Kunming’s earthquake: magnitude, intensity and non-structural hazards

I grew up in Yunnan, so earthquakes, landslides and mudslides were familiar to me long before I became an engineer. Tonight, an earthquake struck Kunming, the capital of Yunnan Province and my hometown.

At 6:31 pm local time, a magnitude 4.3 earthquake occurred in the city’s Panlong District at a depth of 10 km, according to the China Earthquake Networks Center.

As a structural engineer, I want to clarify the difference between magnitude and intensity. Magnitude describes the energy released by an earthquake. Intensity describes the shaking and effects experienced at a particular location. It can vary across a city with distance, ground conditions and other factors.

Based on the reported parameters, my preliminary estimate is around intensity V near the epicentre, possibly VI in some local areas, and around IV–V elsewhere in the urban area. These are not official measured intensities; the earthquake authorities’ assessment should take precedence.

Much of central Kunming has a seismic design intensity of VIII. Serious damage to the primary structure of buildings properly designed and constructed to the applicable standards is therefore less likely in this event. But falling ceiling panels, façade finishes, glass and other non-structural elements can still injure people—as the circulating footage reminds us.

I have sent this message to all my family, friends, neighbours and mates - Please stay clear of damaged areas, watch for aftershocks and falling debris, and do not re-enter a building with significant new cracks, leaking gas or damaged elements until it has been assessed.

The video is a compilation of clips circulating online. I did not film them and have not independently verified every location personally.

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