2018_EJRNL_PP_ESSAM_ABOUD_1.pdf
Terbatas  
» Gedung UPT Perpustakaan
Terbatas  
» Gedung UPT Perpustakaan
Rahat volcanic field is one of the basaltic fields in Saudi Arabia that has threemajor geohazard events; the historical
eruption (1256 CE), the fissure eruption (~4500–1500 BP), and seismic swarm (1999). These events were
studied and evaluated using geophysical and geochemical studies as well as volcanological studies. Geophysical
studies include gravity, seismic, and magnetotelluric surveys. In the current research, the magnetotelluric data
will be analyzed using 3D inversion technique in order to image the subsurface resistivity setting of the study
area.
Results from3D inversion of theMT data revealed fourmajor resistivity structures. The first is a layer of intermediate
resistivity (40–250?-meters)which is thicker (~800m) to the south-west and thinner to the eastern edge,
mostly covered by exposed Precambrian basement. This layer is underlain by resistive (N1000?-metres) granitic
basement. Intruding into the resistive basement are two near-vertical conductive (b20?-metres) structures.One
is located immediately west of the historic eruption (1256 CE) centre in the north, at a depth of about 15 km. The
other intrusive is on the southern end of the survey area, also at a depth of about 15 km. Two conductive “channels”
trending NW-SE and NE-SWwere observed at depths of about 18 km. The NE-SWaligned “channel” runs
through the northern intrusivewhile theNW-SE trending “channel” runs in themiddle of the study area and connects
both intrusive. The conductive intrusive and “channels” may be attribute partial melts stored in the preexisting
structures within the lower crust. Although the youngest known trachytic eruptions from the study
area are several hundred thousand years old, recent and ongoing seismicity strongly suggest there may bemagmatic
activities in the lower and probably upper crust.