Modeling near-field tsunami observations to improve finite-fault slip models for the 11 March 2011 Tohoku earthquake

The massive tsunami generated by the 11 March 2011 Tohoku earthquake (M_w 9.0) was widely recorded by GPS buoys, wave gauges, and ocean bottom pressure sensors around the source. Numerous inversions for finite-fault slip time histories have been performed using seismic and/or geodetic observations, yielding generally consistent patterns of large co-seismic slip offshore near the hypocenter and/or up-dip near the trench, where estimated peak slip is ~60 m. Modeling the tsunami generation and near-field wave processes using two detailed rupture models obtained from either teleseismic P waves or high-rate GPS recordings in Japan allows evaluation of how well the finite-fault models account for the regional tsunami data. By determining sensitivity of the tsunami calculations to rupture model features, we determine model modifications that improve the fit to the diverse tsunami data while retaining the fit to the seismic and geodetic observations

Frequency banded wave characteristic observed by GPS buoys off the Pacific coast of Japan

Fifteen GPS buoys, which measure the vertical motion of the buoy due to waves and tides by the RTKGPS technology, are moored at a spot of 100-400 m in water depth and within 10-20 km from the shoreline around the Japanese coast. They are the newest equipment on the Nationwide Ocean Wave Information Network for Port and Harbours (NOWPHAS). This study conducted the statistical analysis on four frequency banded wave components (short-period wind wave, long-period wind wave, swell and infra-gravity wave) acquired by the GPS buoys and their nearby coastal wave gauges. A high correlation was found in these frequency banded wave heights, in particular two long period components between a GPS buoy and its nearby coastal wave gauge. The correlation between the long period wave component heights and the significant wave height at the GPS buoys is high, while the ratio of the swell height to the significant wave height varies with the incident wave direction and the meteorological conditions. The\ud swell direction sometimes differs from the wind wave direction. The ratio of the swell height to the significant wave height in the entire band varies around the time when the significant wave height reached its maximum during the 2009 Typhoon Melor event

OBSERVATION OF A STORMY WAVE FIELD WITH X-BAND RADAR AND ITS LINEAR ASPECTS

An X-band nautical radar system was employed to observe the wave field during a stormaround the research pier HORS in Hasaki, Japan. The radar system provides instantaneousdistributions of wave crests in the near-shore region, with image sequences comprising aclear spatial and temporal variation of the wave pattern. The spectra of radar echo signalsand water surface elevations from wave gauge records were compared, and a relatively highcoherence for a particular bandwidth was observed. A sequence of radar images was filteredat the dominant frequency, which was used to estimate the wavenumber distribution of therefraction field. The Fast Fourier Transform (FFT) andMaximum EntropyMethod (MEM)were used to estimate the wavenumbers. The estimated wave angles were then comparedwith linear refraction analyses. The water depths along the pier were also estimated usingthe linear dispersion relationship and compared with the surveyed depths. The linearestimates of hydrodynamic parameters during the passage of the storm are presentedin this paper to demonstrate the potential of radar measurements in capturing essentialcharacteristics of coastal dynamics

Investigation of ocean wind estimating technique using wave data and SMB method

In the ocean surface, there are many kinds of currents due to tides, wind, wave as well as tsunamis.\ud Especially, wind-driven currents may be important for coastal currents. Wind driven-currents are non-stationary\ud phenomena in time and space. Therefore, the grasps of wind-driven currents are important. It is necessary to observe\ud velocity of currents temporally and spatially due to estimate wind-driven currents. However, it is difficult to observe\ud spatial distributions of current velocity and ocean winds by current meter and anemometer of stationary type. HF radar\ud can be observed spatial distributions of current velocity. Although ocean winds cannot be measured directly by HF\ud radar, it is possible to estimate using wave height, wave period, and the Sverdrup-Munk-Bretschneider???s (SMB) method.\ud In this study, ocean winds were estimated by obtained wave height and period from NOWPHAS and SMB\ud method. This estimated method was examined in seven points (Niigata, Fort No.2, Ashika island, Kobe port, Port of\ud Komatsushima, Sea of Genkai and Kanda). In addition, when this technique was not able to be used, another method\ud was examined. Finally, we proposed other methods that were able to be used at any time

OBSERVATION OF LONGSHORE SEDIMENT FLUX DISTRIBUTION BY RADAR NETWORK

科学研究費助成事業(科学研究費補助金)研究成果報告書：基盤研究(B)2009-2011課題番号：2136023

Estimation of the sea surface drag coefficient based on wave data

The sea surface drag coefficient, an important parameter for the energy transfer process in wave prediction model, is generally expressed by a linear function of wind speed. However, it seems inadequate to apply these equations for strong wind conditions because these equations were deduced from the observational or the\ud experimental data under wind speed of lower than 25m/s at fastest. To solve this problem, a wave prediction model ADWAM which includes a data assimilation method seems effective. For the purpose of clarifying the appropriate values of the sea surface drag coefficient in high wind speed, the ADWAM was modified to estimate the sea surface drag coefficients as its control variables of the model. In this study, the sea surface drag coefficient was deduced from the actual wave observation data. As a results, the sea surface drag coefficient, unknown parameter, was confirmed to\ud be modified from arbitrary initial value to an appropriate value. Also, it was confirmed that the sea surface drag coefficient under stormy condition can be estimated based on the wave data observed outside the storm if the waves propagated from the storm were observed

Stochastic coupled simulation of strong motion and tsunami for the 2011 Tohoku, Japan earthquake

© 2016 The Author(s)This study conducts coupled simulation of strong motion and tsunami using stochastically generated earthquake source models. It is focused upon the 2011 Tohoku, Japan earthquake. The ground motion time-histories are simulated using the multiple-event stochastic finite-fault method, which takes into account multiple local rupture processes in strong motion generation areas. For tsunami simulation, multiple realizations of wave profiles are generated by evaluating nonlinear shallow water equations with run-up. Key objectives of this research are: (i) to investigate the sensitivity of strong motion and tsunami hazard parameters to asperities and strong motion generation areas, and (ii) to quantify the spatial variability and dependency of strong motion and tsunami predictions due to common earthquake sources. The investigations provide valuable insights in understanding the temporal and spatial impact of cascading earthquake hazards. Importantly, the study also develops an integrated strong motion and tsunami simulator, which is capable of capturing earthquake source uncertainty. Such an advanced numerical tool is necessary for assessing the performance of buildings and infrastructure that are subjected to cascading earthquake–tsunami hazards

Verification of shore protection effect of beach nourishment on Chigasaki coast

On a stretch of the Chigasaki coast of 1.4 km length extending between Chigasaki fishing port and Chigasaki artificial headland, beach nourishment using coarse materials has been carried out since 2006. Since the start of beach nourishment, various monitoring surveys have been carried out investigation beach changes and verify the effect of beach nourishment. In this study, various monitoring data such as the narrow-mutibeam survey and photographs of the shoreline taken from a fixed position were analyzed. It was found that the beach width of the coast was significantly increased by beach nourishment, and it was effective