Earthquake History of Guam/Northern Marianas
Guam, the largest and southernmost island of the Mariana Islands, rises steeply from the ocean floor, a short distance to the north of the world's greatest known oceanic depth. Felt earthquakes are frequently reported.
Rev. W. C. Repetti, S.J., of the Manila Observatory, published a detailed summary of early historical events ("Catalogue of Earthquakes Felt in Guam 1815-1938") as part of the Manila Seismological Bulletin for 1939. The following notes are excerpted from this report:
During the months of April and May of the years 1825 and 1834 terrible earthquakes were experienced on this island, causing great damage to buildings. On January 25, 1849, a terrible subterranean noise was heard; at the same instant, there was a terrific earthquake with strong vertical and horizontal movements. Damage was reported at Agana and nearby towns; one death was attributed to a sea wave following the tremor. A detailed count of aftershocks from January 25 to March 11 totaled 150. A later report from Satawal, Caroline Islands, about 825 kilometers south-southeast of Guam, indicated that the island had been inundated by sea waves following the earthquake. On July 1, 1862, a moderate shock caused the fall of many tile roofs. On May 16, 1892, some walls were cracked and tiles of the masonry houses fell.
Widespread damage occurred at Agana from a strong earthquake on September 22, 1902. The 11:15 a.m. tremor was again preceded by a loud subterranean noise. Some houses were completely ruined, and, with a few exceptions, all the stone buildings had considerable damage. Numerous landslides occurred, and many bridges were thrown down, interrupting travel between Agana and the port of Piti, 8 kilometers distant. Five injuries were reported. Damage also occurred on the island of Saipan.
A magnitude 7.4 earthquake centered about 250 kilometers southwest of Guam caused additional damage at Agana on December 10, 1909 (December 9, Universal Time). The Women's Hospital, built of local mortar, was so badly damaged as to necessitate tearing down. On October 30, 1936 (October 29, Universal Time), a magnitude 6 3/4 shock occurred about 125 kilometers southwest of Guam. Plaster fell, walls were cracked, and tile fell. The seismic observer at Guam reported 25 tremors during the day of October 30. Over the next month, almost 500 aftershocks were counted from the seismograms. Many of these were too small to be felt.
Another earthquake originated in the same area as the 1909 and 1936 shocks on September 16, 1970. The magnitude 6.2 tremor caused minor damage on Guam; intensity was V on the Modified Mercalli Intensity Scale (MM); and it was reported felt on Saipan. A similar occurrence on November 1, 1975 (magnitude 6.2) produced damage on Guam that reached $1 million. Many businesses lost stock from shelves, and a number of structures were damaged; only one injury was reported (MM VII). The earthquake was felt strongly in many parts of the island. Seismic activity continued in 1977, with at least 11 felt reports (MM I-V).
On January 27, 1978, an earthquake centered near the east coast of Guam caused considerable damage on the island. The magnitude 5.2 shock was felt by almost everyone and caused much alarm among the population. Many homes and at least two government buildings were damaged (MM VII).
Abridged from Earthquake Information Bulletin, Volume 10, Number 6, November - December 1978, by Carl A. von Hake.
For a list of earthquakes that have occurred since this article was written, use the Earthquake Search.