A magnitude 4.7 earthquake struck the Aegean 42 kilometres southeast of Sykia

A magnitude 4.7 earthquake hit the northern Aegean at 10:45 UTC on October 30, 2026, which was 12:45 p.m. in Greece. The U.S. Geological Survey placed the epicenter 42 kilometres southeast of Sykia, at 39.73 degrees north and 24.23 degrees east, at a depth of 10 km. Its record lists no felt reports, no PAGER alert level and a tsunami flag of zero.

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Sykia is a village on the Sithonia peninsula of Chalkidiki, so the label points toward the coast of northern Greece, though the epicenter itself lies out at sea.

The USGS record for event us7000tu7m

The USGS event page carries the identifier us7000tu7m and the origin time of 10:45:03 UTC. A query of the agency’s earthquake feed for events of magnitude 4.6 and above since the start of October 29 UTC returns nearly 30 earthquakes worldwide. The Aegean shock is one of three listed at 4.7, alongside events in Panama and Poland, and it ranks far below the largest entry, a magnitude 6.4 quake southeast of Easter Island. It is the only Greek event in that list.

The detail record for the event shows how firmly the location is pinned. The solution uses 102 stations, the azimuthal gap, the largest angle with no station coverage, is 37 degrees, and the status is reviewed, meaning a USGS analyst has checked the automatic result. The record was last updated at 11:37 UTC, about 52 minutes after the origin time, and its significance score is 340.

The feed query is itself informative about what the list leaves out. It asks for GeoJSON output, a start time of midnight on October 29 UTC, a floor of magnitude 4.6 and ordering by size, so anything smaller, including any aftershocks below that floor, would not show up in it. A Greek station network with denser local coverage could log a longer sequence of small events than the global USGS list shows, which is another reason the instrument record here describes one shock and not the whole sequence.

Reading an mb magnitude

The 4.7 is a body-wave magnitude, written mb. According to the USGS magnitude types table, mb is based on the amplitude of the first-arriving P-waves at periods of about one second, and it is the authoritative global value only when no moment magnitude is available, typically for events between 4.0 and 5.5. The same table says mb tends to saturate at about magnitude 6.5 or larger. A 4.7 sits comfortably inside the range where the measure is designed to work, so the number is a reasonable description of the shaking potential rather than a placeholder.

A moment magnitude computed later by the agency or by a Greek institute could differ by a tenth or two, and local agencies often publish their own figures in the first hours. A reader comparing reports should expect small disagreements between agencies about the same earthquake rather than treat them as separate events.

Depth deserves a caution. Ten kilometres is a round figure, and the record gives no hint of how tightly it is constrained, so the shallow depth should be read as approximate.

For readers in Chalkidiki, the practical read of the record is limited to what it contains. The USGS lists no felt reports and no alert level, flags no tsunami and gives a depth of 10 km at a point offshore, and nothing in it describes ground shaking on land. Magnitude 4.7 is a moderate event, and whether it was noticed in Sithonia or on the Athos coast is not something the agency record settles.

A corner of Greece that keeps shaking

The northern Aegean south of Chalkidiki has been active for more than a year, though most of the recent events have been on the Mount Athos peninsula to the north of this epicenter. A magnitude 5.3 earthquake struck near Karyes, the peninsula’s administrative center, in June 2025 and caused minor damage to monasteries. On March 25, 2026, a magnitude 4.9 shock hit the same area at 21:08 local time, and a local news account quotes Efthymios Lekkas, president of Greece’s earthquake planning and protection organization, describing it as shallow and widely felt but without significant impact. Several aftershocks followed within minutes.

An earlier shock, a magnitude 4.8 on September 22, 2025, came about 11 km west-northwest of Karyes at a depth of 12 km. The Bulgarian News Agency reported that the Athens Institute of Geodynamics supplied the time, epicenter and depth, and that there were no reports of injuries or damage.

The newest event is a different kind of data point. It sits offshore, with no village directly above it, which is why the USGS describes it by distance from Sykia and not by a nearby town. No damage report for October 30 turned up in the sources read for this article, and no Greek institute bulletin was reachable, so what is firmly established is the instrument record: magnitude 4.7, 102 stations, no felt reports listed as of the 11:37 UTC update.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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