The Rhine Falls roar and thunder this morning, the spray looking like fog against the light. A small boat makes its way from the observation rock in the middle of the foaming water masses to Wörth Castle.
Two men disembark. One of them is Mauro Häusler, a geophysicist and Pioneer Fellow at ETH Zurich, the other Lorenz Grämiger from the geology consultancy Dr. von Moos AG. They have just set up seismometers on the rock and at its base.
Now they take a white ETH minivan to another location on the edge of the Rhine Falls. A concrete visitor platform seems the right choice to Häusler. In just ten minutes, he sets up another measuring station and the experiment can begin. The goal is to use seismic surveys to investigate how stable the observation rock in the Rhine Falls is.
On the path to self-employment
For Häusler, the measurements at the Rhine Falls and its rock are something of a test run. Having defended his doctoral thesis in September, he is now about to start his own business. His business idea is to prepare seismic surveys on the stability of rocks and slopes.
To do this, Häusler uses a series of seismometers that sense and record vibrations or shockwaves that propagate underground. In this way, the young entrepreneur takes advantage of the fact that earthquakes, wind, rivers and road traffic all generate vibrations that race through the subsoil as waves.
On their journey, the waves encounter obstacles or disturbances of various kinds. For example, they are deflected at fractures or fissures in the rock. Meanwhile, any unstable, loosened material amplifies the amplitudes of the waves. That means the wave patterns the seismometer is recording provide information on the nature of the subsurface.
In addition, these vibrations stimulate the rocks, mountains or buildings they encounter to vibrate themselves, like a guitar string being plucked. The seismometer also records the objects’ natural vibration frequencies, which gives an indication of how solid they are and which areas of a slope or rock are structurally connected.
If the rock vibrates at the same time and at the same frequency at two measurement points, it is highly probable that they belong to the same structural volume. In general, large volumes oscillate more slowly, i.e. at a lower frequency, than small volumes.
For example, the period of oscillation of most rock instabilities is between 0.1 and 0.3 seconds, while for mountains like the Matterhorn they last more than two seconds, as Häusler discovered; he co-authored a study (see
ETH News
) on the famous peak’s resonant frequencies.
