Modeling of the Tohoku-Oki 2011 Tsunami Generation, Far-Field and Coastal Impact: A Mixed Co-Seismic and SMF Source (original) (raw)
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2015
Tsunami hazard assessment for future megathrust earthquakes requires that we understand the source mechanisms and tsunami generation processes for large historical events, such as the devastating Tohoku-oki tsunami of March 11th 2011. Although associated with a Magnitude 9 earthquake, simulations of the tsunami based solely on this co-seismic source do not reproduce the elevated runup heights of 40 m along the coast of northern Honshu, nor the wave timing and high frequency wave periods recorded at offshore GPS and DART buoys. Here, we show that an additional tsunami source associated with a large submarine mass failure (SMF), triggered North-East of the main source after a 2 min. delay, satisfies the necessary observations. To do so, we model the tsunami sourced from both earthquake and SMF. This dual source reproduces both the recorded onshore runups and the wave heights and wave frequencies recorded at offshore buoys. The significant contribution from an SMF to the Tohoku-oki tsu...
2016
The devastating coastal impact of the 2011 Tohoku-oki tsunami cannot at present be fully explained from a co-seismic source alone, because resulting tsunami simulations do not reproduce the elevated tsunami runup heights of up to 40 m along the (Sanriku) coast of northern Honshu, nor the higher frequency wave periods (3-4 min.) recorded at offshore buoys (both GPS and DART). Here, we model the tsunami generated from the combination of: (i) a new co-seismic source based on a detailed three-dimensional (3D) Finite Element Modeling (FEM) of the heterogeneous subduction zone, with geodetic data assimilation (Grilli et al., 2012a,b; Masterlark 2003, Masterlark and Hugue, 2008); and (ii) an additional tsunami source from a submarine mass failure (SMF) triggered north of the main rupture with a time delay. We show that the multi-source tsunami agrees well with all the available field observations, both offshore and onshore. Both co-seismic and SMF sources are first modeled for 300 s in a 1...
Pure and Applied Geophysics, 2013
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 farand 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 nonhydrostatic 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.
Source Mechanism and Near-field Characteristics of the 2011 Tohoku-oki Tsunami
AGU Fall Meeting Abstracts, 2011
The Tohoku-oki great earthquake ruptured the megathrust fault offshore of Miyagi and Fukushima in Northeast Honshu with moment magnitude of Mw 9.0 on March 11, 2011, and generated strong shaking across the region. The resulting tsunami devastated the northeastern Japan coasts and damaged coastal infrastructure across the Pacific. The extensive global seismic networks, dense geodetic instruments, well-positioned buoys and wave gauges, and comprehensive runup records along the northeast Japan coasts ...
2012
The March 11, 2011 M9 Tohoku-Oki Earthquake, which is believed to be the largest event recorded in Japanese history, created a major tsunami that caused numerous deaths and enormous destruction on the nearby Honshu coast. Various tsunami sources were developed for this event, based on inverting seismic or GPS data, often using very simple underlying fault models (e.g., . Tsunami simulations with such sources can predict deep water and far-field observations quite well, but coastal impact is not as well predicted, being over-or under-estimated at many locations. In this work, we developed a new tsunami source, similarly based on inverting onshore and offshore geodetic (GPS) data, but using 3D Finite Element Models (FEM) that simulate elastic dislocations along the plate boundary interface separating the stiff subducting Pacific Plate, and 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 along the updip portion of the rupture near the trench (several tens of meters).
2011
This study was undertaken with reference to the J apan earthquake of 11 March 2011. The aim of the study is to simulate the wave propagation of the tsunami of this earthquake, by comparing with the available deep ocean pressure se nsors (DART) and tide gauge records. Nonlinear shallow water equations are solved with a finite di fference scheme, using a computational grid with different cell sizes over GEBCO30 bathymetry data. Co-seismic source models proposed by different organizations and researchers were carried out to e xplain the tsunami propagation. The source models were used to model the deformation on sea bottom which is translated directly to the water surface. The approach is based on the dislocation algorithm for a finite rectangular fault and empirical scalin g laws for earthquake sources. Based on the various s ource models, arrival times and maximum wave heights are presented here followed by the analysis of the results. The assumption of the average uniform slip model...
Earth, Planets and Space, 2011
Finite-source rupture models for the great 11 March 2011 off the Pacific coast of Tohoku (M w 9.0) Earthquake obtained by inversions of seismic waves and geodetic observations are used to reconstruct deep-water tsunami recordings from DART buoys near Japan. One model is from least-squares inversion of teleseismic P waves, and another from iterative least-squares search-based joint inversion of teleseismic P waves, short-arc Rayleigh wave relative source time functions, and high-rate GPS observations from northern Honshu. These rupture model inversions impose similar kinematic constraints on the rupture growth, and both have concentrations of slip of up to 42 m up-dip from the hypocenter, with substantial slip extending to the trench. Tsunami surface elevations were computed using the model NEOWAVE, which includes a vertical momentum equation and a non-hydrostatic pressure term in the nonlinear shallow-water equations to account for the time-history of seafloor deformation and propagation of weakly dispersive tsunami waves. Kinematic seafloor deformations were computed using the Okada solutions for the rupture models. Good matches to the tsunami arrival times and waveforms are achieved for the DART recordings for models with slip extending all the way to the trench, whereas shifting fault slip toward the coast degrades the predictions.
Japan's 2011 Tsunami: Characteristics of Wave Propagation from Observations and Numerical Modelling
Pure and Applied Geophysics, 2012
We use a numerical tsunami model to describe wave energy decay and transformation in the Pacific Ocean during the 2011 Tohoku tsunami. The numerical model was initialised with the results from a seismological finite fault model and validated using deep-ocean bottom pressure records from DARTs, from the NEPTUNE-Canada cabled observatory, as well as data from four satellite altimetry passes. We used statistical analysis of the available observations collected during the Japan 2011 tsunami and of the corresponding numerical model to demonstrate that the temporal evolution of tsunami wave energy in the Pacific Ocean leads to the wave energy equipartition law. Similar equipartition laws are well known for wave multi-scattering processes in seismology, electromagnetism and acoustics. We also show that the long-term near-equilibrium state is governed by this law: after the passage of the tsunami front, the tsunami wave energy density tends to be inversely proportional to the water depth. This fact leads to a definition of tsunami wave intensity that is simply energy density times the depth. This wave intensity fills the Pacific Ocean basin uniformly, except for the areas of energy sinks in the Southern Ocean and Bering Sea.