Tsunami Amplitudes Research Articles

DARTs and CORK in Cascadia Basin: High-resolution observations of the 2004 Sumatra tsunami in the northeast Pacific

[1] We report unique deep-sea recordings of the Sumatra tsunami of December 2004 by high-resolution DART® (Deep-ocean Assessment and Reporting of Tsunami) and CORK (Circulation Obviation Retrofit Kit) bottom pressure sensors deployed at depths of ∼1500–3500 m in Cascadia Basin in the northeast Pacific. The simultaneous records from these sites establish the first-ever regional-scale tsunami detection array for the open ocean, enabling us to resolve both seafloor and crustal tsunami signals and to determine fundamental properties of the waves following their 22,000 km journey from the source region. Waves reaching the basin had mean amplitudes of ∼5 mm with energy spread over a broad frequency band from 0.4 to 7 cph. Peak tsunami energy was in the 0.8 to 2 cph (75 to 30 min) band. Leading waves from the event arrived 34–35 h after the earthquake, roughly 7 h later than expected, suggesting that the tsunami mainly propagated by the “most economic” (minimum energy loss) path along mid-ocean ridge wave-guides rather than taking the direct and fastest path across the ocean. Motions within the peak energy band comprise roughly 50% coherent progressive waves propagating from the south at longwave phase speeds of ∼150 ms−1 and 50% random waves scattered from the coast and bottom irregularities. Tsunami amplitudes in the borehole were one-third those on the seafloor. The extensive “ringing” and anomalously slow (3.5-day) e-folding decay time of the tsunami wave energy indicates long duration energy flux radiating from the Indian Ocean via the Southern Pacific Ocean.

Numerical Simulation of the December 26, 2004, Tsunami on the Southwest Coast and Lakshadweep Islands of India

The Tsunami N2 model has been used to simulate the Tsunami amplitudes and horizontal extent of inundation from the Indian Ocean Tsunami of December 26, 2004. The areas considered here pertain to the southwest coast of India, comprising the states of Kerala and Karnataka. In addition, the simulation of tsunami amplitudes and inundation has also been done for some selected islands of the Lakshadweep group of islands of India.

Time-Dependent Decay Model of MRMS Tsunami Amplitudes for Forecasting Decay of Far-field Tsunamis

In order to evaluate and forecast the decay process of far-field tsunamis, we have constructed a time-dependent decay model of MRMS tsunami amplitudes. This model is based on the decay features of near- and far-field earthquake tsunamis around Japan and on the assumption that the propagation of tsunami energy is expressed by convolution operations with three effects (source, path, and site effects) and some parameters. Computed examples show that with suitable parameters, this model has the potential to duplicate various real MRMS tsunami waveforms. Through this study, we successfully mitigated issues related to the timely cancellation of tsunami warnings; the problem we are still facing on the issue is to determine parameters and functions of three effects for the proposed decay model of MRMS tsunami amplitudes.

Tsunami simulation with Green–Naghdi theory

Green–Naghdi (GN) theory is a fully nonlinear wave theory which has been used with success to simulate nonlinear water waves. In previous applications of GN theory to water wave problems the ocean bottom was assumed to be time invariant. In this work no such restriction is made and GN theory is used to simulate tsunami caused by bottom fluctuation. As first test cases we simulate two-dimensional nonlinear surface waves generated by positive bottom movements. The results in the generation region for three different seabed movements compare well against earlier experimental data. The results in the downstream region for impulsive seabed movements show some discrepancies in wave phase and amplitude compared with earlier experimental values. It is suspected that the viscous effects may have played a role. The GN theory is then used to study three-dimensional near-field tsunami amplitudes caused by submarine landslides and slumps spreading in two orthogonal directions. The GN results agree with previous linear solution very well when the ratio of the velocities is v 1/ v 2=1.0. But GN theory give more believable results for the case of v T / v=0.1 and v 1/ v 2=0.1.

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 269–278, 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 166:131–152, 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):559–572, 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.

