地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
和歌山地方の地殻構造と微小地震の発震機構
―1965年共同観測結果―
三雲 健大塚 道男尾池 和夫
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1970 年 23 巻 3 号 p. 213-225

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The focal mechanism of 20 microearthquakes in the Wakayama region have been determined from the seismograms recorded at ten temporary stations and eight routine network stations covering the region.
The hypocenters of the earthquakes have been determined for five different crustal models (with a continuously varied velocity profile), to estimate the accuracy of their location and the emergent angle of seismic rays at the focus. The radiation pattern of P wave first motions for the 15 shocks, which was corrected for an appropriate crustal structure, can be interpreted by the double-couple type mechanism with dipping nodal planes.
The average of the maximum pressure axes is oriented nearly horizontally along the N70°W-S70°E direction, while the axes of the maximum tension show a steep dip in many cases. If a slip dislocation is assumed to be a likely model of the earthquakes, the source would be thrust faulting with a predominant component of dip slip. The other five earthquakes shows, however, the radiation pattern inconsistent with the double-couple type mechanism.

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© 社団法人日本地震学会
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