The U.S. Geological Survey recorded a magnitude 5.0 earthquake in southern Iran at 21:20 UTC on October 31, 2026. The catalog places the epicenter at 28.114 degrees north and 51.508 degrees east, which the agency labels 115 kilometers southeast of the port city of Bushehr. Its reviewed solution assigns a depth of 10 kilometers, a figure that deserves a closer look before anyone reads it as a measured value.
Help yourself and the planet: The Cool Down makes it easy to help yourself while helping the planet, with smart, simple changes to save more and waste less in your everyday life.
We may earn a commission if you sign up.
The same record carries a tsunami flag of 0, no PAGER alert level and no felt-report or shaking-intensity values at the time it was read. Its significance score is 385, a composite number the agency builds from magnitude, reported effects and other inputs. Nothing in the entry describes injuries or damage, and the absence of felt reports in a catalog entry is not the same thing as an absence of shaking on the ground.
Reading the USGS entry for event us7000tukm
The event carries the identifier us7000tukm in the agency’s catalog, and its event page is the reference record for the quake. The magnitude is labeled mb, a body-wave scale, and marked reviewed, meaning an analyst checked the automatic solution. The origin time is 21:20:39 UTC on October 31, which is 12:50 a.m. on November 1 in Iran, where clocks run three and a half hours ahead of UTC. Residents in the Gulf coast region would therefore have felt any shaking in the first hour of the new day, when most were asleep and fewer people were on the road or outdoors to notice it.
The quake also appears in the agency’s weekly feed of magnitude 4.5 and larger events, where the row reads 5.0, 115 km SE of Bushehr, Iran, with a depth value of 10.0. Every event in that feed snapshot carried a tsunami flag of 0. Pulling the same event through the agency’s event web service in GeoJSON form returned the identical magnitude, place string, time and depth, along with an empty alert field, so the three views of the record agree with one another.
A depth of 10 kilometers that was assigned, not measured
The depth field is marked operator assigned. The USGS explains in a frequently asked question on the 10-kilometer default that 10 km is a fixed depth used when the available data cannot support a dependable calculation. In the agency’s words, “In many areas around the world, reliable depths tend to average 10 km or close to it.” A histogram of well-constrained depths in such regions peaks near that value, which makes it a sensible placeholder when the true depth is unknown.
The agency used to default to 33 kilometers before revising the convention. For this event the practical meaning is that the quake can be described as shallow to moderate in the crust, but the precise depth is not established. Depth matters for how strongly a magnitude 5.0 shakes the surface, since the same energy released closer to the ground reaches buildings with less attenuation, so a fixed value limits what can be said about local intensity. A computed depth, if one is later published, may shift both the depth and the magnitude estimate by small amounts, and other agencies publishing their own solutions for the same event can differ from the USGS entry in every parameter, including location.
The tsunami flag and the National Tsunami Warning Center
A flag of 0 means the catalog entry does not indicate a tsunami threat. Tsunami messaging for the United States and Canada comes from the National Tsunami Warning Center, which runs tsunami.gov as part of NOAA’s National Weather Service. When that page was read for this report it showed no warning, advisory, watch or threat in effect, and its only listed event was a magnitude 4.2 quake near Homer, Alaska. The page does not say which body would issue messages for the Persian Gulf, so it cannot be used to speak for regional Gulf agencies.
An earlier magnitude 5.0 event in Bushehr province
Southern Iran has logged an mb 5.0 shock before. A Risklayer Explorer entry for an earthquake in Bushehr, Iran, dated December 5, 2024, lists the same mb 5.0 magnitude, a 10-kilometer depth, a location of 28.44 degrees north and 51.86 degrees east, and four recorded aftershocks. That position sits roughly 50 kilometers northeast of the October 31 epicenter. The page carries no impact or felt-report data, so it offers a comparison of size and place only, and it should not be read as evidence of damage in either case.
Open questions remain. The USGS record contains no casualty or damage information, and reports from Iranian seismological agencies and emergency services were not retrievable while this was prepared. Whether the analyst-reviewed depth will be revised, and whether any aftershocks have been catalogued, can only be settled by the USGS event page itself, which the agency updates as its analysts revise solutions.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
Help yourself and the planet: Get The Cool Down →
We may earn a commission if you sign up.
More from Morning Overview
- The NSA says three phone features should be off whenever you aren’t using them
- Hurricane Hunter radar shows four warning signs that a tropical cyclone is about to strengthen, a University of Miami study found
- Tropical Storm Rachel is dumping up to 12 inches on four Mexican states on its way to major hurricane strength
- The FTC says Lens.com doubled the price shoppers saw in Google ads
