The Role of Built Environment's Physical Urban Form in Supporting Rapid Tsunami Evacuations: Using Computer-Based Models and Real-World Data as Examination Tools

Cities are increasingly becoming hot-spots for nature-originated disasters. While the role of the urban built environment in fostering disaster resilience has been recognized for some time, it has been difficult to translate this potential into practice. This is especially challenging in the case of rapid onset crises such as near-field tsunamis when appropriate urban forms must support the populations' ability to autonomously carry out safe and timely responses. In this respect, much of current research remains focused on large-scale elements of urban configuration (streets, squares, parks, etc.,) through which people move during an emergency. In contrast, the critical micro-scale of evacuees' experiences within the built environment is not commonly examined. This paper addresses this shortfall through a macro- and micro-scale analysis of a near-field tsunami scenario affecting the city of Viña del Mar, Chile, including a mixed-methods approach that combines computer-based models and fieldwork. The results show significant macro-scale tsunami vulnerability throughout major areas of the city, which nonetheless could be mitigated by existing nearby high ground and an urban form that allows short evacuation times. However, micro-scale outcomes show comparatively deficient spatial conditions that during an emergency might lead to dangerous outcomes including bottlenecks, falls and panic. Vertical evacuation, in turn, is confirmed as a suitable option for reducing vulnerability, but further examination of each shelter's characteristics is required

Microwave scattering from surf zone waves

Wave breaking in the surf zone is an important forcing mechanism on the generation of nearshore currents and in the driving of sediment transport. At the same time, wave breaking can have significant spatial and temporal variability that needs to be accounted for in the description of nearshore processes. Remote sensors are best suited to collect wave breaking measurements due to their large footprint and synoptic capabilities, but in order to extract quantitative wave parameters a proper understanding of the imaging mechanisms is essential. Microwave sensors have been shown to be able to measure wave parameters in deep water, but in the surf zone many of the assumptions the algorithms are based upon do not hold. Additionally, the dynamics of breaking waves are different and may affect in a yet determined way the signal. This dissertation first intends to address an observational gap regarding surf zone microwave measurements. A novel combination of synchronous, large coverage marine radar, calibrated pulsed Doppler radar and video observations from a field site enable the analysis of the evolution and characteristics of the wave signature. The combined data sets yield superior discrimination rates between breaking and non-breaking waves. Discrimination also allows the study of the microwave scattering by source, where active breaking is separated from remnant foam and steepening waves. Results show that the backscattered power from breaking waves, specifically from the wave roller, is a several dB larger than that of foam and steepening waves and independent of the environmental conditions and polarization state. While similar results have been obtained for deep water waves and variety of scattering models have been proposed, it is found that none of the models can describe all the data. Additionally, most of the models neglect the roller morphology. Therefore, in the last section a scattering model is introduced, in which the roller is treated as a volume where a collection of water droplets embedded in air can scatter incoherently. Multiple interactions of the scattered fields between particles and the boundaries are also accounted for. Though the model formulation is complex, it depends on a few physical parameters (diameter, volume fraction, medium permittivity) and no calibration constants. Comparison against data shows that the model does a reasonable job in predicting the observed scattering levels, polarization response and grazing angle dependencies, although is not capable to reproduce the maximum scattered levels observed and predicts polarization ratios always less than unity

