At 08:13 UTC on November 2, an earthquake of magnitude 5.1 broke rock nearly 200 km below North Sulawesi, roughly 19 km west-northwest of the city of Tomohon. The U.S. Geological Survey placed the source at a depth of 196.6 km, deep enough that the surface sits about 122 miles above the point where the fault slipped.
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The event carries the catalog number us7000tuuy and sits at 1.392 degrees north, 124.648 degrees east. Its magnitude is an mb value, the body-wave scale seismologists favor for moderate and deep earthquakes, and the solution drew on phase picks from 77 seismic stations. Its significance score came in at 400, a rating that blends magnitude with expected impact.
The USGS record for event us7000tuuy
The agency’s event page for the Tomohon earthquake is the authoritative listing, though the page is built to render in a browser application and returned no readable text to an automated fetch. The same entry, pulled in machine-readable form through the USGS event query service, lists the origin time as 08:13:14 UTC, a tsunami flag of zero, and no felt reports or shaking-intensity estimate attached. Only two products had been filed against it: an origin solution and a set of phase data.
A tsunami flag of zero is what physics would predict. A rupture this far down in the mantle lifts no seafloor in any meaningful way, so the water above it stays calm.
Depth also decides how much a magnitude 5.1 matters on the ground. Seismic energy released at 197 km has to travel through that much rock before reaching the surface, and the shaking spreads over a wide area while losing amplitude. An earthquake of this size at a few kilometers depth can crack plaster and topple shelves near its epicenter; the same size at this depth is usually felt faintly across a broad region, if at all. The absence of felt reports in the USGS entry fits that pattern, although the entry was an early one and people often file reports hours later.
The Molucca Sea slab under the Minahasa peninsula
Earthquakes at such depths do not happen in ordinary crust, which is too warm and ductile to rupture below a few tens of kilometers. They occur inside cold slabs of oceanic plate sinking into the mantle, and northern Sulawesi sits above one of the most unusual such systems on Earth. According to the encyclopedia entry for the Molucca Sea plate, it is the only known example of divergent double subduction, a single oceanic plate diving beneath neighbors on both its sides, with oppositely dipping Benioff zones that meet at the surface. That process built the Sangihe and Halmahera volcanic arcs.
The same entry points to a January 2017 magnitude 7.3 earthquake deep beneath the Celebes Sea, which the USGS attributed to deep reverse faulting within the inclined seismic zone marking the plate’s lower limit.
A source near 197 km under Tomohon is consistent with that slab, and it would be unremarkable in a region where hundreds of earthquakes of varying size have been recorded. The mechanism solution for the November 2 event had not been published in the material read here, so the assignment to the slab is an inference from location and depth, not a finding from the agency.
Tomohon between Mount Lokon and Mount Mahawu
Tomohon is a landlocked city of about 104,260 people by a mid-2025 estimate, set at roughly 700 to 1,000 meters above sea level, which keeps it cooler than Manado on the coast. The reference entry for Tomohon describes it as flanked by two active volcanoes, Mount Lokon at 1,689 m and Mount Mahawu at 1,311 m, with the Mount Lokon Observatory based in the city itself.
Volcano-watchers tend to look twice whenever the ground moves near an active cone. A profile of the Lokon-Empung volcanic complex, which lists the summit at 1,580 m, recalls that the strongest recent eruption came in 1991, when more than 10,000 people were evacuated and ash and rock damaged 1,900 houses. A June 2011 eruption sent an ash column about 35 km high, and Strombolian to Vulcanian activity has recurred sporadically since. Heights for Lokon differ between references, which is why both figures appear here.
Nothing in the USGS entry connects the November 2 earthquake to any volcano. A source at nearly 200 km lies in the sinking slab, far beneath the shallow magma plumbing that feeds eruptions, and deep slab events of this size are a routine feature of the Molucca Sea region.
Unsettled details in the first USGS listing
Several details remain open in the early USGS entry. The mb magnitude can be revised once more stations are reconciled, a common adjustment of a tenth of a unit or so, and a moment tensor would show whether the slab broke in compression or tension. With no felt reports, no intensity map and a zero tsunami flag, there is no recorded evidence of damage near Tomohon from this event, and the listing’s own fields are the only measure available as of November 2.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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