Horizontal polarization of ground motion in the Hayward fault zone at Fremont, California: dominant fault-high-angle polarization and fault-induced cracks

Abstract

S U M M A R YWe 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.

Lineament Domain of Regional Strike-Slip Corridor: Insight from the Neogene Transtensional De Geer Transform Fault in NW Spitsbergen

“…In the presence of a transtensional (transpressional) regime (ROSSETTI et al 2000), either related to a bend in the main fault trajectory or to a local change in the block kinematics, this angle decreases (increases) until it becomes parallel (normal) to the main fault in the case of pure extensional (compressional) kinematics. The presence of en-echelon, sub-ordered elements along major strike-slip faults has been reported also at the local scale (PISCHIUTTA et al 2012;SALVINI et al 1999).…”

Speedy Techniques to Evaluate Seismic Site Effects in Particular Geomorphologic Conditions: Faults, Cavities, Landslides and Topographic Irregularities

“…The orientation of these fractures depends on the direction of the resulting stress localized around the fault. Therefore, an interpretation of the present results could, in our opinion, be proposed by focusing our findings in the frame of the brittle rheology of the hosting rock (Pischiutta et al, 2012).…”

“…It is not an easy task to interpret all experimental observations when these exhibit prevailing polarization directions that are sharply changing and are always non-coincident with the fault strike. In a recent paper, Pischiutta et al (2012), find that the mean polarization azimuth turns out to be perpendicular to the expected synthetic cleavages. We have to remember that four types of fractures can develop in fault zone (Riedel, 1929;Tchalenko, 1968): a) extensional fracture (T); b) synthetic cleavage (R); c) antithetic cleavage (R'); d) pressure solution surfaces (P).…”

Defining fault avoidance zones and associated geotechnical properties using MASW: a case study on the Springfield Fault, New Zealand

“…Furthermore, ground motion polarization that is commonly observed in fault zones is interpreted as fracture-controlled (e.g. Pischiutta et al, 2012;Panzera et al, 2014). These studies show that the frequency bands at which directional amplification occurs reflects asymmetry in rock damage.…”