Hybrid approach to estimating nearshore bathymetry using remote sensing

The characterization of bathymetry and its time evolution is very important for both oceanographic science applications, and for societal reasons relating to coastal engineering and development. Historically, the process of depth surveying has been costly and labor-intensive. This is especially true in nearshore regions, hence a method that is both economic and reliable is of great interest. In this regard, depth inversion techniques take advantage of the interaction between the surface wave field and the underlying bathymetry such that observations of surface wave propagation can be coupled with a dispersion relation to infer bathymetry. Using field measurements, several different types of wave observation data have been tested in inversion methods, e.g. arrays of pressure sensors (Holland, 2001), marine radar (Bell, 1999), aerial photogrammetry (Dugan et al., 2001) and video imagery (Stockdon and Holman, 2000). Typically, these studies use the linear wave dispersion relation and measured wave phase speeds (c) to perform the inversion, and agreement is generally good in intermediate water depths in the absence of currents; errors increase as waves enter shallow water, increase in nonlinearity, and eventually break. In addition, numerical techniques exist that account for some nonlinear processes (e.g. Kennedy et al., 2000b; Misra et al., 2003) but they require more input data, usually in the form of high resolution free surface measurements. These nonlinear methods can potentially make improved depth estimates, however, they have only been tested with synthetic data. In this study, we undertake a novel approach for investigating phase speeds of nonlinear waves and the potential for using them for depth inversions. The approach is novel in the sense that our observational data set consists of both in situ and remotely sensed data and also high resolution numerical data for interpolating between the in situ measurements. Our observations were made from a set of laboratory experiments conducted in large scale wave flume. Laboratory wave conditions included both regular and random waves and a range of wave heights and periods were considered. The final data set used for the depth inversion algorithm was reduced to regular cases only. The wave height profile H(x) is simulated with high spatial resolution using a combined refraction/difraction model REF/DIF1 (Kirby and Dairymple, 1994), where the in situ data is used for calibration. Next, wave parameters such as phase speed, wavenumber and frequency are estimated based on the remote video measurements. The resulting hybrid data set is used as input for performing depth inversion including nonlinearity using the composite dispersion relation of Kirby and Dalrymple (1986). Results indicate that inclusion of nonlinearity significantly improves the retrieved depths, especially in shallow water. The resulting degree of accuracy is comparable with previous observations for intermediate water. Analysis of the error suggests that the main source of error can be attributed to the phase speed estimation, thus it is apparent that the composite dispersion equation is capable of explaining the principal physical process well

Discriminating the occurrence of inundation in tsunami early warning with one-dimensional convolutional neural networks

Tsunamis are natural phenomena that, although occasional, can have large impacts on coastal environments and settlements, especially in terms of loss of life. An accurate, detailed and timely assessment of the hazard is essential as input for mitigation strategies both in the long term and during emergencies. This goal is compounded by the high computational cost of simulating an adequate number of scenarios to make robust assessments. To reduce this handicap, alternative methods could be used. Here, an enhanced method for estimating tsunami time series using a one-dimensional convolutional neural network model (1D CNN) is considered. While the use of deep learning for this problem is not new, most of existing research has focused on assessing the capability of a network to reproduce inundation metrics extrema. However, for the context of Tsunami Early Warning, it is equally relevant to assess whether the networks can accurately predict whether inundation would occur or not, and its time series if it does. Hence, a set of 6776 scenarios with magnitudes in the range Mw 8.0–9.2 were used to design several 1D CNN models at two bays that have different hydrodynamic behavior, that would use as input inexpensive low-resolution numerical modeling of tsunami propagation to predict inundation time series at pinpoint locations. In addition, different configuration parameters were also analyzed to outline a methodology for model testing and design, that could be applied elsewhere. The results show that the network models are capable of reproducing inundation time series well, either for small or large flow depths, but also when no inundation was forecast, with minimal instances of false alarms or missed alarms. To further assess the performance, the model was tested with two past tsunamis and compared with actual inundation metrics. The results obtained are promising, and the proposed model could become a reliable alternative for the calculation of tsunami intensity measures in a faster than real time manner. This could complement existing early warning system, by means of an approximate and fast procedure that could allow simulating a larger number of scenarios within the always restricting time frame of tsunami emergencies.Tide gauge data were obtained from the Sea Level Station Monitoring Facility of the Intergovernmental Oceanographic Commission (http://www.ioc-sealevelmonitoring.org/list.php). The coarser bathymetric and topographic data from the General Bathymetric Chart of the Ocean (https://www.gebco.net/data_and_products/gridded_bathymetry_data/). The authors acknowledge SHOA for providing nautical charts and coastal zone plans used to generate high resolution topo-bathymetric grids for research purposes. We are deeply grateful with A. Gubler that prepared a first version of the high resolution bathymetry grids. The authors acknowledge the computer resources at CTE-POWER (https://www.bsc.es/supportkc/docs/CTE-POWER/overview) and the technical support provided by BSC. We are greatly thankful the EDANYA Group at Málaga University for sharing the Tsunami-HySEA code. Most figures were generated with Python91,92,93 and Global Mapping Tools94. JN deeply thanks support of Mitiga Solutions during his secondment. PAC would like to thank funding by ANID, Chile Grants FONDEF ID19I10048, Centro de Investigación para la Gestión Integrada del Riesgo de Desastres (CIGIDEN) ANID/FONDAP/15110017, and Centro Científico Tecnológico de Valparaíso, ANID PIA/APOYO AFB180002. NZ has received funding from the Marie Skłodowska-Curie grant agreement H2020-MSCA-COFUND-2016-75443.Peer ReviewedPostprint (published version

