Wavelet analysis of land subsidence time-series: Madrid Tertiary aquifer case study
R. Tomas, J. L. Pastor
Universidad de Alicante, Dpto. de Ingenieria Civil, Escuela Politecnica Superior de Alicante, Alicante, Spain
M. Bejar-Pizarro, P. Ezquerro, J. Fernandez-Merodo, C. Guardiola-Albert, G. Herrera
Geohazards InSAR Laboratory and Modeling Group, Instituto Geologico y Minero de Espagna, Madrid, Spain
R. Boni', C. Meisina, F. Zucca
Department of Earth and Environmental Sciences, University of Pavia, Pavia, Italy
P. Teatini, C. Zoccarato, A. Franceschini
Dept. of Civil, Environmental and Architectural Engineering, University of Padova, Italy
ABSTRACT
Interpretation of land subsidence time-series to understand the evolution of the
phenomenon and the existing relationships between triggers and measured displacements
is a great challenge. Continuous wavelet transform (CWT) is a powerful signal processing
method mainly suitable for the analysis of individual nonstationary time-series.
CWT expands time-series into the time-frequency space allowing identification of
localized nonstationary periodicities. Complementarily, Cross Wavelet Transform (XWT)
and Wavelet Coherence (WTC) methods allow the comparison of two time-series that may
be expected to be related in order to identify regions in the time-frequency domain
that exhibit large common cross-power and wavelet coherence, respectively, and therefore
are evocative of causality. In this work we use CWT, XWT and WTC to analyze piezometric
and InSAR (interferometric synthetic aperture radar) time-series from the Tertiary aquifer
of Madrid (Spain) to illustrate their capabilities for interpreting land subsidence and
piezometric time-series information.