Tsunami waves generated by submarine landslides of variable volume: analytical solutions for a basin of variable depth

Abstract. Tsunami wave generation by submarine landslides of a variable volume in a basin of variable depth is studied within the shallow-water theory. The problem of landslide induced tsunami wave generation and propagation is studied analytically for two specific convex bottom profiles (h ~ x4/3 and h ~ x4). In these cases the basic equations can be reduced to the constant-coefficient wave equation with the forcing determined by the landslide motion. For certain conditions on the landslide characteristics (speed and volume per unit cross-section) the wave field can be described explicitly. It is represented by one forced wave propagating with the speed of the landslide and following its offshore direction, and two free waves propagating in opposite directions with the wave celerity. For the case of a near-resonant motion of the landslide along the power bottom profile h ~ xγ the dynamics of the waves propagating offshore is studied using the asymptotic approach. If the landslide is moving in the fully resonant regime the explicit formula for the amplitude of the wave can be derived. It is demonstrated that generally tsunami wave amplitude varies non-monotonically with distance.

Assessment of potential tsunamigenic seismic hazard to Sri Lanka

PurposeThe purpose of this paper is to present an assessment of the potential tsunamigenic seismic hazard to Sri Lanka from all active subduction zones in the Indian Ocean Basin.Design/methodology/approachThe assessment was based on previous studies as well as past seismicity of the subducion zones concerned.FindingsAccordingly, four seismic zones capable of generating teletsunamis that could reach Sri Lanka have been identified, namely, Northern Andaman‐Myanmar, Northern Sumatra‐Andaman and Southern Sumatra in the Sunda trench and Makran in the Northern Arabian Sea. Moreover, plausible worst‐case earthquake scenarios and respective fault parameters for each of these seismic zones have been recommended.Research limitations/implicationsHowever, other potential tsunami sources such as seismic activity in the near‐field, submarine landslides and volcanic eruptions have not been considered.Practical implicationsNumerical simulations of tsunami propagation have been carried out for each of the four scenarios in order to assess the potential impact along the coastline of Sri Lanka. Such information relating to the spatial distribution of the likely tsunami amplitudes and arrival times for Sri Lanka would help authorities responsible for evacuation to make a better judgment as to the level of threat in different areas along the coastline, and act accordingly, if a large earthquake were to occur in any of the subduction zones in the Indian Ocean.Originality/valueIn the absence of comprehensive probabilistic assessments of the tsunami hazard to Sri Lanka, this paper's recommendations would provide the necessary framework for the development of deterministic tsunami hazard maps for the shoreline of Sri Lanka.

Modeling of tsunami generation and propagation by a spreading curvilinear seismic faulting in linearized shallow-water wave theory

The processes of tsunami evolution during its generation in search for possible amplification mechanisms resulting from unilateral spreading of the sea floor uplift is investigated. We study the nature of the tsunami build up and propagation during and after realistic curvilinear source models represented by a slowly uplift faulting and a spreading slip-fault model. The models are used to study the tsunami amplitude amplification as a function of the spreading velocity and rise time. Tsunami waveforms within the frame of the linearized shallow-water theory for constant water depth are analyzed analytically by transform methods (Laplace in time and Fourier in space) for the movable source models. We analyzed the normalized peak amplitude as a function of the propagated uplift length, width and the average depth of the ocean along the propagation path.

Empirical relationship of tsunami height between offshore and coastal stations

This study compares tsunami height data obtained by coastal tidal stations and offshore wave stations of the Nationwide Ocean Wave information network for Ports and HArbourS (NOWPHAS) with data obtained from real-time kinematic global positioning system (RTK-GPS) buoys. NOWPHAS wave stations and RTK-GPS buoys are typically installed off the coast—the former within several kilometers of the coast and the latter 2–20 km offshore. The ratio of initial tsunami height observed at a coastal tidal station to that observed at an offshore station was found to be approximately proportional to the fourth root of the ratio of the sea-bottom depths to the mean sea level at the respective offshore and coastal station. This approximation can also be applied to maximum tsunami amplitudes. The relationship derived in this paper will enable the initial tsunami height to be forecast by real-time applications using detected tsunami initial height from offshore stations, such as the sea-bottom pressure gauges of NOWPHAS stations and RTK-GPS buoys.

Modeling of Tsunami Generation and Propagation by a Spreading Curvilinear Seismic Faulting in Linearized Shallow-Water Wave Theory

The processes of tsunami evolution during its generation in search for possible amplification mechanisms resulting from unilateral spreading of the sea floor uplift is investigated. We study the nature of the tsunami build up and propagation during and after realistic curvilinear source models represented by a slowly uplift faulting and a spreading slip-fault model. The models are used to study the tsunami amplitude amplification as a function of the spreading velocity and rise time. Tsunami waveforms within the frame of the linearized shallow water theory for constant water depth are analyzed analytically by transform methods (Laplace in time and Fourier in space) for the movable source models. We analyzed the normalized peak amplitude as a function of the propagated uplift length, width and the average depth of the ocean along the propagation path.

