Using Potential Geophysical Methods to Locate a Shallow Thrust Fault in AlJaww Plain
Alklih, Mohamad *1; Salib, Mina 1; Zakaria, Hasan 1
(1) The Petroleum Institute, Abu Dhabi, United Arab Emirates.
A geophysical investigation in Al Jaww Plain was carried out by a group of students from the Petroleum Institute in Abu Dhabi. Al Jaww Plain is located to the southeast of Al Ain city in the eastern side of the U.A.E. near the border with the Sultanate of Oman. The geophysical investigation involved the use of gravity and magnetic methods. Localized short seismic refraction profiles were also conducted. The objectives of this investigation can be divided into two categories. The main objectives include the localization of a reverse thrust fault, identifying the extension of the Oman Ophiolites and estimating bed rock depths. The secondary objective includes performing an instrumental drift study of the gravimeter and magnetometer used.
The integrated geophysical surveys provided key subsurface information needed to better understand the structure of Al Jaww Plain and the surrounding areas. The interpretation of the combined results for the gravity and magnetics enabled confirmation of the existence of an expected reverse thrust fault to the eastern edge of the studied area. Measured gravity anomalies for some profiles suggested that the fault is approximately located at a longitude of 55.9203oE. However, the orientation of the fault changes around that longitude in the directions of NW to SE. Moreover, the Semail Ophiolites are gravitationally and magnetically distinct which allows their lateral extent to be easily identified. The measured gravity and magnetic anomalies gradually increase from a low near the center of Al Jaww Plain to a high when getting closer to the Ophiolites outcrops. The interpretation showed that the Ophiolites are limited to the east of Al Jaww Plain and probably extend till 55.9347oE. Moving to the secondary objectives, seismic refraction calculations revealed that waves' refraction happened at an average depth of 35 m. By using the provided water wells data from the National Drilling Company (NDC), the refractor layer is a claystone type underlying layers of weathered materials such as gravel, sand and silt. The gravimeter drift study revealed that the optimum time interval needed to visit the base station was 3 hours while it was 30 minutes for the magnetometer drift study.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain