Maximum Inundation Distance Research Articles

Understanding flow characteristics from tsunami deposits at Odaka, Joban Coast, using a deep neural network (DNN) inverse model

Abstract. The 2011 Tohoku-oki tsunami inundated the Joban coastal area in the Odaka region of the city of Minamisoma, up to 2818 m from the shoreline. In this study, the flow characteristics of the tsunami were reconstructed from deposits using the DNN (deep neural network) inverse model, suggesting that the tsunami inundation occurred in the Froude supercritical condition. The DNN inverse model effectively estimated the tsunami flow parameters in the Odaka region, including the maximum inundation distance, flow velocity, maximum flow depth, and sediment concentration. Despite having a few topographical anthropogenic undulations that caused the inundation height to fluctuate greatly, the reconstructed maximum flow depth and flow velocity were reasonable and close to the values reported in the field observations. The reconstructed data around the Odaka region were characterized by an extremely high velocity (12.1 m s−1). This study suggests that the large fluctuation in flow depths on the Joban Coast compared with the stable flow depths in the Sendai Plain can be explained by the inundation in the supercritical flow condition.

Assessing tsunami vertical evacuation processes based on probabilistic tsunami hazard assessment for west coast of Aceh Besar, Indonesia

BackgroundTsunamis are rare events compared to other disasters but have devastating consequences. In the last 100 years, more than 24 tsunamis and more than 235,000 fatalities have occurred globally. Indonesia has a high risk of a tsunami disaster. Since the devastating 2004 tsunami in the Indian Ocean, much research and preparatory work have been done to reduce the impact of future tsunamis in Indonesia, including in the province of Aceh, especially along the western coast where West Aceh is located. This coastal area was destroyed by a tsunami as high as 15–30 m, resulting in the loss of life, housing, tourist areas, industrial areas, and other public facilities. Given that tsunami disasters are rare and sometimes occur long in advance, human memory and awareness are reduced, making research on the level of tsunami awareness of disasters a challenging task.MethodProbabilistic Tsunami Hazard Assessment (PTHA) is a method that has been developed to predict tsunami hazards with a return period of hundreds to thousands of years, beyond the limited availability of historical data. The PTHA method can provide important information that supports tsunami risk management measures. This study aims to estimate recurrence period-based tsunami risk on the west coast of the district of Aceh Besar using the PTHA method. In this study, the source of the tsunami is caused by fault activity at sea. Seven tsunami scenarios based on fault parameters (earthquakes of magnitudes Mw 8.0 to 9.2 with interval 0,2) with the fault location focusing on the Aceh-Andaman Mega Thrust Segment, as applied in this study. This segment was a similar source to the 2004 Indian Ocean tsunami that created a rupture area along a distance of 1155 km, with six parts of the fault.ResultThe maximum inundation distance reached 6 km for the flat area, with a flow depth of 13 m. The site has a cliff that is close to the shoreline, with an inundation distance shorter than the distance across the flat area. With an arrival time of less than 25 min, it is recommended to have an evacuation building and evacuation road in a wide inundated area, and an arrangement of hills close to the beach as an evacuation area, in order to reduce the number of casualties. For 100 years return period or exceedance probability rate 0.01, the average flow depth on the coast may exceed 5 m, and the maximum flow depth for a 1000-year return period or annual probability of 0.001 is 12 m. With the potential tsunami in the future, continuous tsunami drills and tsunami education are needed so that people can maintain an awareness of the threat posed by tsunamis.

Reconstruction of flow conditions from 2004 Indian Ocean tsunami deposits at the Phra Thong island using a deep neural network inverse model

Abstract. The 2004 Indian Ocean tsunami caused significant economic losses and a large number of fatalities in the coastal areas. The estimation of tsunami flow conditions using inverse models has become a fundamental aspect of disaster mitigation and management. Here, a case study involving the Phra Thong island, which was affected by the 2004 Indian Ocean tsunami, in Thailand was conducted using inverse modeling that incorporates a deep neural network (DNN). The DNN inverse analysis reconstructed the values of flow conditions such as maximum inundation distance, flow velocity and maximum flow depth, as well as the sediment concentration of five grain-size classes using the thickness and grain-size distribution of the tsunami deposit from the post-tsunami survey around Phra Thong island. The quantification of uncertainty was also reported using the jackknife method. Using other previous models applied to areas in and around Phra Thong island, the predicted flow conditions were compared with the reported observed values and simulated results. The estimated depositional characteristics such as volume per unit area and grain-size distribution were in line with the measured values from the field survey. These qualitative and quantitative comparisons demonstrated that the DNN inverse model is a potential tool for estimating the physical characteristics of modern tsunamis.

