AlpTransit Gotthard Network

The AlpTransit Gotthard Network is operated under a contract with AlpTransit Gotthard AG. The purpose of the network is to monitor seismicity related to the construction of the Gotthard basetunnel.

Network

The network was originally installed in October 2005 in the region of Faido, TI. In the beginning the network consisted of 9 surface stations, including station FUSIO from the permanently installed SDSNet, and 2 stations in the tunnel. Station PIORA was installed in December 2007 close to the Piora zone. In October 2009, two stations (CHIR2, NARA) were moved to new sites in the north (CUNA, CURA) to extend monitoring capabilities towards the region of Sedrun. This was done in response to the northward movement of the excavation work. Stations are equipped with Lennartz short-period sensors (LE-3D 1s), Kinemetrics strong-motion sensors (EpiSensors ES-T), and Streckeisen STS-2 broadband seismometers. We use Nanometrics Taurus as digitizers. Data from all stations are streamed in real-time via ADSL to the SED data center in Zurich, except for station LUKA1 where only an ISDN link could be established. A map showing the stations is shown below. Photos of the installation can be found on the right.

Figure 1. AlpTransit Gotthard Network. Sensors used are marked by different symbols as indicated. Station FUSIO belongs to the permanently installed SDSNet.

Earthquake Activity

A total of 112 earthquakes have been recorded between October 2005 and August 2007. These earthquakes occurred in the vicinity of the subsection Faido, with the main activity between October 2005 and October 2006. Magnitudes of these earthquakes ranged from Ml=-0.9 to Ml=2.4. The largest event with a magnitude of Ml=2.4 was felt at the surface by people in nearby villages. Since September 2007 no earthquakes have been detected in the vicinity of the subsection Faido.

Figure 2. Hypocenter locations (circles) of earthquakes recorded between October 2005 and June 2007 in the vicinity of Gotthard basetunnel, section Faido. Circles are scaled by magnitude and color coded by time of occurrence as indicated. Stations are marked by triangles. Black line marks approximate location of the Gotthard basetunnel. Note, that earthquakes occurred very close to the tunnel.

In 2008, seismic activity shifted northwards. Since January 2008 a total of 75 earthquakes were recorded, of which 67 earthquakes could be located. These earthquakes occurred north of the Piora zone and are related to the excavation work between the Piora zone and the subsection Sedrun. Magnitudes of the earthquakes ranged between Ml=-0.4 and Ml=2.0; the largest event had a magnitude of Ml=2.0 and occurred in December 2009.

Figure 3. Hypocenter locations (circles) of earthquakes recorded between January 2009 and August 2010 in the vicinity of the Gotthard basetunnel. Circles are scaled by magnitude and color coded by time of occurrence as indicated. Earthquakes in 2009 are color coded with grey colors. Stations are marked by triangles. Black line marks approximate location of the Gotthard basetunnel. The bi-modal distribution in focal depths is a result of changes in the network geometry that observed the event.