ALBERT

Beschreibung: Long-term variability of storm surge frequency in the Venice Lagoon: an update thanks to eighteenth century sea level observations Natural Hazards and Earth System Sciences Discussions, 2, 7465-7486, 2014 Author(s): F. Raicich Sea level observations made in the Venice Lagoon between 1751 and 1792 have been recovered, consisting of two time series of daily data on high and low waters at Venice and Chioggia. From comparisons with modern observations the quality of the 18th century data appears to be good enough to allow a useful analysis. A composite time series of daily mean sea level is obtained by merging the 18th century data and 1872–2004 observations at Venice Punta della Salute. The absence of reliable information on vertical references prevents the connection of the two 18th century time series with each other and with modern observations. However, daily sea level anomalies relative to the mean sea level enable to recognize storm surge events, that appear to occur more frequently in the second half of the 18th century than in the late 19th and 20th centuries, particularly during the 1751–1769 period. The record-breaking storm surge of 4 November 1966 turns out to be a remarkable event also in comparison with the events extracted from the 18th century time series. Further work is required to fill the gap between the old and modern observations.

Beschreibung: Ground-penetrating radar observations for estimating the vertical displacement of rotational landslides Natural Hazards and Earth System Sciences Discussions, 2, 7487-7506, 2014 Author(s): C. Lissak, O. Maquaire, J.-P. Malet, F. Lavigne, C. Virmoux, C. Gomez, and R. Davidson The objective of this paper is to demonstrate the applicability of Ground Penetrating Radar (GPR) for monitoring the displacement of slow-moving landslides. GPR data is used to estimate the vertical movement of rotational slides in combination with other surveying techniques. The experimental site is located along the Normandy coast (North East France) here several rotational landslides are continuously affected by a seasonal kinematic pattern (low displacement rates of 0.01 to 0.10 m yr −1 ) and periodically by major acceleration events (high displacement of 1.0 to 7.0 m per event).

Beschreibung: Continental Portuguese Territory Flood Susceptibility Index – contribution for a vulnerability index Natural Hazards and Earth System Sciences Discussions, 2, 7521-7552, 2014 Author(s): R. Jacinto, N. Grosso, E. Reis, L. Dias, F. D. Santos, and P. Garrett This work defines a national flood susceptibility index for the Portuguese continental territory, by proposing the aggregation of different variables which represent natural conditions for permeability, runoff and accumulation. This index is part of the national vulnerability index developed in the scope of Flood Maps in Climate Change Scenarios (CIRAC) project, supported by the Portuguese Association of Insurers (APS). This approach expands on previous works by trying to bridge the gap between different floods mechanisms (e.g. progressive and flash floods) occurring at different spatial scales in the Portuguese territory through: (a) selecting homogeneously processed datasets, (b) aggregating their values to better translate the spatially continuous and cumulative influence in floods at multiple spatial scales. Results show a good ability to capture, in the higher susceptibility classes, different flood types: progressive floods and flash floods. Lower values are usually related to: mountainous areas, low water accumulation potential and more permeable soils. Validation with independent flood datasets confirmed these index characteristics, although some overestimation can be seen in the southern region of Alentejo where, due to a dense hydrographic network and an overall low slope, floods are not as frequent as a result of lower precipitation mean values. Future work will focus on: (i) including extreme precipitation datasets to represent the triggering factor, (ii) improving representation of smaller and stepper basins, (iii) optimizing variable weight definition process, (iii) developing more robust independent flood validation datasets.

