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|Authors: ||Marra, F.*|
|Title: ||Large amplification of ground motion at rock sites within a fault zone in Nocera Umbra (central Italy)|
|Title of journal: ||J. of Seismology|
|Series/Report no.: ||/4(2000)|
|Issue Date: ||2000|
|Keywords: ||site effects|
|Abstract: ||During the two mainshocks of September 26, 1997 in the Umbria-Marche border a strong-motion accelerograph
recorded peak ground accelerations as large as 0.6 g, approximately, in the town of Nocera Umbra, at distances of
10 to 15 km from the epicentres. This value is significantly larger than expected on the basis of the usual regressions
with magnitude and distance. A broad-band amplification up to a factor of 10 was consistently estimated in previous
papers, using both weak and strong motion data recorded at the accelerograph site during local moderate earthquakes.
To study the cause of this amplification we deployed six seismologic stations across the tectonic contact
between the Ceno-Mesozoic limestone and the Mesozoic marly sandstone where the accelerograph is installed.
Seismograms of 21 shallow aftershocks in the magnitude range from 2.2 to 4.0 and a subcrustal Mw = 5.3 event
are analysed. Regardless of epicentre location, waveforms show a large complexity in an approximately 200 m
wide band adjacent to the tectonic contact. This is interpreted as the effect of trapped waves in the highly fractured,
lower velocity materials within the fault zone.|
|Appears in Collections:||Papers Published / Papers in press|
04.06.04. Ground motion
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