Papers on Instrumentation

High quality data from LaCoste-Romberg Gravimeters with Electrostatic Feedback: A challenge for superconducting Gravimeters. W. Zürn, H.-G. Wenzel and G. Laske, 1991, Bull. Inform. Marrees Terrestres, Vol. 110, p. 7942 - 7952,  http://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=5393650

From Chandler wobble to free oscillations: comparison of cryogenic gravimeters and other instruments in a wide period range. Richter, B. and Wenzel, H.-G. and Zürn, W. and Klopping, F., 1995, Phys. Earth Planet. Int., Vol. 91, 131-148.  https://doi.org/10.1016/0031-9201(95)03041-T

What can superconducting gravimeters contribute to normal mode seismology? R. Widmer-Schnidrig, Bull. Seismol. Soc. Am. Vol. 93, p. 1370-1380, 2003,  https://doi.org/10.1785/0120020149

Forbriger, T., 2007. Reducing magnetic field induced noise in broad-band seismic recordings. Geophys. J. Int., 169: 240 – 258. https://doi.org/10.1111/j.1365-246X.2006.03295.x 

Forbriger, T., Widmer-Schnidrig, R., Wielandt, E., Hayman, M., Ackerley, N., 2010. Magnetic field background variations can limit the resolution of seismic broad-band sensors. Geophys. J. Int., 183: 303 - 312. https://doi.org/10.1111/j.1365-246X.2010.04719.x

Johannes Käufl, 2015. Temperaturstabilität seismischer Sensoren. Masterarbeit. Geophysikalisches Institut, Karlsruher Institut für Technologie. https://doi.org/10.5445/IR/1000050712

Nearly diurnal free wobble and tides

Stacking gravity tide observations in central Europe for the retrieval of the complex eigenfrequency of the nearly diurnal free-wobble. J. Neuberg, J. Hinderer und W. Zürn, 1987, Geophys. J. Roy. Astr. Soc. Vol. 91, 853-868. https://doi.org/10.1111/j.1365-246X.1987.tb01671.x

Free oscillatons

Observation of low order toroidal modes from the 1989 Macquarie rise event. (R. Widmer, W. Zürn and G. Masters, Geophys. J. Int. p. 226-236, Vol. 111, 1992), https://doi.org/10.1111/j.1365-246X.1992.tb00572.x

Observation of Coriolis coupled modes below 1 mHz. W. Zürn, G. Laske, R. Widmer-Schnidrig and F. Gilbert, 2000, Geophys. J. Int. Vol. 143, p. 113-118, https://doi.org/10.1046/j.1365-246x.2000.00220.x

Globale Eigenschwingungen der Erde. W. Zürn, and R. Widmer-Schnidrig, 2002, Physik Journal Vol. 1, p. 49-55
(Preprint, lange Version)

Widmer-Schnidrig, R., 2006. Application of regionalized multiplet stripping to retrieval of aspherical structure constraints. Geophys. J. Int. (2006)  https://doi.org/10.1046/j.1365-246X.2002.01004.x

Laske G. and Widmer-Schnidrig R., 2007. Theory and Observations: Normal mode and surface wave observations. Treatise on Geophysics, Vol. 1: Seismology and structure of the Earth, B. Romanowicz and A. Dziewonski, Editors. Elsevier, 2007. https://doi.org/10.1016/b978-0-444-53802-4.00003-8 

Zürn, W., Ferreira, A.M.G., Widmer-Schnidrig, R., Lentas, K., Rivera, L., Clévédé, E., 2015. High-quality lowest-frequency normal mode strain observations at the Black Forest Observatory (SW-Germany) and comparison with horizontal broad-band seismometer data and synthetics, Geophysical Journal International, Volume 203, Issue 3, 1 December 2015, Pages 1787–1803, https://doi.org/10.1093/gji/ggv381 

Surface waves

Frequency dependent polarisation measurements of long-period surface waves and their implications for global phase-velocity maps. G. Laske, G. Masters and W. Zürn, 1994, Phys. Earth and Planet. Interiors. https://doi.org/10.1016/0031-9201(94)90037-X

Surface wave dispersion and upper mantle structure beneath southern Germany from joint inversion of network recorded teleseismic events. S. Stange and W. Friederich, 1993, Geophys. Res. Lett. Vol. 20, p. 2375-2378. https://doi.org/10.1029/93GL02685

Shear wave splitting in the mantle below BFO

Shear wave splitting in the records of the German Regional Seismic Network. L. P. Vinnik, V. G. Krishna, R. Kind, P. Bormann and K. Stammler. 1994, Geophys. Res. Lett. Vol. 21, No. 6, p. 457 - 460. https://doi.org/10.1029/94GL00396

Receiver functions for BFO

Receiver functions at the stations of the German Regional Seismic Network (GRSN). R. Kind, G. L. Kosarev and N. V. Petersen, 1995, Geophys. J. Int. Vol. 121, No. 1, p. 191 - 202. https://doi.org/10.1111/j.1365-246X.1995.tb03520.x

