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

The M _w = 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.     

Evaluation of the use of paleotsunami deposits to reconstruct inundation distance and runup heights associated with prehistoric inundation events,Crescent City,southern Cascadia margin

Historic‐ and prehistoric‐tsunami sand deposits are used to independently establish runup records for tsunami hazard mitigation and modeled runup verification in Crescent City, California, located in the southern Cascadia Subduction Zone. Inundation from historic (1964) farfield tsunami (~5–6 m runup height) left sand sheet deposits (100–200 m width) in wetlands located behind a low beach ridge [3–4 m elevation of the National Geodetic Vertical Datum of 1988 (NAVD88)]. The most landward flooding lines (4·5–5 m elevation) in high‐gradient alluvial wetlands exceed the 1964 sand sheet records of inundation by 1–2 m in elevation. The most landward flooding in low‐gradient alluvial wetlands exceed the corresponding sand sheet record of inundation distance by 1000 m. Nevertheless, the sand sheet record is an important proxy for high‐velocity inundation. Sand sheet deposition from the 1964 historic tsunami closely corresponds to the landward extent of large debris transport and structural damage in the Crescent City waterfront. The sand sheet deposits provide a proxy for maximum hazard or ‘kill zone’ in the study area. Six paleotsunami sand sheets (0·3–3 ka) are recorded in the back‐ridge marshes in Crescent City, yielding a ~450 year mean recurrence interval for nearfield Cascadia tsunami. Two paleotsunami sand deposit records, likely correlated to Cascadia ruptures between 1·0 and 1·5 ka, are traced to 1·2 km distance and 9–10 m elevation, as adjusted for paleo‐sea level. The paleotsunami sand deposits demonstrate at least twice the runup height, and four times the inundation distance of the farfield 1964 tsunami sand sheet in the same marsh system. The preserved paleotsunami deposits in Crescent City are compared to the most landward flooding, as modeled by other investigators from a predicted Cascadia (~ Mw 9) rupture. The short geologic record (~1·5 ka) yields slightly lower runup records than those predicted for the modeled Mw 9 rupture scenario in the same marsh, but it generally verifies predicted maximum tsunami runup for use in the planning of emergency response and rapid evacuation. Copyright © 2011 John Wiley & Sons, Ltd.     

Field Survey and Geological Effects of the 15 November 2006 Kuril Tsunami in the Middle Kuril Islands

The near-field expression of the tsunami produced by the 15 November 2006 Kuril earthquake (M_w 8.1–8.4) in the middle Kuril Islands, Russia, including runup of up to 20 m, remained unknown until we conducted a post-tsunami survey in the summer of 2007. Because the earthquake occurred between summer field expeditions in 2006 and 2007, we have observations, topographic profiles, and photographs from three months before and nine months after the tsunami. We thoroughly surveyed portions of the islands of Simushir and Matua, and also did surveys on parts of Ketoi, Yankicha, Ryponkicha, and Rasshua. Tsunami runup in the near-field of the middle Kuril Islands, over a distance of about 200 km, averaged 10 m over 130 locations surveyed and was typically between 5 and 15 m. Local topography strongly affected inundation and somewhat affected runup. Higher runup generally occurred along steep, protruding headlands, whereas longer inundation distances occurred on lower, flatter coastal plains. Sediment transport was ubiquitous where sediment was available—deposit grain size was typically sand, but ranged from mud to large boulders. Wherever there were sandy beaches, a more or less continuous sand sheet was present on the coastal plain. Erosion was extensive, often more extensive than deposition in both space and volume, especially in areas with runup of more than 10 m. The tsunami eroded the beach landward, stripped vegetation, created scours and trim lines, cut through ridges, and plucked rocks out of the coastal plain.     

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.     

