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Figure 2. Geologic map of Mahia Peninsula, Lachlan Ridge, and Lachlan Basin, showing simplified structure. Seafloor geology was mapped via correlation of unconformities and seismic reflectors, which were tied to onshore outcrops, Hawke Bay–1 well (Fig. 3B), and dated seafloor samples (Figs. 4B, 4C,5A, and 5B). New Zealand time-scale stage abbreviations (e.g., Wn-Wc) are listed in Figures 4B and 5A. Unconformities 1, 6, 9, and 12–14 are illustrated in Figures 4D and 5C.

Figure 2. Geologic map of Mahia Peninsula, Lachlan Ridge, and Lachlan Basin... Available to Purchase

Published: 01 November 2002
Figure 2. Geologic map of Mahia Peninsula, Lachlan Ridge, and Lachlan Basin, showing simplified structure. Seafloor geology was mapped via correlation of unconformities and seismic reflectors, which were tied to onshore outcrops, Hawke Bay–1 well ( Fig. 3B ), and dated seafloor samples ( Figs. 4B
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Figure 7. Structural map of Mahia Peninsula, Lachlan Ridge, Lachlan Basin, and adjacent areas. Bathymetry contours are in meters. The distribution of uplifted marine terraces on Mahia Peninsula is from Berryman (1993a, 1993b). Onshore structure is from Francis (1993a, 1993b) and Mazengarb and Speden (2000). Large, bold roman numerals are structural segments of the Lachlan fault.

Figure 7. Structural map of Mahia Peninsula, Lachlan Ridge, Lachlan Basin, ... Available to Purchase

Published: 01 November 2002
Figure 7. Structural map of Mahia Peninsula, Lachlan Ridge, Lachlan Basin, and adjacent areas. Bathymetry contours are in meters. The distribution of uplifted marine terraces on Mahia Peninsula is from Berryman (1993a , 1993b) . Onshore structure is from Francis (1993a , 1993b) and Mazengarb
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Figure 1. Regional tectonic setting of Hawke Bay, Lachlan Ridge, and the central part of the upper plate of the Hikurangi subduction zone. (A) Australian plate/Pacific plate boundary zone through the New Zealand region, with relative-motion velocities from the NUVEL-1A model (DeMets et al., 1994). (B) Crustal section c–c′ modified from Beanland (1995) and Begg et al. (1996). (C) Regional structure on an illuminated digital terrain model generated from a bathymetric compilation that includes EM12Dual multibeam and MR1 swath data from the continental margin (Lewis et al., 1997), and Royal New Zealand Navy analogue soundings from the continental shelf. Line c–c′ shows the position of the crustal section in B. Lines a–a′ and b–b′ are cross sections in Figure 3.

Figure 1. Regional tectonic setting of Hawke Bay, Lachlan Ridge, and the ce... Available to Purchase

Published: 01 November 2002
Figure 1. Regional tectonic setting of Hawke Bay, Lachlan Ridge, and the central part of the upper plate of the Hikurangi subduction zone. (A) Australian plate/Pacific plate boundary zone through the New Zealand region, with relative-motion velocities from the NUVEL-1A model ( DeMets et al., 1994
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Figure 6. Seismic profiles (acquired at 3.5 kHz) across the Lachlan Ridge anticline and Lachlan fault (A, segment III; B and C, segment II; D, segment I). (Segments are mapped in Fig. 7.) Vertical axes are in milliseconds, with depth-conversion scale calculated by assuming a water velocity of 1.5 km/s. Reflection labels, seabed samples, and New Zealand time-scale stage abbreviations (e.g., Wq) are explained in Figure 5. C20, C21, and C13 are dated sediment cores. Profile locations are indicated in Figures 2 and 7. LGM—Last Glacial Maximum. Gas-rich horizon in A was dated by interpolation of sedimentation rate between the seabed and the erosion surface cut during the last glacial transgression. Vertical displacement across the fault tip was measured by projecting horizons through the fault surface and converting depth by assuming a velocity of 1.6 km/s. Fine dotted lines on profile C denote submerged marine terraces with water depths indicated in meters.

