| 講演要旨(和文) | | 一昨年,我々はP波反射法測線に3成分地震計1点を加えることにより,S波速度構造が求まる可能性を示した.この時の方法はあまり現実的ではなかったが,この考え自体は魅力的である.なぜなら,3成分地震計1点だけであれば,ほとんど追加費用なく探査に加えられるからだ.昨年,我々はより現実的な方法を提案した.それは,ラディアル成分の観測点ギャザーを作り,波線追跡法によりP-SV反射波の走時をVp/Vsを変数として計算し,観測走時と合わせることにより,Vsを求めるというものである.ここでP-SV波のスローネスが大オフセットではVsによらないため,Vp/Vsと反射面とを独立に求められることを利用している.今回は傾斜層がある場合においてもこの方法が有効であることを示す.この方法は,P波速度構造が先に求まっていることが条件であるが,観測・解析の手間もあまりかからず簡単かつ現実的なS波速度推定法として期待できる. |
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| | 講演要旨(英文) | | In our previous paper of 2008, we showed a possibility of examining S-wave velocity profile by analyzing P-to-SV reflected waves observed at one 3-component seismometer together with P-wave reflection profiling. Although the method proposed in the previous paper has ambiguity about obtaining S-wave velocity, the approach itself is attractive because one additional 3-component seismometer requires little additional cost. Last year we proposed another method based on fitting observed travel-time curves of P-to-SV waves on the receiver gather of the radial component to theoretical times calculated by using ray tracing, and showed the validity of the method for the model whose layer boundaries were horizontal. The variables in the method were the ratio of P-wave velocity to S-wave velocity and the reflection layer, because P-wave velocity structure was already known. Slowness of the reflected wave does not depend on S-wave velocity but on P-wave velocity at large offsets, which separated the effect of these two variables on the receiver gather. In this paper, we showed the validity of the method for models whose layer boundaries were inclined. This method is easy to apply without much time and effort, if P-wave velocity profile was already determined using vertical component reflection profiling. |
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