A new earthquake shock affected Tuscany on the morning of Wednesday, August 12: an event of magnitude 3.7 – followed by a smaller one of magnitude 2.2 – located on the northern coast of the region, distinctly felt between Massa‑Carrara, Lucca and Pisa, with clear reports also from the province of Livorno, where many people perceived a brief but sharp tremor. This shock fits into a seismic framework that, in recent days, has been providing experts with new elements to understand the deep geology of the Pisan plain and coastal areas.
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The link with August 4
The magnitude 4.1 earthquake recorded on Tuesday, August 4, clearly felt throughout the Pisa province, represented a significant event for an area that historically does not host high-energy earthquakes. Experts from the Seismology Group of the University of Pisa completed the initial analyses, identifying the origin of the earthquake in a seismic structure buried under the Pisan plain, a few kilometers from the coast and at about 9 km depth. The main event was located a few kilometers southwest of Pisa, thanks to recordings from the seismic network of the University of Pisa (equipment purchased by Cisup within the PNRR Etic), integrated with those from Ingv and the University of Genoa. The moment magnitude was estimated at Mw 4.1, with a normal-type focal mechanism and a small strike-slip component: a behavior consistent with what is already known about the area’s tectonics.
What emerges
According to seismologists, the August 4 shock represents the activation of a extensional structure located at about 8–9 km depth. An interesting element concerns the geometry of the cluster: the hypocenters are arranged along a North–South oriented band, compatible with one of the nodal planes of the focal mechanism. However, the limited number of events does not allow for certain identification of which fault plane was activated: further aftershocks and relative location analyses will be necessary in the coming days.
Aftershocks and innovative techniques
After the main shock on August 4, about ten aftershocks were recorded, all of lower magnitude and concentrated in the same area. In the epicentral area, the number of seismic stations is limited: this makes it difficult to identify smaller earthquakes, which are however essential to reconstruct the fault geometry. To overcome this limitation, seismologists from the University of Pisa will apply innovative waveform analysis methods, developed internally by the research group, capable of locating even very weak events with very few stations available. The goal is to obtain a detailed reconstruction of the entire sequence, useful to precisely define the responsible tectonic structure.
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Connection with the August 12 shock
The magnitude 3.7 shock recorded on August 12 on the northern coast of Tuscany does not belong to the same sequence as August 4, but confirms a broader framework: the coastal band between Pisa, Lucca and Massa‑Carrara is affected by deep seismic structures, often silent, that only events of this intensity allow to “illuminate”. The fact that the August 12 earthquake was clearly felt also in the province of Livorno indicates that the energy propagated efficiently along the coastal plain, a geological environment that tends to amplify seismic waves.
What it means for the territory
This is not a sequence evolving towards stronger events: experts speak of normal seismic activity related to deep structures. Ongoing analyses will allow better mapping of the hidden geology under the Pisan plain and the northern Tuscan coast. Events like those of August 4 and 12 are valuable for understanding areas that, although not highly hazardous, can generate shocks felt by the population.
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