Far-field Tsunami Research Articles

NUMERICAL STUDY OF MORPHOLOGICAL CHANGES BY FAR-FIELD TSUNAMI IMPACTS

In this study, we present an integrated numerical model for sedimentation by long waves and also investigate morphological changes by far-field tsunami impacts. A set of models, each of which is responsible for hydrodynamics, sediment transport and morphological evolutions, are introduced with a basic concept of morphodynamic physics and are fully connected through two-way approach. Finite volume scheme, which turns out to be stable and suitable for long-term(more than 10 hours) tsunami simulations is used in the numerical discretization. An accuracy and applicability of developed model is evaluated through numerical tests covering one-dimensional or two-dimensional sedimentation problems in the shallow region. Then, we applied developed model to a field-scale tsunami, which had caused a significant bathymetric changes in harbors.

Bayesian inversion for finite fault earthquake source models – II: the 2011 great Tohoku-oki, Japan earthquake

We present a fully Bayesian inversion of kinematic rupture parameters for the 2011 M_w 9 Tohoku-oki, Japan earthquake. Albeit computationally expensive, this approach to kinematic source modelling has the advantage of producing an ensemble of slip models that are consistent with physical a priori constraints, realistic data uncertainties, and realistic but simplistic uncertainties in the physics of the kinematic forward model, all without being biased by non-physical regularization constraints. Combining 1 Hz kinematic GPS, static GPS offsets, seafloor geodesy and near-field and far-field tsunami data into a massively parallel Monte Carlo simulation, we construct an ensemble of samples of the posterior probability density function describing the evolution of fault rupture. We find that most of the slip is concentrated in a depth range of 10–20 km from the trench, and that slip decreases towards the trench with significant displacements at the toe of wedge occurring in just a small region. Estimates of static stress drop and rupture velocity are ambiguous. Due to the spatial compactness of the fault rupture, the duration of the entire rupture was less than approximately 150 s.

Observed and Modeled Currents from the Tohoku-oki, Japan and other Recent Tsunamis in Northern California

We investigate the currents produced by recent tsunamis in Humboldt Bay and Crescent City, California. The region is susceptible to both near-field and far-field tsunamis and has a historic record of damaging events. Crescent City Harbor, located approximately 100 kms north of Humboldt Bay, suffered US $28 million in damages from strong currents produced by the 2006 Kuril Islands tsunami and an additional US $26 million from the 2011 Japan tsunami. In order to better evaluate these currents in northern California, we deployed a Nortek Aquadopp 600 kHz 2D acoustic Doppler current profiler (ADCP) with a 1-min sampling interval in Humboldt Bay, near the existing National Oceanic and Atmospheric Administration (NOAA) National Ocean Service (NOS) tide gauge station. The instrument recorded the tsunamis produced by the Mw 8.8 Chile earthquake on February 27, 2010 and the Mw 9.0 Japan earthquake on March 11, 2011. One other tsunami was recorded on the Humboldt Bay tide gauge during the period of ADCP operation, but was not visible on the ADCP, suggesting a threshold water level value of about 0.2 m to produce an observable ADCP record. The 2010 tsunami currents persisted in Humboldt Bay for approximately 30 h with peak amplitudes of about 0.35 m/s. The 2011 tsunami signal lasted for over 40 h with peak amplitude of 0.84 m/s. The strongest currents corresponded to the maximum change in water level approximately 67 min after the initial wave arrival. No damage was observed in Humboldt Bay for either event. In Crescent City, currents for the first three and one-half hours of the 2011 Japan tsunami were estimated using security camera video footage from the Harbor Master, approximately 70 m away from the NOAA–NOS tide gauge station. The largest amplitude tide gauge water-level oscillations and most of the damage occurred within this time window. The currents reached a velocity of approximately 4.5 m/s and six cycles exceeded 3 m/s during this period. Measured current velocities both in Humboldt Bay and in Crescent City were compared to calculated velocities from the Method of Splitting Tsunamis (MOST) numerical model. The frequency and pattern of current amplification and decay at both locations are replicated by the MOST model for the first several hours after the tsunami onset. MOST generally underestimates 2011 peak current velocities by about 10–30 %, with a few peaks by as much as 50 %. At Humboldt Bay, MOST predicted attenuation of the signal after 4 h but the actual signal persisted at a nearly constant level for at least twice as long. The results from this project demonstrate that ADCPs can effectively record tsunami currents for small to moderate events and can be used to calibrate and validate models (i.e., MOST) in order to better understand hazardous tsunami conditions within harbors.