Reconstruction of Tsunami Inland Propagation on December 26, 2004 in Banda Aceh, Indonesia, through Field Investigations

This paper presents the results from an extensive field data collection effort following the December 26, 2004 earthquake and tsunami in Banda Aceh, Sumatra. The data were collected under the auspices of TSUNARISQUE, a joint French-Indonesian program dedicated to tsunami research and hazard mitigation, which has been active since before the 2004 event. In total, data from three months of field investigations are presented, which detail important aspects of the tsunami inundation dynamics in Banda Aceh. These include measurements of runup, tsunami wave heights, flow depths, flow directions, event chronology and building damage patterns. The result is a series of detailed inundation maps of the northern and western coasts of Sumatra including Banda Aceh and Lhok Nga. Among the more important findings, we obtained consistent accounts that approximately ten separate waves affected the region after the earthquake; this indicates a high-frequency component of the tsunami wave energy in the extreme near-field. The largest tsunami wave heights were on the order of 35 m with a maximum runup height of 51 m. This value is the highest runup value measured in human history for a seismically generated tsunami. In addition, our field investigations show a significant discontinuity in the tsunami wave heights and flow depths along a line approximately 3 km inland, which the authors interpret to be the location of the collapse of the main tsunami bore caused by sudden energy dissipation. The propagating bore looked like a breaking wave from the landward side although it has distinct characteristics. Patterns of building damage are related to the location of the propagating bore with overall less damage to buildings beyond the line where the bore collapsed. This data set was built to be of use to the tsunami community for the purposes of calibrating and improving existing tsunami inundation models, especially in the analysis of extreme near-field events.     

Modeling of the 2011 Japan Tsunami: Lessons for Near-Field Forecast

During the devastating 11 March 2011 Japanese tsunami, data from two tsunami detectors were used to determine the tsunami source within 1.5 h of earthquake origin time. For the first time, multiple near-field tsunami measurements of the 2011 Japanese tsunami were used to demonstrate the accuracy of the National Oceanic and Atmospheric Administration (NOAA) real-time flooding forecast system in the far field. To test the accuracy of the same forecast system in the near field, a total of 11 numerical models with grids telescoped to 2 arcsec (~60 m) were developed to hindcast the propagation and coastal inundation of the 2011 Japanese tsunami along the entire east coastline of Japan. Using the NOAA tsunami source computed in near real-time, the model results of tsunami propagation are validated with tsunami time series measured at different water depths offshore and near shore along Japan’s coastline. The computed tsunami runup height and spatial distribution are highly consistent with post-tsunami survey data collected along the Japanese coastline. The computed inundation penetration also agrees well with survey data, giving a modeling accuracy of 85.5 % for the inundation areas along 800 km of coastline between Ibaraki Prefecture (north of Kashima) and Aomori Prefecture (south of Rokkasho). The inundation model results highlighted the variability of tsunami impact in response to different offshore bathymetry and flooded terrain. Comparison of tsunami sources inferred from different indirect methods shows the crucial importance of deep-ocean tsunami measurements for real-time tsunami forecasts. The agreement between model results and observations along Japan’s coastline demonstrate the ability and potential of NOAA’s methodology for real-time near-field tsunami flooding forecasts. An accurate tsunami flooding forecast within 30 min may now be possible using the NOAA forecast methodology with carefully placed tsunameters and large-scale high-resolution inundation models with powerful computing capabilities.     

Manifestation of the 2011 Great Tohoku Tsunami on the Coast of the Kuril Islands: A Tsunami with Ice

The tsunami generated by the 2011 Tohoku Earthquake (M _w = 9.0) reached maximum heights of about 5 m along the coast of the Kuril Islands. The most essential feature of this event was sea ice about 0.5 m thick moved by the ocean water. The tsunami did not cause any essential damage on the Kuril Islands, but significantly affected coastal zones and produced interesting effects. The problem of a tsunami accompanied by marine ice is discussed and illustrated with photos.     

W Phase Inversion and Tsunami Inundation Modeling for Tsunami Early Warning: Case Study for the 2011 Tohoku Event

Centroid moment tensor solutions for the 2011 Tohoku earthquake are determined by W phase inversions using 5 and 10 min data recorded by the Full Range Seismograph Network of Japan (F-net). By a scaling relation of moment magnitude to rupture area and an assumption of rigidity of 4 × 10¹⁰ N m^?2, simple rectangular earthquake fault models are estimated from the solutions. Tsunami inundations in the Sendai Plain, Minamisanriku, Rikuzentakata, and Taro are simulated using the estimated fault models. Then the simulated tsunami inundation area and heights are compared with the observations. Even the simulated tsunami heights and inundations from the W phase solution that used only 5 min data are considerably similar to the observations. The results are improved when using 10 min of W phase data. These show that the W phase solutions are reliable to be used for tsunami inundation modeling. Furthermore, the technique that combines W phase inversion and tsunami inundation modeling can produce results that have sufficient accuracy for tsunami early warning purposes.     