Figure 6. Seismic profiles (acquired at 3.5 kHz) across the Lachlan Ridge a... Available to Purchase

Published: 01 November 2002
Figure 6. Seismic profiles (acquired at 3.5 kHz) across the Lachlan Ridge anticline and Lachlan fault (A, segment III; B and C, segment II; D, segment I). (Segments are mapped in Fig. 7 .) Vertical axes are in milliseconds, with depth-conversion scale calculated by assuming a water velocity of 1.5
Journal Article

Late Cenozoic evolution and earthquake potential of an active listric thrust complex above the Hikurangi subduction zone, New Zealand Available to Purchase

Philip M. Barnes, Andrew Nicol, Tony Harrison
Journal: GSA Bulletin
Published: 01 November 2002
GSA Bulletin (2002) 114 (11): 1379–1405.
DOI: https://doi.org/10.1130/0016-7606(2002)114<1379:LCEAEP>2.0.CO;2
...Figure 2. Geologic map of Mahia Peninsula, Lachlan Ridge, and Lachlan Basin, showing simplified structure. Seafloor geology was mapped via correlation of unconformities and seismic reflectors, which were tied to onshore outcrops, Hawke Bay–1 well ( Fig. 3B ), and dated seafloor samples ( Figs. 4B...
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Structural reconstruction of seismic line CM05-01 (reproduced from Burgreen-Chan et al., 2015, and used with permission of John Wiley and Sons). LB = Lachlan Basin; LF = Lachlan fault; LR = Lachlan Ridge; RR = Ritchie Ridge; VE = vertical exaggeration.

Structural reconstruction of seismic line CM05-01 (reproduced from Burgree... Available to Purchase

Published: 01 April 2018
Figure 4. Structural reconstruction of seismic line CM05-01 (reproduced from Burgreen-Chan et al., 2015 , and used with permission of John Wiley and Sons). LB = Lachlan Basin; LF = Lachlan fault; LR = Lachlan Ridge; RR = Ritchie Ridge; VE = vertical exaggeration.
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Series of northwest-southeast interpreted seismic profiles showing the geometry of the 11 depositional sequences, and major structures. NWR—Napier-Wairoa Ridge; EA—Elsthorpe anticline; KR—Kidnappers Ridge; LR—Lachlan Ridge; MR—Motu-o-Kura Ridge; KWTC— Kairakau-Waimarama thrust complex; KB—Kidnappers Basin; LB—Lachlan Basin; MB—Motu-o-Kura Basin. See Figure 3 for location. TWTT—two-way traveltime.

Series of northwest-southeast interpreted seismic profiles showing the geom... Available to Purchase

Published: 01 May 2011
Figure 9. Series of northwest-southeast interpreted seismic profiles showing the geometry of the 11 depositional sequences, and major structures. NWR—Napier-Wairoa Ridge; EA—Elsthorpe anticline; KR—Kidnappers Ridge; LR—Lachlan Ridge; MR—Motu-o-Kura Ridge; KWTC— Kairakau-Waimarama thrust complex
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Figure 8. Sixty-fold migrated seismic reflection profile H90–5 across the southern Lachlan Basin and Lachlan Ridge (including segment II of the Lachlan fault). Top, uninterpreted; bottom, interpreted. Profile location indicated in Figures 2 and 7. Reflection labels and seabed samples are explained in Figures 4 and 5. Bold arrows above profile designate seismic profile tie lines. Note the Pliocene–Pleistocene uplift and tilting of older extensional growth sequences between reflectors 13 and 11 beneath the western flank (hanging wall) of the ridge.

Figure 8. Sixty-fold migrated seismic reflection profile H90–5 across the s... Available to Purchase

Published: 01 November 2002
Figure 8. Sixty-fold migrated seismic reflection profile H90–5 across the southern Lachlan Basin and Lachlan Ridge (including segment II of the Lachlan fault). Top, uninterpreted; bottom, interpreted. Profile location indicated in Figures 2 and 7 . Reflection labels and seabed samples
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Stratigraphy of the present-day two-dimensional basin and petroleum system model for seismic line CM05-01 in Hawke Bay (modified from figure 9 of Burgreen-Chan et al., 2015, and used with permission of John Wiley and Sons). The transect is subdivided by a red dashed line into four structural sections: inboard, Lachlan Basin, Lachlan footwall, and outboard. 1D = one-dimensional; LR = Lachlan Ridge.

