M5.5 Earthquake 60 km SW of San Carlos, Mexico — July 31, 2021
2021-07-31 15:39:20 UTC (2021-07-31) · approx. 8:39 AM UTC-7 local
Felt by 25 people across nearby locations. Maximum shaking intensity MMI 4.1 (moderate).
On July 31, 2021 at 15:39 UTC, a magnitude 5.5 shallow crustal earthquake struck 60 km SW of San Carlos, Mexico, at a depth of 10.0 km and coordinates 27.5909°, -111.4970°. The earthquake was reported felt by 25 peopleacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 4.1 (moderate). The USGS PAGER system issued a green alert level for this event, indicating no significant casualties or damage expected. The nearest populated place is Empalme (population 38,599).
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.
The epicenter is located in Mexico, a region characterized by the Middle America Trench, where the Cocos Plate subducts beneath the North American Plate. The nearest mapped fault system is the Middle America Trench. View all earthquakes in Mexico.
Learn more: Magnitude scale · Aftershock sequences
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
Did You Feel It? — community-reported shaking
Aggregated felt-report intensity from 25 citizen responses to the USGS Did You Feel It? system. Each colored zone represents the average MMI from reports in that area.
Source: U.S. Geological Survey Did You Feel It?. View on USGS · submit your own report
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 | 1,701,497 |
| MMI 4 | light | 252,902 |
Earthquake Details
-111.4970°E
Technical Information
Common Questions
How strong was the magnitude 5.5 earthquake near San Carlos, Mexico?
The magnitude 5.5 earthquake that struck 60 km SW of San Carlos, Mexico on July 31, 2021 at 15:39 UTC had a depth of 10.0 km. It was felt by 25 people with maximum shaking intensity of MMI 4.1 (moderate). For context, this was a moderate earthquake that could be widely felt.
Where did the earthquake occur?
The earthquake epicenter was located at 27.5909°, -111.4970°, which is 60 km SW of San Carlos, Mexico. The nearest populated place is Empalme (population 38,599). View all earthquakes in Mexico.
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.
Has Mexico had earthquakes this big before?
The largest recorded earthquake in Mexico was the M8.1 Chiapas earthquake of September 8, 2017. Today's magnitude 5.5 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: us6000f109). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, July 31, 2021). M5.5 Earthquake 60 km SW of San Carlos, Mexico — July 31, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us6000f109/