August 8, 1993 Earthquake: Tuman Bay, Apra Harbor, Guam, US Territories

Name: August 8, 1993 Earthquake: Tuman Bay, Apra Harbor, Guam, US Territories
Start: 1993-08-08
Location: Tuman Bay, Apra Harbor, Guam, US Territories

August 8, 1993 · M7.8 · $250 million

A magnitude 7.8 earthquake struck Tuman Bay, Apra Harbor, Guam, US Territories on August 8, 1993 at 08:34:24 UTC, 59 km below the surface. It caused a tsunami.

Map

Where it struck, with the other significant earthquakes within 200 km. Circles are sized and colored by magnitude; select one for its page.

The earthquake

Date: August 8, 1993
Time: 08:34:24 UTC
Place: Tuman Bay, Apra Harbor, Guam, US Territories
Magnitude: 7.8 (Mw)
Magnitude scales: Mw 7.8 · Ms 8 · mb 7.1
Focal depth: 59 km (37 mi)
Intensity: IX, violent shaking, on the Modified Mercalli scale
Tsunami: Yes: the tsunami it caused
Epicenter: 12.982° N, 144.801° E
Country: US Territories
Region: Central and South Pacific
USGS record: The USGS’s page for this earthquake

Mw: moment magnitude, based on the slip on the fault and the area that slipped. Ms: surface-wave magnitude. mb: body-wave (P-wave) magnitude. NCEI’s headline magnitude is the best of these for the earthquake.

The toll

Injuries: 48
Damage: $250 million

Where the literature gives no number, NCEI records a description on a scale of 1 to 4, printed here in its words. Damage is in millions of US dollars of the year of the event, not adjusted for inflation.

From Wikipedia

The 1993 Guam earthquake occurred on August 8 at 6:34:26 pm local time with a moment magnitude of 7.8 and a maximum Mercalli intensity of IX (Violent). The thrust earthquake generated a non-destructive tsunami.

Text from Wikipedia, “1993 Guam earthquake”, licensed CC BY-SA 4.0. Quoted as written; the full article has the rest.

What happened

The USGS’s account of the effects of this earthquake.

Forty-eight people injured on Guam. Extensive damage (IX) to hotels in the Tumon Bay area. Cracks tens of meters long and 25-50 cm wide, caused by liquefaction in the underlying soil, damaged facilities at the commercial port and naval base at Apra Harbor. Damage (VII) occurred at several locations in the northern half of the island. One end of the approach to a bridge at Pago Bay fell more than 35 cm. Many landslides and rockslides were reported, mainly in the southern half of the island. The preliminary estimate of loss from damage to commercial buildings is placed at 112 million U.S. dollars and loss from damage to private residences is estimated at several million U.S. dollars. Slight damage (V) on Saipan. Felt (VI) on Rota and (V) on Tinian.

Tsunami generated with maximum wave heights at selected tide stations as follows:

98 cm at Muroto-misaki, Shikoku;
68 cm on Chichi-shima, Bonin Islands;
58 cm at Tosashimizu, Shikoku;
56 cm at Aburatsu, Kyushu;
46 cm at Mera and Owase, Honshu;
44 cm at Ayukawahama, Honshu;
42 cm at Omae-zaki, Honshu;
34 cm at Hanasaki and Kushimoto, Honshu;
34 cm at Hirara, Ryukyu Islands;
28 cm at Ofunato, Honshu;
24 cm at Kochi, Shikoku;
19 cm at Port Allen, Kauai;
15 cm at Lahania, Maui;
14 cm at Haleiwa, Oahu;
12 cm at Hachinohe, Honshu and Kahului, Maui;
7 cm at Kapoho, Hawaii and Nawiliwili, Kauai;
5 cm at Honokohau, Hawaii.

Abridged from Significant Earthquakes of the World, 1993.

From the USGS event page for usp0005y3k. U.S. Geological Survey text and figures are in the public domain.

Magnitude estimates

The magnitudes the USGS catalog lists for this earthquake, by scale and by who computed them. NCEI’s own scales are in the table above.

Mag.	Scale	Computed by	Notes
7.8	Mw, moment	USGS National Earthquake Information Center	Preferred · Reviewed
7.75	Mw, moment	ISC-GEM global catalog	Final · ±0.1
7.7	Mwc, centroid moment	Global CMT project	Preliminary
7.62	Me, energy	Choy, USGS energy magnitude	Reviewed
7.8	Mww, W-phase moment	Duputel, W-phase inversion	Preliminary
7.74	Mw, moment	USGS finite-fault model	Finite-fault model · Reviewed

What the record says

NCEI’s account, from the sources it cites.

Forty-eight people injured on Guam. Extensive damage (IX) to hotels in the Tumon Bay area. Cracks tens of meters long and 25-50 cm wide, caused by liquefaction in the underlying soil, damaged facilities at the commercial port and naval base at Apra Harbor. Damage (VII) occurred at several locations in the northern half of the island. One end of the approach to a bridge at Pago Bay fell more than 35 cm. Many landslides and rockslides were reported, mainly in the southern half of the island. The preliminary estimate of loss from damage to commercial buildings is placed at $112 million U.S. dollars and loss from damage to private residents is estimated at several million U.S. dollars. Slight damage (V) on Saipan. (Reference #1053). Reference #1250 lists $250 million damage.

Miraculously, no lives were lost nor were there any serious

injuries. The strict building codes in Guam that help protect structures against the damaging winds associated with tropical cyclones (typhoons) appeared also to help structures withstand the destructive forces of this major earthquake. (Reference #459)

The earthquake generated a small tsunami that was recorded at a number of tide gauge stations in Guam and Hawaii.

Sources NCEI cites

The publications NCEI lists for this record. The numbers match the “reference #” notes in its account above.

#3851 Comartin, Craig D., Technical Editor (1995). Guam Earthquake of August 8, 1993 Reconnaissance Report, Earthquake Spectra, Supplement B to Volume 11, Publication 95-02, April 1995, p. 1-24.
#3444 Hattori, Paul (1993). Earthquake damage from event of 08AUG93 @08:35 to Observatory property and effect on programs, unusual reports. Memo to John Wood, forwarded to James Lander via email; Guam Observatory, 8 p.
#1053 National Earthquake Information Center (NEIC) (1971 to 2013). Preliminary Determination of Epicenters (PDE), a weekly and monthly publication, National Earthquake Information Center, U.S. Geological Survey, Golden, Colorado, 1971 to 2013.
#1250 Centre for Research on the Epidemiology of Disasters (CRED) and the U.S. Office of Foreign Disaster Assistance (OFDA) (2001). EM-DAT: The OFDA/CRED International Disaster Database, Universite Catholique de Louvain, Brussels, Belgium, link
#459 International Tsunami Information Center (1968 - present). Tsunami Newsletter. Honolulu, Hawaii, USA [published periodically, 1968-present].

Other significant earthquakes nearby

Within 200 km, the deadliest first.

Significant earthquakes of 1993 The 1900s Every quake the USGS located in 1993 Recent earthquakes near here This day in weather history

Sources

Significant earthquakes from NOAA’s National Centers for Environmental Information, Global Historical Hazard Database, cited as NCEI/WDS, doi:10.7289/V5PN93H7. Public domain. Read 2026-10-01. NCEI earthquake 5360. The written accounts and the magnitude estimates are from the USGS earthquake catalog, event usp0005y3k, matched to this record by time, place and magnitude.