The Swiss National Strong Motion Network (SSMNet)
Dial-up network
In
the early 80's the Swiss Seismological Service together
with the formerly Federal
Office for Water and Geology (FOWG) started to
plan a strong motion network capable to study the
following seismological and engineering aspects:
- Characteristics of strong ground motion at different sites.
- Attenuation of strong ground motion with distance.
- Investigation of site effects due to different local geology.
- Investigation of the dynamic behaviour of main types of dams in Switzerland.
Financial support for purchase and installation of
the instruments was provided by the dam owners through
the Swiss
Association of Producers and Distributors of Electricity
(Verband Schweizerischer Elektrizitätswerke-VSE).
The annual costs for service, maintenance and data
compilation is covered by the government and contracted
to the Swiss Seismological Service. The installation
and commissioning of this network with a total of
110 strong motion stations was carried out between
1992 and 1998. Due to different requirements and aspects,
this network is subdivided in two subnetworks:
- free-field network (57 stations)
- dam-related network (53 stations)
The dial-up network uses a mix of GeoSig SMACH SM-2 12bit/16bit and SYSCOM MR-2002 12bit sensors, with the trigger level varying according to local noise conditions. By 2000, all recording systems were upgraded with a time code receiver (DCF or GPS).
In addition to these two networks another station
array with strong motion accelerographs is located
in all the Nuclear Power Plants of Switzerland.
This network is, contrary to the others, operated
by the Nuclear Power Plants themselves.
Annual
Strong Motion Bulletins
Please feel free to download the annual reports:
Modern Strong Motion Network
Since 2006, improvements to the SSMNet have followed the same structure as the SDSNet infrastructure - new strong motion stations are continuously monitored in real time with high dynamic range instruments at high sampling rates (Baer et al. 2007). Currently, strong motion sensors are co-located with broadband sensors at 13 sites, and similar instrumentation is installed at ~30 free-field, mainly urban locations. The network is remarkably dense in the Basel Area, the Wallis and the Graubünden, where the Swiss earthquake hazard is highest.
The strong motion sensors are uniformly all EpiSensors, set to 2g clip level, with ~155dB dynamic range and flat frequency response from 200Hz (above the Nyquist frequency at all sampling rates we use) to DC. The dataloggers, typically Nanometrics Taurus, are the current equivalent of the 24-bit SDSNet dataloggers.
Data from strong motion co-located with broadband are sampled at 120sps, and at 250sps at the standalone strong motion sites. Commercial ADSL lines are used for the standalone stations. Once the data reaches the SED, it is acquired, processed and archived in a similar manner to the broadband SDSNet stations.
