Run-up Height Research Articles

Modelling with Volna-OP2—Towards Tsunami Threat Reduction for the Irish Coastline

Tsunamis are infrequent events that have the potential to be extremely destructive. The last major tsunami to effect the Irish coastline was the Lisbon 1755 event. That event acts as a candidate worst case scenario for hazard assessment and the impacts on the Irish Coastline are presented here. As there is no general consensus on the 1755 earthquake source, multiple sources highlighted in the literature are investigated. These sources are used to generate the initial conditions and the resultant tsunami waves are simulated with the massively parallelised Volna-OP2 finite volume tsunami code. The hazard associated with the event is captured on three gradated levels. A reduced faster than real time tsunami ensemble is produced for the North-East Atlantic on a regional level in 93 s using two Nvidia V100 GPUs. By identifying the most vulnerable sections of the Irish coastline from this regional forecast, some locally refined simulations are further carried out in a faster than real time setting. As arrival times on the coastline can be on the O (mins), these faster than real time reduced ensembles are of great benefit for tsunami warning. Volna-OP2’s capabilities in this respect are clearly demonstrated here. Finally, high resolution inundation simulations, which build upon the ensemble results, are carried out. To date this study provides the best estimate of assessing the hazard associated with a Lisbon-type tsunami event for the Irish coastline. The results of the inundation mapping highlight that along the vulnerable sections of coastline, inundation is constrained to low-lying areas with maximum run-up heights of 3.4 m being found.

Field surveys and numerical modelling of the 2004 December 26 Indian Ocean tsunami in the area of Mumbai, west coast of India

ABSTRACTIn the aftermath of the 2004 Indian Ocean (Sumatra-Andaman) tsunami, numerous survey teams investigated its effects on various locations across the Indian Ocean. However, these efforts were focused only on sites that experienced major destruction and a high death toll. As a consequence, some Indian Ocean coastal megacities were not examined. Among the cities not surveyed was Mumbai, the principal west coast port and economical capital of India with a population of more than 12 million. Mumbai is at risk of tsunamis from two major subduction zones in the Indian Ocean: the Sumatra–Andaman subduction zone (SASZ) and the Makran subduction zone (MSZ). As a part of the present study, we conducted a field survey of the 2004 Indian Ocean tsunami effects in Mumbai, analysed the available tide gauge records and performed tsunami simulations. Our field survey in 2018 January found run-up heights of 1.6−3.3 m in the Mumbai area. According to our analysis of tide gauge data, tsunami trough-to-crest heights in Okha (550 km to the north of Mumbai) and in Mormugao (410 km to the south of Mumbai) were 46 cm and 108 cm, respectively. Simulations of a hypothetical MSZ Mw 9.0 earthquake and tsunami, together with the Mw 9.1 Sumatra–Andaman earthquake and tsunami, show that the tsunami heights generated in Mumbai by an MSZ tsunami would be significantly larger than those generated by the 2004 Sumatra–Andaman tsunami. This result indicates that future tsunami hazard mitigation for Mumbai needs to be based on a potential large MSZ earthquake rather than an SASZ earthquake.

Field Survey and Numerical Modelling of the December 22, 2018 Anak Krakatau Tsunami