The El Salvador and Philippines Tsunamis of August 2012: Insights from Sea Level Data Analysis and Numerical Modeling

We studied two tsunamis from 2012, one generated by the El Salvador earthquake of 27 August (Mw 7.3) and the other generated by the Philippines earthquake of 31 August (Mw 7.6), using sea level data analysis and numerical modeling. For the El Salvador tsunami, the largest wave height was observed in Baltra, Galapagos Islands (71.1 cm) located about 1,400 km away from the source. The tsunami governing periods were around 9 and 19 min. Numerical modeling indicated that most of the tsunami energy was directed towards the Galapagos Islands, explaining the relatively large wave height there. For the Philippines tsunami, the maximum wave height of 30.5 cm was observed at Kushimoto in Japan located about 2,700 km away from the source. The tsunami governing periods were around 8, 12 and 29 min. Numerical modeling showed that a significant part of the far-field tsunami energy was directed towards the southern coast of Japan. Fourier and wavelet analyses as well as numerical modeling suggested that the dominant period of the first wave at stations normal to the fault strike is related to the fault width, while the period of the first wave at stations in the direction of fault strike is representative of the fault length.

From earthquake size to far-field tsunami amplitude: development of a simple formula and application to DART buoy data

From earthquake size to far-field tsunami amplitude: development of a simple formula and application to DART buoy data

The October 28, 2012 Mw 7.8 Haida Gwaii underthrusting earthquake and tsunami: Slip partitioning along the Queen Charlotte Fault transpressional plate boundary

The Pacific/North American plate boundary is undergoing predominantly right-lateral strike–slip motion along the Queen Charlotte and Fairweather transform faults. The Queen Charlotte Fault (QCF) hosted the largest historical earthquake in Canada, the 1949 MS 8.1 strike–slip earthquake, which ruptured from offshore northern Haida Gwaii several hundred kilometers northwestward. On January 5, 2013 an Mw 7.5 strike–slip faulting event occurred near the northern end of the 1949 rupture zone. Along central and southern Haida Gwaii the relative plate motion has ∼20% oblique convergence across the left-stepping plate boundary. There had been uncertainty in how the compressional component of plate motion is accommodated. The October 28, 2012 Mw 7.8 Haida Gwaii earthquake involved slightly (∼20°) oblique thrust faulting on a shallow (∼18.5°) northeast-dipping fault plane with strike (∼320°) parallel to the QCF, consistent with prior inferences of Pacific Plate underthrusting beneath Haida Gwaii. The rupture extended to shallow depth offshore of Moresby Island beneath a 25–30km wide terrace of sediments that has accumulated in a wedge seaward of the QCF. The shallow thrusting caused seafloor uplift that generated substantial localized tsunami run-up and a modest far-field tsunami that spread across the northern Pacific, prompting a tsunami warning, beach closure, and coastal evacuation in Hawaii, although ultimately tide gauges showed less than 0.8m of water level increase. The mainshock rupture appears to have spread with a ∼2.3km/s rupture velocity over a length of ∼150km, with slip averaging 3.3m concentrated beneath the sedimentary wedge. The event was followed by a substantial aftershock sequence, in which almost all of the larger events involve distributed intraplate normal faulting extending ∼50km oceanward from the QCF. The highly oblique slip partitioning in southern Haida Gwaii is distinctive in that the local plate boundary-parallel motion on the QCF may be accommodated either by infrequent large strike–slip ruptures or by aseismic creep, as seems to be the case for deeper oblique relative plate motion beneath Haida Gwaii, while the sedimentary terrace accumulates plate boundary-perpendicular compressional strain that releases in almost pure thrust faulting earthquakes, seaward of the QCF.

