Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-TT Technology & Techniques

[S-TT52] Airborne surveys and monitoring of the Earth

Wed. May 27, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Shigekazu Kusumoto(Graduate School of Science and Engineering for Research, University of Toyama), Shigeo Okuma(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST)), Yuji Mitsuhata(AdvancedIndustrial Science and Technology), Takao Koyama(Earthquake Research Institute, University of Tokyo)

6:15 PM - 7:30 PM

[STT52-P04] Three-dimensional resistivity modelling of GREATEM survey data from the Nojima Fault, Awaji Island, south-east Japan.

*ALLAH, Sabry ABD1, Toru MOGI1, Hisatoshi ITO2, Akira JOMORI3, Youichi YUUKI4, Elena FOMENKO5, Kenzo KIHO2, Hideshi KAIEDA2, Koichi SUZUKI2, Kazuhiro TSUKUDA2 (1.Institute of Seismology and Volcanology, Hokkaido University, 2.Civil Engineering Research Laboratory, Central Research Institute of Electrical Power Industry, 3.NeoScience Co., 5-11-22 Osato, Sennan, Osaka, 590-0526, Japan, 4.Geotechnical Center, Oyo Co., 2-61-5 Toro, Saitama, 331-8688, Japan., 5.Faculty of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Moscow)

Keywords:3D EM forward modeling, GREATEM, Numerical approximations, Airborne Electromagnetic, Fault zone survey

An airborne electromagnetic (AEM) survey using the grounded electrical-source airborne transient electromagnetic (GREATEM) system was conducted over the Nojima Fault on Awaji Island, south-east Japan, to assess GREATEM survey applicability for studying coastal areas with complex topographic features. To obtain high-quality data with an optimised signal-to-noise ratio, a series of data processing techniques was used to acquire the final transient response curves from the field survey data.
The 1D inversion results were feasible in that the horizontal resistivity contrast was not much higher than the true contrast, but they were not reasonable in that the horizontal resistivity values were greatly changed. To circumvent this problem, we performed numerical forward modelling using a finite-difference staggered-grid method (Fomenko and Mogi, 2002) adding a finite-length electrical dipole source routine to generate a three-dimensional (3D) resistivity structure model from GREATEM survey data of the Nojima Fault area. The 3D model was based on an initial model consisting of two adjacent onshore and offshore layers of different conductivity such that, a highly conductive sea of depth (10?40 m) is placed on top of a uniform half-space, assuming the presence of topographic features on the inland side. We examined the fit of the magnetic transient responses between field data and 3D forward-model computed data, the latter were convolved with the measured system response of the corresponding dataset. The inverted 3D resistivity structures showed that the GREATEM system has the capability to map underground resistivity structures as deep as 500 m onshore and offshore. The GREATEM survey delineated how seawater intrudes on the land side of the fault and indicated that the fault is a barrier to seawater invasion.