Orthogonal relation between wavefield polarization and fast <i>S</i> wave direction in the Val d'Agri region: An integrating method to investigate rock anisotropy

Pischiutta, Marta; Pastori, Marina; Improta, Luigi; Salvini, Francesco; Rovelli, A.

doi:10.1002/2013jb010077

Cited by 22 publications

(25 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Moreover, Pischiutta et al . [] found a recurrent orthogonal relation between horizontal polarization and seismic anisotropy in the Val d'Agri area. They postulated that the existence of an anisotropic medium represented by fractured rocks causes shear wave velocity to be larger in the crack‐parallel component (making S wave velocity to be higher in fracture‐parallel direction) and compliance to be larger perpendicular to the crack strike (causing ground motion polarization in the fracture‐perpendicular direction).…”

Section: Discussionmentioning

confidence: 99%

“…To test these findings, we follow Pischiutta et al . [], and in the next section, we compare ground motion polarization with the seismic anisotropy study by Holt et al . [].…”

Section: Discussionmentioning

confidence: 99%

“…Conversely to Pischiutta et al . [], here the comparison between seismic anisotropy and ground motion polarization is more tentative because (i) only two of the four total stations installed in the fault damage zone (Dar6 and Dar7) show a clear directional amplification effect and (ii) S wave fast directions vary between these stations.…”

Section: Discussionmentioning

confidence: 99%

“…This amplification is strongly anisotropic, with ground motion polarization occurring in the ≈N50° direction. Because this effect is evident only at on‐fault stations, it is likely caused by fractured rocks in the fault damage zone, in agreement with previous studies in other regions [ Pischiutta et al ., , , ], which confirms that the process is ubiquitous in fault zones. This directional amplification is not observed on the ambient noise analysis.…”

Section: Discussionmentioning

confidence: 99%

“…[] and subsequently exploited by Pischiutta et al . [, ]. We thus define four classes of increasing reliability based on R and I values: we exclude from statistics values of AZ for which R < 0.5 and I < 45°, and linearly normalize between 0 and 1 the R and I values ranging in the intervals 0.5 < R < 1 and 45° < I < 90°, making linearized values R l and I l .…”

Section: Data and Ground Motion Polarization Analysismentioning

confidence: 99%

See 4 more Smart Citations

Fracture‐related wavefield polarization and seismic anisotropy across the Greendale Fault

et al. 2015

Self Cite

View full text Add to dashboard Cite

We investigate seismic signatures of fracturing in a newly ruptured strike‐slip fault by determining the wavefield polarization in the New Zealand Canterbury Plains area and across the Greendale Fault, which was responsible for the 3 September 2010 Darfield Mw 7.1 earthquake. Previous studies suggested that fractured rocks in fault damage zones cause directional amplification and ground motion polarization in the fracture‐perpendicular direction as an effect of stiffness anisotropy, and cause velocity anisotropy with shear wave velocity larger in the fracture‐parallel component. An array of 14 stations was installed following the Darfield earthquake. We assess polarization both in the frequency and time domains through the individual‐station horizontal‐to‐vertical spectral ratio and covariance matrix analysis, respectively, and compare the results to previously reported anisotropy measurements from shear wave splitting. Stations installed in the Canterbury Plains have an amplification peak between 0.1 and 0.3 Hz for both earthquakes and ambient noise. We relate the amplification to the resonance of a considerable thickness (c. 1 km) of soft sediments lying over the metamorphic bedrock. Analysis of seismic events revealed the existence of another peak in amplification between 2 and 5 Hz at two on‐fault stations, which was not visible in the noise analysis. In contrast to the lower frequency peak, the ones between 2 and 5 Hz are more strongly anisotropic, attaining amplitudes up to a factor of 4 in the N52° direction. To interpret this effect we model the fracture pattern in the fault damage zone produced by the fault kinematics. We conclude that the horizontal polarization is orthogonal to extensional fractures, which predominate in the shallow layers (<2 km) with an expected strike of N139°. Fracture orientation is consistent with coseismic surface rupture observations, confirming the reliability of the model. S wave splitting is produced by velocity anisotropy in the entire rock volume crossed along the seismic path; thus, it is affected by deeper material than the amplification study. We explain the rotation of S wave fast component observed by Holt et al. (2013) near the fault in terms of the dominant synthetic cleavages at greater depths (>2 km), expected in N101° direction on the basis of the model. Thus, different fracture distribution at different depths may explain different results for amplification compared to anisotropy. We propose polarization amplification analysis as a complementary method to S wave splitting analysis. Polarization analysis is rapidly computed and robust, and it can be applied to either earthquakes or ambient noise recordings, giving useful information about the predominant fracture patterns at various depths.

show abstract

Section: Discussionmentioning

confidence: 99%

“…To test these findings, we follow Pischiutta et al . [], and in the next section, we compare ground motion polarization with the seismic anisotropy study by Holt et al . [].…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Data and Ground Motion Polarization Analysismentioning

confidence: 99%

See 3 more Smart Citations