Stratigraphy of the present-day two-dimensional basin and petroleum system ... Available to Purchase

Published: 01 April 2018
structural sections: inboard, Lachlan Basin, Lachlan footwall, and outboard. 1D = one-dimensional; LR = Lachlan Ridge.
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Figure 9. Sixty-fold migrated seismic reflection profile H90–7 across the central Lachlan Basin and Lachlan Ridge (including segment II of the Lachlan fault). Top, uninterpreted; bottom, interpreted. Profile location indicated in Figures 2 and 7. Faults labeled 1–6 are discussed in the text. See Figure 10 for depth-converted section and restoration. Reflection labels and seabed samples are explained in Figures 4 and 5. The bracketed section labeled “1 to 8” in the footwall basin is approximately equivalent to sequences bounded by unconformities 1–8 in the Lachlan Basin. Position of reflector 14 beneath the crest of the ridge is defined by dated samples Z391 and D7. Bold arrows above profile designate seismic profile tie lines.

Figure 9. Sixty-fold migrated seismic reflection profile H90–7 across the c... Available to Purchase

Published: 01 November 2002
Figure 9. Sixty-fold migrated seismic reflection profile H90–7 across the central Lachlan Basin and Lachlan Ridge (including segment II of the Lachlan fault). Top, uninterpreted; bottom, interpreted. Profile location indicated in Figures 2 and 7 . Faults labeled 1–6 are discussed in the text
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Figure 11. Sixty-fold migrated seismic reflection profile H90–9 across the northern Lachlan Ridge (including segment III of the Lachlan fault). Profile location is indicated in Figures 2 and 7. Reflection labels are explained in Figures 4 and 5. The bracketed section labeled “1 to 10” in the footwall basin is approximately equivalent to sequences bounded by unconformities 1–10 in the Lachlan Basin. Bold arrows above profile designate seismic profile tie lines.

Figure 11. Sixty-fold migrated seismic reflection profile H90–9 across the ... Available to Purchase

Published: 01 November 2002
Figure 11. Sixty-fold migrated seismic reflection profile H90–9 across the northern Lachlan Ridge (including segment III of the Lachlan fault). Profile location is indicated in Figures 2 and 7 . Reflection labels are explained in Figures 4 and 5 . The bracketed section labeled “1 to 10
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Figure 5. Details of Quaternary stratigraphy beneath Lachlan Basin and Lachlan Ridge. (A) New Zealand time scale and key nannoflora coccolith and foraminifera datums relevant to samples analyzed. Abbreviations include FAD—first appearance datum, LAD—last appearance datum, H.—Helicosphaera, E.—Emiliania, L.—Loxostomum, G.—Gephyrocapsa, P.—Pseudoemiliania, Gl.—Globorotalia, N.—Notorotalia. (B) Marine core samples from Lachlan Ridge (Fig. 2). Vertical bars to the right of the number indicate the relative stratigraphic positions from which the samples were recovered, shown here against (C) seismic data from the central Lachlan Basin (Fig. 2). Vertical bars to the left of the sample number indicate the biostratigraphic age ranges derived from analysis of nannoflora and foraminifera by Stratigraphic Solutions Ltd. and Institute of Geological and Nuclear Sciences Ltd. (C) Single- channel seismic reflection profile illustrating high-resolution details of nine regionally extensive erosional unconformities (1–9) of Quaternary age. The dashed reflector labeled ? may also be an erosional surface. Labels W1 to W4 are erosional surfaces recognized by Lewis (1971, 1973a). (D) Interpreted sequence stratigraphy. Abbreviations include LSWP—lowstand wave planation, HST—highstand systems tract, TST—transgressive systems tract, MR/TS—marine ravinement or transgressive surface. (E) Inferred correlation of erosion surfaces with oxygen isotope stages from a benthic foraminifera record in equatorial Pacific site ODP Site 677 (Shackleton et al., 1990; Tiedemann et al., 1994). (F) Vertical lines indicate the magnitude of corresponding sea-level lowstands relative to present, after calibrations by Pillans et al. (1998) and Rohling et al. (1998). (G) Correlation of marine terraces uplifted on Mahia Peninsula (Berryman, 1993a, 1993b). (H) Map showing locations of sections x–x′ and y–y′. Contours are water depths in meters. (I) Schematic section x–x′ illustrating development of uplifted coastal terraces and offshore sedimentary units and unconformities east of Mahia Peninsula. Abbreviations include LST—lowstand systems tract, LGM—approximate Last Glacial Maximum sea level. (J) Schematic section y–y′ illustrating development of progressively tilted, lowstand, wave-planed erosion surfaces on the flanks of southern Lachlan Ridge.

