Hiroyasu Kawai

CHARACTERISTICS OF THE 2011 TOHOKU TSUNAMI WAVEFORM ACQUIRED AROUND JAPAN BY NOWPHAS EQUIPMENT

The 2011 Tohoku Tsunami was observed around Japan by NOWPHAS equipment. These devices include GPS buoys which measure water surface levels by real-time kinematic GPS technology and which are moored at sites 10 km to 20 km offshore where water depths range from 100 m to 400 m, seabed wave gauges at depths between 20 m and 60 m, and coastal tide gauges. A GPS buoy moored offshore of Kamaishi Port recorded the first tsunami crest, which rose in two steps and exceeded 6 m approximately 30 min after the earthquake. Data from some sets comprising GPS buoys, nearby seabed wave gauges, and coastal tide gauges determined the extent of the tsunami propagation and amplification on the coast. Resonance caused by the tsunami continued a day or more after the initial tsunami arrival in some stations. A Doppler-type wave directional meter located in the Tokyo Bay entrance acquired data on the vertically uniform distribution of the tsunami current traveling in and out the bay. The tsunami was detected at almost all of the tide gauges around Japan, even in the semi-closed Ariake and Yatsushiro Bays located on the East China Sea coast of the Kyushu region.

2010 Chile and 2011 Tohoku Tsunami Profiles Measured by GPS Buoys and Coastal Wave and Tide Gauges in a Nationwide Ocean Wave Information Network for Ports and Harbors

AbstractThis paper introduces the tide data acquisition and processing procedures in the Nationwide Ocean Wave Information Network for Ports and Harbors (NOWPHAS), especially those for global positioning system (GPS) buoys that measure water surface elevations using real-time kinematic GPS technology at water depths of 100–400 m and 10–20 km from the coastline. It then describes specific features of the 2010 Chile tsunami and the 2011 Tohoku tsunami, including foreshock and main shock profiles, which were measured along the Japanese coast by the NOWPHAS equipment. In the main shock of the 2011 Tohoku tsunami, the GPS buoy at a water depth of 204 m off Kamaishi Bay showed that the first wave crest consisted of primary slow and subsequent quick rises, and exceeded 6 m approximately 30 min after the earthquake occurrence. Some geometrically adjacent sets of GPS buoys, coastal wave gauges, and coastal tide gauges revealed the tsunami propagation and amplification near the coast.

Frequency Banded Wave Characteristic Observed by GPS Buoys off the Pacific Coast of Japan

析する.ただし,徳島海陽沖は2010年から運用が開始さ れているので除外する.GPS波浪計は,ブイの上下・水 平動をRTK-GPSにより1s間隔で計測している.波向は その水平動から共分散法(清水ら,2007)により1°単位 で求めている. NOWPHASのGPS波浪計や沿岸波浪計のデータ処理で は,ゼロアップクロス法による有義波高H1/3,有義波周 期T1/3の他に,周期帯を6つ(f1:32.0s以上,f2:16.0 ~25.6s,f3:10.7~14.2s,f4:8.0s~9.8s,f5:T1~ 7.5s,f6:T2以下,T1,T2:設置水深によって定める境 界周期)に区分し,観測スペクトルの0次モーメントか ら周期帯別波高H1~H6を算出している(永井ら,2001). GPS波浪計による周期帯別の波向は,数値フィルターに より対応する周期帯の水平動を抽出後,共分散法により 求めている.本研究ではそのうち4つ(f1~ f4)の周期 帯について検討を行う.f5,f6は,設置水深により境界 太平洋側のGPS波浪計で観測された沖合の周期帯別波浪特性 Frequency Banded Wave Characteristic Observed by GPS Buoys off the Pacific Coast of Japan

CHARACTERISTICS OF UNUSUAL SEA LEVEL OBSERVED ALONG SOUTHERN KANTO COASTS

銚子漁港 気象庁 銚子 1997~2008年 勝浦 国土地理院 勝浦 1997~2008年 布良 気象庁 館山 1997~2008年 千葉 海洋情報部 千葉 1997~2008年 東京 気象庁 東京 1997~2008年 横浜新港 海洋情報部 横浜 1997~2008年 横須賀 海洋情報部 横浜 1997~2008年 久里浜 港空研 横浜 1997~2008年 油壺 国土地理院 横浜 1997~2008年 真鶴 国土地理院 網代 1999~2008年 初島 国土地理院 網代 1999~2008年 伊東 国土地理院 網代 1997~2008年 岡田 気象庁 大島 1997~2008年 田子 国土地理院 石廊崎 1997~2008年 内浦 気象庁 三島 1997~2008年 南関東沿岸における異常潮位の出現特性 CHARACTERISTICS OF UNUSUAL SEA LEVEL OBSERVED ALONG SOUTHERN KANTO COASTS

Development of A Simplified Method for Judging Storm Surge Risk around Ariake Sea

For the purpose of developing a simplified method for judging storm surge risk around Ariake Sea, many numerical computations for storm surge were carried out. A lot of various typhoon data, which are the input data for the storm surge computations, were created by a stochastic typhoon model with the Monte Carlo simulation. The relationships between the storm surges and typhoon parameters (the central atmospheric pressure, the radius of the maximum wind speed and the course) were investigated on the basis of the computation results. Then, the conditions of typhoons that may cause severe storm surges were clarified at several coastal areas around Ariake Sea.