Earthquake Research Institute, University of Tokyo
抄録
The travel-time table for the JMA standard model of the crust and upper mantle is extended to include more distant ranges up to 30° by increment of epicentral distance of 0.1° and travel times to the hundredths of a second. Travel times are calculated by the ray theory for very fine increments of take-off angles. Besides the travel times take-off angles at sources, incident angles to the earth's surface, apparent velocities, depths of ray bottom and geometrical spreading factors are also derived. These tables include effects of the 20°-discontinuity without smoothing and are useful for precise location of earthquake hypocenters, precise determination of fault-plane solutions and fine structure of the crust and upper mantle. The travel times in the present study have differences of less than 0.5 second from those of the ICHIKAWA-MOCHIZUKI table (1971) for the JMA standard model. Differences of travel time between previously proposed tables and models for Japan amount to about 10 seconds. Travel times are also compared with a velocity model accompanying the low-velocity layer in the upper mantle. Contrary to the general acceptance no travel time jumps are observed and receding travel times and apparent velocities with epicentral distances are obtained for the velocity decreasing at the top of the low-velocity layer.
気象庁現用の標準地殻・上部マントル構造に対する走時表を波線理論にもとづき,百分の1秒単位で震央距離0.1°毎に30°迄拡張した.走時の他,震源における射出角,地表への入射角,みかけ速度,波線最深点及び幾何学的減衰についても表を求めた.これらの走時表は""20°-不連続""等の速度構造の特徴が反映されており,高精度の震源・発震機構の決定,地殻・上部マントルの微細構造や地震規模・波形解析に有用である.求められた走時は市川・望月(1971)とは最大0.5秒の差がある.日本附近について発表されてきた速度モデルには最大10秒の走時差が存在する.初動走時に関する限り低速度の影響を考慮しなくともよい.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
58
号
2
ページ
311 - 383
発行年
1983-10-22
ISSN
00408972
書誌レコードID
AN00162258
フォーマット
application/pdf
日本十進分類法
453
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
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12. Extended Travel-Time Tables for the JMA Standard Model of the Crust and Upper Mantle Structure beneath the Japanese Islands
ji0582002.pdf
(4.18MB)