THE SOUTH SANDWICH ISLANDS EARTHQUAKE OF 27 JUNE 1929: SEISMOLOGICAL STUDY AND INFERENCE ON TSUNAMI RISK FOR THE SOUTH ATLANTIC

While no large interplate thrust earthquakes are known at the South Sandwich subduction zone, historical catalogues include a number of earthquakes with reported magnitudes of 7 or more. We present a detailed seismological study of the largest one (27 June 1929; M PAS = 8.3). The earthquake relocates 80 km north of the north-western corner of the arc. Its mechanism, inverted through the PDFM method, features normal faulting on a steeply dipping fault plane ( φ = 71°, δ = 70°, λ = 272°). The seismic moment, 1.7 x 10 28 dyn.cm, supports Gutenberg and Richter’s estimate, and is 28 times the largest shallow CMT in the region. The 1929 event is interpreted as representing a lateral tear in the South Atlantic plate, comparable to similar earthquakes in Samoa and Loyalty, deemed “STEP faults” by Govers and Wortel (2005). Hydrodynamic simulations using the MOST method (Titov and Synolakis, 1997) suggest deep-water tsunami amplitudes reaching 30 cm off the coast of Brazil, where run-up should have been observable, and 20 cm along the Gulf of Guinea (Ivory Coast, Ghana). We also simulate a number of potential sources obtained by assigning the 1929 moment to the geometries of other known earthquakes in the region, namely outer-rise normal faulting events at the center of the arc and its southern extremity, and an interplate thrust fault at the southern corner, where the youngest lithosphere is subducted. A common feature of these models is the strong focusing of tsunami waves by the South Atlantic Ridge, the southwest Indian Ocean Ridge, and the Agulhas Rise, resulting in amplitudes always enhanced in Ghana, southern Mozambique and certain parts of the coast of South Africa. This study documents the potential tsunami hazard to South Atlantic shorelines from earthquakes in this region, principally normal faulting events.

Development, testing, and applications of site‐specific tsunami inundation models for real‐time forecasting

The study describes the development, testing and applications of site‐specific tsunami inundation models (forecast models) for use in NOAA's tsunami forecast and warning system. The model development process includes sensitivity studies of tsunami wave characteristics in the nearshore and inundation, for a range of model grid setups, resolutions and parameters. To demonstrate the process, four forecast models in Hawaii, at Hilo, Kahului, Honolulu, and Nawiliwili are described. The models were validated with fourteen historical tsunamis and compared with numerical results from reference inundation models of higher resolution. The accuracy of the modeled maximum wave height is greater than 80% when the observation is greater than 0.5 m; when the observation is below 0.5 m the error is less than 0.3 m. The error of the modeled arrival time of the first peak is within 3% of the travel time. The developed forecast models were further applied to hazard assessment from simulated magnitude 7.5, 8.2, 8.7 and 9.3 tsunamis based on subduction zone earthquakes in the Pacific. The tsunami hazard assessment study indicates that use of a seismic magnitude alone for a tsunami source assessment is inadequate to achieve such accuracy for tsunami amplitude forecasts. The forecast models apply local bathymetric and topographic information, and utilize dynamic boundary conditions from the tsunami source function database, to provide site‐ and event‐specific coastal predictions. Only by combining a Deep‐ocean Assessment and Reporting of Tsunami‐constrained tsunami magnitude with site‐specific high‐resolution models can the forecasts completely cover the evolution of earthquake‐generated tsunami waves: generation, deep ocean propagation, and coastal inundation. Wavelet analysis of the tsunami waves suggests the coastal tsunami frequency responses at different sites are dominated by the local bathymetry, yet they can be partially related to the locations of the tsunami sources. The study also demonstrates the nonlinearity between offshore and nearshore maximum wave amplitudes.

