April 25, 1993



The earthquake was located within the Cataract Creek fault system on the Colorado Plateau. The fault system consists of a zone of northwest trending faults approximately 20 miles in width and 70 miles in length. It extends from South of the Grand Canyon to South of Flagstaff. The southeastern end of the Cataract Creek fault system may have been the cause of the 1906 Flagstaff earthquake of ML = 6.2, which did some damage to un-reinforced masonry structures in the downtown Flagstaff area.

Although a ML = 4.5 event shook the South Rim of the Grand Canyon last March, this years 4.9 tremor is the largest in AZ since the 1976 ML = 5.1 that shook the Chino Valley-Prescott area. Ground motion from the earthquake was recorded at station FLAG, located in Flagstaff, for about 5 minutes 40 seconds. However, the event was only felt for 10 to 20 seconds. Seismograph stations as far as Alaska and Virginia recorded the event. The depth of the event has been fixed at 10 km. A network of portable seismograph stations was in operation in the epicenter area for two weeks following the event. The temporary network provided detailed information on the size and location of aftershocks, and may provide a clue as to the specific fault that caused this activity. There were over 600 earthquakes detected in the two weeks the stations were operating, of which, approximately 130 were locatable.

The earthquake data is as follows: