第32回ジオダイナミクスセミナー
　　　Geodynamics　Seminar

　“Seismic tomography from local earthquakes
　　beneath Betic-Rif Cordilleras (Southern
　　Spain-Northern Morocco) and its relationship
　　with local geophysical signatures.”
　　　　　　　　　　
　　講師：Dr. Inma Serrano（グラナダ大学研究員）

　〜追加講演〜　
　「古地球磁場強度変動と古気候変動」
　　
　　講師：小玉一人（高知大学海洋コア研究センター教授）
　　　
　　　　　　　
　　　　　主催　：　愛媛大学地球深部ダイナミクス研究センター
　　　　　日時　：　２００２年２月１５日（金）　午後17時〜
　　　　　場所　：　愛媛大学理学部講義棟　２０１教室

　　　　　　　　

要　旨

　　“Seismic tomography from local earthquakes beneath Betic-Rif
　　　Cordilleras (Southern Spain-Northern Morocco) and its
　　　relationship with local geophysical signatures.”
　　　　　　　　　　　Dr. Inma Serrano

　Three-dimensional P and S wave velocity structures of the crust under the Granada Basin in Southern Spain are obtained with a spatial resolution of 5 km in the horizontal direction and 2 to 4 km in depth. We used a total of 15407 P and 13704 S wave high-quality arrival times from 2889 local earthquakes recorded by both permanent seismic networks and portable stations desployed in the area. The wave velocities inverted wave used to obtain three-dimensional distributions of Poisson's ratio and the porosity parameter (Vp* Vs). The 3-D velocity images show strong lateral heterogeneities in the regin. Significant velocity variations up to 7% in P and S velocities are revealed in the crust below the Granada basin.
　The combined use of different geophysical techniques (gravity and magnetic researches) point to the existence of a large basic rock body, probably of gabbros, below the carbonate sedimentary rocks below western Granada Basin. While the high resolution seismic tomography clearly indicates a positive anomaly, the surface magnetic and aeromagnetic measurements show that also a positive anomaly is related to the body, while the negative anomaly of the dipole is very smooth. The conclusion is that the combined use of seismic tomography and magnetic mesurements provide the best evidences for the research of the basic rock bodies in the upper crust while the gravity measurements is affected by whole the crustal structure and the overprinting of the different rock types.
　Afterwards, we applied this tomographic method to image an aseismic srike-slip fault in North Morocco and found that the ocurrence of earthquakes is not only controlled by the state of tectonic stress but also dictated by the material heterogeneity in the crust. We have attempted to construct an integrated model of seismic, electric, magnetic as well as heat flow properties across northeast of Morocco from analysis of arrival times of 221 local earthquakes and from the previous geophysical surveys carried out in north Morocco. The seismic images obtained show distinct features that may be related to the main tectonic events developed since the Miocene in the region.



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