊半島最南部，ドローン測量による海陸統合型の標高データの取得と海岸・浅海底の地形分類

紀伊半島最南部，ドローン測量による海陸統合型の標高データの取得と海岸・浅海底の地形分類

Devonian ( c. 388–375 Ma) Horn River Group of Mackenzie Platform (NW Canada) is an open-shelf succession recording oceanic anoxic events

At least four horizons of enhanced anoxia (anoxic horizons; AHs) are recognized in the uppermost Eifelian–Middle Frasnian mudrock-dominated strata of the Mackenzie Valley and Peel area of NW Canada. Aluminium-normalized Mo and U logs in two cored sections reveal AH-I at the Eifelian–Givetian boundary, AH-II in basal Frasnian, and AH-III and AH-IV bundled in the Middle Frasnian interval. These four horizons are characterized by attenuated siliciclastic components. Spectral gamma-ray K + Th and U are the best tools to trace these horizons in wells and outcrops. AHs are biostratigraphically correlated with ‘black-shale events’ in several basins of the world. Depositional environment is depicted as a stratified basin where the water-column chemocline defined co-sedimentation of anoxic mudrocks in topographic lows and oxic grey shales and carbonate banks on seafloor elevations. Based on inductively coupled plasma elemental data from 1687 samples, siliciclastic-lean basinal mudrock units that host AHs are strongly enriched in Mo (median EFMo ∼ 97–172 EFMo/EFU ≈ (3–3.5) × SW, where EFMo and EFU are respectively Al-normalized Mo and U in enrichment factor notation and SW is average present-day seawater value) compared with siliciclastic-rich units (median EFMo ∼ 17–37) and show strong EFU/EFMo covariation ( r ≈ 0.8 in Canol Formation and Bluefish Member). Supported by a lack of geological evidence for an oceanographic barrier, this enrichment indicates unrestricted water exchange with Panthalassa. At the same time, development of oligotrophy is indicated by a lack of P enrichment and weak to non-existent enrichment in Zn and Cu. These features are reconciled through a model by earlier workers that involves a global shift to a warm greenhouse mode with slowed oceanic convection, expanded oxygen minimum zones and a failure of nutrient resupply from the upwelling. The onset of mass degassing in continental large igneous provinces represents a potential trigger for this mid-Devonian shift. Devonian black-shale events in this scenario represent genuine oceanic anoxic events marking hothouse episodes in their nascent form. Supplementary material: Details of methods, analytical protocols and data scatterplots, stratigraphic cross-sections showing traceability of anoxic horizons, and inductively coupled plasma elemental and Rock-Eval 6 data used in this study are available at: https://doi.org/10.6084/m9.figshare.c.4212428

Carbon stocks and accumulation rates in Red Sea seagrass meadows

Seagrasses play an important role in climate change mitigation and adaptation, acting as natural CO2 sinks and buffering the impacts of rising sea level. However, global estimates of organic carbon (Corg) stocks, accumulation rates and seafloor elevation rates in seagrasses are limited to a few regions, thus potentially biasing global estimates. Here we assessed the extent of soil Corg stocks and accumulation rates in seagrass meadows (Thalassia hemprichii, Enhalus acoroides, Halophila stipulacea, Thalassodendrum ciliatum and Halodule uninervis) from Saudi Arabia. We estimated that seagrasses store 3.4 ± 0.3 kg Corg m−2 in 1 m-thick soil deposits, accumulated at 6.8 ± 1.7 g Corg m−2 yr−1 over the last 500 to 2,000 years. The extreme conditions in the Red Sea, such as nutrient limitation reducing seagrass growth rates and high temperature increasing soil respiration rates, may explain their relative low Corg storage compared to temperate meadows. Differences in soil Corg storage among habitats (i.e. location and species composition) are mainly related to the contribution of seagrass detritus to the soil Corg pool, fluxes of Corg from adjacent mangrove and tidal marsh ecosystems into seagrass meadows, and the amount of fine sediment particles. Seagrasses sequester annually around 0.8% of CO2 emissions from fossil-fuels by Saudi Arabia, while buffering the impacts of sea level rise. This study contributes data from understudied regions to a growing dataset on seagrass carbon stocks and sequestration rates and further evidences that even small seagrass species store Corg in coastal areas.