Tsunami Sediment Characteristics at the Thai Andaman Coast

This paper describes and summarizes the 2004 Indian Ocean tsunami sediment characteristics at the Thai Andaman coast. Field investigations have been made approximately 3 years after the 2004 Indian Ocean tsunami event. Seven transects have been examined at five locations. Sediment samples have been collected for grain-size analyses by wet-sieve method. Tsunami sediments are compared to three deposits from coastal sub-environments. The mean grain-size and standard deviation of deposits show that shoreface deposits are fine to very fine sand, poorly to moderately well sorted; swash zone deposits are coarse to fine sand, poorly to well sorted; berm/dune deposits are medium to fine sand, poorly to well sorted; and tsunami deposits are coarse to very fine sand, poorly to moderately well sorted. A plot of deposit mean grain-size versus sorting indicates that tsunami deposits are composed of shoreface deposits, swash zone deposits and berm/dune deposits as well. The tsunami sediment is a gray sand layer deposited with an erosional base on a pre-existing soil (rooted soil). The thickness of the tsunami sediment layer is variable. The best location for observation of the recent tsunami sediment is at about 50–200 m inland from the coastline. In most cases, the sediment layer is normally graded. In some cases, the sediment contains rip-up clasts of muddy soils and/or organic matter. The vertical variation of tsunami sediment texture shows that the mean grain-size is fining upward and landward. Break points of slope in a plot of standard deviation versus depth mark a break in turbulence associated with a transition to a lower or higher Reynolds number runup. This can be used to evaluate tsunami sediment main layer and tsunami sediment sub layers. The skewness of tsunami sediment indicates a grain size distribution with prominent finer-grain or coarse-grain particles. The kurtosis of tsunami sediment indicates grain-size distributions which are flat to peak distribution (or multi-modal to uni-modal distribution) upward. Generally, the major origins of tsunami sediment are swash zone and berm/dune zone sands where coarse to medium sands are the significant material at these locations. The minor origin of tsunami sediment is the shoreface where the significant materials are fine to very fine sands. However, for a coastal area where the shoreface slope is mild, the major origin of tsunami sediment is the shoreface. The interpretation of runup number from tsunami sediment characteristics gets three runups for the 2004 Indian Ocean tsunami at the Thai Andaman coast. It corresponds to field observations from local eyewitnesses. The 1st runup transported and deposited more coarse particles than the following runups. Overall, the pattern of onshore tsunami sediment transportation indicates erosion at swash zone and berm/dune zone, followed by dynamic equilibrium at an area behind the berm/dune zone and after that deposition at inland zone until the limit of sediment inundation. The total deposition is a major pattern in onshore tsunami sediment transportation at the deposition zone which the sediment must find in the direction of transport.     

Tsunami Probability in the Caribbean Region

We calculated tsunami runup probability (in excess of 0.5 m) at coastal sites throughout the Caribbean region. We applied a Poissonian probability model because of the variety of uncorrelated tsunami sources in the region. Coastlines were discretized into 20 km by 20 km cells, and the mean tsunami runup rate was determined for each cell. The remarkable ~500-year empirical record compiled by O’Loughlin and Lander (2003) was used to calculate an empirical tsunami probability map, the first of three constructed for this study. However, it is unclear whether the 500-year record is complete, so we conducted a seismic moment-balance exercise using a finite-element model of the Caribbean-North American plate boundaries and the earthquake catalog, and found that moment could be balanced if the seismic coupling coefficient is c = 0.32. Modeled moment release was therefore used to generate synthetic earthquake sequences to calculate 50 tsunami runup scenarios for 500-year periods. We made a second probability map from numerically-calculated runup rates in each cell. Differences between the first two probability maps based on empirical and numerical-modeled rates suggest that each captured different aspects of tsunami generation; the empirical model may be deficient in primary plate-boundary events, whereas numerical model rates lack backarc fault and landslide sources. We thus prepared a third probability map using Bayesian likelihood functions derived from the empirical and numerical rate models and their attendant uncertainty to weight a range of rates at each 20 km by 20 km coastal cell. Our best-estimate map gives a range of 30-year runup probability from 0–30% regionally.     