Beschreibung: Inversion method for initial tsunami waveform reconstruction Natural Hazards and Earth System Sciences Discussions, 2, 7735-7772, 2014 Author(s): V. V. Voronin, T. A. Voronina, and V. A. Tcheverda This paper deals with the application of r-solution method to recover the initial tsunami waveform in a tsunami source area by remote water-level measurements. Wave propagation is considered within the scope of a linear shallow-water theory. An ill-posed inverse problem is regularized by means of least square inversion using a truncated SVD approach. The properties of obtained solution are determined to a large extent by the properties of an inverse operator, which were numerically investigated. The method presented allows one to control instability of the numerical solution and to obtain an acceptable result in spite of ill-posedness of the problem. It is shown that the accuracy of tsunami source reconstruction strongly depends on the signal-to-noise ratio, the azimuthal coverage of recording stations with respect to the source area and bathymetric features along the wave path. The numerical experiments were carried out with synthetic data and various computational domains including a real bathymetry. The method proposed allows us to make a preliminary prediction of the efficiency of the inversion with a given set of the recording stations and to find out the most informative part of the existing observation system. This essential property of the method can prove to be useful in designing a monitoring system for tsunamis.

Beschreibung: Generalized drought assessment in Dongliao river basin based on water resources system Natural Hazards and Earth System Sciences Discussions, 2, 6703-6746, 2014 Author(s): B. S. Weng, D. H. Yan, H. Wang, T. L. Qin, and J. Yin Drought is firstly a resource issue, and with its development it transforms into a disaster issue. The occurrences of drought events usually feature determinacy and randomness. Drought issue has become one of the major factors to affect sustainable economic and social development. In this paper, we propose the generalized drought assessment index (GDAI) based on water resources system for assessing drought events. The GDAI considers water supply and water demand using a distributed hydrological model. We demonstrate the use of the proposed index in the Dongliao river basin (DRB) in the northeast China. The results simulated by the GDAI are then compared to observed drought disaster records in DRB. As second, the temporal distribution of drought events and the spatial distribution of drought frequency from the GDAI are compared with the traditional approach (i.e. the SPI, the PDSI, and the RWD). Then, generalized drought times (GDT), generalized drought duration (GDD), and generalized drought severity (GDS) were calculated by theory of runs. Application of the GDT, the GDD, and the GDS of various drought levels (i.e. mild drought, moderate drought, severe drought, and extreme drought) to the period 1960–2010 shows that the centers of gravity of them are all distributed in the middle reached of DRB, and change with time. The proposed methodology helps water managers in water-stressed regions to quantify the impact of drought, consequently, to make decisions regarding coping with drought issue.

Beschreibung: Modeling rapid mass movements using the shallow water equations Natural Hazards and Earth System Sciences Discussions, 2, 6775-6809, 2014 Author(s): S. Hergarten and J. Robl We propose a new method to model rapid mass movements on complex topography using the shallow water equations in Cartesian coordinates. These equations are the widely used standard approximation for the flow of water in rivers and shallow lakes, but the main prerequisite for their application – an almost horizontal fluid table – is in general not satisfied for avalanches and debris flows in steep terrain. Therefore, we have developed appropriate correction terms for large topographic gradients. In this study we present the mathematical formulation of these correction terms and their implementation in the open source flow solver GERRIS. This novel approach is evaluated by simulating avalanches on synthetic and finally natural topographies and the widely used Voellmy flow resistance law. The results are tested against analytical solutions and the commercial avalanche model RAMMS. The overall results are in excellent agreement with the reference system RAMMS, and the deviations between the different models are far below the uncertainties in the determination of the relevant fluid parameters and involved avalanche volumes in reality. As this code is freely available and open source, it can be easily extended by additional fluid models or source areas, making this model suitable for simulating several types of rapid mass movements. It therefore provides a valuable tool assisting regional scale natural hazard studies.

Beschreibung: Magnetotelluric investigation in the High Agri Valley (southern Apennine, Italy) Natural Hazards and Earth System Sciences Discussions, 2, 6747-6773, 2014 Author(s): M. Balasco, A. Giocoli, S. Piscitelli, G. Romano, A. Siniscalchi, T. A. Stabile, and S. Tripladi In this paper we present the result of a Magnetotelluric (MT) investigation carried out across the High Agri Valley (HAV), southern Italy. Several MT soundings were carried out in order to obtain a ~15 km long 2-D resistivity model with an investigation depth of ~10 km. The main aim was to provide valuable data on the geological and structural setting of the HAV. The MT model was compared with pre-existing geological, geophysical and seismic data. The MT model can be schematized as a superposition of three stack lateral varying layers with different thickness and resistivity values: a surficial low-medium resistivity layer, associated to the Quaternary deposits and to the allochthonous units, and a deeper high resistivity layer, related to the Apulia Platform, separated by a thin layer connected to the mélange zone and to the Pliocene terrigenous marine deposits. Sharp lateral resistivity variations are interpreted as faults that, on the basis of accurate focal mechanism computations, display normal-faulting kinematics.

