Ground Motion Relations While TBM Drilling in Unconsolidated Sediments

The induced ground motions due to the tunnel boring machine (TBM), which has been used for the drilling of the urban metro tunnel in Karlsruhe (SW Germany), has been studied using the continuous recordings of seven seismological monitoring stations. The drilling has been undertaken in unconsolidated sediments of the Rhine River system, relatively close to the surface at 6–20 m depth and in the vicinity of many historic buildings. Compared to the reference values of DIN 4150-3 (1–80 Hz), no exceedance of the recommended peak ground velocity (PGV) limits (3–5 mm/s) was observed at the single recording site locations on building basements during the observation period between October 2014 and February 2015. Detailed analyses in the time and frequency domains helped with the detection of the sources of several specific shaking signals in the recorded time series and with the comparison of the aforementioned TBM-induced signals. The amplitude analysis allowed for the determination of a PGV attenuation relation (quality factor Q ~ 30–50) and the comparison of the TBM-induced ground motion with other artificially induced and natural ground motions of similar amplitudes

On the effects of wrongly aligned seismogram components for shear wave splitting analysis

Seismic anisotropy inside the Earth’s interior, especially in the upper and lowermost mantle, is commonly studied by measuring shear wave splitting. This is mostly done by the determination of the splitting parameters fast polarization direction and delay time as well as the splitting intensity. The applied techniques highly rely on the correct temporal alignment of the single component traces (vertical, North, East referred to as Z, N, E components) of an earthquake relative to each other. Mixing wrongly aligned recording components would result in misleading and wrong data representations, including the particle motions in both the ZNE and the ray (LQT) coordinate systems and waveforms in the LQT coordinate system. The main pitfall in this context is that start and end times of the single traces in general differ due to data storage details. Unfortunately, the code of the widely used MATLAB based shear wave splitting software package SplitLab contains an error which can cause a wrong relative temporal alignment of the input seismograms in some cases. This effect distorts under certain conditions splitting signals or simulates non-existing ones. We show examples and offer a remedy