On December 22, 2018, the eruption and flank collapse of the Anak Krakatau volcano generated a tsunami in the Sunda Strait causing catastrophic damage to uninhabited coastlines proximal to the source. Along the heavily populated shores of Banten and Lampung provinces in Java and Sumatra, tsunami waves caused severe damage, extensive inundation and more than 430 deaths. An international tsunami survey team (ITST) deployed 6 weeks after the event documented the tsunami effects including runup heights, flow depths and inundation distances, as well as sediment deposition patterns and impacts on infrastructure and the natural environment. The team also interviewed numerous eyewitnesses and educated residents about tsunami hazards. This ITST was the first to visit and document the extreme tsunami effects on the small islands in the Sunda Strait closest to Anak Krakatau (Rakata, Panjang, Sertung, Sebesi and Panaitan). Along the steep slopes of Rakata and Sertung islands, located less than 5 km from and facing directly towards the southwest flank of Anak Krakatau, all of the dense coastal vegetation was stripped to bare earth up to elevations of more than 80 m, while on the northeast tip of Sertung Island, facing away from the source, a single tree remained standing after flow depths of > 11 m above ground struck there. The runup distributions on the islands encircling Anak Krakatau highlight the directivity of the tsunami source suggesting that the collapse occurred towards the southwest. This manifested as tsunami runup of 10 m that stripped away coastal forests to bare rock for up to 400 m inland in the Ujung Kulon National Park, located 50 km to the south-southwest. Inundation and damage were mostly limited to within 400 m of the shoreline, likely the result of the relatively short wavelengths caused by the landslide generated tsunami. A significant variation in tsunami impact was observed along the shorelines of the Sunda Strait, with runup heights rapidly decreasing with distance from the inferred tsunami source. To model the event we applied a hot-start initial condition that roughly reproduced the measured tsunami runup heights along Rakata and Sertung. The waveforms were then propagated through the Sunda Straight using a Boussinesq-type wave model. The results showed a good fit to the observed heights along the Java and Sumatra coastlines, the northern coast of Panaitan Island and Ujung Kulon Nation Park. The model also produced an acceptable fit to the observed amplitudes at tide gauges. Despite the regional volcanic and tsunamigenic history of the region, and 6-months of eruptive activity prior to the event, the tsunami largely caught the local population off guard. This further highlights the need for community-based education and awareness programs as essential to save lives in locales at risk from locally generated tsunamis.

Extreme Inundation Statistics on a Composite Beach

The runup of initial Gaussian narrow-banded and wide-banded wave fields and its statistical characteristics are investigated using direct numerical simulations, based on the nonlinear shallow water equations. The bathymetry consists of the section of a constant depth, which is matched with the beach of constant slope. To address different levels of nonlinearity, time series with five different significant wave heights are considered. The selected wave parameters allow for also seeing the effects of wave breaking on wave statistics. The total physical time of each simulated time-series is 1000 h (~360,000 wave periods). The statistics of calculated wave runup heights are discussed with respect to the wave nonlinearity, wave breaking and the bandwidth of the incoming wave field. The conditional Weibull distribution is suggested as a model for the description of extreme runup heights and the assessment of extreme inundations.

Probabilistic Tsunami Heights Model using Bayesian Machine Learning

Song, M.-J. and Cho, Y.-S., 2020. Probabilistic tsunami heights model with Bayesian machine learning. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1291–1296. Coconut Creek (Florida), ISSN 0749-0208.Tsunamis, which are long-period oceanic waves, are known as catastrophic disasters and can cause large losses of human life, as well as property damage. To date, tsunami research has focused on developing numerical models to predict accurate tsunami heights and run-up heights, because hydraulic experiments are associated with high costs for laboratory installation and maintenance. Recently, artificial intelligence (AI) has been progressed, demonstrating enhanced performances in science and engineering fields. This study explored the use of AI to estimate maximum tsunami heights. Bayesian machine learning, a neural network method, was employed, and numerical simulation was performed for historical and probable maximum tsunami events.

Field-based Observation of the Entrainment Threshold of Cobbles with Motion Loggers

Brayne, R.P.; Lorang, M.S.; Naylor, L.A., and Reinhardt, L., 2020. Field-based observation of the entrainment threshold of cobbles with motion loggers. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 392–397. Coconut Creek (Florida), ISSN 0749-0208.Beaches composed of pebble to boulder-sized material are a common feature of coastal regions and provide effective protection against wave attack. The wave-related entrainment threshold of these coarse particles is of utmost importance to defining the onset of dynamic beach behavior. Wave-competence equations derived to predict the boundary between particle stability and entrainment when acted on by waves (e.g. Lorang, 2000) are useful when designing artificial gravel beaches as shore protection structures because they help inform the size of material required to mimic the dynamic behavior of their natural counterpart. The objective of this study is to use motion loggers embedded within native cobbles to measure the entrainment threshold during storm wave events to provide much-needed field data with which to test the accuracy of the Lorang (2000) equations. The movement of 14 cobbles were observed over a range of conditions (0.10 m < HS < 0.52 m) during five separate 1.5-hour-long experiments on coarse pebble/cobble beach at Flathead Lake, Montana, USA. The entrainment threshold was positively related to wave power and was accurately predicted by the Lorang (2000) equations using significant wave height, mean period and beach slope to estimate swash velocities and run-up height as driving variables. More experiments are required to constrain the value(s) used for the beach stability coefficient Kr, although the values found here correspond with the widely used Hudson Formula (Hudson, 1952). Alternatively, directly quantifying swash velocities and run-up elevations from video analysis would greatly improve the results rather than estimating these primary variables. These results provide a unique insight into the wave-competence approach to designing dynamic revetments and artificial gravel beaches as shore protection alternatives to rip-rap and seawalls at a time when rising sea level and a potential increase in storm intensity are likely to increase the wave impact on coastal regions.

