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タイトル: Travel Time Curve of Near Earthquakes in Japan Area and Some Related Problems. : 1. Procedures and Preliminary Results.
その他のタイトル: 日本付近の走時曲線 : 1.方法といろいろな深さの地震に対する結果
著者: the Research Group for the Travel Time Curve
著者(別言語): 走時曲線研究グループ
発行日: 1967年11月30日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第45冊第3号, 1967.11.30, pp. 625-656
抄録: Recent advancements in the observations of natural and artificial earthquakes and in the improvement in the speed and memory size of electronic computers are sufficient to give us aspiration for the attempt of revising the travel time tables of near earthquakes which have been used in routine works for nearly thirty years in Japan. The Research Group for the Travel Time Curve was thus organized in view of the practical and theoretical applications of the earthquake observations as well as the studies of the crustal structure in this part of our planet. The Group aimed at the determination of travel time curves of earthquakes with different depths best fitted to the observations by the method of least squares for earthquakes originating in and around Japan by simultaneous adjustment of origin times and hypocentral locations of all the earthquakes studied. The station corrections for the arrival times for all the observatories are also to be determined at the same time. In the present study, our effort was inevitably confined to the study of travel time curves of near earthquakes up to the epicentral distance of 1500km, owing to the areal limitation of our country and paucity of observing stations in other neighbouring countries and in the oceanic area. But high seismicity in the region concerned allowed us to obtain many data even in the limited interval of eleven years (1954-1964). Several preliminary attempts and tests were made to select a feasible procedure for the purpose. For the time being, the memory size of an available computer and other factors confined us to the determination, at one time, of a travel time for the earthquakes with a given constant depth of hypocenter. Similar analyses were carried out for each earthquake group of respective hypocentral depths. In view of the practical significance, some preliminary studies and tests are briefly described in Part I, while the results of our final analyses are described in Part II. Major items treated in Part I are as follows; Selection of the formula to express the travel time curve and rejection criterion of inappropriate data (Section 2), dependency of the resulting travel time curve on the assumed epicenter location (Section 3), effect of the starting assumption of the location of the epicenter on the final epicenter coordinates approximated successively by the iterative application of Geiger's method (Section 4), convergency of the epicenter location and the travel time curve in alternate successive determinations of the travel time curve and epicenter location (Section 5), calculation of the travel time curve for epicentral distances less than 170 km (Section 6), method of simultaneous determination of the travel time curve and station correction for the arrival of the P-wave, together with the origin time and epicenter locations of all the earthquakes by means of arrival times of the P-waves of many earthquakes at the stations throughout our country (Section 7). In Part II, the last procedure reached at in Section 7 is applied, first to a group of earthquakes with a hypocentral depth of 40km as determined by the Japan Meteorological Agency. Some detailed reviews of the method and the results are given in Section 8. Similar analyses were next made of other groups of earthquakes with hypocentral depths of 0, 20, 60, and 80 km respectively, and the results are shown in Section 9. In Section 10, a comparison of the travel time curve obtained here for earthquakes of zero km depth is made with the travel times obtained in explosion seismic experiments carried out in Japan by the Research Group for Explosion Seismology.
URI: http://hdl.handle.net/2261/12350
ISSN: 00408972


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