The 1977 earthquake, over today's red-dot buildings

Find your building or street#

Type a street. The map moves there and shows the buildings on the list. For a building, the card gives the time the wave arrives, its probable period and what engineers measured in 1977 for buildings of similar periods in the same square kilometre. It does not say what would happen to it.

How long the wave takes to arrive#

The 4 March 1977 focus lay about 94 kilometres below Vrancea, roughly 183 kilometres from central Bucharest in a straight line. In the calculation, the P wave reaches the city about 23.7 seconds after the rupture begins and the S wave about 41.5 seconds after. Their gap, 17.8 seconds (between 17.1 and 18.4, depending on the speed ratio), is close to the 18 seconds of weak, almost purely vertical motion at the start of the INCERC record (Bălan and others, 1982). The speeds used, 4.4 and 7.7 km/s, were chosen for this model, not measured along the waves' path to Bucharest; the similar intervals do not validate the absolute times.

The city is small next to the distance to the focus. In the calculation, the S front passes over the 2,550 buildings in 2.4 seconds, and it reaches nine in ten within a total interval of 0.9 seconds. The 'Slow motion' button stretches these seconds so you can see the estimated order. The interval is shorter than one sway of the ground, which in 1977 had a period of 1.4–1.6 seconds.

What follows lasts much longer: the strong phase of the record held 10–15 seconds of a minute or more, and long, low-amplitude waves appear after 30–40 seconds. The earthquake was a multiple event, with the focus migrating south-west. The calculation treats it as one source, at the USGS location (19:21:54 UTC, that is 21:21:54 local time); absolute times are approximate.

What was measured in 1977, by square kilometre#

During two periods, 4–8 and 25–28 April 1977, more than 200 students of the Institute of Construction and the Institute of Architecture, led by the city's seismic microzonation commission, recorded the damage to about 18,000 Bucharest buildings. The city was divided into squares of about one square kilometre; in 66 of them about 300 buildings each were surveyed. Each got a damage degree from 0 (none) to 5 (collapse) and was put in a band of its own period. The result is an average per square, per band and per category: masonry with flexible floors, masonry with rigid floors, reinforced-concrete frames.

The authors' conclusion deserves reading before the colours. The same survey gives different MSK intensities in the same square, depending on the buildings' period, and flexible concrete-frame buildings were more damaged than rigid masonry ones, the reverse of what the scale assumes. So there is no single intensity per street; there is one value per period band. Bulevardul Magheru, judged the worst hit right after the quake, shows small damage for low buildings and very large damage for those with a period over one second.

Squares without a column were not surveyed or have no buildings in the chosen band. We did not fill the gaps or interpolate between squares. The authors found no direct correlation between damage and the surface-layer parameters they examined; they proposed an explanation in Bucharest's deeper geology, for which they lacked sufficient data.

What the USGS model says#

USGS reconstructed the 1977 earthquake as a ShakeMap, from 747 intensity observations, three stations and a source extended along a fault. Over Bucharest it gives MMI intensity between 7.2 and 8.0 and peak acceleration between 0.21 and 0.27 g; at INCERC 2.1–2.2 m/s² was measured, about 0.22 g. Its values lie on a grid spaced roughly 1.3 by 1.9 kilometres and do not capture all the local effects that influence damage.

In the squares where buildings fell, the model's intensity averages 7.89; in the others, 7.84. The difference between these averages is small. The 'USGS model' layer lets you compare individual squares.

Where buildings collapsed and what the 1977 survey recorded#

We placed the 28 sites of total or partial collapse from the INCDFP layer used on the earthquake page on the survey squares. These are the sites mapped in that layer, not the full count of documented collapses in Bucharest. Three buildings were rebuilt and still stand today. We compared their locations with damage recorded for buildings with periods between 0.7 and 1.3 seconds. This comparison has values from table V.1 only for reinforced-concrete frames, in 16 central squares; we do not know the period or structure of each of the 28 buildings.

In 5 of these 16 squares (numbers 21, 31, 34, 51, 52), the mean damage degree for reinforced-concrete frames reaches 4 or 5 in the 1.0–1.3-second band. Values for the 0.7–1.0-second band are lower or absent. Of the 28 collapsed buildings, 11 are located in one of the five squares. If we also include squares within 350 metres of a building's position, the count rises to 20; 350 metres is a chosen comparison buffer, not a measured error margin.

This overlay describes locations; it does not test whether average damage would have predicted collapses. The collapsed buildings cluster in the centre, and the 16 squares with long-period values were selected, not sampled at random. We also do not know how many buildings contributed to each average in the table.

Where the comparison fails: for 5 collapsed buildings we have no long-period value in their own square; one lies outside the surveyed squares altogether. Squares 31, 34, 51 have a mean degree of 4–5 in the 1.0–1.3-second band but contain none of the 28 buildings. Block OD16, in Militari, lies in a square with just one value, for low buildings.

The survey covered about 300 buildings per square, chosen along streets; the table does not say how many fell in each period and structural group. A square's average may conceal large differences between buildings.

What the page cannot say#

• Whether a particular building would stand. The red dot marks an RsI classification made through an engineering assessment; the class signals susceptibility to collapse in the design earthquake. For an individual building's condition, read its assessment report.
• What the ground was like, street by street. The record is in squares of about a kilometre, placed approximately on today's map, and has nothing between them.
• What a building is made of. The period is estimated from the storey count with the European code's formula; masonry or concrete is unknown.
• Buildings that are not on the list. The list has 2,796 rows. Absence from this table says nothing about a building's safety or whether an assessment report exists elsewhere.
• What was strengthened, and how. 'Strengthened' rows appear on the map, but the list does not say what work was done.
• The 1940 earthquake. We found no comparable record by square; the period macroseismic maps we consulted cover the whole country. That is why the page has 1977 only.
• The next earthquake. It may have a different epicentre and duration; it will find a changed city.
• An assessment. For a particular building, ask the administrator or AMCCRS for the assessment report.