Site-specific deterministic and probabilistic tsunami hazard assessment for Diba-Oman and Diba-Al-Emirates

Destructive tsunamis were reported in the Oman Sea after large earthquakes. The Northern Sultanate of Oman and United Arab Emirates (UAE) were subjected to two confirmed tsunamis on 27 November 1945, caused by an Mw 8.1 earthquake in Makran subduction zone, and on 24 September 2013 following the Mw 7.7 Baluchistan earthquake. In this study, deterministic and probabilistic tsunami hazard assessments are performed for the coasts of Diba-Oman and Diba-UAE, which are located on the western coast of the Oman Sea. The tsunami risk of these coasts increases due to the construction of many infrastructures and urban concentration in these localities. The study focuses on earthquake-induced tsunamis, thus requiring the estimation of the maximum credible earthquake. The generation area is the Makran subduction zone, which is divided herein into EMSZ (East Makran subduction zone) and WMSZ (West Makran subduction zone). The maximum credible earthquakes of Mw 8.8 for the EMSZ and Mw 7.2 for the WMSZ are utilized as specific scenarios for the deterministic approach. The Mw 8.8 EMSZ scenario results in a maximum tsunami inundation distance of more than 300 m. Maximum inundation distance larger than 300 m occurs due to the Mw 7.2 western MSZ scenario. For these scenarios, numerical simulations show a maximum flow depth exceeding 1.75 m. The probabilistic hazard assessment utilizes the logic tree approach to estimate the probability of exceedance of 0.25, 0.5, 0.75, and 1.0 m wave height in 100 and 500 years exposure times. This analysis indicates that the likelihood that a maximum wave height exceeds 0.5 m ranges from 10 to 40% in 100 years and from 30 to 80% in 500 years.

Probabilistic tsunami hazard analysis for Tuzla test site using Monte Carlo simulations

Abstract. In this study, time-dependent probabilistic tsunami hazard analysis (PTHA) is performed for Tuzla, Istanbul, in the Sea of Marmara, Turkey, using various earthquake scenarios of Prince Island Fault (PIF) within the next 50 and 100 years. The Monte Carlo (MC) simulation technique is used to generate a synthetic earthquake catalogue, which includes earthquakes having moment magnitudes between Mw6.5 and 7.1. This interval defines the minimum and maximum magnitudes for the fault in the case of an entire fault rupture, which depends on the characteristic fault model. Based on this catalogue, probability of occurrence and associated tsunami wave heights are calculated for each event. The study associates the probabilistic approach with tsunami numerical modeling. The tsunami numerical code NAMI DANCE was used for tsunami simulations. According to the results of the analysis, distribution of probability of occurrence corresponding to tsunami hydrodynamic parameters is represented. Maximum positive and negative wave amplitudes show that tsunami wave heights up to 1 m have 65 % probability of exceedance for the next 50 years and this value increases by 85 % in the Tuzla region for the next 100 years. Inundation depth also exceeds 1 m in the region with probabilities of occurrence of 60 % and 80 % for the next 50 and 100 years, respectively. Moreover, probabilistic inundation maps are generated to investigate inundated zones and the amount of water penetrated inland. Probability of exceedance of 0.3 m wave height ranges between 10 % and 75 % according to these probabilistic inundation maps, and the maximum inundation distance calculated in the entire earthquake catalogue is 60 m in this test site. Furthermore, synthetic gauge points are selected along the western coast of Istanbul by including Tuzla coasts. Tuzla is one of the areas that shows high probability exceedance of 0.3 m wave height, which is around 90 %, for the next 50 years while this probability reaches up to more than 95 % for the next 100 years.