Widespread deformation of basin-plain sediments in Aysén fjord (Chile) due to impact by earthquake-triggered, onshore-generated mass movements

Abstract The 2007 Mw 6.2 earthquake in Aysen fjord caused widespread basin-plain deformation and has had prehistorical predecessors. Both superficial and buried deformed basin-plain deposits are mapped using multibeam bathymetry and seismic-reflection (sparker) profiling. The seismic signature of the sediment was ground-truthed with short cores on key locations. Deformed basin-plain deposits induced by the 2007 earthquake can be divided in frontally emergent and confined deposits, with both a deep and shallow basal shear surface. All deformed basin-plain deposits with a deep basal shear surface are induced by the weight and impact of a slope-adjacent mass-flow wedge. The frontally emergent – most mobile – basin-plain deformation is triggered by mass flows originating from onshore mass movements (i.e. debris flows, rock slides and avalanches) propagating into the fjord. This basin-plain deformation results in vertical seafloor offsets of up to 20 m. Therefore it might be even more important for far-field tsunami propagation than the impact of the onshore mass movements on the sea surface. In the depressions created by the basin-plain deformation, megaturbidites occur, while more distally, sandy density-flow deposits cover the seafloor. The data also indicates that these density flows propagate slower than the basin-plain deformation. Based on correlations with the two main eruptions of the Hudson Volcano, we hypothesize that during the Holocene three to four similar events have struck the fjord. The small variability of the structural characteristics of the Liquine-Ofqui Fault Zone in the northern Patagonian fjordland and historical seismic swarms in this area make us conclude that similar hazards should be taken into account for most of the fjords in this region.

水の圧縮性と地殻弾性を考慮した津波の分散関係解析：遠地津波予測の精度向上に向けて

水の圧縮性と地殻弾性を考慮した津波の分散関係解析：遠地津波予測の精度向上に向けて

Comparison of the 2010 Chile and 2011 Japan Tsunamis in the Far Field

In this study we analyze water level data from coastal tide gauges and deep-ocean tsunameters to explore the far-field characteristics of two major trans-Pacific tsunamis, the 2010 Chile and the 2011 Japan (Tohoku-oki) events. We focused our attention on data recorded in California (14 stations) and New Zealand (31 stations) as well as on tsunameters situated along the tsunami path and proximal to the study sites. Our analysis considers statistical analyses of the time series to determine arrival times of the tsunami as well as the timing of the largest waves and the highest absolute sea levels. Fourier and wavelet analysis were used to describe the spectral content of the tsunami signal. These characteristics were then compared between the two events to highlight similarities and differences between the signals as a function of the receiving environment and the tsunami source. This study provides a comprehensive analysis of far-field tsunami characteristics in the Pacific Ocean, which has not experienced a major tsunami in nearly 50 years. As such, it systematically describes the tsunami response characteristics of modern maritime infrastructure in New Zealand and California and will be of value for future tsunami hazard assessments in both countries.

Mapping of historical tsunamis in the Indian and Southwest Pacific Oceans

Asia and Southwest Pacific Oceans experienced considerable effects due to tsunamis, including the Indian Ocean event in 2004, many local events along the Indonesian coast in 2005, 2006 and 2010, and the tsunami in Japan in 2011. This study started by collecting an assessment of the earthquake return periods and their tsunamigenic ratios. Previous studies show that recurrence of Mw 7.5, 8.0, 8.5 and 9.0 earthquakes are 20–50, 60–120, 200–300 and 450–650 years and Mw 7.5 and Mw 8.0 earthquake has potential of 0.5 and 0.8 to generate a tsunami. Historical tsunamis were selected to characterize the tsunami hazards in this region. A total of 30 tsunami scenarios were selected from 110 possible historical events that occurred within the last 400 years for a far-field tsunami simulation. The simulation calculated the maximum tsunami heights along shoreline that were subsequently evaluated based on reported survey data. Simulated results showed that Japan faced the highest levels of local tsunami impacts, followed by Indonesia, the Philippines and Papua New Guinea. Local tsunamis were not observed in Thailand, Sri Lanka and India, although these areas were greatly affected by the devastating event in 2004. China and Taiwan were affected by local tsunamis and tsunamis that occurred in Japan. Other countries in the South China Sea, such as Vietnam, Malaysia, and Singapore, had comparatively small impacts due to their geographical locations. The maximum tsunami height map developed here will improve our understanding of the general impacts of historical tsunamis in Asian and Southwest Pacific countries.