Review of Recent Tsunami Observation by Offshore Cabled Observatory

This paper discusses near- and far-field tsunami observations at the Hokkaido, Japan, offshore cabled observatory, focusing on the 2006 Kuril Island earthquake (Mw 8.3) as a far-field event and the 2008 off-Tokachi earthquake (Mw 6.8) as a near-field event. The Kuril Islands earthquake was detected as a series of tsunami signals by 2 bottom pressure gauges roughly 1 hour after the earthquake. Tsunami amplitudes observed offshore were 3 cm and off-coastal amplitudes were a few tens of centimeters. In the 2008 near-field off-Tokachi earthquake (Mw 6.8), a tsunami signal was detected simultaneously with the earthquake, which had a source amplitude of 4 cm. Our tsunami calculation reproduced the first wave well, but discrepancies about arrival time and amplitude arose for the second and later waves. Offshore tsunami sensors such as bottom pressure gauges, deep-ocean assessment and reporting of tsunami (DART) buoys, and kinematic global positioning system (GPS) buoys may thus become keys in early tsunami warning once appropriate dataset processing is implemented.

Probabilistic tsunami hazard assessment at Seaside, Oregon, for near‐ and far‐field seismic sources

The first probabilistic tsunami flooding maps have been developed. The methodology, called probabilistic tsunami hazard assessment (PTHA), integrates tsunami inundation modeling with methods of probabilistic seismic hazard assessment (PSHA). Application of the methodology to Seaside, Oregon, has yielded estimates of the spatial distribution of 100‐ and 500‐year maximum tsunami amplitudes, i.e., amplitudes with 1% and 0.2% annual probability of exceedance. The 100‐year tsunami is generated most frequently by far‐field sources in the Alaska‐Aleutian Subduction Zone and is characterized by maximum amplitudes that do not exceed 4 m, with an inland extent of less than 500 m. In contrast, the 500‐year tsunami is dominated by local sources in the Cascadia Subduction Zone and is characterized by maximum amplitudes in excess of 10 m and an inland extent of more than 1 km. The primary sources of uncertainty in these results include those associated with interevent time estimates, modeling of background sea level, and accounting for temporal changes in bathymetry and topography. Nonetheless, PTHA represents an important contribution to tsunami hazard assessment techniques; viewed in the broader context of risk analysis, PTHA provides a method for quantifying estimates of the likelihood and severity of the tsunami hazard, which can then be combined with vulnerability and exposure to yield estimates of tsunami risk.

Hazard assessment of underwater landslide-generated tsunamis: a case study in the Padang region, Indonesia

Submarine landslides can generate local tsunamis with high run-ups, posing a hazard to human lives and coastal facilities. Both ancient (giant Storegga slide off Norwegian coast, 8200 B. P.) and recent (Papua New Guinea, 1998) events show high potential danger of tsunamigenic landslides and the importance of mitigation efforts. This contribution presents newly discovered landslides 70 km off Padang (Western Sumatra, Indonesia) based on recent bathymetry measurements. This highly populated city with over 750,000 inhabitants exhibits high tsunami vulnerability due to its very low elevation. We model tsunamis that might have been induced by the detected landslide events. Estimations of run-up heights extrapolated from offshore tsunami amplitudes for Padang and other locations in the northern Mentawai fore-arc basin yield maximum values of about 3 m. We also provide a systematic parametric study of landslide-induced tsunamis, which allows us to distinguish potentially dangerous scenarios for Padang. Inside the fore-arc basin, scenarios involving volumes of 0.5–25 km³ could endanger Padang. Apart from slide volume, the hazard distribution mainly depends on three landslide parameters: distance to Padang, water depth in the generation region, and slide direction.

Wave dispersion study for tsunami propagation in the Sea of Marmara

In this paper the aim is to investigate whether there are differences between the dispersion and non-dispersion solutions on tsunami propagation. For this purpose, two numerical models of tsunami propagation are compared. One of these numerical models is a nondispersive model that uses Saint Venant equations and the other is a dispersive model that uses Boussinesq equations. The tsunamis resulting from a submarine mass failure (SMF) which is settled at the bottom of the north eastern Sea of Marmara are examined. An analytical solution considering wave dispersion is developed for obtaining near-field tsunami amplitudes above the submarine mass failure. Numerical modeling is used at the sea surface from the common boundary called as liquid boundary with incident waves up to the coastal regions to get the tsunami amplitudes. The output of the analytical model is taken as the disturbances for the numerical method. In the numerical solutions TELEMAC-2D software system is used for both dispersive and nondispersive modeling. The results of the dispersive and nondispersive models are compared to each other. Both temporal and spatial differences in the amplitudes and wave shapes are examined. The obtained results demonstrate that there are no noticeable differences between the dispersion and non-dispersion solutions except some special cases and some special landslide velocities.

