An Indian Ocean tsunami triggered remotely by an onshore earthquake in Balochistan, Pakistan

This paper describes and documents instrumentally recorded tsunami waves that are interpreted as secondary effects of a 7.7 magnitude earthquake in southern Pakistan on 24 September 2013. The tsunami waves were almost unnoticed because the wave heights were low and the tsunami occurred at low tide. The historical record of tsunami events within the Arabian Sea (northern Indian Ocean) is fragmentary. Large tsunamigenic earthquakes are known to be generated in the Makran subduction zone, the area that forms the boundary of the Arabian and Eurasian plates. Submarine sliding is reported along the Owen Fracture Zone, which marks the boundary between the Arabian and Indian plates. Hence, the tsunami hazard potential within the Arabian Sea is enigmatic. Our analysis is based on sea-level oscillations recorded at various tide-gauge stations along the coastlines of Oman, Pakistan, and Iran, as well as eyewitness accounts of the event in Oman. Our results indicate that the waves were in the range of 1 m or less in height. They were first recorded along the eastern coast of Oman, and propagated toward the west. We suggest that the waves must have been triggered by a submarine slide on the Makran margin. Cascading effects resulting in large submarine slope failures within the Arabian Sea are more frequent than postulated. The hazard potential is underestimated, as such secondary effects of distant ruptures onshore were previously not taken into account.