Tsunamiopasnost' Krymskogo poberezh'ya Chernogo morya i Kerchenskogo proliva pri katastroficheskih tsunamigennyh zemletryaseniyah, blizkih po lokalizatsii k istoricheskomu YAltinskomu zemletryaseniyu 12 sentyabrya 1927 goda

Purpose. The main purpose of the work is to assess a possible tsunami hazard for the region of location of the Crimean Bridge constructed across the Kerch Strait, since up to present, numerical simulations of the tsunamigenic earthquakes in the Black Sea have never taken the Kerch Strait region (except for the water area at the strait entrance) into consideration as a possible object for a tsunami hazard. Methods and Results. To assess a tsunami hazard for the Kerch Strait and, particularly, for the region of location of the constructed Crimean Bridge, the present paper considers the historical catastrophic tsunamigenic earthquake in the southeastern part of the Crimea Peninsula on September 12, 1927 as well as possible strong earthquakes, the source locations and magnitudes of which can be close to those of the above-mentioned one. The available data on localization and intensity of the earthquake on September 12, 1927 allowed to model the source of such an earthquake. Besides, within the framework of the nonlinear shallow water equations, simulated were the tsunami generation and the tsunami waves’ propagation from the single- and two-block seismic sources in the Black Sea along the Crimea Peninsula, at the Kerch Strait entrance and in its water area. The seismic sources of close localization were similarly simulated for two possible tsunamigenic earthquakes in the southeastern part of the Crimea Peninsula. Conclusions. For all the considered scenarios, generation and propagation of the tsunami waves over the water area regions under study were numerically simulated, the histograms of distribution of the wave run-up maximum heights along the Crimea Peninsula and the Kerch Strait coasts were constructed. It is shown that for all the scenarios, in the region of the Crimean Bridge western pillars the tsunami wave heights do not exceed 0.3–0.5 m, whereas in the region of its eastern pillars, possible wave heights are within the range 0.6–1.95 m. The results represented in the paper are compared with the available data on the wave heights in a number of settlements of the Crimea Peninsula coast and at the Kerch Strait entrance, obtained by the other authors.

Mysterious tsunami in the Caribbean Sea following the 2010 Haiti earthquake possibly generated by dynamically triggered early aftershocks

Dynamically triggered offshore aftershocks, caused by passing seismic waves from main shocks located on land, are currently not considered in tsunami warnings. The M7.0 2010 Haiti earthquake epicenter was located on land 27 km north of the Caribbean Sea and its focal mechanism was oblique strike-slip. Nevertheless, a tsunami recorded on a Caribbean Deep-Ocean Assessment and Reporting of Tsunami (DART) buoy and a tide gauge produced runup heights of 1–3 m along Haiti southeast coast. Earthquake finite-fault model inversions of the DART waveform suggest that a reverse fault doublet with magnitudes of M6.8 and M6.5 located 85 km southwest of the epicenter may have excited the tsunami. This doublet collocates with dynamically triggered aftershocks, derived from back-projection analysis, that occurred 20-60 s after the main shock of the Haiti earthquake. The aftershocks are within a region of maximum dynamic strain predicted by the main shock, on a possibly tectonically active submarine ridge southwest of Haiti's Southern Peninsula. The agreement between the tsunami finite-fault source models and the seismic and tectonic evidence suggests that earthquakes on land, even strike-slip faults, can generate tsunamis by dynamically triggering offshore aftershocks.