Field observations of sediment transport across the rocky coast of east Taiwan: Impacts of extreme waves on the coastal morphology by Typhoon Soudelor

After the 2015 Typhoon Soudelor, large boulders and mixed sediments deposited extensively across the beach along the east coast of Taiwan. Field measurements of these storm-related sediments provide the first-hand evidence to document the impacts of extreme waves induced by Typhoon Soudelor. Although the maximum inundation distance is only 170 m due to the lack of beach buffer zone, the weight of the largest boulder was estimated over 1 t and the maximum run-up was estimated up to 11.9 m. The clast distribution of the washover and the beach face sediments exhibited reverse directions of coarsening, reflecting different stages of wave propagation. Our field records show that a super typhoon like Soudelor can potentially leave footprints of extreme values in the geologic records. Therefore, a comprehensive understanding on the occurrence of the sediments and the depositional environment should be carefully considered to pin down the origin of the archived extreme events. In addition, the formation of the higher extreme wave berm and the destruction of the lower swell berm at the Yen-liao Beach displayed the power of the storm surges, suggesting the important role of the run-up on the evolution of the berm.

The December 2018 Anak Krakatau Volcano Tsunami as Inferred from Post-Tsunami Field Surveys and Spectral Analysis

We present analysis of the December 2018 Anak Krakatau tsunami in Sunda Strait, Indonesia, from a combination of post-tsunami field surveys, bathymetric changes and spectral analysis of the tsunami tide gauge records. Post-tsunami surveys revealed moderate tsunami height along the coast of Sumatra and Java with maximum surveyed runup of 13.5 m and maximum inundation distance of 330 m. At small islands located close to the volcano, extreme tsunami impacts were observed indicating not only a huge tsunami was generated by large amounts of collapse material which caused notable changes of seafloor bathymetry, but also indicates the role of those small islands in reducing tsunami height that propagated to the mainland of Indonesia. Our spectral analysis of tide gauge records showed that the tsunami’s dominant period was 6.6–7.4 min, indicating the short-period nature of the 2018 Sunda Strait tsunami.

Eastern Australia’s submarine landslides: implications for tsunami hazard between Jervis Bay and Fraser Island

A hazard assessment of submarine landslide-generated tsunami for the east Australian continental slope between Jervis Bay and Fraser Island is presented. Submarine landslides are present in water depths of approximately 400 to 3500 m along the entire length of continental margin, but are increasingly prevalent northward of Coffs Harbour without clustering at any particular water depth. Two hundred sixty individual submarine landslide scars that are greater than 1 km in width have been identified. Of these, 36 have been calculated to produce a tsunami flow depth equal to or greater than 5 m at the coastline for an assumed landslide downslope velocity of 20 ms−1. Landslides that are both thick (> 100 m) and wide (> 5 km) have the greatest potential to generate the largest coastal flow depths (> 10 m). The water depth of a landslide’s centre of mass strongly influences the onshore height of the tsunami’s surge with the larger events generated in shallower water depths (~ 500–1500 m). The maximum flow depth at the coastline is larger for thicker (50–250+ m) canyon landslides which occur on steeper slopes (> 4°), compared to thinner (< 50 m) plateau landslides which generally produce smaller tsunami. Maximum inundation distances and run-up heights of 1.6 km and 22 m respectively have been calculated for landslide velocities of 20 ms−1 and these values vary significantly depending on local coastal topography. There is no evidence for a submarine landslide large enough and young enough to have generated a Holocene age megatsunami for the east coast of Australia.

Field Survey of the 2018 Sulawesi Tsunami Deposits

On 28 September 2018, a Mw 7.5 earthquake struck Sulawesi Island, soon followed by a destructive tsunami. This study provides a case history of tsunami deposition where submarine landslides or coastal collapses have contributed to and intensified tsunami generation. The sedimentary features resulting from this complex tsunami mechanism are not yet well understood. We surveyed tsunami deposits at six locations along the coastline of Palu Bay, in addition to measuring tsunami flow depth, run-up height, and inundation distance at each site. In general, the tsunami height was less than 8 m with a maximum inundation distance of 310 m. The tsunami deposits are thin with simple sedimentary structures such as fining upward sequences. These sedimentary characteristics are typical of tsunami deposits elsewhere around the world. This work is a preliminary study, in that numerical modeling including sediment transport has not been performed. Further work is needed to distinguish tsunamis with different source mechanisms.

