Magnitude 4.4 earthquake shakes Vorarlberg – aftershocks into the morning

Perceptions among the population

Clear perceptions were also reported from Frastanz. One account stated: „Hat sich angehört wie eine Sprengung in der Nähe“. Another person from Frastanz wrote: „Erste Vermutung, da hat sich einer mit TNT auf der Baustelle in der Felsenau verschätzt“. These reactions showed that many residents initially did not think of a natural quake at all.

The Earthquake Service stated: „Es kann bei dieser Magnitude vereinzelt zu leichten Schäden wie Rissen im Verputz kommen“. Greater damage or injuries were initially not reported. A quake magnitude of 4.4 is by no means commonplace in Austria: „Eine Stärke, die man in Österreich nicht allzu häufig zu spüren bekommt, bleiben die allermeisten spürbaren Beben für gewöhnlich doch recht deutlich unter der 4er-Grenze“, it was said in this regard.

Magnitude assessment

Further tremors followed the main quake. A total of seven additional aftershocks were recorded after the quake. The strongest aftershock occurred at 6:15 a.m. and had a magnitude of 2.1; the one immediately after the main quake at 2:04 a.m. still had a magnitude of 1.2. The remaining aftershocks were all between 0.2 and 0.8.

The aftershocks extended from 2:04 a.m. in the early morning until 7:16 a.m. in the morning. The phase of measurable aftershocks thus lasted around five hours. However, only the stronger tremors were noticeable during this period, since quakes below a magnitude of 2 are in the rarest of cases actually noticed by people.

The incident in Vorarlberg was not the only one in Austria in these days. Already in the night from Thursday to Friday, the earth had trembled at the Styrian-Lower Austrian border, in the region around the Semmering. At pretty much exactly 2 a.m. in the early morning, many people in the Styrian-Lower Austrian border region were torn from their sleep.

Aftershocks in detail

This quake at the Semmering also reached a magnitude of 4.4, as GeoSphere Austria reported. „Vier der sieben wurden der Region rund um Gloggnitz in Niederösterreich zugeordnet, der auch das Hauptbeben zugeordnet worden ist, drei haben in der Steiermark stattgefunden“, the Earthquake Service summarized the distribution of the aftershocks.

The earthquake services pointed out that it depends on the focal depth and the region in which the epicenter is located from when a quake is felt. Quakes below a magnitude of 2 are, however, in the rarest of cases actually noticed by people. The main quake in Vorarlberg thus lay clearly above the perception threshold.

The temporal and spatial clustering of the events was remarkable. „Also auch wenn die acht eine Bundeslandgrenze trennt, hatten ihr Epizentrum im Radius weniger Kilometer“, it was said in connection with the situation. The two main quakes were several hundred kilometers apart, which underlined the random nature of the occurrence.

Parallel quake at the Semmering

Social media played an important role in documentation. Numerous people reported in under the corresponding Facebook posting and described their perceptions, including the sentence: „Spiegel haben geklirrt“. Such reports helped the authorities better assess the actual extent of perception.

So far there have been no reports from Vorarlberg of injuries or severe property damage. The authorities continued to monitor the situation. The Earthquake Service pointed out that minor damage such as cracks in plaster could occasionally be possible at this magnitude.

Overall, the events made clear that Austria is repeatedly affected by perceptible earthquakes. Two quakes of magnitude 4.4 within a few hours in different regions are statistically striking. Experts emphasized at the same time that such values are not unusual in the region, but that they rarely occur directly one after the other.

Reports on social media

For the coming days, the experts expected further weak aftershocks. These are normal and generally pose no danger. The population was nevertheless asked to watch for cracks on buildings and to report them if necessary.

In conclusion, it can be stated that the earthquake in Vorarlberg was clearly perceptible but, according to the current state of affairs, had no severe consequences. The precise evaluation of the data by GeoSphere Austria was ongoing.