Gravimeter search for compact dark matter objects moving in the Earth

Dark matter could be composed of compact dark objects (CDOs). These objects may interact very weakly with normal matter and could move freely {\it inside} the Earth. A CDO moving in the inner core of the Earth will have an orbital period near 55 min and produce a time dependent signal in a gravimeter. Data from superconducting gravimeters rule out such objects moving inside the Earth unless their mass $m_D$ and or orbital radius $a$ are very small so that $m_D\, a < 1.2\times 10^{-13}M_\oplus R_\oplus$. Here $M_\oplus$ and $R_\oplus$ are the mass and radius of the Earth.Comment: 8 pages, 7 figure

Windkraftanlagen als seismische Störquellen

Windkraftanlagen werden in den letzten Jahren durch den Gesetzgeber in der Bundesrepublik massiv gefördert. Bauanträge für vier Anlagen mit einer Nabenhöhe von 100m und einer Entfernung zu den geophysikalischen Sensoren des BFO von 500 - 1000m wurden im Herbst 2003 bei den zuständigen Behörden eingereicht. Diese Pläne haben uns gezwungen, zu untersuchen, in wieweit diese Anlagen unsere hochempfindlichen Messungen von Bodenbeschleunigung, Neigung (engl.: tilt) und Extension (engl.: linear strain) negativ beeinflussen könnten. Es gilt auch einen Abstand zum BFO zu schätzen, ab dem mit keiner negativen Beeinflussung unserer Messungen durch Windkraftanlagen zu rechnen ist. Unsere Vorgehensweise besteht aus diesen Teilen: (i) Seismische Langzeitmessungen im Innern einer der Windkraftanlagen bei Loßburg/24 Höfe. (ii) Numerische Modellierung der induzierten Deformation verursacht durch eine Windkraftanlage und Vergleich mit den unter (i) erhobenen lang-periodischen Daten. (iii) Kurzzeitige seismische Messungen im Umfeld der selben Windkraftanlagen. (iv) Schätzung des Abklingverhaltens der Erschütterungen aus (iii) und Extrapolation der Pegel zu größeren Entfernungen. (v) Charakterisierung des seismischen Hintergrundrauschens am BFO. (vi) Vergleich von (iv) und (v) mit der Frage: In welcher Entfernung erreicht das abklingende Signal der Windkraftanlage den am BFO vorhandenen Rauschpegel? (vii) Schlussfolgerungen. Dieser kurze Bericht wurde ursprünglich als Posterbeitrag an der Jahrestagung der Deutschen Geophysikalischen Gesellschaft (DGG) 2004 in Berlin präsentiert

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

We present spectra concentrating on the lowest-frequency normal modes of the Earth obtained from records of the invar-wire strainmeters and STS-1 broad-band seismometers located in the Black Forest Observatory, Germany after the disastrous earthquakes off the NW coast of Sumatra in 2004 and off the coast near Tohoku, Japan in 2011. We compare the spectra to ones obtained from synthetic seismograms computed using a mode summation technique for an anelastic, elliptical, rotating, spherically symmetric Earth model. The synthetics include strain–strain-coupling effects by using coupling coefficients obtained from comparisons between Earth tide signals recorded by the strainmeters and synthetic tidal records. We show that for the low-frequency toroidal and spheroidal modes up to 1 mHz, the strainmeters produce better signal-to-noise ratios than the broad-band horizontal seismometers. Overall, the comparison with the synthetics is satisfactory but not as good as for vertical accelerations. In particular, we demonstrate the high quality of the strainmeter data by showing the Coriolis splitting of toroidal modes for the first time in individual records, the first clear observation of the singlet 2S0/1 and the detection of the fundamental radial mode 0S0 with good signal-to-noise ratio and with a strain amplitude of 10^−11. We also identify the latter mode in a record of the Isabella strainmeter after the great Chilean quake in 1960, the detection of which was missed by the original studies

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

International audienceWe present spectra concentrating on the lowest-frequency normal modes of the Earth obtained from records of the invar-wire strainmeters and STS-1 broad-band seismometers located in the Black Forest Observatory, Germany after the disastrous earthquakes off the NW coast of Sumatra in 2004 and off the coast near Tohoku, Japan in 2011. We compare the spectra to ones obtained from synthetic seismograms computed using a mode summation technique for an anelastic, elliptical, rotating, spherically symmetric Earth model. The synthetics include strain– strain-coupling effects by using coupling coefficients obtained from comparisons between Earth tide signals recorded by the strainmeters and synthetic tidal records. We show that for the low-frequency toroidal and spheroidal modes up to 1 mHz, the strainmeters produce better signal-to-noise ratios than the broad-band horizontal seismometers. Overall, the comparison with the synthetics is satisfactory but not as good as for vertical accelerations. In particular, we demonstrate the high quality of the strainmeter data by showing the Coriolis splitting of toroidal modes for the first time in individual records, the first clear observation of the singlet 2 S 0 1 and the detection of the fundamental radial mode 0 S 0 with good signal-to-noise ratio and with a strain amplitude of 10 −11. We also identify the latter mode in a record of the Isabella strainmeter after the great Chilean quake in 1960, the detection of which was missed by the original studies

A rockslide-generated tsunami in a Greenland fjord rang the Earth for 9 days

Climate change is increasingly predisposing polar regions to large landslides. Tsunamigenic landslides have occurred recently in Greenland, but none have been reported from the eastern fjords. In September 2023, we detected the start of a 9-day-long global 10.88 mHz (92 s) monochromatic very long-period (VLP) seismic signal, originating from East Greenland. We demonstrate how this event started with a 25×106 m3 glacial thinning-induced rock-ice avalanche plunging into Dickson Fjord, triggering a 200 m high tsunami. Simulations show the tsunami stabilized into a 7 m-high long-duration seiche with a near-identical frequency (11.45 mHz) and slow amplitude decay as the seismic signal. An oscillating, fjord-transverse single-force with a maximum amplitude of 5×1011 N reproduces the seismic amplitudes and their radiation pattern relative to the fjord, demonstrating how a seiche directly caused the 9-day-long seismic signal. Our findings highlight how climate change is causing cascading, hazardous feedbacks between the cryosphere, hydrosphere, and lithosphere