Geochemistry, Geophysics, Geosystems
Supporting Information for
New insights into the tectonic inversion of North Canterbury and the regional structural
context of the 2010-2011 Canterbury earthquake sequence, New Zealand
Philip M. Barnes1, Francesca C. Ghisetti2, and Andrew R. Gorman3
1National
Institute of Water & Atmospheric Research (NIWA), Private Bag 14901, Kilbirnie, Wellington, New Zealand,
60 Brabant Drive, Mapua, 7005, New Zealand, 3University of Otago, PO Box 56, Dunedin, 9054, New
Zealand
2TerraGeoLogica,
Contents of this file
Figures S1 to S10
Introduction
This Supporting Information file includes graphical material with captions illustrating:
(1) un-interpreted depth converted seismic reflection profiles corresponding to the interpreted
seismic sections and geological cross sections illustrated in the main body of the paper
(Figures S1, S4, S5, S6 and S9),
(2) correlations of seismic reflection data from Pegasus Bay with the onshore Bexley bore
stratigraphy from the coastal area of Christchurch (Figure S2),
(3) a comparison of marine seismic data in Pegasus Bay with seismic data tied to Resolution 1
well south of Banks Peninsula (Figure S3),
(4) near-shore seismic data from across the immediate offshore region of the February 22nd
2011 Mw 6.2 earthquake rupture, illustrating a possible monoclinal fold in the Pliocene
Kowai Formation (Figure S7),
(5) un-interpreted depth converted seismic data from southern Pegasus Bay across the
immediate offshore region of the December 23rd 2011 Mw 5.9 earthquake rupture (Figure
S8),
(6) an example of progressive restoration of the Pegasus Bay Fault modelled with Move
software (Midland Valley) (Figure S10).
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Note that the order of the Figures S1 to S10 below is designed to follow their call out in the
main body of the paper.
Figure S1. Un-interpreted depth converted multichannel seismic profiles of central (a) and
southern (b) Pegasus Bay. These are the same sections shown with relative interpretations in
Figures 3a and 3b. Note the weakly reflective area in part b resulting from shallow gas masking.
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Figure S2. Interpreted boomer (a) and airgun multichannel seismic (b) profiles KAH-10 from
southern Pegasus Bay, correlated 2.4 km across New Brighton’s beach to the onshore Bexley bore
stratigraphy [Brown, 1998]. Age abbreviations, Wc, New Zealand Castlecliffian Stage; Wn,
Nukumaruan Stage. PGS2/1, post-last glacial transgressive erosion surface associated with marine
oxygen isotope stages 2 to 1 transition. Location of profiles and Bexley bore are shown in Figure
2.
3
Figure S3. Comparison of part of multichannel seismic reflection profile CB-83-8 crossing the
Resolution 1 well south of Banks Peninsula [section A-A’; Shell BP Todd, 1984], and part of profile
GG07-002 from Pegasus Bay (section B-B’) (modified slightly from interpretations provided by
Gareth Reynolds, Geosphere Ltd (pers. comm., June 2011). The comparison illustrates the general
similarity of the seismic reflection sequence beneath the shelf on both sides of Banks Peninsula.
Note the clinoform reflection architecture in the Tokama Siltstone Formation between 0.75 s and
1.3 s two way travel time.
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Figure S4. Un-interpreted depth converted multichannel seismic profiles across northern and
eastern Pegasus Bay shown with vertical exaggeration of 2.5. A composite depth section
interpretation of these lines displayed with no vertical exaggeration is shown in Figure 6a, whilst
location of Figure 6a is shown on Figure 5.
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Figure S5. Un-interpreted depth converted multichannel seismic profiles across Pegasus Bay
shown with vertical exaggeration of 2.5. Depth section interpretations of these lines (with no
vertical exaggeration) are shown on the southern parts of Figure 6b (part a, GG07-102) and c
(parts b and c, GG07-101, KAH-6), whilst the locations of Figure 6b and c are shown on Figure 5.