Figure 5. Details of Quaternary stratigraphy beneath Lachlan Basin and Lach... Available to Purchase

Published: 01 November 2002
Figure 5. Details of Quaternary stratigraphy beneath Lachlan Basin and Lachlan Ridge. (A) New Zealand time scale and key nannoflora coccolith and foraminifera datums relevant to samples analyzed. Abbreviations include FAD—first appearance datum, LAD—last appearance datum, H .— Helicosphaera , E
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Isochor maps of the 11 depositional sequences (sequence 11 to sequence 1) and the postglacial wedge (sequence 0) identified from seismic data interpretation. Estimated thicknesses result from approximate time-depth conversions with linear increase of the average velocity deduced from seismic data (Multiwave, 2005). The successive maps show the progressive landward migration of the sequences and associated depocenters through time, the change in forearc configuration at ca. 430 ka (S5), and the formation and the evolution of the subbasins (Motu-o-Kura, Lachlan I and II, Mahia, and Kidnappers Basins). The main tectonic structures are visible as solid (presumed active) or dashed (presumed inactive) black lines. Age boundary of each depositional sequence is indicated (see Fig. 11). NWR—Napier-Wairoa Ridge; KR—Kidnappers Ridge; LR—Lachlan Ridge; MR—Motu-o-Kura Ridge; KWTC—Kairakau-Waimarama thrust complex; KB—Kidnappers Basin; MaB—Mahia Basin; LBI and II—Lachlan Basin I and II; MB—Motu-o-Kura Basin.

Isochor maps of the 11 depositional sequences (sequence 11 to sequence 1) a... Available to Purchase

Published: 01 May 2011
, and Kidnappers Basins). The main tectonic structures are visible as solid (presumed active) or dashed (presumed inactive) black lines. Age boundary of each depositional sequence is indicated (see Fig. 11 ). NWR—Napier-Wairoa Ridge; KR—Kidnappers Ridge; LR—Lachlan Ridge; MR—Motu-o-Kura Ridge; KWTC—Kairakau
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Tectonic setting of the active Hikurangi subduction margin and forearc basin. (A) Arrangement of major morphostructural elements of the Hikurangi margin, North Island, New Zealand, including: the Hikurangi Trough, the imbricate frontal wedge emergent in the coastal ranges, the Neogene forearc basin, the axial ranges and the backarc basins. The location of the Pleistocene volcanic arc is indicated. Triangles indicate the location of active (black) and dormant volcanoes (gray). (B) Map showing the arrangement of morphostructural elements in the Hawke Bay region. (C) Schematic cross section A-A′ modified from Beanland (1995), Begg et al. (1996), and Barnes et al. (2002). RF—Ruahine fault; MF—Mohaka fault; KR—Kidnappers Ridge; LB—Lachlan Basin; LR—Lachlan Ridge; MR—Motu-o-Kura Ridge.

Tectonic setting of the active Hikurangi subduction margin and forearc basi... Available to Purchase

Published: 01 May 2011
section A-A′ modified from Beanland (1995) , Begg et al. (1996) , and Barnes et al. (2002) . RF—Ruahine fault; MF—Mohaka fault; KR—Kidnappers Ridge; LB—Lachlan Basin; LR—Lachlan Ridge; MR—Motu-o-Kura Ridge.
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Tectonic setting of the active Hikurangi subduction margin. A) Australian–Pacific plate boundary in the New Zealand region. Light gray shading corresponds to submerged continental crust, and dark gray shading represents the emergent continental crust of the New Zealand microcontinent. B) Arrangement of the major morphostructural elements of the Hikurangi subduction margin in the North Island, including the Hikurangi Trough, the imbricate frontal wedge emergent in the coastal ranges, the Neogene forearc basin domain, the axial ranges of the frontal ridge, the backarc basin, and the Pleistocene volcanic arc. The dashed line A–A′ corresponds to the trace of the crustal cross section. C) Crustal cross section A–A′ modified from Beanland (1995) and Barnes et al. (2002), showing the structure of the central part of the subduction margin. RF, Ruahine Fault; MF, Mohaka Fault; KR, Kidnappers Ridge; LB, Lachlan Basin; LR, Lachlan Ridge; MR, Motu-o-Kura Ridge. D) Map showing the main morphostructural elements in the Hawke's Bay region.