Hydraulic control on the development of megaflood runup deposits

Runup deposits are veneers of alluvium that drape floodway valley side walls above the height of giant bars deposited during megafloods. Given sufficient sediment supply, the highest giant bars, deposited in re-entrants along the flood margins, tend to grow to close to the maximum time-averaged water level of the flood. However, considerable fluctuations in the water level, caused by sediment-charged floodwaters surging over shorter time-scales, are responsible for the higher runup deposits. Here, the theoretical calculations of the expected maximum runup heights are compared with surveyed heights of six runup deposits in the Chuja Valley, Altai, Siberia. The limitations and strengths of the theoretical approach are identified and modified parameters proposed that can be used to provide partial explanation for the differences between theory and observation. Conceptually, surging can be viewed as caused by four interrelated elements: (1) propagation of undular weir flow; (2) macroturbulence; (3) flow separation; and (4) standing, reflection and interference waves. The heights of the observed runup deposits primarily are related to the depth of the flood water above the bar tops and, to a lesser extent, the Froude number, but tend to lie below the maximum surge heights of the modelled flow. Changes in the effective geometry of the flow re-entrant, mediating flow patterns, as water depth increases is likely the cause of mismatch between theory and observation. Runup deposits may also lie at lower elevations than predicted because of sediment supply considerations and the return flow of surges ‘combing’ down deposits. Nonetheless, the difference between observed and predicted runup heights is often only a few tens of metres such that, for deep floods, runup deposits potentially are useful palaeostage indicators. The analysis also indicates that upper-stage plane beds do not dominate bar tops, rather bar top deposition was primarily to lower-stage plane beds, from dense suspensions.

Run-up, inundation, and sediment characteristics of the 22 December 2018 Sunda Strait tsunami, Indonesia

Abstract. A tsunami caused by a flank collapse of the southwest part of the Anak Krakatau volcano occurred on 22 December 2018. The tsunami affected the coastal areas located at the edge of the Sunda Strait, Indonesia. To gain an understanding of the tsunami event, field surveys were conducted a month after the incident. The surveys included measurements of run-up height, inundation distance, tsunami direction, and sediment characteristics at 20 selected sites. The survey results revealed that the run-up height reached 9.2 m in Tanjungjaya and an inundation distance of 286.8 m was found at Cagar Alam, part of Ujung Kulon National Park. The tsunami propagated radially from Anak Krakatau and reached the coastal zone with a direction between 25 and 350∘ from the north. Sediment samples were collected at 27 points in tsunami deposits with a sediment thickness of 1.5–12.7 cm. The average distance from the coast of the area with significant sediment deposits and the deposit limit are 45 % and 73 % of the inundation distance, respectively. Sand sheets were sporadic, highly variable, and highly influenced by topography. Grain sizes in the deposit area were finer than those at their sources. The sizes ranged from fine sand to boulders, with medium sand and coarse sand being dominant. All sediment samples had a well-sorted distribution. An assessment of the boulder movements indicates that the tsunami run-up had minimum velocities of 4.0–4.5 m s−1.

Submarine landslide source models consistent with multiple tsunami records of the 2018 Palu tsunami, Sulawesi, Indonesia

Previous studies have suggested submarine landslides as sources of the tsunami that damaged coastal areas of Palu Bay after the 2018 Sulawesi earthquake. Indeed, tsunami run-up heights as high as 10 m determined by field surveys cannot be explained by the earthquake source alone although the earthquake is definitely the primary cause of the tsunami. The quantitatively re-examined results using the earthquake fault models reported so far showed that none of them could fully explain the observed tsunami data: tsunami waveforms inferred from video footage and the field survey run-up tsunami height distribution. Here, we present probable tsunami source models including submarine landslides that are consistent with the observed tsunami data. We simulated tsunamis generated by submarine landslides using a simplified depth-averaged two-dimensional model. The estimated submarine landslide model consisted of two sources in the northern and southern parts of the bay, and it explained the observed tsunami data well. Their volumes were 0.02 and 0.07 km3. The radius of the major axis and the maximum thickness of the initial paraboloid masses and the maximum horizontal velocity of the masses were 0.8 km, 40 m and 21 m/s in the northern bay, and 2.0 km, 15 m and 19 m/s in the southern bay, respectively. The landslide source in the northern bay needed to start to move about 70 s after the earthquake to match the calculated and observed arrival times.