Evaluation of video-based linear depth inversion performance and applications using altimeters and hydrographic surveys in a wide range of environmental conditions

The performance of a linear depth inversion algorithm, cBathy, applied to coastal video imagery was assessed using observations of water depth from vessel-based hydrographic surveys and in-situ altimeters for a wide range of wave conditions (0.3 < significant wave height < 4.3 m) on a sandy Atlantic Ocean beach near Duck, North Carolina. Comparisons of video-based cBathy bathymetry with surveyed bathymetry were similar to previous studies (root mean square error (RMSE) = 0.75 m, bias = −0.26 m). However, the cross-shore locations of the surfzone sandbar in video-derived bathymetry were biased onshore 18–40 m relative to the survey when offshore wave heights exceeded 1.2 m or were greater than half of the bar crest depth, and broke over the sandbar. The onshore bias was 3–4 m when wave heights were less than 0.8 m and were not breaking over the sandbar. Comparisons of video-derived seafloor elevations with in-situ altimeter data at three locations onshore of, near, and offshore of the surfzone sandbar over ∼1 year provide the first assessment of the cBathy technique over a wide range of wave conditions. In the outer surf zone, video-derived results were consistent with long-term patterns of bathymetric change (r2 = 0.64, RMSE = 0.26 m, bias = −0.01 m), particularly when wave heights were less than 1.2 m (r2 = 0.83). However, during storms when wave heights exceeded 3 m, video-based cBathy over-estimated the depth by up to 2 m. Near the sandbar, the sign of depth errors depended on the location relative to wave breaking, with video-based depths overestimated (underestimated) offshore (onshore) of wave breaking in the surfzone. Wave speeds estimated by video-based cBathy at the initiation of wave breaking often were twice the speeds predicted by linear theory, and up to three times faster than linear theory during storms. Estimated wave speeds were half as fast as linear theory predictions at the termination of wave breaking shoreward of the sandbar. These results suggest that video-based cBathy should not be used to track the migration of the surfzone sandbar using data when waves are breaking over the bar nor to quantify morphological evolution during storms. However, these results show that during low energy conditions, cBathy estimates could be used to quantify seasonal patterns of seafloor evolution.

Risks of reef erosion.

Oceans Coral reefs serve as natural barriers that protect coastal regions from storms and erosion, but climate change, ocean acidification, and other stressors from human activities are increasingly causing coral reefs to degrade. Yates et al. report evidence of seafloor erosion in five coral reef ecosystems in the Atlantic, Pacific, and Caribbean. Comparison with historical data shows that over the past few decades, seafloor elevation has decreased by 0.09 to 0.8 m at the study sites—far more than expected on the basis of model predictions. Together with sea level rise from climate change, the seafloor erosion at these sites results in deeper water and puts coastal populations at increased risk. Biogeosciences 14 , 1739 (2017).

New insights on tsunami genesis and energy source

AbstractConventional tsunami theories suggest that earthquakes with significant vertical motions are more likely to generate tsunamis. In tsunami models, the vertical seafloor elevation is directly transferred to the sea‐surface as the only initial condition. However, evidence from the 2011 Tohoku earthquake indicates otherwise; the vertical seafloor uplift was only 3–5 m, too small to account for the resultant tsunami. Surprisingly, the horizontal displacement was undeniably larger than anyone's expectation; about 60 m at the frontal wedge of the fault plate, the largest slip ever recorded by in situ instruments. The question is whether the horizontal motion of seafloor slopes had enhanced the tsunami to become as destructive as observed. In this study, we provide proof: (1) combining various measurements from the 2011 Tohoku event, we show that the earthquake transferred a total energy of 3.1e + 15 joule to the ocean, in which the potential energy (PE) due to the vertical seafloor elevation (including seafloor uplift/subsidence plus the contribution from the horizontal displacement) was less than a half, while the kinetic energy (KE) due to the horizontal displacement velocity of the continental slope contributed a majority portion; (2) using two modern state‐of‐the‐art wave flumes and a three‐dimensional tsunami model, we have reproduced the source energy and tsunamis consistent with observations, including the 2004 Sumatra event. Based on the unified source energy formulation, we offer a competing theory to explain why some earthquakes generate destructive tsunamis, while others do not.

Divergence of seafloor elevation and sea level rise in coral reef ecosystems

Abstract. Coral reefs serve as natural barriers that protect adjacent shorelines from coastal hazards such as storms, waves, and erosion. Projections indicate global degradation of coral reefs due to anthropogenic impacts and climate change will cause a transition to net erosion by mid-century. Here, we provide a comprehensive assessment of the combined effect of all of the processes affecting seafloor accretion and erosion by measuring changes in seafloor elevation and volume for five coral reef ecosystems in the Atlantic, Pacific, and Caribbean over the last several decades. Regional-scale mean elevation and volume losses were observed at all five study sites and in 77 % of the 60 individual habitats that we examined across all study sites. Mean seafloor elevation losses for whole coral reef ecosystems in our study ranged from −0.09 to −0.8 m, corresponding to net volume losses ranging from 3.4 × 106 to 80.5 × 106 m3 for all study sites. Erosion of both coral-dominated substrate and non-coral substrate suggests that the current rate of carbonate production is no longer sufficient to support net accretion of coral reefs or adjacent habitats. We show that regional-scale loss of seafloor elevation and volume has accelerated the rate of relative sea level rise in these regions. Current water depths have increased to levels not predicted until near the year 2100, placing these ecosystems and nearby communities at elevated and accelerating risk to coastal hazards. Our results set a new baseline for projecting future impacts to coastal communities resulting from degradation of coral reef systems and associated losses of natural and socioeconomic resources.

