Exploration of the extension of two lava tubes, faults and dikes using very low frequency-electromagnetic technique in NE Jordan

The very low frequency-electromagnetic (VLF-EM) technique was used to delineate two sub-parallel lava tubes, faults and dikes in Umm El-Quttein area, NE Jordan. The investigation of the lava tubes was conducted through 22 VLF-EM profiles across lava strike; the length of profiles ranged from 700 to 1700 m. The lava tubes outcrop at two sites: Azzam cave and Al-Howa tunnel, characterized by slightly weathered basalt, columnar joints and fissure zones; qualitative interpretation of Fraser and Karous-Hjelt maps differentiate those zones as linear, elongated and circular anomalous zones. The 2-D tipper inversion of VLF-EM data and resistivity imaging had the potential to screen out three anomalous zones of likely resistivity contrast: the lava tube body with resistivity over 2500 Omega.m, the fractured zones with resistivity less than 500 Omega.m, and the host vesicular basalt with resistivity of 1500 Omega.m. The strike of lava tubes varied from SW to NE direction with depth less than 20 m and width from 10 to 30 m.