Modeling wave effects on storm surge and coastal inundation

We present a parametric study of surface wave effects on storm surge and coastal inundation. Hurricane wind forcing terms, atmosphere pressure gradient terms, and radiation open boundary conditions are implemented into an existing quasi-3D nearshore model, NearCoM-TVD, which uses a shock-capturing TVD scheme and can better simulate the wetting-drying process during inundation than a conventional finite difference model. Systematic numerical experiments are carried out in an idealized continental shelf-beach-land system to identify the role of waves in modeling storm surge and inundation under different storm characteristics. Four storm parameters, including storm intensity, storm size, translation speed and incident angle are investigated. Modeling results reveal that the presence of waves can increase the maximum storm surge heights significantly through wave setup, and the contribution of waves varies considerably depending on the storm characteristics. In addition to direct wave forcing, the wave-enhanced bottom stress in the surfzone also promotes higher wave setup and hence higher surge heights. Waves also have a major influence on the maximum inland inundation distance, however, we find that waves do not always favor more inundation as expected. For storms traveling at very slow translation speeds or nearly parallel to the coast, waves surprisingly exert a negative effect on the maximum inundation distance. We argue that wave-enhanced bottom stress combined with longer forcing duration in such storms counteract the positive effect of wave setup, and thus less inundation is predicted in wave-current coupled simulations. Our results highlight the necessity of fully-incorporating wave effects in storm surge and inundation modeling.

Sedimentary and geochemical signature of the 2016 Kaikōura Tsunami at Little Pigeon Bay: A depositional benchmark for the Banks Peninsula region, New Zealand

The 14 November 2016 Kaikōura Tsunami inundated Little Pigeon Bay in Banks Peninsula, New Zealand, and left a distinct sedimentary deposit, on the ground and within the cottage near the shore. Sedimentary (grain size) and geochemical (electrical conductivity and X-Ray Fluorescence) analyses on samples collected over successive field campaigns are used to characterize the deposits. Sediment distribution observed in the cottage in combination with flow direction indicators suggests that sediment and debris laid down within the building were predominantly the result of a single wave that had been channeled up the stream bed rather than from offshore. Salinity data indicated that the maximum tsunami-wetted and/or seawater-sprayed area extended 12.5 m farther inland than the maximum inundation distance inferred from the debris line observed a few days after the event. In addition, the salinity signature was short-lived. An overall inland waning of tsunami energy was indicated by the mean grain size and portable X-Ray Fluorescence elemental results. ITRAX data collected from three cores along an inland transect indicated a distinct elevated elemental signature at the surfaces of the cores, with an associated increase in magnetic susceptibility. Comparable signatures were also identified within subsurface stratigraphic sequences, and likely represent older tsunamis known to have inundated this bay as well as adjacent bays in Banks Peninsula. The sedimentary and geochemical signatures of the 2016 Kaikōura Tsunami at Little Pigeon Bay provide a modern benchmark that can be used to identify older tsunami deposits in the Banks Peninsula region.

The 8 September 2017 Tsunami Triggered by the Mw 8.2 Intraplate Earthquake, Chiapas, Mexico

The 8 September 2017, Mw 8.2 earthquake offshore Chiapas, Mexico, is the largest earthquake in recorded history in Chiapas since 1902. It caused damage in the states of Oaxaca, Chiapas and Tabasco, including more than 100 fatalities, over 1.5 million people were affected, and 41,000 homes were damaged in the state of Chiapas alone. This earthquake, an intraplate event on a normal fault on the oceanic subducting plate, generated a tsunami recorded at several tide gauge stations in Mexico and on the Pacific Ocean. Here, we report the physical effects of the tsunami on the Chiapas coast and analyze the societal implications of this tsunami on the basis of our post-tsunami field survey. The associated tsunami waves were recorded first at Huatulco tide gauge station at 5:04 (GMT) 12 min after the earthquake. We covered ground observations along 41 km of the coast of Chiapas, encompassing the sites with the highest projected wave heights based on our preliminary tsunami model (maximum tsunami amplitudes between 94.5° and 93.0°W). Runup and inundation distances were measured along eight sites. The tsunami occurred at low tide. The maximum runup was ~ 3 m at Boca del Cielo, and maximum inundation distance was 190 m in Puerto Arista, corresponding to the coast in front of the epicenter and in the central sector of the Gulf of Tehuantepec. Tsunami scour and erosion was evident along the Chiapas coast. Tsunami deposits, mainly sand, reached up to 32 cm thickness thinning landward up to 172 m distance.

