SHORT COMMUNICATION ‘‘Shock event’’, an impact phenomenon observed in water wells around the Arabian Gulf coastal city Dammam, Saudi Arabia: possible relationship with Sumatra tsunami event of December 26, 2004 Arun Kumar Æ Syed A. Alam Received: 4 July 2009 / Accepted: 13 July 2009 / Published online: 1 September 2009 Ó Springer Science+Business Media B.V. 2009 Abstract A sudden disturbance in water level was recorded by hydrographs monitoring wells in the coastal city Dammam, Saudi Arabia on December 26, 2004. The water level was being recorded from the shallow (1–3 M deep) coastal aquifer at that time. In two wells, this disturbance was observed *12 h after the Sumatra earthquake/tsunami event of December 26, 2004. The timing of this event is synchronous in two wells near the coast, but an inland well away from the coast line did not show any such disturbance. It is hypothesized that this disturbance, we call it the ‘‘shock event’’, is resulted by sudden impact of tsunamis traveling in the Arabian Gulf from southeast toward northwest. As the tsunamis propagated, they suddenly impacted the coastal shallow groundwater aquifer resulting in the ‘‘shock event’’. Keywords Shock event Á Arabian Gulf Á Sumatra tsunami of December 26th, 2004 Á Coastal aquifers Á Tsunami travel time Á Hydrograph 1 The ‘‘shock event’’ Hydrographs monitoring constant variation in water levels in observation wells (4 in. diameter) on an Arabian Gulf coastal town Dammam in Saudi Arabia (Fig. 1) provided a strange recording on December 26, 2004. The recording of daily water level went on for 5 years, but such a sudden disturbance was never observed on the hydrographs. In hydrograph recording, the horizontal scale represents water level, and the vertical scale represents time (1 unit = 1 h; Fig. 2). The hydrographs were monitored every 8–10 days. In two wells located near the coast, a sudden short-lived disturbance was simultaneously recorded (Fig. 2), but there was no effect on the inland well that is 12 km away from the A. Kumar (&) Á S. A. Alam Center for Petroleum and Minerals, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia e-mail: arunkumarlko@hotmail.com; arun@kfupm.edu.sa 123 Nat Hazards (2010) 53:407–412 DOI 10.1007/s11069-009-9427-7