TY  - JOUR
TI  - 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
AV  - public
Y1  - 2015/12//
EP  - 1803
KW  - Transient deformation
KW  -  Broad-band seismometers
KW  -  Surface waves and free oscillations
N2  - 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.
ID  - discovery1483179
PB  - OXFORD UNIV PRESS
IS  - 3
N1  - This article has been accepted for publication in the Geophysical Journal International, copyright © The Authors 2015. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
VL  - 203
SP  - 1787
JF  - Geophysical Journal International
A1  - Zuern, W
A1  - Ferreira, AMG
A1  - Widmer-Schnidrig, R
A1  - Lentas, K
A1  - Rivera, L
A1  - Clevede, E
UR  - http://dx.doi.org/10.1093/gji/ggv381
SN  - 0956-540X
ER  -