Revised MeTHuVA method for assessment of tsunami human vulnerability of Bakirkoy district, Istanbul

Among the coastal districts of mega city Istanbul, Bakirkoy is one of the most critical one with the importance of air and marine transportation and presence of many other coastal facilities and structures that are prone to suffer from marine hazards. In the history, the Sea of Marmara has experienced numerous earthquake and landslide events and associated tsunamis. Therefore, tsunami risk assessment is essential for all coastal districts of Istanbul, including Bakirkoy district. In this study, a further developed methodology for tsunami human vulnerability and risk assessment Metropolitan Tsunami Human Vulnerability Assessment (MeTHuVA) is applied for Bakirkoy district of Istanbul, considering earthquake generated tsunamis. High-resolution tsunami hazard analysis is performed with the integration of coastal inundation computation with tsunami numerical tool NAMI DANCE and tsunami human vulnerability assessment with GIS-based multi-criteria decision analysis methods (MCDA). Using analytical hierarchy process method of MCDA, a hierarchical structure is established, composed of two main elements of tsunami human vulnerability: Vulnerability at Location and Evacuation Resilience. Tsunami risk assessment for Bakirkoy district is calculated by integrating result of hazard and vulnerability assessments with a risk relation that includes a parameter (n), which represents the preparedness and awareness level of the community. Tsunami simulations revealed that the maximum inundation distance is over 350 m on land and water penetrates almost 1700 m along Ayamama stream. Inundation is observed in eleven neighborhoods of Bakirkoy district. In the inundation zone, maximum flow depth is found to be over 5.7 m. The inundated area forms 4.2% of whole Bakirkoy district, and 62 buildings are located in the inundation zone. Hazard, vulnerability and risk assessment results for different neighborhoods of Bakirkoy district are presented and discussed.

Assessing potential impact of tsunami on Penang Island via TUNA-RP simulation

The Indian Ocean mega tsunami that occurred on 26 December 2004 resulted in the death of over 200,000 people worldwide, including 52 deaths in Penang Island, Malaysia. This rare but devastating tsunami highlights the vulnerability to future tsunamis for Malaysian coastal communities living in affected areas. To assess the potential impact of future tsunami, numerical tsunami models are used to project the maximum inundation distances and maximum runup heights along the affected coastal areas. In this paper, the in-house one-dimensional tsunami runup model codenamed TUNA-RP is enhanced and used to investigate the relations between the steepness of beach slope and tsunami impact, specifically inundation distance and runup height. The simulation results of TUNA-RP show that the inundation distances and runup heights decrease exponentially as the steepness of beach slope increases. Inundation distance and runup height at seven high-risk coastal areas in Penang Island, such as Teluk Bahang, Batu Feringghi and Tanjung Bungah, are presented in this paper to highlight risks and vulnerability. At certain locations along Penang beaches, a worst-case scenario may result in a tsunami with runup heights of 10 m which is highly dangerous, that might potentially take the lives of hundreds or thousands. Recognizing this vulnerability to tsunami risks for Penang, further research is essential for developing tsunami resilience in the face of this tsunami hazard.

Tsunami run-up and inundation along the coast of Sabah and Sarawak, Malaysia due to a potential Brunei submarine mass failure.

Submarine landslides, also known as submarine mass failures (SMFs), are major natural marine disasters that could critically damage coastal facilities such as nuclear power plants and oil and gas platforms. It is therefore essential to investigate submarine landslides for potential tsunami hazard assessment. Three-dimensional seismic data from offshore Brunei have revealed a giant seabed mass deposited by a previous SMF. The submarine mass extends over 120km from the continental slope of the Baram Canyon at 200m water depth to the deep basin floor of the Northwest Borneo Trough. A suite of in-house two-dimensional depth-averaged tsunami simulation model TUNA (Tsunami-tracking Utilities and Application) is developed to assess the vulnerability of coastal communities in Sabah and Sarawak subject to potential SMF tsunami. The submarine slide is modeled as a rigid body moving along a planar slope with the center of mass motion parallel to the planar slope and subject to external forces due to added mass, gravity, and dissipation. The nonlinear shallow water equations are utilized to simulate tsunami propagation from deepwater up to the shallow offshore areas. A wetting-drying algorithm is used when a tsunami wave reaches the shoreline to compute run up of tsunami along the shoreline. Run-up wave height and inundation maps are provided for seven densely populated locations in Sabah and Sarawak to highlight potential risks at each location, subject to two scenarios of slide slopes: 2° and 4°. The first wave may arrive at Kudat as early as 0.4h after the SMF, giving local communities little time to evacuate. Over a small area, maximum inundated depths reaching 20.3m at Kudat, 26.1m at Kota Kinabalu, and 15.5m at Miri are projected, while the maximum inundation distance of 4.86km is expected at Miri due to its low-lying coast. In view of the vulnerability of some locations to the SMF tsunami, it is important to develop and implement community resilience program to reduce the potential damage that could be inflicted by SMF tsunamis.

