Crustal stress and fault strength in the Canterbury Plains, New Zealand

Holt, R. A.; Savage, Martha K.; Townend, John; Syracuse, E. M.; Thurber, C. H.

doi:10.1016/j.epsl.2013.09.041

Cited by 34 publications

(46 citation statements)

References 61 publications

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“…Changes of pore fluid pressure can also have potential effects on the orientation of S H , as shown by Martínez-Garzón et al (2013). Holt et al (2013) observed a ratio of stress drop to background shear stress of 0.4 for the central segment of the 2010 M W 7.1 Darfield earthquake in New Zealand, if the apparent stress rotation was caused by the earthquake. This finding is close to our ratio of 0.5.…”

Section: Discussionmentioning

confidence: 99%

“…However, due to a lack of seismicity prior to the main shock on that segment of the Darfield fault, the pre-event S H direction is unknown. If S H had not rotated due to the earthquake, but had the same direction prior and following the main shock, Holt et al (2013) argue that a zone of high pore fluid pressure on the fault segment could account for this stress inhomogeneity. In our case the S H direction on the Kross fault could be constrained prior to and following the main shocks, suggesting the rotation we estimate is primarily caused by coseismic slip on the Kross fault. )…”

Section: Discussionmentioning

confidence: 99%

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Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

et al. 2015

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two magnitude M W ∼ 6 earthquakes occurred on two adjacent N-S faults in the western South Iceland Seismic Zone. The first main shock was followed approximately 3 s later by the rupture on a parallel fault, about 5 km to the west. An intense aftershock sequence was mostly confined to the western fault and an E-W aligned zone, extending west of the main shock region into the Reykjanes oblique rift. In this study, a total of 325 well-constrained focal mechanisms were obtained using data from the permanent Icelandic SIL seismic network and a temporary network promptly installed in the source region following the main shocks, which allowed a high-resolution stress inversion in short time intervals during the aftershock period. More than 800 additional focal mechanisms for the time period 2001-2009, obtained from the permanent SIL network, were analysed to study stress changes associated with the main shocks. Results reveal a coseismic counter-clockwise rotation of the maximum horizontal stress of 11 ± 10 • (95 per cent confidence level) in the main rupture region. From previous fault models obtained by inversion of geodetic data, we estimate a stress drop of about half of the background shear stress on the western fault. With a stress drop of 8-10 MPa, the pre-event shear stress is estimated to 16-20 MPa. The apparent weakness of the western fault may be caused by fault properties, pore fluid pressure and the vicinity of the fault to the western rift zone, but may also be due to the dynamic stress increase on the western fault by the rupture on the eastern fault. Further, a coseismic change of the stress regime-from normal faulting to strike-slip faulting-was observed at the northern end of the western fault. This change could be caused by stress heterogeneities, but may also be due to a southward shift in the location of the aftershocks as compared to prior events.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

et al. 2015

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“…We also show the stress inversion obtained by Holt et al . [] for the four clusters. Stereonets represent the horizontal plane (red = σ 1 ; green = σ 2 ; blue = σ 3 ; black dotted line = S Hmax ).…”

Section: The Study Areamentioning

confidence: 99%

“…Holt et al . [] selected 2815 earthquakes and analyzed focal mechanisms and anisotropy. Well‐resolved stress inversions were determined from 56 clusters of earthquakes.…”

Section: Data and Ground Motion Polarization Analysismentioning

confidence: 99%

“…This selection was determined to investigate possible variations of polarization in relation to the seismic source and path. The green cluster [Cl‐2 in Holt et al ., ] is located in the Rolleston faults [ Syracuse et al ., ] at the eastern edge of the Greendale Fault. It is a broad area of intense seismicity where focal mechanisms indicate predominant left‐lateral motion and minor evidence of horizontal extension.…”

Section: Data and Ground Motion Polarization Analysismentioning

confidence: 99%

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

et al. 2015

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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.

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Revisiting the Canterbury earthquake sequence after the 14 February 2016 M_w 5.7 event

Herman

Furlong

2016

Geophysical Research Letters

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On 14 February 2016, an Mw 5.7 (GNS Science moment magnitude) earthquake ruptured offshore east of Christchurch, New Zealand. This earthquake occurred in an area that had previously experienced significant seismicity from 2010 to 2012 during the Canterbury earthquake sequence, starting with the 2010 Mw 7.0 Darfield earthquake and including four Mw ~6.0 earthquakes near Christchurch. We determine source parameters for the February 2016 event and its aftershocks, relocate the recent events along with the Canterbury earthquakes, and compute Coulomb stress changes resolved onto the recent events and throughout the greater Christchurch region. Because the February 2016 earthquake occurred close to previous seismicity, the Coulomb stress changes resolved onto its nodal planes are uncertain. However, in the greater Christchurch region, there are areas that remain positively loaded, including beneath the city of Christchurch. The recent earthquake and regional stress changes suggest that faults in these regions may pose a continuing seismic hazard.

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Crustal stress and fault strength in the Canterbury Plains, New Zealand

Cited by 34 publications

References 61 publications

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

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

Revisiting the Canterbury earthquake sequence after the 14 February 2016 M_w 5.7 event

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Crustal stress and fault strength in the Canterbury Plains, New Zealand

Cited by 34 publications

References 61 publications

Temporal stress changes associated with the 2008 May 29MW 6 earthquake doublet in the western South Iceland Seismic Zone

Temporal stress changes associated with the 2008 May 29MW 6 earthquake doublet in the western South Iceland Seismic Zone

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

Revisiting the Canterbury earthquake sequence after the 14 February 2016 Mw 5.7 event

Contact Info

Product

Resources

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Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

Revisiting the Canterbury earthquake sequence after the 14 February 2016 M_w 5.7 event