What the classes mean#

A class is set only by a technical assessment from a certified engineer. Law 212/2022 defines them by what would happen to the building in the design earthquake, the reference quake used when designing new buildings.

• RsI

  May collapse, wholly or in part. City Hall puts a notice panel at the entrances of a residential building in this class: that is the 'red dot'.

• RsII

  Major damage that endangers people, but collapse is unlikely.

• RsIII

  Moderate damage that may endanger people.

• RsIV

  In the design earthquake, its expected seismic response is similar to that of a building designed to today's codes.

• U1, U2, U3

  1990s codes under repealed rules: strengthening deadlines of 2, 5 or 10 years. City Hall says they cannot be converted automatically into RsI–RsIV.

The list has 415 RsI buildings, 388 of them on this map.

Method, in short#

Recorded, calculated, illustrative. Recorded are the damage degrees in map V.25 a–e and in table V.1 of Bălan's book (the reinforced-concrete-frame column), entered twice, independently: the two readings matched in 139 of 140 boxes, and the table column matched the map in 51 of 56 comparable values. The column colour is calculated from the simple average of the available building-type values; we do not know how many buildings each type represents. Also calculated are the arrival seconds, each building's estimated period when its storey count is known, and the position of the squares on today's map. Illustrative are the curve by which the columns grow in time, their height and the size of the boxes.

The squares. Figure V.23 of the book has the grid of squares on a 1977 plan of the city. We matched the plan's landmarks (the main roads) to OpenStreetMap roads; the resulting positions are approximate, with no measured error margin. Each square comes out at about 1.05 by 0.98 kilometres. The numbers in map V.25 attach to squares through the numbers in V.23.

Building period: T = Ct · H^0.75, with H of 3.0–3.5 m per storey and Ct between 0.05 (masonry, other structures) and 0.075 (reinforced-concrete frames), after EN 1998-1. The card shows every band intersected by the estimated range. If the list has no storey count, the period is unknown.

Wave arrival: a point source at the USGS location, speeds of 4.4 km/s (S) and 7.7 km/s (P). The columns grow in time along an illustrative curve that peaks 12 seconds after the S wave, the length of the strong phase in the INCERC record.

Buildings: rows of the AMCCRS list of 19 May 2026 with a point on the exact address, from OpenStreetMap or the DupăCutremur export (CC BY 4.0): 2,550 of 2,796. The page 'Bucharest's red-dot buildings, one by one' also places 74 buildings by the middle of a number range; we did not use them here because each building gets a square attached.

Rights and sources: the Zenodo record attributes copyright in Bălan's book to its publisher; OpenStreetMap is ODbL; DupăCutremur is CC BY 4.0 (Re:Rise, geo-spatial.org); the USGS data are published by the US Geological Survey; the list is published by AMCCRS.

Sources#

The earthquake and the ground

• Bălan, Cristescu, Cornea (1982), the 4 March 1977 earthquake, Editura Academiei: ch. V (the 18,000-building survey, fig. V.23, V.25 a–e, table V.1), pp. 131, 147, 238–240. Scan on Zenodo; copyright attributed to the publisher
• USGS ComCat, event usp0000mtc: 4 Mar 1977, 19:21:54 UTC, 45.772° N 26.761° E, depth 94 km, Mw 7.5
• USGS ShakeMap Atlas v4 for the same event (747 intensity observations, 3 stations; source Radulian & Popa 1996)
• ISC Bulletin, event 700695 (alternative location: 45.879° N 26.655° E, 85 km)
• EN 1998-1:2004, §4.3.3.2.2: approximate fundamental period T = Ct·H^0.75 (Ct 0.05 and 0.075)
• Lungu, Arion (2012), Seismic risk and/or real estate risk for the Bucharest heritage buildings, 15 WCEE (Berg et al. 1980 and the 1940 earthquake, quoted there)

The buildings

• AMCCRS (Bucharest City Hall), list of buildings with a technical expertise and a seismic risk class, table updated 19 May 2026
• OpenStreetMap: addresses, roads and administrative boundaries, downloaded 28–29 Sep 2026 (ODbL)
• DupăCutremur (Re:Rise and geo-spatial.org), points for the AMCCRS list buildings, export of 20 Jul 2026, CC BY 4.0
• The buildings that fell in 1977: INCDFP's layer of buildings affected by earthquakes, as used in the 1977 earthquake page

Classes and law

• Law 212/2022 on measures to reduce the seismic risk of buildings (arts. 1, 3)
• AMCCRS, clarifications on myths about seismic risk classes and technical expertises, 4 Mar 2025

Related pages and other maps

• 'Bucharest's red-dot buildings, one by one': the same list, on each building's outline
• 'The 4 March 1977 earthquake': the fallen blocks, in 3D
• 'How strong?': seismic hazard by locality (Order MDLPA 1037/2026)
• INCDFP, 'The seismic risk of Bucharest': a 2D/3D app with hazard, historic damage and emergency routes

The same list, on each building's outline: Bucharest's red-dot buildings, one by one. The blocks that fell in 1977: The 4 March 1977 earthquake. All the earthquake pages in one place: Romania's earthquakes.