Tsunami hazard assessment along Diba-Oman and Diba-Al-Emirates coasts

Tsunami is among the most devastating natural hazards phenomenon responsible for significant loss of life and property throughout history. The Sultanate of Oman and United Arab Emirates are among the Indian Ocean countries that were subjected to one confirmed tsunami in November 27, 1945 due to an Mw 8.1 earthquake in Makran Subduction Zone. In this study, we present preliminary deterministic tsunami hazard assessment for the coasts of Diba Oman and Diba Al-Emirates, which are located on the western coast of the Oman Sea. The tsunami vulnerability of these cities increases due to the construction of many critical infrastructures and urban concentration along their coasts. Therefore, tsunami hazard assessment is necessary to mitigate the risk on the socio-economic system and sustainable developments. The major known source of tsunamis able to impact both coasts of Oman and United Arab Emirates is the Makran Subduction Zone (MSZ) which extends for approximately 900 km. The deterministic approach uses specific scenarios considering the maximum credible earthquakes occurring in the MSZ and computes the ensuing tsunami impact in the coasts of the study area. The maximum wave height graphs and inundation maps are obtained for tsunami scenarios caused by 8.8 earthquake magnitude in eastern MSZ and 8.2 magnitude from western MSZ. The Mw8.8 eastern MSZ causes a maximum inundation distance of 447 meters and a maximum flow depth of 1.37 meter. Maximum inundation distance larger than 420 meters occurs due to the Mw8.2 western MSZ scenario. For this scenario, numerical simulations show a maximum flow depth of about 2.34 meters.

Estimating tsunami run-up

Tsunami risk reduction activities rely on a sound knowledge of the hazard characteristics. Our understanding of these characteristics is derived from empirical measurements, numerical models or established rules. Conventional methods used to delineate areas vulnerable to tsunami inundation are often calculated from estimated maximum wave height at the coast and “rules-of-thumb”. Applying such rules may give unreliable results for decision-makers. Using basic hydraulic principles and assumptions, this paper improves on the existing rules by developing and testing new equations for predicting tsunami maximum depth profiles and inundation distances. The proposed equations require knowledge of shoreline wave-crest level, the onshore ground profile and an index for onshore roughness (a ratio of distance between protrusions to a local friction factor). As a tsunami wave moves inland, the equations demonstrate that there will usually be an exponential decline in peak water depth. The equations also confirm that a smaller spacing between onshore roughness elements, such as trees or houses, will give a steeper decline in peak depth due to increased friction as a wave moves inland. Furthermore, where ground level is rising faster than friction head is being lost, it is predicted that the water level of a tsunami will rise above the shoreline wave-crest level. The ground slope at which run-up starts to exceed shoreline wave-crest level can be predicted from the shoreline wave-crest level and roughness spacing. Results predicted by the new equations are verified by comparison with tsunami run-up measurements made in Samoa and Java.

Insights from geochemistry and diatoms to characterise a tsunami's deposit and maximum inundation limit

Abstract Geochemical proxies and diatom assemblages were used in combination with grain size characteristics not only to describe the deposit left behind by the 27 February 2010, Maule tsunami at Las Canas, Maule Region, Chile, but also to trace the maximum inundation limit of the event. The sandy deposit was laid down between 160 and 260 m inland behind an eroded sand dune and a lagoon but reached only 60% of the total tsunami inundation distance of 380 m, which was marked by organic debris, pumice clasts and wooden logs. It consisted of coarse to medium sand that thinned and fined inland. At the most seaward point, the 22 cm thick deposit exhibited a fining upward unit overlain by a couplet of coarsening–fining upward units, suggesting deposition by at least two waves, while farther inland the fining upward deposit was probably left behind by only one wave. Chemical proxies (Ca/Ti vs Sr/Ba) allow us to distinguish the deposit from the surrounding soil and indicate that it was sourced from the beach and/or dune area, with diatom assemblages confirming the marine origin of the deposit. Saltwater indicators (e.g. Cl, S) provide evidence for the maximum inundation limit beyond the extent of the sandy deposit, despite dilution and dissolution by 500 mm of rainfall in the six months since the tsunami. Marine and marine/brackish diatom assemblages decreased landward but were found up to the inundation limit and immediately beyond, suggesting the effect of diatom-bearing sea spray at the wave front or redistribution of the detrital assemblage associated with tsunami inundation due to wind. While the latter might result in a slight over-estimation of the inundation distance, they can be used in combination with chemical proxies to trace the maximum inundation distance of recent and past tsunamis, thus allowing for a better estimation of the magnitude of past events. Post-depositional processes were found to have affected the thinner sandy deposits (

