Vasily V. Titov

Extreme inundation flows during the Hokkaido-Nansei-Oki Tsunami

The tsunami generated by the July 12, 1993 Hokkaido-Nansei-Oki Mw=7.8 earthquake produced in Japan the worst local tsunami-related death toll in fifty years, with estimated 10–18m/sec overland flow velocities and 30m runup. These extreme values are the largest recorded in Japan this century and are among the highest ever documented for non-landslide generated tsunamis. We model this event to confirm the estimated overland flow velocities, and we find that, given reasonable ground deformation data, current state-of-the-art shallow-water wave models can predict tsunami inundation correctly including extreme runup, current velocities and overland flow. We find that even small local topographic structures affect the runup to first-order, and that the resolution of the bathymetric data is more important than the grid resolution. Our results qualitatively suggest that—for this event—coastal inundation is more correlated with inundation velocities than with inundation heights, explaining also why threshold-type modeling has substantially underpredicted coastal inundation for this and other recent events.

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

[1] 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.

Tsunami: scientific frontiers, mitigation, forecasting and policy implications

Tsunamis are an ever-present threat to lives and property along the coasts of most of the worlds oceans. As the Sumatra tsunami of 26 December 2004 reminded the world, we must be more proactive in developing ways to reduce their impact on our global society. This article provides an overview of the state of knowledge of tsunamis, presents some challenges confronting advances in the field and identifies some promising frontiers leading to a global warning system. This overview is then used to develop guidelines for advancing the science of forecasting, hazard mitigation programmes and the development of public policy to realize a global system. Much of the information on mitigation and forecasting draws upon the development and accomplishments of a joint state/federal partnership that was forged to reduce tsunami hazards along US coastlines—the National Tsunami Hazard Mitigation Programme. By integrating hazard assessment, warning guidance and mitigation activities, the programme has created a roadmap and a set of tools to make communities more resilient to local and distant tsunamis. Among the tools are forecasting, educational programmes, early warning systems and design guidance for tsunami-resilient communities. Information on international cooperation is drawn from the Global Earth Observing System of Systems (GEOSS). GEOSS provides an international framework to assure international compatibility and interoperability for rapid exchange of data and information.

Northwest Sumatra and Offshore Islands Field Survey after the December 2004 Indian Ocean Tsunami

An International Tsunami Survey Team (ITST) conducted field surveys of tsunami effects on the west coast of northern and central Sumatra and offshore islands 3–4 months after the 26 December 2004 tsunami. The study sites spanned 800 km of coastline from Breuh Island north of Banda Aceh to the Batu Islands, and included 22 sites in Aceh province in Sumatra and on Simeulue Island, Nias Island, the Banyak Islands, and the Batu Islands. Tsunami runup, elevation, flow depth, inundation distance, sedimentary characteristics of deposits, near-shore bathymetry, and vertical land movement (subsidence and uplift) were studied. The maximum tsunami elevations were greater than 16 m, and the maximum tsunami flow depths were greater than 13 m at all sites studied along 135 km of coastline in northwestern Sumatra. Tsunami flow depths were as much as 10 m at 1,500 m inland. Extensive tsunami deposits, primarily composed of sand and typically 5–20 cm thick, were observed in northwestern Sumatra.

Smong: How an Oral History Saved Thousands on Indonesia's Simeulue Island during the December 2004 and March 2005 Tsunamis

The tsunamis on 26 December 2004 and 28 March 2005 killed only 7 people on Simeulue Island in Indonesias Aceh province. At Langi, on the north end of Simeulue, which is 40 km south of the December earthquakes epicenter, maximum wave heights exceeded 10 m less than 10 minutes after the shaking ceased. In the more populous south, wave heights averaged 3 m and caused significant structural damage, destroying entire villages. Oral histories recount a massive 1907 tsunami and advise running to the hills after “significant” shaking (∼1 minute). All the interviewed Simeulue survivors knew of this event and of the necessary action. However, Jantang, on the Aceh mainland, suffered far more casualties. Simeulues oral history provided an extraordinarily powerful mitigation tool that saved countless lives where even a high-tech warning system with a 15-minute response time would have been of no help.

Implications of the 26 December 2004 Sumatra–Andaman Earthquake on Tsunami Forecast and Assessment Models for Great Subduction-Zone Earthquakes

Results from different tsunami forecasting and hazard assessment mod- els are compared with observed tsunami wave heights from the 26 December 2004 Indian Ocean tsunami. Forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation. An empirical forecast relationship based only on seismic moment provides a close estimate to the observed mean regional and maximum local tsunami runup heights for the 2004 Indian Ocean tsunami but underestimates mean regional tsunami heights at azimuths in line with the tsunami beaming pattern (e.g., Sri Lanka, Thailand). Standard forecast models developed from subfault discretization of earthquake rupture, in which deep- ocean sea level observations are used to constrain slip, are also tested. Forecast models of this type use tsunami time-series measurements at points in the deep ocean. As a proxy for the 2004 Indian Ocean tsunami, a transect of deep-ocean tsunami amplitudes recorded by satellite altimetry is used to constrain slip along four subfaults of the M 9 Sumatra-Andaman earthquake. This proxy model performs well in comparison to observed tsunami wave heights, travel times, and inundation patterns at Banda Aceh. Hypothetical tsunami hazard assessments models based on end- member estimates for average slip and rupture length (M w 9.0-9.3) are compared with tsunami observations. Using average slip (low end member) and rupture length (high end member) (M w 9.14) consistent with many seismic, geodetic, and tsunami inversions adequately estimates tsunami runup in most regions, except the extreme runup in the western Aceh province. The high slip that occurred in the southern part of the rupture zone linked to runup in this location is a larger fluctuation than expected from standard stochastic slip models. In addition, excess moment release (9%) deduced from geodetic studies in comparison to seismic moment estimates may gen- erate additional tsunami energy, if the exponential time constant of slip is less than approximately 1 hr. Overall, there is significant variation in assessed runup heights caused by quantifiable uncertainty in both first-order source parameters (e.g., rupture length, slip-length scaling) and spatiotemporal complexity of earthquake rupture.