Microwave backscattering from surf zone waves

The microwave backscatter properties of surf zone waves are analyzed using field observations. By utilizing a preexisting, independent, water surface discrimination technique, the microwave returns were extracted along individual waveforms and the data from shoaling (steepening) waves, surf zone breaking waves, and remnant foam were separated and quantified. In addition, a wave tracking analysis technique allows the returns to be examined on a wave-by-wave basis as individual waves progress through the shoaling zone and break on a nearshore sand bar. Normalized radar cross sections (NRCS), polarization ratios, Doppler spectra, and scatterer velocities were collected using a dual-polarized, X-band radar operating at lower grazing angles than previously reported (1°–3.5°). The results indicate that the maximum NRCS levels are from the active breaking portions of the wave and were consistently about -20 dB, regardless of radar polarization, azimuth angle, wave height, or wind speed. In addition, breaking waves induce broadening of the Doppler spectra and mean scatterer velocities that correlate well with the carrier wave celerity. Analysis of the polarization ratios suggest that the active breaking portions of the wave are depolarized but that higher polarization ratios (>0 dB) are found on the leading edges shoreward of the active breaking portions of the waves, which indicates a clear distinction between two scattering regimes. These results are consistent with scattering from a very rough surface that is being mechanically generated by the breaking process, showing a good agreement with the expected grazing angle dependency of a Lambertian scatterer.Keywords: microwave backscattering, wave breaking, nearshore, remote sensin

Stand-alone tsunami alarm equipment

One of the quickest means of tsunami evacuation is transfer to higher ground soon after strong and long ground shaking. Ground shaking itself is a good initiator of the evacuation from disastrous tsunami. Longer period seismic waves are considered to be more correlated with the earthquake magnitude. We investigated the possible application of this to tsunami hazard alarm using single-site ground motion observation. Information from the mass media is sometimes unavailable due to power failure soon after a large earthquake. Even when an official alarm is available, multiple information sources of tsunami alert would help people become aware of the coming risk of a tsunami. Thus, a device that indicates risk of a tsunami without requiring other data would be helpful to those who should evacuate. Since the sensitivity of a low-cost MEMS (microelectromechanical systems) accelerometer is sufficient for this purpose, tsunami alarm equipment for home use may be easily realized. Amplitude of long-period (20 s cutoff) displacement was proposed as the threshold for the alarm based on empirical relationships among magnitude, tsunami height, hypocentral distance, and peak ground displacement of seismic waves. Application of this method to recent major earthquakes indicated that such equipment could effectively alert people to the possibility of tsunami

A new remote predictor of wave reflection based on runup asymmetry

Reflected waves account for a significant part of the nearshore energy budget and influence incoming waves, nearshore circulation and sediment transport. The use of swash parameters to estimate wave reflection is investigated at three different beaches ranging from highly reflective to dissipative. It is observed that it is essential to account for swash processes when estimating reflection, in particular at intermediate and reflective beaches with a steep beachface. Our results show that runup asymmetry in uprush/backwash can be used as a proxy for dissipation in the swash zone: larger asymmetry values indicating greater dissipation. In our dataset, a reflection predictor based on runup asymmetry has better skill in comparison to empirical predictors based on surf similarity, because runup is a process that integrates both surf and swash zone wave transformation. Runup asymmetry behaves as a swash similarity parameter and reflects an equilibrium between swash period, slope and dissipation.</p

No hay planeta B, hay plan B : marca de calzado ecológico para jóvenes activistas

Memoria (Diseñador Gráfico)Es importante analizar el problema de la escasez de alternativas de calzados que representen los cambios socio culturales que enfrentan los jóvenes chilenos entre 20 y 30 años, porque a través de estos se manifiesta su identidad, intereses e inquietudes. El calzado ha cambiado a lo largo de los años debido a la disponibilidad de nuevos materiales, tecnologías y según las distintas necesidades culturales, también diferentes factores económicos, políticos y sociales que juegan un papel importante en su diseño. Es importante retratar el modo de vida contemporáneo a partir de las problemáticas, gustos e inquietudes de cada periodo para dar cuenta de los cambios socio culturales