Claassen, C., Kashner, T., Kashner, T., et al. (2011). Psychiatric Emergency "Surge Capacity" Following Acts of Terrorism and Mass Violence with High Media Impact: What is Required? (Abstract only.) General Hospital Psychiatry. 33(3):287-93.
The authors examined emergency psychiatric treatment-seeking emergency room visits in the weeks after four events (the Oklahoma City Bombing, the Columbine High School shooting, the Wedgewood Baptist Church shooting, and the 9/11 terrorist attacks). They found that in the week following each event, there was minimal change in the number of visits.