Beschreibung: Estimation of three-dimensional crustal movements in the 2011 Tohoku-oki, Japan earthquake from TerraSAR-X intensity images Natural Hazards and Earth System Sciences Discussions, 2, 7383-7408, 2014 Author(s): W. Liu, F. Yamazaki, M. Matsuoka, T. Nonaka, and T. Sasagawa The Tohoku-Oki earthquake on 11 March 2011 caused significant widespread crustal movements. In a previous study, we proposed a method for capturing two-dimensional (2-D) surface displacements from a pair of pre- and post-event TerraSAR-X (TSX) intensity images. However, it is difficult to detect three-dimensional (3-D) displacements from one pair of TSX images. In this study, three pairs of pre- and post-event TSX images taken on different paths were used to estimate 3-D crustal movements. The relationship between the actual 3-D displacements and the converted 2-D movements in the SAR images was derived based on the observation model of a SAR sensor. The 3-D movements were then calculated from three sets of detected 2-D movements that occurred within a short time period. Compared with GPS observations, the proposed method was found to be capable of detecting the 3-D crustal movements with sub-pixel accuracy.

Beschreibung: Amalgamation in landslide maps: effects and automatic detection Natural Hazards and Earth System Sciences Discussions, 2, 7651-7678, 2014 Author(s): O. Marc and N. Hovius Inventories of individually delineated landslides are a key to understanding landslide physics and mitigating their impact. They permit assessment of area-frequency distributions and landslide volumes, and testing of statistical correlations between landslides and physical parameters such as topographic gradient or seismic strong motion. Amalgamation, i.e. the mapping of several adjacent landslides as a single polygon, can lead to potentially severe distortion of the statistics of these inventories. This problem can be especially severe in datasets produced by automated mapping. We present 5 inventories of earthquake-induced landslides mapped with different materials and techniques and affected by varying degrees of amalgamation. Errors on the total landslide volume and power-law exponent of the area-frequency distribution, resulting from amalgamation, may be up to 200 and 50%, respectively. We present an algorithm based on image and DEM analysis, for automatic identification of amalgamated polygons. On a set of about 2000 polygons larger than 1000 m 2 , tracing landslides triggered by the 1994 Northridge earthquake, the algorithm performs well, with only 2.7–3.6% wrongly amalgamated landslides missed and 3.9–4.8% correct polygons wrongly identified as amalgams. This algorithm can be used broadly to check landslide inventories and allow faster correction by automating the identification of amalgamation.

Beschreibung: Seismology of the Oso-Steelhead landslide Natural Hazards and Earth System Sciences Discussions, 2, 7309-7327, 2014 Author(s): C. Hibert, C. P. Stark, and G. Ekström We carry out a combined analysis of the short- and long-period seismic signals generated by the devastating Oso-Steelhead landslide that occurred on 22 March 2014. The seismic records show that the Oso-Steelhead landslide was not a single slope failure, but a succession of multiple failures distinguished by two major collapses that occurred approximately three minutes apart. The first generated long-period surface waves that were recorded at several proximal stations. We invert these long-period signals for the forces acting at the source, and obtain estimates of the first failure runout and kinematics, as well as its mass after calibration against the mass-center displacement estimated from remote-sensing imagery. Short-period analysis of both events suggests that the source dynamics of the second are more complex than the first. No distinct long-period surface waves were recorded for the second failure, which prevents inversion for its source parameters. However, by comparing the seismic energy of the short-period waves generated by both events we are able to estimate the volume of the second. Our analysis suggests that the volume of the second failure is about 15–30% of the total landslide volume, which is in agreement with ground observations.