Tsunami Source of the 2010 Mentawai, Indonesia Earthquake Inferred from Tsunami Field Survey and Waveform Modeling

The 2010 Mentawai earthquake (magnitude 7.7) generated a destructive tsunami that caused more than 500 casualties in the Mentawai Islands, west of Sumatra, Indonesia. Seismological analyses indicate that this earthquake was an unusual “tsunami earthquake,” which produces much larger tsunamis than expected from the seismic magnitude. We carried out a field survey to measure tsunami heights and inundation distances, an inversion of tsunami waveforms to estimate the slip distribution on the fault, and inundation modeling to compare the measured and simulated tsunami heights. The measured tsunami heights at eight locations on the west coasts of North and South Pagai Island ranged from 2.5 to 9.3 m, but were mostly in the 4–7 m range. At three villages, the tsunami inundation extended more than 300 m. Interviews of local residents indicated that the earthquake ground shaking was less intense than during previous large earthquakes and did not cause any damage. Inversion of tsunami waveforms recorded at nine coastal tide gauges, a nearby GPS buoy, and a DART station indicated a large slip (maximum 6.1 m) on a shallower part of the fault near the trench axis, a distribution similar to other tsunami earthquakes. The total seismic moment estimated from tsunami waveform inversion was 1.0 × 10²¹ Nm, which corresponded to M_w 7.9. Computed coastal tsunami heights from this tsunami source model using linear equations are similar to the measured tsunami heights. The inundation heights computed by using detailed bathymetry and topography data and nonlinear equations including inundation were smaller than the measured ones. This may have been partly due to the limited resolution and accuracy of publically available bathymetry and topography data. One-dimensional run-up computations using our surveyed topography profiles showed that the computed heights were roughly similar to the measured ones.     

Salinity in Soils and Tsunami Deposits in Areas Affected by the 2010 Chile and 2011 Japan Tsunamis

The accumulation of data sets of past tsunamis is the most basic but reliable way to prepare for future tsunamis because the frequency of tsunami occurrence and their magnitude can be estimated by historical records of tsunamis. Investigation of tsunami deposits preserved in geological layers is an effective measure to understand ancient tsunamis that occurred before historical records began. However, the areas containing tsunami deposits can be narrower than the area of tsunami inundation, thus resulting in underestimation of the magnitude of past tsunamis. A field survey was conducted after the 2010 Chile tsunami and 2011 Japan tsunami to investigate the chemical properties of the tsunami-inundated soil to examine the applicability of tsunami inundation surveys considering water-soluble salts in soil. The soil and tsunami deposits collected in the tsunami-inundated areas are rich in water-soluble ions (Na⁺, Mg²⁺, Cl^?, Br^? and SO ₄ ^2? ) compared with the samples collected in the non-inundated areas. The analytical result that the ratios of Na⁺, Mg²⁺, Br^? and SO ₄ ^2? to Cl^? are nearly the same in the tsunami deposits and in the tsunami-inundated soil suggests that the deposition of these ions resulting from the tsunami inundation does not depend on whether or not tsunami deposits exist. Discriminant analysis of the tsunami-inundated areas using the ion contents shows the high applicability of these ions to the detection of tsunami inundation during periods when the amount of rainfall is limited. To examine the applicability of this method to palaeotsunamis, the continuous monitoring of water-soluble ions in tsunami-inundated soil is needed as a future study.     