TSUNAMI HAZARD AND CASUALTY ESTIMATION IN A COASTAL AREA THAT NEIGHBORS THE INDIAN OCEAN AND SOUTH CHINA SEA

In the Indian Ocean and the South China Sea, many hundreds of thousands of lives have been lost due to tsunami events, and almost half of the lives lost occurred following the 2004 Indian Ocean event. Potential tsunami case scenarios have been simulated in these regions by a number of researchers to calculate the hazard level. The hazard level is based on a variety of conditions, such as the tsunami height, the inundation area, and the arrival time. However, the current assessments of the hazard levels do not focus on the tsunami risk to a coastal population. This study proposes a new method to quantify the risk to the coastal population in the region that includes the Indian Ocean and the South China Sea. The method is simple and combines the use of readily available tsunami data, far-field tsunami simulation models to determine the regional risk and global population data. An earthquake-generated tsunami was simulated, following an earthquake that had a magnitude larger than 8.5 Mwand occurred along a potential subduction zone. The 2004 Indian Ocean event seemed to be a "worst case scenario"; however, it has been estimated that a potential tsunami, occurring in a coastal region with a high population density, could cause significantly greater casualties.

PROBABILISTIC TSUNAMI HAZARD ANALYSIS AND RISK TO COASTAL POPULATIONS IN THAILAND

The study of tsunami hazards in Thailand has been an ongoing topic of research. However, the hazards from tsunami sources based on probabilistic study and population risk are still unclear. In this study, potential tsunami sources along rupture zones were selected. A series of far-field tsunami simulations were performed with scaled fault parameters based on fault lengths from 100–600 km. The results show that within a few centuries, the maximum tsunami height could be 2–5 m at the west coast and less than 2 m at the east coast. The potential tsunami exposure (PTE) of populations in an estimated inundation zone was calculated using global population data in relation to tsunami height. The results show that much attention should be paid to fault ruptures longer than 300 km (≈ 8.5 moment magnitude, Mw) that originate from 4°–6° N and 14°–17° N for the Sumatra subduction zone and the Manila trench, respectively. A quarter of a million people are at risk of exposure to a maximum 9 m tsunami height after 100 min of the arrival of the first wave at the Andaman coast. One million people near the Gulf of Thailand are at risk of a tsunami height less than 3 m after 9 hr.

Far-field impact and coastal sedimentation associated with the 2006 Java tsunami in West Australia

A detailed assessment of the impact of a far-field tsunami on the Australian coastline was carried out in the Steep Point region of Western Australia following the July 17 2006 Java tsunami. Tsunami inundation and run-up were mapped on the basis of eyewitness accounts, debris lines, vegetation damage and the occurrence of recently deposited fish, starfish, corals and sea urchins well above high-tide mark. A topographic survey using kinematic GPS with accuracies of 0.02 m in the horizontal and 0.04 m in the vertical recorded flow depths of between 1 and 2 m, inundation of up to 200 m inland, and a maximum recorded run-up of 7.9 m AHD (Australian Height Datum). The tsunami impacted the sparsely populated Steep Point coastline close to low tide. It caused widespread erosion in the littoral zone, extensive vegetation damage and destroyed several campsites. Eyewitnesses reported three waves in the tsunami wave train, the second being the largest. A sand sheet, up to 14 cm thick and tapering landwards over 200 m, was deposited over coastal dunes. The deposits are predominantly composed of moderately well-sorted, medium-grained carbonate sand with some gravel and organic debris. A basal unconformity defines the boundary between tsunami sediments and underlying aeolian dune sand. Evidence for up to three individual waves is preserved as normally graded sequences mantled by layers of dark grey, organic-rich fine silty sand. Given the strong wind regimes in the area and the similarity of the underlying dune deposits to the tsunami sediments, it is likely that seasonal erosion will remove all traces of these sediment sheets within years to decades.