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Figure S6. Un-interpreted depth converted multichannel seismic profiles of northern Pegasus Bay
shown with vertical exaggeration of 2.5. These are the same sections shown with relative
interpretations in Figure 8, whilst depth section interpretations of parts a (GG06-04) and b (GG0603) (displayed with no vertical exaggeration) are shown in the northern parts of Figure 6b and c,
respectively. Depth section interpretations of parts c (GG06-01) and d (KAH-2) (displayed with no
vertical exaggeration) are shown on Figure 10e and g, respectively. The locations of Figure 10e
and g are shown on Figure 5.
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Figure S7. Seismic profile parallel to shore immediately east of the Mw 6.2 February 22nd 2011
earthquake rupture [from Barnes et al., 2011]. The multichannel profile Kah-13, lying 3.7 km
offshore of New Brighton and the Heathcote Estuary images clearly the irregular surface of the
Banks Peninsula volcanics, and a possible monocline developed in the overlying Kowai Formation
(Fmn) (note that in this figure North is to the right). An un-interpreted depth section of this profile
with North to the left and vertical exaggeration of 2.5 is shown in Figure S1b. The late Miocene
volcanics form a northward-thinning wedge over the Paleogene and older Miocene sequences
that are imaged in the northern part of the profile (see Figure S5c). The bold red line is the
approximate projection of the February 22nd fault rupture modelled by Beavan et al. [2011, 2012].
Note the wavy reflectors in the Late Pleistocene sequence off the Heathcote Estuary are possibly
produced by velocity artifacts associated with shallow gas in the near-surface sediments (yellow
shading). See location of the profile on Figure 5.
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Figure S8. Interpreted depth converted multichannel seismic profiles KAH-1 and KAH-2 from
southern Pegasus Bay. Reflections highlighted are: yellow, top Kowai Formation; orange, top
Tokama Formation; upper pink, top Banks Peninsula volcanics; purple dashed, base of volcanics;
blue, top Paleogene; lower pink, top basement. There is no obvious late Quaternary deformation
in the immediate offshore vicinity of the December 23rd Mw 5.9 earthquake ruptures, suggesting
that these earthquakes may not have ruptured the top of basement. The locations of the profiles
are shown on Figure 5.
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Figure S9. Un-interpreted boomer (a and b) and airgun multichannel seismic (c) profiles from
northern and central Pegasus Bay. These are precisely the same sections shown with
interpretations in Figure 9.
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Figure S10. Progressive structural restoration of the Pegasus Bay Fault on profile GG06-03
demonstrating Quaternary compressional inversion of two imbricates of an inherited
extensional fault of late Cretaceous age. Modelling parameters applied are shown on the right
of each step. Whilst most of our other structural restorations of various faults on other sections
applied trishear fault propagation folding with high propagation to slip ratios (c.5 – 20) during
late stages of the restorations, we selected to illustrate this profile in which a combination of
trishear and fault parallel flow (FPF) has been applied to completely restore the pre-inversion
stratigraphy. See Figure 10c for the complete restoration of profile GG06-03.
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References
Brown, L. J. (1998), Bexley Groundwater Testbore Results. Report U98/26. Institute of Geological
and Nuclear Sciences Client report 62698D.12. 68p.
Shell BP Todd (1984), Interpretation and prospectivity of PPL38203, Canterbury Basin, New Zealand.
Ministry of Economic Development New Zealand. Unpubl. Petrol. Rep., PR1046.
Barnes, P. M., C. Castellazzi, A. Gorman, and S. Wilcox (2011), Submarine Faulting Beneath
Pegasus Bay, Offshore Christchurch. Short-term Canterbury Earthquake Recovery Project 2:
Offshore Faults. Prepared for the New Zealand Natural Hazards Research Platform [Contract
reference 2011-NIW-01-NHRP]. NIWA Client Report No: WLG2011-28, 46p.
Beavan J., E. Fielding, M. Motagh, S. Samsonov, and N. Donnelly (2011), Fault location and slip
distribution of the 22 February 2011 Mw 6.2 Christchurch, New Zealand, earthquake from
geodetic data, Seismol. Res. Lett. 82, 789-799.
Beavan, J., M. Motagh, E. J. Fielding , N. Donnelly, and D. Collett (2012), Fault slip models of the
2010–2011 Canterbury, New Zealand, earthquakes from geodetic data and observations of
post-seismic ground deformation, N. Z. J. Geol. Geophys.,
55, 207-221, DOI:
10.1080/00288306.2012.697472.
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