Open AccessLong‐duration asynchronous ground motions in the Colfiorito plain, central Italy, observed on a two‐dimensional dense array
Author(s) -
Di Giulio G.,
Rovelli A.,
Cara F.,
Azzara R. M.,
Marra F.,
Basili R.,
Caserta A.
Publication year - 2003
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2002jb002367
Subject(s) - geology , seismogram , seismology , outcrop , seismic array , refraction , bedrock , surface wave , geophysics , geodesy , geomorphology , physics , optics
In winter 1998 a small‐aperture (∼200 m), four‐station array was operating in the middle of the Colfiorito plain. Waveforms of seven small magnitude (2.1 < M < 3.7) local earthquakes are analyzed in this study. The peculiarity of the array seismograms is a ∼2‐min long duration of the horizontal ground motion. The predominant frequency in the plain is around 1 Hz. In this frequency band, earthquake‐induced ground shaking is synchronous for a few seconds during direct S waves; after this time window, wave trains show an increasingly chaotic behavior within the array. The energy variation of the horizontal ground shaking between the array and a nearby rock outcrop exceeds a factor of 500 at 1 Hz. In order to help understanding of observations and construct models for future numerical simulations, the buried structure of the Colfiorito plain has been investigated through seismic refraction profiles and geoelectric measurements. A three‐dimensional reconstruction of the basin structure reveals an extremely complex bedrock topography, which is probably a recurrent feature for intermontane basins in tectonically active regions. Apparent velocities and backazimuths in the frequency band 0.5–1.5 Hz indicate that a 180‐m deep depression NW of the array is responsible for the generation of edge‐diffracted surface (Love) waves. Their arrival to the array breaks the synchronism of vertically reverberating waves which predominate in the first seconds of the S‐wave window.