Atmospheric effects on seismic data

Observation of Gravity changes during the Passage of cold fronts T. Müller and W. Zürn 1983, J. Geophysics, Vol. 53, p. 155-162. https://n2t.net/ark:/88439/y040712

Zürn, W., Wielandt, E., 2007. On the minimum of vertical seismic noise near 3 mHz. Geophys. J. Int., 168: 647- 658. https://doi.org/10.1111/j.1365-246X.2006.03189.x 

Zürn W., Exß J., Steffen H. Kroner C. Jahr T. and Westerhaus M., 2014. On reduction of long-period horizontal seismic noise using local barometric pressure. Geophys. J. Int., 2014. https://doi.org/10.1111/j.1365-246X.2007.03553.x  

On noise reduction in vertical seismic records below 2 mHz using local barometric pressure. W. Zürn and R. Widmer, Geophys. Res. Lett. p. 3537-3540, Vol. 22, 1995, https://doi.org/10.1029/95GL03369

Volcanic eruptions

Bichromatic excitation of long-period Rayleigh and air waves by the mount Pinatubo and El Chichon volcanic eruptions R. Widmer and W. Zürn, 1992, Geophysical Research Letters, Vol. 19, P. 765-768. https://doi.org/10.1029/92GL00685

Zürn W. and Widmer, R., World-wide observation of bichromatic long-period Rayleigh waves excited during the June 15, 1991 eruption of Mount Pinatubo. Chapter In: Fire and Mud: The 1991--1992 Eruptions of Pinatubo Volcano, Philippines, Editors.  R.S. Punongbayan and C.G. Newhall, Washington University Press. https://pubs.usgs.gov/pinatubo/zurn/

Absolute gravity at BFO

In march of 2001 our colleagues from EOST Strasbourg visited BFO for the first time with their FG5 absolute gravimeter. The meter was setup in the Heinrich Kluft (outside the pressure gate) in a 2m tall, heated (~18C) styrofoam box. During one week the sensor measured g for 10 minute long intervals around the full and the half hour. The FG5 is a free-fall absolute gravimeter in which the position of a freely falling corner cube is interferometrically measured over a distance of ~25 cm. The time between successive drops was 10s. As preliminary result we show here a screen dump of the measurements. A theoretical tidal model suitable for BFO has already been subtracted from the raw measurements.

Background free oscillations

The background free oscillations (also known as hum) were originally detected in recordings of STS-1 seismometers of the GSN and in recordings of both spring gravimeters by LaCoste-Romberg and superconducting gravimeters by GWR. (e.g. Suda et al., SCIENCE, Vol. 279, p. 2089-2091, 1998) To our surprise we found that these modes with an rms amplitude of only 1 ngal are also present in the recordings of 7 out of 14 STS-2 seismometers of the German Regional Seismic Network (GRSN). We show here a sonogram covering two years of data from the STS-2 at BFO.

Kurrle, D., and  Widmer‐Schnidrig, R. (2008),  The horizontal hum of the Earth: A global background of spheroidal and toroidal modes, Geophys. Res. Lett.,  35, L06304, https://doi.org/10.1029/2007GL033125

Superconducting gravimeter SG-056

Clara Bützler, 2017. Drift des supraleitenden Gravimeters SG056 am BFO Bachelorarbeit. Geophysikalisches Institut, Karlsruher Institut für Technologie. https://doi.org/10.5445/IR/1000082191 

Zhang Y., 2013, Coherency analysis between SGs at BFO and Strasbourg, MSc thesis, University of Stuttgart, Institute of Geodesy.

Wind turbines near BFO

Plans to build electricity generating windturbines in the immediate vicinity of our observatory have led us to evaluate the influence of windturbines on seismic background noise levels. The PDF poster (2.1 Mb) presented at the annual meeting of the German geophysical society (DGG) in Berlin in March 2004) summarizes our findings.

Signal attenuation with increasing distance from the windmill is shown in figure 7 of the poster. For selected frequencies with high coherency the fall-off is shown in fig. 8: vertical component at 12 Hz (fig. 8a, 170kB PostScript) , radial component at 9.5 Hz (fig. 8b, 170kB PostScript) , radial component at 2.5 Hz (fig 8c, 170kB PostScript) , transverse component at 2.5 Hz (fig 8d, 170kB PostScript) .

The observation, that already now, we are limited in our ability to detect high-frequency teleseismic signals by industrial noise from the nearby industry (4.7 Mb pdf) is an important piece of evidence in our line of arguments (note the reduced noise levels during lunch break from 11-12 UT or 12:00 - 13:00 local time). The same figure with a figure caption in German is here (119 MB compressed PostScript).

Three component sonogram of industrial noise recorded with the STS-2 at BFO is here (349 kB PostScript).

Signal decay with separation from a wind turbine is inspected here (168 kB PostScript).

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