Numerical Study of the Impact of Climate Change on Irregular Wave Run-up Over Reef-Fringed Coasts

Wave hydrodynamics over fringing reefs is largely controlled by the reef surface roughness and hydrodynamic forcing. It is believed that climate change will result in a net increase in the water depth over the reef flat, a degrading of the surface roughness of coral reefs and changes in extreme incident wave heights. For an accurate assessment of how climate change affects the safety of reef-fringed coasts, a numerical study of the impact of climate change on irregular wave run-up over reef-fringed coasts was carried out based on a Boussinesq wave model, FUNWAVE-TVD. Validated with experimental data, the present model shows reasonable prediction of irregular wave evolution and run-up height over fringing reefs. Numerical experiments were then implemented based on the anticipated effects of climate change and carried out to investigate the effects of sea level rise, degrading of the reef surface roughness and increase of extreme incident wave height on the irregular wave run-up height over the back-reef beach respectively. Variations of run-up components (i.e., spectral characteristics of run-up and mean water level) were examined specifically and discussed to better understand the influencing mechanism of each climate change-related effect on the run-up.

Tsunami earthquakes: Vertical pop-up expulsion at the forefront of subduction megathrust

Published slip distribution models, based on geodetic, seismological and tsunami data, of the Mw 7.8, 2010 Mentawai tsunami earthquake offshore south-central Sumatra, suggest that the large tsunami wave was generated by a narrow swath of high seafloor uplift along the accretionary wedge front, implying higher vertical throw than that consistent with slip on the shallow-dipping megathrust. Here we present high-resolution seismic reflection profiles across the 2010 rupture zone that image the youngest deformation at the accretionary wedge front. The profiles reveal conjugate, steeply-dipping, active thrust faults that branch upwards from the megathrust and bound triangular pop-ups. The seismologically determined co-seismic slip (≥10 m) on the 6°-dipping decollement probably caused a comparable amount of upward expulsion of these ∼3 km–wide, flat-topped pop-ups. Co-seismic throw on the ≈60° dipping thrusts that bound the pop-up plateaus maximize the uplift of the seafloor and overlying water-column, providing an additional localised tsunami source. Tsunami simulations show that such combined deformation, i.e. the broad-scale seafloor displacement caused by slip on the megathrust and the localized 8–10 m seafloor uplift across a 6–9 km-wide pop-up belt involving up to three pop-ups, is able to reproduce the 2010 tsunami amplitude measured by a DART buoy, and observed run-up heights in the Mentawai Islands. This simple mechanism, observed in analogue sandbox shortening experiments, may thus efficiently generate the oversize waves that characterize Tsunami-Earthquakes. Systematic mapping of pop-ups along accretionary wedge fronts may help identify trench segments prone to produce the special class of seismic events that spawn exceptionally large tsunamis.

Deep learning video analysis as measurement technique in physical models

In coastal engineering context, the use of video imagery is widespread. Especially in field settings along sandy coasts, many types of data have been derived from video imagery, often using non-learning analysis techniques. Recent advances in the field of computer vision and deep learning allow for the automation of image segmentation. In this paper, these techniques are combined with video imagery of physical model tests, resulting in an innovative non-intrusive measurement technique. This technique is validated for three different applications: the measurement of surface elevation, wave run-up and bed level development. In addition to demonstrating its potential as an alternative for existing measurement instruments, it is shown that the added detail in the spatial or temporal domain provided by the technique can lead to new insights. Examples of this are the detailed analysis on the variability of the run-up height over the width of the flume and the spatial distribution of run-up velocities over the slope.