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

ABSTRACTHistoric‐ 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.

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.

Feasibility of Using Decay Characteristics on Trends and Fluctuations of Tsunami for Forecasting Far-field Tsunami

Feasibility of Using Decay Characteristics on Trends and Fluctuations of Tsunami for Forecasting Far-field Tsunami

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.

Analysis of the Tsunami Generated by the Great 1977 Sumba Earthquake that Occurred in Indonesia

Abstract The great outer-rise earthquake ( M w 8.3) occurred near the Sunda trench, Indonesia, on 19 August 1977. The earthquake has been previously studied using seismological data. The earthquake generated a large tsunami that caused severe damage in Sumbawa and Sumba Islands in Indonesia. The tsunami was also observed at tide gauges in Australia. We numerically computed a far-field tsunami, and we compared the observed tsunami waveforms on three tide gauges with the computed waveforms. We also numerically computed the tsunami inundation and compared the observed tsunami run-up of 8 m and tsunami inundation distance of 500 m in Lunyuk on Sumbawa Island with the computed ones. To explain the observed tsunami waveforms, tsunami run-up, and tsunami inundation distance, the slip amount is found to be 3 m on the assumed fault model (with a fault length of 200 km and fault width of 70 km). The rigidity is assumed to range between 6.0 and 6.8×10 10 N m -2 , and the range of the total seismic moment is calculated to be between 2.5 and 2.9×10 21 N m ( M w 8.2), which is similar to those estimated by the previous seismological studies. Additionally, we calculated the ratio between the observed tsunami run-up and the computed maximum tsunami height along the coastline of Lunyuk. This ratio, called the amplification factor, may possibly be used to roughly estimate the tsunami run-up from a tsunami numerical calculation result on a coarse grid system.

The tsunami of 2007 September 12, Bengkulu province, Sumatra, Indonesia: post-tsunami field survey and numerical modelling

SUMMARY The M w = 8.4 earthquake on 2007 September 12, offshore of the Bengkulu province of Sumatra, Indonesia, generated a moderate tsunami with run-up heights of up to 4 m as measured by Indonesian and international researchers in the days following the earthquake. The tsunami was observed along 250 km of coastline and caused damage at several locations. The largest wave heights and most severe inundation were observed about 50 km to the northwest of Bengkulu; elsewhere the effects were less severe—with the exception of substantial inundation at a site 150 km to the south. In addition to presenting the field data, we conduct a modelling study and compare the run-up heights and water-level predictions from four different seismic deformation models used to initialize a tsunami propagation and inundation model. Our comparative results suggest that, for this event, the estimates of fault parameters available immediately after determination of the earthquake size and location predicted the near-field run-up heights and distribution and far-field wave equally well as estimates obtained using more detailed descriptions of the seafloor deformation, as typically available hours or days after an event. We conclude that while detailed slip patterns can be important to the near-field run-up distribution, simple fault models can be used to rapidly assess the likely near- and far-field tsunami effects of a particular earthquake.

Feasibility of Using Tsunami Coda and Envelope for Forecasting Far-field Tsunami - Their Definitions and Application to 2006 Kuril Island Earthquake Tsunami -

As the first step toward forecasting the decay process of far-field tsunamis, we have introduced the concept of using and codas as measures in this paper. We applied these measures to the tsunami waveform data of the 2006 Kuril Island earthquake tsunami observed using tide gauges located in Japan. Analytical results indicate that the tsunami coda envelopes decayed exponentially with time and that the fluctuation in the nondimensional wave amplitude was interpreted by the Rayleigh distribution. Further, we found that these characteristics were commonly observed in the region facing the Pacific Ocean. Thus, the two measures can be used to reveal the characteristics of the tsunami decay process, and applying them to tsunami waveforms in realtime might realize appropriate cancelation of tsunami warnings.