Earthquakes of 6.5-7.0 in Macquarie Island Region and 6.5 West of Sabang, Indonesia: Magnitude and Tsunami Assessment
The first event, centered west of Macquarie Island, registered magnitudes ranging from 6.5 to 7.0 according to various sources, though the USGS settled at 6.9 magnitude.
INDIAN OCEAN — On July 28, 2025, two notable earthquakes struck distinct areas. The first event, centered west of Macquarie Island, registered magnitudes ranging from 6.5 to 7.0 according to various sources, though the USGS settled at 6.9 magnitude.
The second, located 258 km west-northwest of Sabang, Indonesia, measured 6.5 on the moment magnitude scale. Both occurred at shallow depths of 10 km, with no immediate reports of casualties or damage due to their remote oceanic positions.
Analysis indicates these events align with tectonic activity along plate boundaries in the region. The Macquarie Island quake, at coordinates approximately 57.56°S, 156.85°E, reflects movement on the Pacific-Antarctic Ridge. The Sabang event, at 6.700°N, 93.123°E, relates to subduction zones near the Andaman Sea.
No tsunami threats materialized, as confirmed by monitoring agencies. Seismic patterns suggest potential for aftershocks, though none significant have been recorded.
Event Details: Macquarie Island Region Earthquake
This quake occurred at 22:10 UTC on July 28, 2025, equivalent to 06:10 UTC+08:00 on July 29. Initial assessments varied, with some agencies reporting 7.0 and others 6.7 or 6.8. The epicenter's isolation, south of New Zealand, minimized impacts on populated areas. Historical data shows similar events in this ridge system, often without surface effects.
Depth at 10 km classifies it as shallow, potentially amplifying intensity if near land. However, distance from Macquarie Island, an uninhabited Australian territory, precluded damage.
Monitoring stations detected the event promptly, enabling rapid evaluations. Discrepancies in magnitude likely stem from preliminary calculations refined over time.
Event Details: Sabang, Indonesia Earthquake
The second quake hit at 18:41 UTC on July 28, 2025, or 02:41 UTC+08:00 on July 29. Centered in the Indian Ocean, it posed no immediate threats to coastal areas. The location, far offshore, reduced risks to infrastructure on Sumatra. Seismic networks confirmed the 6.5 magnitude without revisions noted.
Shallow depth contributed to potential felt shaking, but remoteness limited observations. The Andaman-Nicobar arc's tectonics drive such activity, with historical quakes in the area. No aftershocks of concern followed. Agencies issued no alerts, reflecting low hazard potential.
Official Statements
USGS stated: "M 6.5 - 258 km WNW of Sabang, Indonesia, 2025-07-28 18:41:48 UTC, depth 10.0 km."
USGS indicated: "M 6.2 - Macquarie Island region, 2025-07-26 16:15:04 UTC, depth 10.0 km." (Note: Related event; main quake data aligns with higher magnitudes from other sources.)
Pacific Tsunami Warning Center announced: "An earthquake with a preliminary magnitude of 7.0 occurred in the Macquarie Islands region at 811 AM CHST on Tuesday July 29 2025. Based on all available data... no destructive tsunami is expected."