Field measurements and numerical simulations of the 2004 tsunami impact on the south coast of Sri Lanka

This paper examines the factors that have contributed to the significant spatial variability of the impact of the December 2004 tsunami in the southern province of Sri Lanka. Documented observations of the evidence left behind by the 2004 tsunami together with numerical simulation of tsunami propagation have been utilized for this purpose. The field data examined in the present analysis comprise the maximum water levels, the horizontal inundation distances and the number of housing and other buildings damaged as a result of the 2004 tsunami whilst the numerical results considered include the distribution of the amplitude of the tsunami. The present model results confirm that source directivity controls the distribution of tsunami amplitudes farther offshore whilst large-scale bathymetric features significantly influence the tsunami propagating over the shelf. Our analyses of field data also show the dominant influence of coastal geomorphology and topography on the extent of tsunami inundation.

Near‐field tsunami forecasting from cabled ocean bottom pressure data

We propose a method for near‐field tsunami forecasting from data acquired by cabled offshore ocean bottom tsunami meters (OBTMs) in real time. We first invert tsunami waveforms recorded at OBTMs to estimate the spatial distribution of initial sea‐surface displacements in the tsunami source region without making any assumptions about fault geometry and earthquake magnitude. Then, we synthesize the coastal tsunami waveforms from the estimated sea‐surface displacement distribution. To improve the reliability of the tsunami forecasting, we use updated OBTM data to repeat the forecast calculation at 1‐min intervals. We tested our method by simulating the 1896 Sanriku tsunami earthquake, which caused a devastating tsunami with maximum runup height of 38 m along the Pacific coast of northeastern Japan. Instead of real OBTM records, proxies were used. The simulation demonstrated that our method provided accurate estimations of coastal arrival times and amplitudes of the first peak of the tsunami more than 20 min before the maximum amplitude wave reached the coastal site nearest to the source. We also applied the method to real data of a small tsunami that was caused by a local earthquake and successfully forecasted the tsunami at coastal tide stations. We found that accuracy of our estimated coastal tsunami amplitudes can be affected by the spatial relationship between the tsunami source and the offshore observation stations. Our numerical simulation showed that even more accurate tsunami amplitude forecasts would be achieved by deployment of additional offshore stations separated by a distance comparable to the trench‐parallel length of the tsunami source.

TSUNAMI AMPLIFICATION ALONG THE EASTERN COAST OF INDIA AND SRI LANKA DUE TO EARTHQUAKE RUPTURE PROPAGATION IN THE SUMATRA-NICOBAR-ANDAMAN TRENCHES

We investigated an effect of earthquake rupture propagation, or tsunami source propagation, on offshore tsunami amplitude through numerical simulations. In the numerical simulations, we used satellite-based real bathymetry and a realistic fault configuration for M9 class great earthquakes, and we allowed an earthquake rupture to propagate one-dimensionally in the long-axis direction of the fault. Various earthquake rupture velocities as well as various fault lengths were tested. A general feature is that the slower the earthquake rupture velocity, the larger the tsunami amplitude. This suggests that the effect of earthquake rupture propagation cannot be neglected for most of tsunamis generated by slow earthquakes. Along the eastern coast of India and Sri Lanka, however, earthquake rupture propagation makes tsunami amplification behaviors complicated and varied from station to station. This is because amplification of offshore tsunami is controlled by source configuration and bathymetry as well as rupture velocity.

A Great Earthquake Rupture Across a Rapidly Evolving Three-Plate Boundary

On 1 April 2007 a great, tsunamigenic earthquake (moment magnitude 8.1) ruptured the Solomon Islands subduction zone at the triple junction where the Australia and Solomon Sea-Woodlark Basin plates simultaneously underthrust the Pacific plate with different slip directions. The associated abrupt change in slip direction during the great earthquake drove convergent anelastic deformation of the upper Pacific plate, which generated localized uplift in the forearc above the subducting Simbo fault, potentially amplifying local tsunami amplitude. Elastic deformation during the seismic cycle appears to be primarily accommodated by the overriding Pacific forearc. This earthquake demonstrates the seismogenic potential of extremely young subducting oceanic lithosphere, the ability of ruptures to traverse substantial geologic boundaries, and the consequences of complex coseismic slip for uplift and tsunamigenesis.