Publication Date:
2017-04-04
Description:
We investigate shear wave polarization in the Hayward fault zone near Niles Canyon, Fremont,
CA. Waveforms of 12 earthquakes recorded by a seven-accelerometer seismic array around
the fault are analysed to clarify directional site effects in the fault damage zone. The analysis
is performed in the frequency domain through H/V spectral ratios with horizontal components
rotated from 0◦ to 180◦, and in the time domain using the eigenvectors and eigenvalues of the
covariance matrix method employing three component records. The near-fault ground motion
tends to be polarized in the horizontal plane. At two on-fault stations where the local strike
is N160◦, ground motion polarization is oriented N88 ± 19◦ and N83 ± 32◦, respectively.
At a third on-fault station, the motion is more complex with horizontal polarization varying
in different frequency bands. However, a polarization of N86 ± 7◦, similar to the results at
the other two on-fault stations, is found in the frequency band 6–8 Hz. The predominantly
high-angle polarization from the fault strike at the Hayward Fault is consistent with similar
results at the Parkfield section of the San Andreas Fault and the Val d’Agri area (a Quaternary
extensional basin) in Italy. In all these cases, comparisons of the observed polarization
directions with models of fracture orientation based on the fault movement indicate that the
dominant horizontal polarization is near-orthogonal to the orientation of the expected predominant
cracking direction. The results help to develop improved connections between fault
mechanics and near-fault ground motion.
Description:
Published
Description:
1255–1272
Description:
JCR Journal
Description:
open
Keywords:
Earthquake ground motions.
;
Interface waves
;
Site effects
;
Wave propagation
;
04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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