Earthquake Alert: M4.6 Event Detected in Japan

An earthquake measuring magnitude 4.6 has been detected near 79 km E of Onagawa Chō, Japan, occurring at 14:00 UTC on Tuesday, August 4, 2026. Here is everything you need to know about what happened, what it means, and what to do.

The Basics

According to USGS data, this earthquake originated at a depth of 40.4 km beneath the surface. At a focal depth of 40.4 km, this is classified as a shallow earthquake (0–70 km). Shallow events are typically the most damaging: the seismic energy has less distance to travel before reaching the surface, resulting in stronger and more abrupt ground shaking at the epicentre.

A magnitude 4.6 earthquake is considered a moderate event. In practical terms, this means it is felt strongly by everyone; minor to moderate damage possible in vulnerable buildings.

Why Does This Area Get Earthquakes?

Japan sits at the convergence of the Pacific, Philippine Sea, Eurasian, and North American tectonic plates, making it one of the most seismically active countries on Earth.

Japan experiences roughly 1,500 earthquakes per year that are strong enough to be felt. The country has developed one of the world's most sophisticated earthquake early-warning networks, capable of alerting millions of citizens within seconds of a major rupture.

How Much Energy Is That, Really?

The magnitude scale can be deceptive to non-specialists because it looks like a simple number. In reality, it is logarithmic: each step up releases around 32 times more energy.

A magnitude 4.6 earthquake releases approximately roughly 500 tonnes of TNT of energy. For comparison, this exceeds the energy released by most conventional explosive events and is sufficient to shift tectonic stress in measurable ways across a wide region.

Moderate earthquakes are felt by virtually everyone near the epicentre. Strong shaking lasting 10–30 seconds can topple unsecured items, crack plaster, and cause poorly anchored objects to fall. Aftershocks are common following moderate events.

Should People Be Worried?

Significant damage can occur to vulnerable structures — particularly unreinforced masonry, old adobe buildings, and poorly maintained older construction. Well-engineered modern buildings are designed to withstand this level of shaking with minimal structural impact, though contents may shift and non-structural elements (ceilings, partitions) can be damaged.

Aftershocks are a normal part of the earthquake process and should be expected in the hours and days following any notable event. Most aftershocks are smaller than the main shock, but they can be significant — and structures weakened by the main event may be more vulnerable to subsequent shaking.

Staying Safe

Keep an earthquake emergency kit accessible at home. It should include at least 72 hours of water (4 litres per person per day), non-perishable food, a first aid kit, torch, battery-powered radio, copies of important documents, and essential medications. Reviewing and restocking this kit annually is strongly recommended.

Fasten heavy furniture — bookshelves, water heaters, cabinets — to walls using earthquake straps. Store breakable items on lower shelves and heavy items closest to the floor. These simple steps significantly reduce the risk of injury from falling objects.

If you are in Japan, follow J-Alert instructions and refer to local municipal evacuation maps. Many buildings constructed after the 1981 revised building code are designed to withstand strong shaking.

For real-time updates on this earthquake and all seismic activity worldwide, visit our live earthquake map. You can also read our full earthquake safety guide for detailed preparedness advice.

Community Felt Reports

If you felt this earthquake, your experience contributes to an important scientific dataset. The USGS "Did You Feel It?" (DYFI) system and QuakeWatch's own community reports platform collect first-hand accounts of shaking intensity from people across the affected region. These reports — describing where people were, what they felt, and what moved or was damaged — help seismologists map shaking intensity across an area much larger than any single seismograph can cover. Visit the earthquake's detail page on our live map to submit your own report.