Identifikasi Pendekatan Shallow Water Equation Dalam Simulasi 2D Gelombang Tsunami di Pantai Keburuhan Purworejo

Kabupaten Purworejo merupakan salah satu dari lima daerah yang terkena dampak run-up tsunami Jawa 17 Juli 2006. Berdasarkan hasil Rapid Survey oleh BPDP dan BPPT, sepanjang Pantai Keburuhan merupakan lokasi terjadinya run-up tsunami di Kabupaten Purworejo di koordinat 109.912 LS -7.85 BT sebesar 1,7 meter. Tujuan dari penelitian ini adalah memperkirakan waktu tempuh tsunami, distribusi tinggi gelombang tsunami dan daerah jangkauan tsunami akibat dampak gempa tsunami Jawa 17 Juli 2006 di Pantai Keburuhan, Purworejo. Metode yang digunakan adalah metode deskriptif analitis dengan pendekatan kuantitatif. Data yang digunakan pada penelitian ini adalah titik tinggi, batimetri, parameter gempa, peramalan pasang surut wilayah perairan Pantai Keburuhan, data citra Geo Eye 1, dan kelerengan pantai. Pemodelan tsunami menggunakan perangkat lunak COMCOT v1.7 dengan kejadian gempa Jawa 17 Juli 2006. Berdasarkan pengolahan data, diketahui bahwa kecepatan gelombang maksimal sebesar 3.8788 m/s. Pada menit ke- 40, amplitudo awal gelombang tsunami sebesar 1.644 meter telah mencapai Pantai Keburuhan. Daerah jangkauan tsunami terluas dan jarak jangkauan maksimum terjauh terjadi di Pantai Keburuhan adalah 1,23 km2 dan 1,4 km. Berdasarkan hasil verifikasi dengan nilai RSR sebesar 0,26. Hasil validasi simulasi tsunami menggunakan COMCOT v1.7 diketahui bahwa tinggi run-up tsunami model sudah cukup sesuai dengan data run-up yang terjadi saat kejadian, dengan nilai RSR sebesar 0,29 dan CF sebesar 1,63.

The Effect of Surface Ruptures on the Propagation of Tsunamis: An Analysis of 1993 Hokkaido Earthquake

An earthquake occurs when the energy condensed at certain points in the Earth's crust exceeds a certain threshold. Changes in depth of the seabed (induced by subsurface deformation) can cause irregular undulations and tsunamis. Surface ruptures usually start at one point and propagate in diverse directions (typically one or two). In this study, we used numerical analysis to examine the effects of surface ruptures on the generation and propagation of tsunamis. The 1993 Hokkaido earthquake was chosen for the test, and three subfaults were adopted to account for the history and process of the rupture. The results revealed the clear effects of surface rupture near the epicenter, showing either an increase or decrease in run-up heights (depending on spatial locations). Although the effects on run-up heights along the coast of the East Sea were unclear, the maximum effect (observed at specific points) generated twice the normal run-up heights.

Post-Event Field Survey of the 22 December 2018 Anak Krakatau Tsunami

On 22 December 2018, volcanic activity of Anak Krakatau, Indonesia, triggered a tsunami that caused more than 437 casualties on surrounding coastlines. Soon after the event, before the physical evidence of the tsunami disappeared, a postevent field survey was carried out. Measurements of tsunami inundation and impact are important to better model and understand the tsunami triggering processes to support future tsunami mitigation efforts. The impacted area on the western coast of Banten, Java Island, was surveyed to acquire tsunami inundation and run-up height data, together with field characteristics of the tsunami deposits. Data were acquired at 36 locations along three transects of tsunami deposits. From these, the maximum tsunami run-up height (up to 13 m) in the surveyed locations was identified on the southern part of the Banten Coast in the Tanjung Lesung area, an area located to the south of Anak Krakatau Volcano. The tsunami deposits were relatively thin along the transect, including a fining upward sequence without any clear evidence of fresh volcanic material, in disagreement with other reported volcano-induced tsunami deposits. Characteristics of the 2018 Anak Krakatau tsunami deposits are more similar to earthquake-induced tsunami deposits, hence complicating the paleotsunami reconstruction in Sunda Strait, where tsunami mechanisms are from both volcano and earthquakes along the Sunda subduction zone.

