Geomagnetic field anomalies over the Lombok Island region: an attempt to understand the local tectonic changes |
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Authors: | Teti Zubaidah M Korte M Mandea Y Quesnel B Kanata |
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Institution: | 1. Helmholtz Centre Potsdam, Deutsches GeoForschungsZentrum (GFZ), Sektion 2.3 Erdmagnetfeld, Telegrafenberg, 14473, Potsdam, Germany 2. Jurusan Teknik Elektro, Fakultas Teknik Universitas Mataram, Mataram, Indonesia 3. Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement (CEREGE), Aix-en-provence, France
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Abstract: | During the last years, several investigations on the earthquakes and related tectonic structures along the Java Trench have
been conducted. In this study, we focus on the Lombok Island—West Nusa Tenggara (Indonesia), which lies between the centres
of the highest intensity of contiguous negative–positive geomagnetic anomalies in this region. The geological and tectonic
structures, however, are not known in detail for this island, whereas a better knowledge of these conditions could lead to
better estimate the potential earthquake risks and thus a possible improvement of the existing early warning system. We have
performed a ground-based geomagnetic survey at 56 stations in the Lombok Island during October–November 2006 for a detailed
mapping and interpretation of geomagnetic anomalies related to the geological and tectonic characteristics. The 2D and 3D
magnetic maps show a general geomagnetic anomaly pattern in the Lombok Island which consists of repeated contiguous negative–positive
anomalies. Two forward models have been proposed for a profile connecting a strongest apparent dipolar structure. The first
model assumes a uniformly magnetized sphere as the source of the anomaly, and could be interpreted as a specific local structure
composed by a quite large magnetic body. The second model considers several rocks with different susceptibilities and magnetizations,
and could be interpreted as a discontinuity in the geological structures. This model agrees with the local geological surface
conditions and the known large scale regional tectonic structure. Therefore, it is used to interpret our results in terms
of tectonic characteristics, which suggests the potential existence of a new tectonic element (e.g. a local normal fault)
in this region. |
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