Moderate earthquakes may cause minor damage
Earthquakes are classified by depth: shallow (0-70 km), intermediate (70-300 km), and deep (300-700 km). This event occurred at a shallow depth of 33.0 kilometers.
| Coordinates | 51.2560°N, 178.1990°W |
| Depth | 33.0 km |
| Magnitude Type | ms |
| USGS Status | Reviewed by a seismologist |
| Reports from the Public | No reports |
| Tsunami Risk | No significant tsunami risk flagged |
Epicenter location of the Magnitude 5.5 earthquake, 128 km WSW of Adak, Alaska
A magnitude 5.5 earthquake occurred near 128 km WSW of Adak, Alaska on September 9, 1991 at 03:03 PM UTC. This shallow earthquake originated at a depth of 33.0 kilometers below the Earth's surface. The earthquake was detected by several seismic monitoring stations operated by the USGS. The ms magnitude measurement indicates this was a surface wave magnitude event, which is appropriate for earthquakes of this size and depth. Earthquakes of magnitude 4.5 to 5.9 are classified as moderate earthquakes by the USGS. This event contributes to our understanding of seismic activity in the region.
No felt reports available for this event.
Did you feel the shaking? Your story matters—share it with the USGS to help map this quake's impact!
During an earthquake, remember to Drop, Cover, and Hold On. Stay indoors and take cover under a sturdy table or desk, protecting your head and neck. If you're outside, move to an open area away from buildings, trees, and power lines. After the shaking stops, check for injuries and damage, and be prepared for aftershocks. Residents in the affected area should be aware of potential secondary hazards that are common in your region. Prepare an emergency kit with essential supplies including water, non-perishable food, first aid supplies, flashlight, and batteries. Stay informed by following updates from local authorities and emergency services. Consider submitting a felt report to help seismologists better understand this event's impact.