Tectonic setting of the active Hikurangi subduction margin. A) Australian... Available to Purchase

Published: 01 March 2009
, Kidnappers Ridge; LB, Lachlan Basin; LR, Lachlan Ridge; MR, Motu-o-Kura Ridge. D) Map showing the main morphostructural elements in the Hawke's Bay region.
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Figure 4. Compilation and interpretation of stratigraphic data within Lachlan Basin, Lachlan Ridge, and beneath Mahia Peninsula. (A) The stratigraphic column is a 5.5-km-thick composite well section derived from splicing Opoutama-1 data with the upper part of Hawke Bay–1. See well locations in Figures 1C and 3A. (B) New Zealand time-scale stages (with age ranges compiled and integrated by Field et al. (1997) and Naish et al. (1999) and scaled in millions of years on the left) including Wq—Haweran, Wp—Waipipian, Wo—Opoitian, Tk—Kapitean, Tt—Tongaporutuan, Sw—Waiauan, Sl—Lillburnian, Sc—Clifdenian, Pl—Altonian, Po—Otaian, Lw—Waitakian, Ld—Duntroonian, Lwh—Whaingaroan, Ar—Runangan, Ak—Kaitian, Ab—Bortonian, Dp—Porangan, Dh—Heretaungan, Dm—Mangaorapan, Dw—Waipawan, Dt—Teurian, Mh—Haumurian, Mp—Piripauan, Rt—Teratan, Rm—Mangaotanean, Ra—Arowhanan, Cn—Ngaterian. (C) Marine rock-dredge and core samples from the crest and flanks of Lachlan Ridge and from the inner-shelf platform east of Mahia Peninsula. See sample locations in Figure 2. Vertical bars to the left of the sample number indicate the biostratigraphic age ranges derived from analysis of nannoflora, foraminifera, and pollens by Stratigraphic Solutions Ltd. and Institute of Geological and Nuclear Sciences Ltd. Vertical bars to the right of the number indicate the relative stratigraphic positions from which the samples were recovered, shown here against (D) seismic data from the central Lachlan Basin. Sample numbers commencing with D and C are from Strong et al. (1989). Samples F640a and Z391 are from Lewis (1974), and numbers commencing with X are new samples recovered by NIWA in 1998. Bold gray lines left of reflections 11, 12, 13, and 14 are seismic ties to Hawke Bay–1 well (Fig. 3B). Details of the Quaternary section are shown in Figure 5.

Figure 4. Compilation and interpretation of stratigraphic data within Lachl... Available to Purchase

Published: 01 November 2002
Figure 4. Compilation and interpretation of stratigraphic data within Lachlan Basin, Lachlan Ridge, and beneath Mahia Peninsula. (A) The stratigraphic column is a 5.5-km-thick composite well section derived from splicing Opoutama-1 data with the upper part of Hawke Bay–1. See well locations
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Figure 10. Progressive restoration of deformed stratigraphy in the central Lachlan Ridge from (A) present-day depth section to (D) late Miocene reflector 13 (seismic profile shown in Fig. 9). The present depth section was constructed manually by using interval velocities derived from processing multichannel seismic data. Restorations were constructed by conserving line lengths of unconformities. The eroded positions of reflectors 11, 12, and 13 over the crest of the ridge are inferred. Note that calculations of post–reflector 11 reverse displacement on the Lachlan fault, by using a listric fault model (Seeber and Sorlien, 2000), indicate that the length of reflector 11 projected above seabed in panel A, and the amount of associated horizontal shortening restored between panels A and B are probably underestimated. Note also in panel D that a substantial thrust complex had developed prior to the middle Miocene to late Miocene development of listric extensional detachments. Reactivation of listric extensional faults to be sites of thrust movements commenced in the early Pliocene prior to unconformity 11, as shown in panel B.

