The Canfranc underground laboratory, located under the Central Pyrenees (Spain) more than 120 km from the Bay of Biscay and 290 km from the Mediterranean Sea, hosts two 70-m-long high-resolution laser strainmeters, referred to as GAL16 and LAB780. The instruments are operating since end 2011, but, unfortunately, strain data acquisition suffered several interruptions, because of power outages during local severe storms, failures of the vacuum pumps, and, mainly, laser tube replacements. We present and discuss the tidal analysis of about 4.6 years of LAB780 data (ranging January 2012 to November 2018) in the diurnal band. The strain spectrum shows clear tidal peaks also for the weak Psi1 and Phi1 harmonics, which are very close to the Free Core Resonance (FCR) frequency. The observed S1 amplitude is comparable to the theoretical one, provided that both the solid Earth and the ocean loading tides are combined; however, its phase indicates a thermal effect due to the day/night temperature variation, whose annual modulation slightly affects both P1 and K1. Carefull removal of thermal effects and the good Psi1 and Phi1 signal-to-noise ratios allow a robust determination of the FCR frequency, fully consistent with determinations from VLBI and gravity data. Moreover, while ocean loading tides, computed using FES2014 and TPXO9-atlas models, are in full agreement with strain data as for the major diurnal harmonics, we show that the computed amplitude of the small J1 tide (included in FES2014 only) is larger than strain observations, which in turn are in agreement with tidal gauge data.
|Titolo:||Free Core Resonance and Ocean Loading from Diurnal Strain Tides Recorded by the Canfranc (Spain) Underground Geodetic Interferometers|
AMORUSO, Antonella (Corresponding)
|Data di pubblicazione:||2019|
|Appare nelle tipologie:||4.2 Abstract|