Dimension Reduction for Gaussian Process Emulation: An Application to the Influence of Bathymetry on Tsunami Heights

High accuracy complex computer models, also called simulators, require large resources in time and memory to produce realistic results. Statistical emulators are computationally cheap approximations of such simulators. They can be built to replace simulators for various purposes, such as the propagation of uncertainties from inputs to outputs or the calibration of some internal parameters against observations. However, when the input space is of high dimension, the construction of an emulator can become prohibitively expensive. In this paper, we introduce a joint framework merging emulation with dimension reduction in order to overcome this hurdle. The gradient-based kernel dimension reduction technique is chosen due to its ability to drastically decrease dimensionality with little loss in information. The Gaussian process emulation technique is combined with this dimension reduction approach. Theoretical properties of the approximation are explored. Our proposed approach provides an answer to the dimension reduction issue in emulation for a wide range of simulation problems that cannot be tackled using existing methods. The efficiency and accuracy of the proposed framework is demonstrated theoretically and compared with other methods on an elliptic partial differential equation (PDE) problem. We finally present a realistic application to tsunami modeling. The uncertainties in the bathymetry (seafloor elevation) are modeled as high-dimensional realizations of a spatial process using a geostatistical approach. Our dimension-reduced emulation enables us to compute the impact of these uncertainties on resulting possible tsunami wave heights near-shore and on-shore. Considering an uncertain earthquake source, we observe a significant increase in the spread of uncertainties in the tsunami heights due to the contribution of the bathymetry uncertainties to the overall uncertainty budget. These results highlight the need to include the effect of uncertainties in the bathymetry in tsunami early warnings and risk assessments.

Seismic attributes for description of reef growth and channel system evolution — Case study of Intisar E, Libya

A 3D seismic survey over the Intisar E field in the Ajdabiya Trough of the Sirte Basin, Libya, revealed a channel-like feature in Eocene carbonates that wraps around the pinnacle reef that contains the reservoir. We have used coherence, curvature, and spectral decomposition seismic attributes to determine the morphology and gray-level co-occurrence matrix attributes to define seismic facies within the feature. These indicated that the channel originated by submarine scouring caused by downslope movement of turbidity currents. Erosion was followed by the deposition of successive layers of carbonate debris in the channel. Stratigraphic correlations with the adjacent pinnacle reef revealed that the channel was cut during the late stage of reef growth, and a second channel formed after the Intisar E reef ceased to grow. Differences in seafloor elevation over the reef probably diverted turbidity currents so channels were not cut into the reef, breaching the reservoir. This interpreted geologic history may explain why some pinnacle reefs in the Intisar complex contained giant reservoirs, whereas others were barren.

Baltic Sea coastal erosion; a case study from the Jastrzębia Góra region

Abstract The coastline in the Jastrzębia Góra area can be divided into three major zones of general importance: a beach and barrier section, a cliff section, and a section protected by a heavy hydrotechnical construction. These areas are characterised by a diverse geology and origin, and hence different vulnerability to erosion. In addition, observations have demonstrated a different pace of erosion within each zone. Based on the results obtained by remote sensing methods (analysis of aerial photographs and maps), it has been determined that the coastline in the barrier area, i.e., to the west of Jastrzębia Góra, moved landwards by about 130 m, in a period of 100 years, and 80 m over about 50 years. A smaller displacement of the shoreline could be observed within the cliff. Between the middle of the twentieth and the start of the twenty-first centuries the shore retreated by about 25 m. However, in recent years, an active landslide has led to the displacement of the uppermost part of the cliff locally up to 25 m. Another issue is, functioning since 2000, a heavy hydrotechnical construction which has been built in order to protect the most active part of the cliff. The construction is not stable and its western part, over a distance of 50 m, has moved almost 2 m vertically downwards and c. 2.5 m horizontally towards the sea in the past two years. This illustrates that the erosional factor does not comprise only marine abrasion, but also involves land-based processes determined by geology and hydrogeology. Changes in the shoreline at the beach and barrier part are constantly conditioned by rising sea levels, the slightly sloping profile of the sea floor and low elevation values of the backshore and dune areas. Cliffs are destroyed by mass wasting and repetitive storm surges that are responsible for the removal of the colluvium which protects the coast from adverse wave effects. Presumably, mass movements combined with groundwater outflow from the cliff, plus sea abrasion cause destabilisation of the cliff protection construction.