It happened on 14 September
The morning when the earth shook right up here
On 14 September 1866, at ten past five in the morning, An earthquake strikes the Berry region. The intensity at the epicentre is 7 on the macroseismic scale, which indicates significant damage.
The tremor travelled across half of France. It was felt as far as Paris, where the national database of historical earthquakes classified it as a 3.5, felt by a few people. Here, The Fontainebleau Bee discusses this in its 16th issue : ‘The previous day’s newspapers,’ she writes, ‘reported earthquakes in Seine-et-Oise, in the Seine and elsewhere, which were felt on Friday 14 September at around five o’clock in the morning.’.
One Friday morning, before daybreak, The region came to life at the same time as a part of the Berry region.
The day we heard space-time vibrating
On 14 September 2015, the two LIGO twin detectors, in Livingston, Louisiana, and Hanford, Washington, record the same shiver at seven-millisecond intervals.
This is the first direct detection of gravitational waves, which were predicted a hundred years ago. The signal comes from the merger of two black holes, each with a mass of around thirty solar masses, 1.3 billion light-years away.
The discovery will not be announced until 11 February 2016. It will win the 2017 Nobel Prize in Physics.
Measuring an earthquake that occurred before seismographs were invented
How do we know, 160 years later, just how violently the earth shook one morning in 1866? There was not a single seismograph in France.
We know this because people have written about it. The national database of historical earthquakes records, for this single tremor alone, three hundred and twelve localities, each with an intensity derived from the residents’ descriptions. A moving object, a sleeper waking up, a window pane vibrating: each account counts as one degree on the scale.
One hundred and forty-nine years later, it took two detectors, each four kilometres long, to ‘hear’ space-time. In 1866, all it took was for one local resident to put pen to paper.