Figure 10. Progressive restoration of deformed stratigraphy in the central ... Available to Purchase

Published: 01 November 2002
Figure 10. Progressive restoration of deformed stratigraphy in the central Lachlan Ridge from (A) present-day depth section to (D) late Miocene reflector 13 (seismic profile shown in Fig. 9 ). The present depth section was constructed manually by using interval velocities derived from processing
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Figure 14. Methods for estimating vertical deformation associated with the Lachlan fault. (A) Cross section b–b′ (Fig. 3B) showing inferred projections of stratigraphic horizons across the hanging wall of segment III; the projections are based on two alternative positions of a fault-parallel fold axis located 3 km and 1 km west of the fault. See text for explanation. Reflector labels and ages are explained in Figures 4 and 5. (B) Interpretation of anticlinal growth of the southern Lachlan Ridge, where active reverse faulting of segment II is blind. Unconformity 1 (18 ka) is projected beneath the topographic relief of the ridge axis, where Tertiary rocks are exposed. Minimum and maximum projections of unconformities 4 (ca. 340 ka) and 6 (ca. 630 ka) over the crest of the fold provide relative vertical-motion estimates during the time interval between development of the unconformities (assuming surfaces 4 and 6 formed analogously to surface 1). Relative footwall subsidence is unaccounted for. The profile is illustrated in Figure 6C. MSL—mean sea level.

Figure 14. Methods for estimating vertical deformation associated with the ... Available to Purchase

Published: 01 November 2002
axis located 3 km and 1 km west of the fault. See text for explanation. Reflector labels and ages are explained in Figures 4 and 5 . (B) Interpretation of anticlinal growth of the southern Lachlan Ridge, where active reverse faulting of segment II is blind. Unconformity 1 (18 ka) is projected
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Figure 15. Cumulative vertical-separation (fault displacement and folding) variations along the strike of Lachlan Ridge. The positions of horizons 14 (top of the Paleogene section, ca. 24 Ma), 13 (upper Miocene, ca. 9–8 Ma), and 6 (upper Quaternary, ca. 0.63 Ma) were determined in the hanging-wall and footwall sequences on successive seismic profiles and cross sections (as labeled on fine vertical lines crossing the structure at the approximate locations [but not the orientations] of the profiles) by using the method in Figure 14A. Labels on the fine vertical lines indicate the locations of data in Table 1 and Figures 6, 8, 9, 11, and 12. Note the southwest plunge of the structural complex indicated by the decrease in hanging-wall elevation and the greater cumulative vertical displacements in the northeast. MSL—mean sea level.

Figure 15. Cumulative vertical-separation (fault displacement and folding) ... Available to Purchase

Published: 01 November 2002
Figure 15. Cumulative vertical-separation (fault displacement and folding) variations along the strike of Lachlan Ridge. The positions of horizons 14 (top of the Paleogene section, ca. 24 Ma), 13 (upper Miocene, ca. 9–8 Ma), and 6 (upper Quaternary, ca. 0.63 Ma) were determined in the hanging-wall
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Figure 1. Location map showing the North Island, Taupo Volcanic Zone, and Hikurangi margin. NIGHT shot locations (yellow stars), seismograph sites (orange triangles), digital OBS (red triangles), and multichannel seismic profile (red line) are shown. A transect through these instruments across the forearc and backarc is shown in Figure 2. Filled purple triangles are broadband seismograph stations, and white triangles are short-period seismographs deployed during the CNIPSE experiment from January 8 to June 27, 2001. Earthquakes recorded during this time are shown by purple dots. The gray shaded area is the modeled rupture (strike 45°, dipping between 59° and 68° to the northwest, and extending from 5 to 30 km depth) for the 1931 Mw 7.8 Hawke's Bay earthquake (Haines and Darby, 1987); this earthquake has been interpreted to have ruptured through the overlying plate, from the downdip end of the plate interface (Reyners, 2000). Kidnappers and Lachlan Ridges are shown by dashed lines. The inset regional map shows the location of the Hikurangi Plateau, part of the Pacific plate that is subducting to the west at a rate of ∼42 mm/yr (DeMets et al., 1994) beneath the Australian plate.

Figure 1. Location map showing the North Island, Taupo Volcanic Zone, and H... Available to Purchase

Published: 01 September 2006
of the plate interface ( Reyners, 2000 ). Kidnappers and Lachlan Ridges are shown by dashed lines. The inset regional map shows the location of the Hikurangi Plateau, part of the Pacific plate that is subducting to the west at a rate of ∼42 mm/yr ( DeMets et al., 1994 ) beneath the Australian plate.