Satellite Data for a Rapid Assessment of Tsunami Inundation Areas after the 2011 Tohoku Tsunami

The Mw = 9.0 earthquake that occurred off the coast of Japan’s Tohoku region produced a great tsunami causing catastrophic damage and loss of life. Within hours of the tsunami event, satellite data were readily available and massive media coverage immediately circulated thousands of photographs and videos of the tsunami. Satellite data allow a rapid assessment of inundated areas where access can be difficult either as a result of damaged infrastructure (e.g., roads, bridges, ports, airports) or because of safety issues (e.g., the hazard at Nuclear Power Plant at Fukushima). In this study, we assessed in a day tsunami inundation distances and runup heights using satellite data (very high-resolution satellite images from the GeoEye1 satellite and from the DigitalGlobe worldview, SRTM and ASTER GDEM) of the Tohoku region, Northeast Japan. Field survey data by Japanese and other international scientists validated our results. This study focused on three different locations. Site selection was based on coastal morphologies and the distance to the tsunami source (epicenter). Study sites are Rikuzentakata, Oyagawahama, and Yagawahama in the Oshika Peninsula, and the Sendai coastal plain (Sendai City to Yamamoto City). Maximum inundation distance (6 km along the river) and maximum runup (39 m) at Rikuzentakata estimated from satellite data agree closely with the 39.7 m inundation reported in the field. Here the ria coastal morphology and horn shaped bay enhanced the tsunami runup and effects. The Sendai coastal plain shows large inundation distances (6 km) and lower runup heights. Natori City and Wakabayashi Ward, on the Sendai plain, have similar runup values (12 and 16 m, respectively) obtained from SRTM data; these are comparable to those obtained from field surveys (12 and 9.5 m). However, at Yagawahama and Oyagawahama, Miyagi Prefecture, both SRTM and ASTER data provided maximum runup heights (41 to 45 m and 33 to 34 m, respectively), which are higher than those measured in the field (about 27 m). This difference in DEM and field data is associated with ASTER and SRTM DEM’s pixel size and vertical accuracy, the latter being dependent on ground coverage, slope, aspect and elevation. Countries with less access to technology and infrastructure can benefit from the use of satellite imagery and freely available DEMs for an initial, pre-field surveys, rapid estimate of inundated areas, distances and runup, and for assisting in hazard management and mitigation after a natural disaster.

The 11 March 2011 Tohoku Tsunami Survey in Rikuzentakata and Comparison with Historical Events

On 11 March 2011, a moment magnitude M w = 9.0 earthquake occurred off the Japan Tohoku coast causing catastrophic damage and loss of human lives. In the immediate aftermath of the earthquake, we conducted the reconnaissance survey in the city of Rikuzentakata, Japan. In comparison with three previous historical tsunamis impacting the same region, the 2011 event presented the largest values with respect to the tsunami height, the inundation area and the inundation distance. A representative tsunami height of 15 m was recorded in Rikuzentakata, with increased heights of 20 m around rocky headlands. In terms of the inundation area, the 2011 Tohoku tsunami exceeded by almost 2.6 times the area flooded by the 1960 Chilean tsunami, which ranks second among the four events compared. The maximum tsunami inundation distance was 8.1 km along the Kesen River, exceeding the 1933 Showa and 1960 Chilean tsunami inundations by factors of 6.2 and 2.7, respectively. The overland tsunami inundation distance was less than 2 km. The tsunami inundation height linearly decreased along the Kesen River at a rate of approximately 1 m/km. Nevertheless, the measured inland tsunami heights exhibit significant variations on local and regional scales. A designated “tsunami control forest” planted with a cross-shore width of about 200 m along a 2 km stretch of Rikuzentakata coastline was completely overrun and failed to protect the local community during this extreme event. Similarly, many designated tsunami shelters were too low and were overwashed by tsunami waves, thereby failing to provide shelter for evacuees—a risk that had been underestimated.