Public health emergencies like earthquakes and tsunamis underscore the need for an evidence-based approach to disaster preparedness. Using the Japanese administrative database and the geographical information system (GIS), the interruption of hospital-based mechanical ventilation administration by a hypothetical disaster in three areas of the southeastern mainland (Tokai, Tonankai, and Nankai) was simulated and the repercussions on ventilator care in the prefectures adjacent to the damaged prefectures was estimated. Using the database of 2010 including 3,181,847 hospitalized patients among 952 hospitals, the maximum daily ventilator capacity in each hospital was calculated and the number of patients who were administered ventilation on October xx was counted. Using GIS and patient zip code, the straight-line distances among the damaged hospitals, the hospitals in prefectures nearest to damaged prefectures, and ventilated patients' zip codes were measured. The authors simulated that ventilated patients were transferred to the closest hospitals outside damaged prefectures. The increase in the ventilator operating rates in three areas was aggregated. One hundred twenty-four and 236 patients were administered ventilation in the damaged hospitals and in the closest hospitals outside the damaged prefectures of Tokai, 92 and 561 of Tonankai, and 35 and 85 of Nankai, respectively. The increases in the ventilator operating rates among prefectures ranged from 1.04 to 26.33-fold in Tokai; 1.03 to 1.74-fold in Tonankai, and 1.00 to 2.67-fold in Nankai. Administrative databases and GIS can contribute to evidenced-based disaster preparedness and the determination of appropriate receiving hospitals with available medical resources.