North Korea said it conducted its fifth underground nuclear test on Friday. Since the first test, almost a decade ago, the size of the resulting earthquakes from the country’s test site have increased, indicating that the devices are becoming increasingly powerful.

The device detonated on Friday looks to have had a force equivalent of 10 kilotons of TNT, according to the South’s Defense Ministry. In contrast, the last device tested by the North, in January, had a force equivalent of six kilotons of TNT, the South’s intelligence agency said. The aboveground Trinity Test in New Mexico in July 1945, which ushered in the nuclear age, had a yield of 20 kilotons.

But power is not the only measure of a device’s lethality. The weapon must also have a way to be delivered. South Korean, American and Japanese officials want to determine whether the North Koreans are capable of building a miniaturized nuclear device that can be mounted on a ballistic missile and successfully detonated at a target hundreds, if not thousands, of miles from the launch site. In the past decade, South Korean and American experts have said that the North appears to be closer to achieving that goal.

Here is a timeline of how North Korea built up the capability of its nuclear weapons. The earthquake magnitudes are from the United States Geological Survey, which differ from those measured by the South Korean authorities. They may also be slightly revised from numbers reported immediately after the events.