The Temporary Seismometric Network of Fadalto (Treviso, Italy)

Centro Ricerche Sismologiche, Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Cussignacco (UD) e Sgonico (TS)

A number of acoustical phenomena were felt by the population of the Val Lapisina and at Sella Fadalto during a period of some months spanning since the end of 2010 to the first part of 2011, within an about 10-km-wide area located between the municipal areas of Vittorio Veneto (TV) and Farra d'Alpago (BL). These events sounded like "bursts" or "rumbles", according to the people reports, and sometimes produced vibrations of glasses and furnishings, as well. During January 2011 the phenomenon became so strong that OGS, on behalf of the Civil Protection of the Veneto Region, started the seismic monitoring of the area by deploying temporary network (Fig. 1).

Figure 1. Seismogram recorded for one of the events occurred in Val Lapisina.

Figure 2. Map of the temporary seismometric network deployed in Fadalto (Treviso, Italy). Left: general overview; right: detail of the area.

The Fadalto temporary network developed and changed in time, as the results came in, in order to get more and more close to the actual location of the phenomena and improve its sensitivity and precision of the locations. The first kernel of the network wa deployed on January 26, 2011, and it used 7 stations. For four stations (i.e. FADA, FA03 e FA04 e VISE), the location remained unchanged, while the other 3 stations were moved. In first two months of monitoring, a total of 12 sites were occupied, and the geometry of the network converged on a less-than-2-km wide area centered at the locality of Fadalto Basso, close to site FADA, which proved to be the epicenter of the phenomenon (Fig. 4).

Fig. 3. Seismic events localized by the temporary network of Fadalto in the period 1-28 February, 2011.

Finally, some details about the instrumentation (Table 1). 5 stations were equipped with 24-bit Reftek 130 digital acquisition units and Lennartz LE3D Lite 1s short-period seismometer. These units recorded in local mode, so that data had to be manually downloaded every 2-3 days. The other 2 stations were equipped with 24-bit digital acquisition units Quanterra Q330, one of them with a Lennartz LE3D Lite 1s short-period seismometer and the other with a broad-band Nanometrics Trillium 40 sensor. Initially, the sampling period was set at 100 sps, however, when it became clear that the target was that high-frequency bursts, the sampling was increased to 200 sps. All stations were equipped with internal GPS, in order to ensure the correct synchronization of the recording time.

Table 1. Details of the instrumentation used for the temporary network of Fadalto.