M5.5 Earthquake in the Mariana Islands region — August 11, 2021
2021-08-11 15:02:51 UTC (2021-08-11) · approx. 1:02 AM UTC+10 local
On August 11, 2021 at 15:02 UTC, a magnitude 5.5 shallow crustal earthquake struck in the Mariana Islands region, at a depth of 10.0 km and coordinates 15.9053°, 147.2583°. The USGS PAGER system issued a green alert level for this event, indicating no significant casualties or damage expected. The nearest populated place is San Jose Village (population 15,000).
Physical scale: An earthquake of magnitude 5.5 releases seismic energy equivalent to roughly 3 kilotons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 3.8 km — a useful intuition for the size of the slip patch on the fault.
Nearest Populated Places
ShakeMap — predicted shaking intensity
Modeled ground-motion intensity contoured on the Modified Mercalli scale (MMI). Computed by the USGS from the moment-tensor solution and regional ground-motion prediction equations.
Source: U.S. Geological Survey ShakeMap. View interactive ShakeMap on USGS
Population exposure (USGS PAGER)
Estimated population that experienced each level of shaking. Based on the USGS PAGER rapid impact assessment, which combines ShakeMap output with global population grids.
| Shaking intensity (MMI) | Description | Population exposed |
|---|---|---|
| MMI 3 | weak | 50,188 |
Earthquake Details
147.2583°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 5.5 earthquake in the Mariana Islands region?
The magnitude 5.5 earthquake that struck in the Mariana Islands region on August 11, 2021 at 15:02 UTC had a depth of 10.0 km. For context, this was a moderate earthquake that could be widely felt.
Where did the earthquake occur?
The earthquake epicenter was located at 15.9053°, 147.2583°, which is in the Mariana Islands region. The nearest populated place is San Jose Village (population 15,000).
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 5.5 earthquakes can continue for days to weeks and gradually diminish over time.
Actions
Authoritative source: USGS event page (event ID: us6000f45x). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, August 11, 2021). M5.5 Earthquake in the Mariana Islands region — August 11, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us6000f45x/