© Lenhardt/Tiere Motus Museum/2016

Forty years ago a catastrophic earthquake occurred in Italy near Gemona. On Thursday 6 May 1976 at 20:59 the ground started shaking, claiming nearly 1,000 deaths and 80,000 people were left homeless.

Impact in Austria

The earthquake was felt throughout Austria and caused building damage in Southern Carinthia too. Because of this earthquake and the resulting experience the construction standards for earthquake-resistant constructions in Austria were revised, and the highest dam in Austria - the Kölnbreinsperre in Malta in Carinthia – was equipped with a seismic station by the ZAMG. As it turned out, the cause of the earthquake was a shift of the Adriatic plate beneath the European plate at a depth of about 15 km.

The effects of the earthquake on 6th of May 1976 were felt almost throughout Austria. The different shadings in the graphic indicate areas of similar impact In Southern Carinthia the consequences were particularly strong due to its proximity to Gemona and Venzone.

© ZAMG/Dept. of Geophysics



Observations

A so-called Conrad pendulum recorded the ground movements in Vienna at the ZAMG clearly which were even noticed sporadically in Vienna. It goes without saying that with today's instruments all recorded ground motions are also being felt. Today's seismometers are much more sensitive and are capable recording earthquakes of a much smaller magnitude worldwide.
The seismic waves of an earthquake in Friuli need more than 1.5 minutes to be recorded in Vienna. However, seismograms were only be replaced every two days. Readings could be done only on the constantly moving seismogram, which was somewhat cumbersome. There could still be a stronger earthquake to come ...

© ZAMG/Dept. of Geophysics

The aftershock activity stopped months later and kept the local population constantly in fear. At that time seismologists were convinced this would be the largest earthquake in Friuli for a long time, and now the earthquake activity would decrease. Seismologists were taken by surprise when on 15 September 1976, a nearly as strong earthquake occurred, just few 10s of kilometers from Gemona, in Tolmezzo. This earthquake caused many more buildings in Gemona and Venzone to collapse, and another 30,000 people lost their homes.

© ZAMG/Dept- of Geophysics

More rapid information

The following figure shows the trend of seismic activity, as detected in Austria from the ZAMG time with the then technical means. Today we would record at least 100 times more earthquake of this region, simply because the Austrian Seismological ZAMG massively is expanding its monitoring network to detect earthquakes. A nightmare for analysts…

For over 20 years the records already are digital and the ZAMG automatically exchanges waveforms with neighboring countries.
Thus, a detection of an earthquake in this area takes is now possible in less than 20 seconds. Much less when compared with the travelling times of seismic waves propagating to the headquarters of the Seismological Service in Vienna…

The research continues …

Austria is a country exposed to intermediate seismicity. This experience by the public often led to believe that this natural hazard is negligible because stronger earthquake fortunately did not affect every generation. However, if a stronger earthquake happens, the damage could be locally substantial.

Therefore, a new seismic hazard map is currently being developed at the ZAMG, which will serve the population and meets international requirements. This is a very comprehensive and challenging task, as soil conditions throughout the country need also be considered. This investigation enables the ZAMG/Geophysics to adapt the national building code. In addition, emergency services in Austria will be much faster and precisely informed on the impact of earthquakes in Austria and effects of strong earthquakes in adjacent countries affecting Austrian territory.

In September 2016 the European Seismological Commission (ESC) will held its General Assembly in Trieste and many presentations will deal with this earthquake 40 years ago.

Walking through Venzone, which was hit by the earthquakes in May and September 1976, one finds numerous testimonies of damages (the picture shows damages in the Duomo die San Andrea Apostolo) related to that devastating earthquake.

© Lenhardt 2016

An overview on this series of earthquakes in 1976 offers the museum "Tiere Motus" in Palazzo Orgnani Martina in Venzone which is worth visiting. Please check opening times.

Links:

Earthquake: https://de.wikipedia.org/wiki/Erdbeben_von_Friaul_1976
Building Code in Austria (in German): http://www.oge.or.at/oge_norm.htm
Exhibition: http://www.tieremotus.it/en/index.html