Onshore tsunami deposits caused by the 1993 Southwest Hokkaido and 1983 Japan Sea earthquakes

Onshore tsunami deposits resulting from the 1993 Southwest Hokkaido and 1983 Japan Sea earthquakes were described to evaluate the feasibility of tsunami deposits for inferring paleoseismic events along submarine faults. Tsunami deposits were divided into three types, based on their composition and aerial distribution: (A) deposits consisting only of floating materials, (B) locally distributed siliclastic deposits, and (C) widespread siliclastic deposits. The most widely distributed tsunami deposits consist of the first two types. Type C deposits are mostly limited to areas where the higher tsunami runup was observed. The scale of tsunami represented by vertical tsunami runup is an important factor controlling the volume of tsunami deposits. The thickest deposits, about 10 cm, occur behind coastal dunes. To produce thick siliclastic tsunami deposits, a suitable source area, such as sand bar or dune, must be available in addition to sufficient vertical tsunami runup. Estimation of the amounts of erosion and deposition indicates that tsunami deposits were derived from both onshore and shoreface regions. The composition and grain size of the tsunami deposits strongly reflect the nature of the sedimentary materials of their source area. Sedimentary structures of the tsunami deposits suggest both low and high flow régimes. Consequently, it seems very difficult to identify tsunami deposits based only on grain size distribution or sedimentary structure of a single site in ancient successions.     

Coastal Impacts of the March 11th Tohoku, Japan Tsunami in the Galapagos Islands

On March 11, 2011 at 5:46:23 UTC (March 10 11:46:23 PM Galapagos Local Time), the M_w 9.0 Great East Japan Earthquake occurred near the Tohoku region off the east coast of Japan, spawning a Pacific-wide tsunami. Approximately 12,000 km away, the Galapagos Islands experienced moderate tsunami impacts, including flooding, structural damage, and strong currents. In this paper, we present observations and measurements of the tsunami effects in the Galapagos, focusing on the four largest islands in the archipelago; (from west to east) Isabela, Santiagio, Santa Cruz, and San Cristobal. Access to the tsunami affected areas was one of the largest challenges of the field survey. Aside from approximately ten sandy beaches open to tourists, all other shoreline locations are restricted to anyone without a research permit; open cooperation with the Galapagos National Park provided the survey team complete access to the Islands coastlines. Survey locations were guided by numerical simulations of the tsunami performed prior to the field work. This numerical guidance accurately predicted the regions of highest impact, as well as regions of relatively low impact. Tide-corrected maximum tsunami heights were generally in the range of 3–4 m with the highest runup of 6 m measured in a small pocket beach on Isla Isabela. Puerto Ayora, on Santa Cruz Island, the largest harbor in the Galapagos experienced significant flooding and damage to structures located at the shoreline. A current meter moored inside the harbor recorded relatively weak tsunami currents of less than 0.3 m/s (0.6 knot) during the event. Comparisons with detailed numerical simulations suggest that these low current speed observations are most likely the result of data averaging at 20-min intervals and that maximum instantaneous current speeds were considerably larger. Currents in the Canal de Itabaca, a natural waterway between Santa Cruz Island and a smaller island offshore, were strong enough to displace multiple 5.5-ton navigation buoys. Numerical simulations indicate that currents in the Canal de Itabaca exceeded 4 m/s (~8 knots), a very large flow speed for a navigational waterway.     

Can the Waves Generated by Fast Ferries be a Physical Model of Tsunami?

The potential of long ship-induced waves to serve as a physical model for tsunami waves (called simply tsunami below) is examined. Such waves (wavelengths more than 200 m at depths down to 10–20 m) are induced by high-speed ferries sailing at near-critical speeds in semisheltered, relatively shallow areas. It is shown based on experience from Tallinn Bay, Baltic Sea, that for many aspects these waves can model nearshore dynamics and runup of tsunami caused by landslides, including processes of wave refraction, diffraction, and sea-bottom interaction in bays and harbors. Many governing nondimensional parameters (such as the nonlinearity, dispersion, Reynolds and Ursell numbers, surf similarity parameter, breaking parameter, etc.) of the largest ship waves and landslide tsunamis have the same order of magnitude. It is especially important that use of ship waves for wave propagation and runup studies allows their spatial structure to be accounted for adequately. Near-critical ship waves can therefore be used as a natural substitute for tsunami, for study under controlled and safe conditions.     