Differences in tsunami generation between the December 26, 2004 and March 28, 2005 Sumatra earthquakes

Source parameters affecting tsunami generation and propagation for the Mw > 9.0 December 26, 2004 and the Mw = 8.6 March 28, 2005 earthquakes are examined to explain the dramatic difference in tsunami observations. We evaluate both scalar measures (seismic moment, maximum slip, potential energy) and finite-source representations (distributed slip and far-field beaming from finite source dimensions) of tsunami generation potential. There exists significant variability in local tsunami runup with respect to the most readily available measure, seismic moment. The local tsunami intensity for the December 2004 earthquake is similar to other tsunamigenic earthquakes of comparable magnitude. In contrast, the March 2005 local tsunami was deficient relative to its earthquake magnitude. Tsunami potential energy calculations more accurately reflect the difference in tsunami severity, although these calculations are dependent on knowledge of the slip distribution and therefore difficult to implement in a real-time system. A significant factor affecting tsunami generation unaccounted for in these scalar measures is the location of regions of seafloor displacement relative to the overlying water depth. The deficiency of the March 2005 tsunami seems to be related to concentration of slip in the down-dip part of the rupture zone and the fact that a substantial portion of the vertical displacement field occurred in shallow water or on land. The comparison of the December 2004 and March 2005 Sumatra earthquakes presented in this study is analogous to previous studies comparing the 1952 and 2003 Tokachi-Oki earthquakes and tsunamis, in terms of the effect slip distribution has on local tsunamis. Results from these studies indicate the difficulty in rapidly assessing local tsunami runup from magnitude and epicentral location information alone.

FIELD SURVEY OF MEXICAN TSUNAMI PRODUCES NEW DATA, UNUSUAL PHOTOS

On October 9, 1995, an earthquake of Mw = 8.0 shook the Pacific coast of central Mexico. Centered offshore of the states of Jalisco and Colima, the earthquake caused extensive damage near Manzanillo and was felt strongly in Mexico City. Approximately 40 people were killed and about 100 injured, and many hotels and tall buildings were destroyed or severely damaged. The earthquake also set off a moderate tsunami that affected approximately 200 km of coastline and sent tsunami run-up ranging from 1 to 5 m from north of Playa de Cuyatlan to south of Tenacatita Bay. In regions with steep onshore topography, the damage was minor, but along the shallowest beaches, the damage was severe.

Tsunami Forecast by Joint Inversion of Real-Time Tsunami Waveforms and Seismic or GPS Data: Application to the Tohoku 2011 Tsunami

Correctly characterizing tsunami source generation is the most critical component of modern tsunami forecasting. Although difficult to quantify directly, a tsunami source can be modeled via different methods using a variety of measurements from deep-ocean tsunameters, seismometers, GPS, and other advanced instruments, some of which in or near real time. Here we assess the performance of different source models for the destructive 11 March 2011 Japan tsunami using model–data comparison for the generation, propagation, and inundation in the near field of Japan. This comparative study of tsunami source models addresses the advantages and limitations of different real-time measurements with potential use in early tsunami warning in the near and far field. The study highlights the critical role of deep-ocean tsunami measurements and rapid validation of the approximate tsunami source for high-quality forecasting. We show that these tsunami measurements are compatible with other real-time geodetic data, and may provide more insightful understanding of tsunami generation from earthquakes, as well as from nonseismic processes such as submarine landslide failures.

Effects of Tides on Maximum Tsunami Wave Heights: Probability Distributions*

A theoretical study was carried out to understand how the probability distribution for maximum wave heights (m) during tsunamis depends on the initial tsunami amplitude (A) and the tides. It was assumed that the total wave height is the linear sum of the tides and tsunami time series in which the latter is decaying exponentially in amplitude with an e-folding time of 2.0 days, based on the behavior of observed Pacificwide tsunamis. Direct computations were made to determine the statistics of maximum height for a suite of different arrival times and initial tsunami amplitudes. Using predicted tides for 1992 when the lunar nodal f factors were near unity during the present National Tidal Datum Epoch 1983–2001, the results show that when A is small compared with the tidal range the probability density function (PDF) of the difference m A is closely confined in height near mean higher high water (MHHW). The m A PDF spreads in height and its mean height o A decreases, approaching the PDF of the tides and MSL, respectively, when A becomes large compared with the tidal range. A Gaussian form is found to be a close approximation to the m A PDF over much of the amplitude range; associated parameters for 30 coastal stations along the U.S. West Coast, Alaska, and Hawaii are given in the paper. The formula should prove useful in probabilistic mapping of coastal tsunami flooding.