Near-reef and nearshore tropical cyclone wave climate in the Great Barrier Reef with and without reef structure

The Great Barrier Reef (GBR) coral coverage is in rapid decline from severe and sustained pressures from lagoon water quality, crown-of-thorns starfish (COTS), coral bleaching, tropical cyclones, pollution and diseases. The two recent GBR coral bleaching events (2016–2017) lead to Great Barrier Reef Marine Park Authority (GBRMPA) shifting their focus from passive management to active intervention (Great Barrier Reef Blueprint for resilience by GBRMPA). These active interventions, potentially able to increase GBR resilience, as there are reefs that, due to their physical location relative to all other reefs, river and estuary entrances, ocean currents, have favourable coral growth conditions. To undertake such interventions, various information is required including tropical cyclone wave climates. This paper develops tropical cyclone wave climates for the entire GBR. These wave climates were developed by simulating several thousand synthetic cyclones derived from the “HadGEM” general circulation model with RCP8.5 climate change scenario. The synthetic cyclones adopted herein include the following climate changes assessed by comparing averages of key forcing parameters between 1950 to 1999 and 2050 to 2099. Their average arrival rate increases from 2.25 to 2.41 cyclones/year and their average maximum wind speed increases from 24 to 28 m/s. Their average radius to maximum winds remains constant at 51 km. Two key challenges were resolved, namely, long runtimes and large files (600 m grid increment covering 1800 km by 280 km). Runtimes were reduced by excluding cyclones where their wind speeds over the entire event never exceeded 10 m/s within GBR itself or within 100 km of the GBR over water. Maximum wave heights were compared with an extended fetch empirical expression, which was based on satellite data of tropical cyclones in open waters, when cyclones were outside the GBR lagoon. These comparisons indicate that predicted wave heights have a lower bias using default wave generation parameters when compared with the extended fetch empirical expression. Prediction uncertainty was estimated at no more than 10% from various cyclonic wind-field models. The existing GBR reefs reduce nearshore wave or runup height by between 1.5 and 2 times compared to the no reef case. The reduction in wave or runup height was found to be minimal for 1 m sea level rise. These two findings indicate that there is more flooding potential from coral removal than SLR within the GBR lagoon.

Frequency-dependent amplification of the Sanriku tsunamis in Ryori Bay

In the present study, the local tsunami amplification observed in Ryori Bay, located on the Sanriku coast of Japan, was investigated using numerical simulations. Large-scale tsunami propagation simulations and tsunami inundation simulations for the bay were systematically conducted to estimate and model the 2011, 1933, and 1896 tsunamis that occurred off the Sanriku coast and which resulted in large run-ups. The simulation results, which are moderately consistent with observations, presented larger run-up heights and inundations for the 1933 and 1896 tsunamis (which followed relatively small earthquakes) compared to those of the 2011 tsunami (which followed a larger earthquake). Furthermore, the frequency analysis indicated that the former two tsunamis comprised higher predominant components. A tsunami inundation simulation using parametrized synthetic waveforms was conducted to identify the contributing factors associated with the large amplification and run-ups. The results indicated that the predominant components are significantly amplified in the bay and the initial decrease in the water surface elevation prior to the primary waves of the two tsunamis leads to an increase in their run-up heights. Furthermore, the simulated waveforms of the tsunamis revealed that the 1933 and 1896 tsunamis had their wavefronts changed into a steep wavefront, i.e., a bore-like wave, during their wave developments in the bay, attributed to shoaling, narrowing bay width, and the nonlinear effect of the wave. These results, therefore, indicate that bores which are known to generate large run-up heights were generated in the bay during the two tsunamis.

Re-Estimation of a Plausible Model of the Earthquake Fault as the Source of the 1771 Great Meiwa Tsunami Based on the Assessment of the Run-Up Height by Okinawa Prefecture, Japan

Plausible parameters of the earthquake fault which caused the 1771 Great Meiwa Tsunami were re-estimated by comparing the result of the tsunami run-up height by the numerical simulation by Okinawa Prefectural Government and those by 1) run-up height derived from previous field works, and 2) a historical record describing the run-up height in Miyako District. The re-estimation shows that the length of the fault off Miyako and Yaeyama districts is 300 km or more. However, the slip of the fault is 20 m off Yaeyama and 8 - 14 m off Miyako.