Waveform and Spectral Analyses of the 2011 Japan Tsunami Records on Tide Gauge and DART Stations Across the Pacific Ocean

We studied the 11 March 2011 Tohoku tsunami through analysis of the sea level records from 21 tide gauge and 16 DART (Deep-ocean Assessment and Reporting of Tsunamis) stations from across the Pacific Ocean. The extreme power of this trans-oceanic tsunami was indicated by the trough-to-crest heights of 3.03 m at Arena Cove on the western coast of the USA and 3.94 m at Coquimbo on the southern coast of Chile. The average value of the maximum amplitude was 163.9 cm for the examined tide gauge records. At many coastal tide gauge stations the largest wave arrived several hours after the first arrival of the tsunami wave, and the tsunami lasted for a long time with an average duration of 4 days. On the contrary, at most of the DART stations in the deep ocean, the first wave was the largest, the tsunami amplitudes were smaller with an average maximum of 51.2 cm, and the durations were shorter with an average of 2 days. The two dominant tsunami periods on the DART records were 37 and 67.4 min, which are possibly attributed to the width and length of the tsunami source fault, respectively. The dimensions of the tsunami source was estimated as 233 km × 424 km. Wavelet analyses of tide gauge and DART records showed that most of the tsunami energy was distributed at the wide period band of around 10–80 min during the first hour after the tsunami arrival, then it was concentrated in a relatively narrower band. The frequency-time plots showed the switches and lapses of tsunami energy at the 35- and 65-min period bands.     

Runup of Tsunami Waves in U-Shaped Bays

The problem of tsunami wave shoaling and runup in U-shaped bays (such as fjords) and underwater canyons is studied in the framework of 1D shallow water theory with the use of an assumption of the uniform current on the cross-section. The wave shoaling in bays, when the depth varies smoothly along the channel axis, is studied with the use of asymptotic approach. In this case a weak reflection provides significant shoaling effects. The existence of traveling (progressive) waves, propagating in bays, when the water depth changes significantly along the channel axis, is studied within rigorous solutions of the shallow water theory. It is shown that traveling waves do exist for certain bay bathymetry configurations and may propagate over large distances without reflection. The tsunami runup in such bays is significantly larger than for a plane beach.     

The 2010 and 2011 Tsunamis in French Polynesia: Operational Aspects and Field Surveys

We present a detailed timeline of the warning procedures as they unfolded at the Laboratoire de Géophysique in Papeete, Tahiti, during the nights of 26–27 February 2010 (Maule, Chile tsunami) and 10–11 March 2011 (Tohoku tsunami). In particular, we discuss how the flow of information available to the warning center (including seismic evaluations obtained both locally and from other warning centers, as well as maregraph and DART buoy data) built up and eventually led to red alerts, which the local authorities used in both cases to impose an evacuation of low-lying areas on 68 islands. While the alerts were successful in Polynesia, a difficulty arose in 2011 when the alert had to be reinstated immediately as the all clear was being declared, since the maximum amplitude was carried by the fourth wave packet. We also present a complete dataset of 119 values of run-up and inundation surveyed in the aftermath of the two tsunamis, principally in the Marquesas Islands where their effects were maximal, and on Tahiti and Moorea for the 2011 event. The highest run-up (4.45 m) was observed in 2011 in the Bay of Taipivai on Nuku Hiva, where seven houses were flooded. We find no clear correlation between run-up values at the same locations in 2010 and 2011, suggesting that local responses are controlled by details specific to each tsunami. In 2010, in the village of Puamau on Hiva Oa (Marquesas), a delayed harbor response, probably due to resonance of the bay upon arrival of short-period components dispersed outside the shallow-water approximation, flung a launch onto a wharf, 7 h after the first arrivals, and 2.5 h after issuance of the all clear.     

Numerical Simulation of the 2011 Tohoku Tsunami Based on a New Transient FEM Co-seismic Source: Comparison to Far- and Near-Field Observations

