4 March 1977
What the map shows and what the ground shows
At twenty-two minutes past nine that evening, a slab of crust broke 94 kilometres beneath the village of Spulber, in Vrancea county. The point marked on the map, the epicentre, lay 34 kilometres from Focșani and 158 kilometres from Bucharest. By the map, the capital was almost five times farther from the disaster.
The epicentre is a shadow, though, the surface projection of a place that sits deep. The journey to the earthquake itself is measured along the hypotenuse. Focșani was 100 kilometres from the rupture, Bucharest 184. The ratio on the map, close to five to one, melts inside the ground to less than two to one.
How much farther Bucharest was than Focșani from the earthquake of 4 March 1977, measured on the map and measured along the straight line to the rupture.
The source
A single spindle of rock, held vertical
The country has earthquakes in several places: Făgăraș, the Banat, Dobrogea, northern Oltenia. Yet of the 476 quakes of magnitude 4 or above recorded since 1900 in Romania and its immediate neighbourhood, 308 came out of a single volume of rock gathered under the Carpathian bend.
Seen from above, that volume is small. Half of those 308 earthquakes fit inside a square twenty-two kilometres on a side, about the size of a large commune. Seen in profile it looks entirely different: it descends from 61 to 184 kilometres, and the median earthquake sits at 136. Anyone living directly above it stands a hundred and thirty-six kilometres away from it, roughly the distance from Bucharest to Brașov, except downward.
The instrument
How far you live from Vrancea
The drawing below keeps the same scale in both directions: a kilometre travelled sideways is exactly as long as a kilometre travelled downward, which never happens on an ordinary map. Pick one of the country's 17,306 settlements and an earthquake from the catalogue.
The mechanism
Depth levels everyone out
The nearest village to the centre of the zone is called Secuiu, in Buzău county, four kilometres away. The farthest settlement in the country is Beba Veche, in the western corner of Timiș, at 482 kilometres. On the map, one of them is a hundred and seventeen times closer than the other.
Drag the depth and watch the ratio between them. At the usual rupture depth, a hundred and thirty-six kilometres, the Buzău village ends up merely 3.7 times closer to the earthquake than the Banat one. Depth brings nobody closer to the earthquake; it moves everybody away, in similar proportions.
Straight-line distance in kilometres from each city to a rupture at the centre of the Vrancea zone, at the chosen depth.
The rest
What happens once distance has been levelled
The closest village to the 1977 epicentre is called Prahuda, a kilometre and a half from it. The earthquake was still 94 kilometres away from it. That evening 1,578 people died, 1,424 of them in Bucharest, a city 184 kilometres from the rupture.
Geometry explains why it was felt everywhere, from Chișinău to Sofia. The rest is done by two things the map never shows. The first is the ground: Bucharest sits on the thick soft sediments of the Romanian Plain, which stretch and amplify long waves at precisely the period at which tall blocks sway. The second is what was put on that ground, above all the interwar buildings weakened by the 1940 earthquake and left unreinforced. On top of which, seismologists' reconstructions show the 1977 rupture travelling south-west, straight towards the capital.
The distance through the crust starts out much the same for the whole country. What follows is settled street by street.
The count
How many you have lived through
Since 1900, Vrancea has produced 36 earthquakes of magnitude 5 or above, nine of them magnitude 6 and four of them magnitude 7.
Each dot is one Vrancea earthquake of magnitude 5 or above, placed on its year. Size follows magnitude. The ones before the chosen year are dimmed.
The last Vrancea earthquake of magnitude 6 struck on 31 May 1990. Since 1900, the longest respite between two such earthquakes lasted thirty-one and a half years, from September 1945 to March 1977. The one we are living in has lasted more than thirty-six.
The numbers
The earthquake catalogue comes from the United States Geological Survey and covers quakes of magnitude 4 and above since 1900, deeper than 50 kilometres, inside the Vrancea rectangle. Settlement coordinates come from GeoNames. Map distances are computed on the sphere; distances through the ground use Pythagoras, as the hypotenuse of the epicentral distance and the depth.
That hypotenuse is the shortest possible path between a person and a rupture. Waves do not quite follow it, since they bend through layers of differing speed, and how much is felt at the surface also depends on the ground, on the size of the rupture and on the direction it travels. Depth fixes where every calculation starts. The layers above settle the result.