One source of information about Guam's earthquake history is the United States Geological Survey
Here's the EIS summary:
Guam experiences occasional earthquakes due to its location on the western edge of the Pacific Plate and near the Philippine Sea Plate. In recent years, earthquakes with epicenters near Guam have had magnitudes ranging from 5.0 to 8.7.
On October 30, 1936 (October 29, Universal Time), a magnitude 6.7 shock occurred about 80 mi (125 km) southwest of Guam. Walls were cracked and plaster and tile fell.T he seismic observer at Guam reported 25 tremors during the day of October 30. Another earthquake originated in the same area as the 1936 shock on September 16, 1970. The magnitude 6.2 tremor caused minor damage on Guam. A similar occurrence on November 1, 1975 (magnitude 6.2) produced damage on Guam that reached $1 million. The earthquake was felt strongly in many parts of the island.
On January 27, 1978, a magnitude 5.2 earthquake centered near the east coast of Guam caused considerable damage on the island. On August 8, 1993, the largest earthquake (magnitude 7.8) recorded on Guam occurred south of the Mariana Islands, injuring 48 people on Guam and causing extensive damage to hotels in the Tumon Bay area. Many landslides and rockslides were reported, mainly in the southern half of the island. The estimate of loss from damage to commercial buildings was placed at $112 million and loss from damage to private residences estimated at several million dollars.