Seismic Hazard Evaluation of the Oman India Pipeline

Abstract

Abstract The proposed Oman India pipeline will traverse approximately 1135 km of the northern Arabian Sea floor and adjacent continental shelves at depths of over 3 km on its route from Ra's al Jifan, Oman, to Rapar Gadhwali, India. The western part of the route crosses active faults that form the transform boundary between the Arabian and Indian tectonic plates. The eastern terminus of the route lies in the vicinity of the great (M - 8) 1819 Kutch, India, earthquake. A probabilistic seismic hazard analysis was used to estimate the values of peak ground acceleration (PGA) with return periods of 200, 500 and 1000 years at selected locations along the pipeline route and the submarine Indus Canyon?a possible source oflarge turbidity flows. The results defined that the ground shaking hazard along the pipeline route and Indus Canyon for evaluation of risks to the pipeline from potential earthquake induced geologic hazards such as liquefaction, slope instability, and turbidity flows. Introduction The Oman India pipeline is the most technically challenging offshore pipeline project in history. Its inaccessibility makes it essential that potential earthquake hazards such as ground shaking, slope instability, liquefaction, and turbidity flows be Bthoroughly understood and mitigated. This study addresses the ground-shaking hazard. The results of this study will be used by others to address the geologic hazards. Pipeline Route. The proposed submarine pipeline originates at Ra's al Jifan on the east coast of Oman and terminates at Rapar Gadhwali on the northern coast of the Gulf of Kutch, India (Fig. I). The total length of the pipeline route is approximately 1135 km. Offshore Ra's al Jifan, the pipeline route traverses the relatively narrow Omani continental shelf, crossing the Siquirah fault and descending the steep continental slope to a depth of 800 m. The route then proceeds in a southeasterly direction towards the Owen Fracture Zone- Murray Ridge Complex, descending to a depth of more than 3000 m. Within this complex, the pipeline route crosses the northern segment of the Owen Fracture Zone and the southern extension of the Dalrymple Trough. From the Murray Ridge Complex, the route continues in an easterly direction and descends onto the Arabian Sea Abyssal Plain and the Indus Fan where it achieves a maximum depth of 3500 m. Several hundred kilometers from the India coast near 66'E, the route turns towards the northeast, crossing several major submarine channels that are incised into the Indus Fan. As it approaches the coast of India, the pipeline route undergoes a steep rise to a depth of 200 m and traverses 140 km of gently sloping continental shelf to its terminus at Rapar Gadhwali. Seismic Hazard Analysis Methodology Ground-shaking hazard was quantified of peak ground acceleration (PGA). Specific seismic design criteria have not been established for the pipeline. In lieu of specified criteria, values of PGA were estimated for return periods of 200, 500 and 1000 years.