In this work, we simulate the 2011 M9 Tohoku-Oki tsunami using new coseismic tsunami sources based on inverting onshore and offshore geodetic data, using 3D Finite Element Models (FEM). Such FEMs simulate elastic dislocations along the plate boundary interface separating the stiff subducting Pacific Plate from the relatively weak forearc and volcanic arc of the overriding Eurasian plate. Due in part to the simulated weak forearc materials, such sources produce significant shallow slip (several tens of meters) along the updip portion of the rupture near the trench. To assess the accuracy of the new approach, we compare observations and numerical simulations of the tsunami's far- and near-field coastal impact for: (i) one of the standard seismic inversion sources (UCSB; Shao et al. 2011); and (ii) the new FEM sources. Specifically, results of numerical simulations for both sources, performed using the fully nonlinear and dispersive Boussinesq wave model FUNWAVE-TVD, are compared to DART buoy, GPS tide gauge, and inundation/runup measurements. We use a series of nested model grids with varying resolution (down to 250 m nearshore) and size, and assess effects on model results of the latter and of model physics (such as when including dispersion or not). We also assess the effects of triggering the tsunami sources in the propagation model: (i) either at once as a hot start, or with the spatiotemporal sequence derived from seismic inversion; and (ii) as a specified surface elevation or as a more realistic time and space-varying bottom boundary condition (in the latter case, we compute the initial tsunami generation up to 300 s using the non-hydrostatic model NHWAVE). Although additional refinements are expected in the near future, results based on the current FEM sources better explain long wave near-field observations at DART and GPS buoys near Japan, and measured tsunami inundation, while they simulate observations at distant DART buoys as well or better than the UCSB source. None of the sources, however, are able to explain the largest runup and inundation measured between 39.5° and 40.25°N, which could be due to insufficient model resolution in this region (Sanriku/Ria) of complex bathymetry/topography, and/or to additional tsunami generation mechanisms not represented in the coseismic sources (e.g., splay faults, submarine mass failure). This will be the object of future work.     

Combined Effects of Tectonic and Landslide-Generated Tsunami Runup at Seward, Alaska During the M W 9.2 1964 Earthquake

We apply a recently developed and validated numerical model of tsunami propagation and runup to study the inundation of Resurrection Bay and the town of Seward by the 1964 Alaska tsunami. Seward was hit by both tectonic and landslide-generated tsunami waves during the $M_{\rm W}$ 9.2 1964 megathrust earthquake. The earthquake triggered a series of submarine mass failures around the fjord, which resulted in landsliding of part of the coastline into the water, along with the loss of the port facilities. These submarine mass failures generated local waves in the bay within 5?min of the beginning of strong ground motion. Recent studies estimate the total volume of underwater slide material that moved in Resurrection Bay to be about 211?million m³ (Haeussler et?al. in Submarine mass movements and their consequences, pp 269?C278, 2007). The first tectonic tsunami wave arrived in Resurrection Bay about 30?min after the main shock and was about the same height as the local landslide-generated waves. Our previous numerical study, which focused only on the local landslide-generated waves in Resurrection Bay, demonstrated that they were produced by a number of different slope failures, and estimated relative contributions of different submarine slide complexes into tsunami amplitudes (Suleimani et?al. in Pure Appl Geophys 166:131?C152, 2009). This work extends the previous study by calculating tsunami inundation in Resurrection Bay caused by the combined impact of landslide-generated waves and the tectonic tsunami, and comparing the composite inundation area with observations. To simulate landslide tsunami runup in Seward, we use a viscous slide model of Jiang and LeBlond (J Phys Oceanogr 24(3):559?C572, 1994) coupled with nonlinear shallow water equations. The input data set includes a high resolution multibeam bathymetry and LIDAR topography grid of Resurrection Bay, and an initial thickness of slide material based on pre- and post-earthquake bathymetry difference maps. For simulation of tectonic tsunami runup, we derive the 1964 coseismic deformations from detailed slip distribution in the rupture area, and use them as an initial condition for propagation of the tectonic tsunami. The numerical model employs nonlinear shallow water equations formulated for depth-averaged water fluxes, and calculates a temporal position of the shoreline using a free-surface moving boundary algorithm. We find that the calculated tsunami runup in Seward caused first by local submarine landslide-generated waves, and later by a tectonic tsunami, is in good agreement with observations of the inundation zone. The analysis of inundation caused by two different tsunami sources improves our understanding of their relative contributions, and supports tsunami risk mitigation in south-central Alaska. The record of the 1964 earthquake, tsunami, and submarine landslides, combined with the high-resolution topography and bathymetry of Resurrection Bay make it an ideal location for studying tectonic tsunamis in coastal regions susceptible to underwater landslides.