AN ABSTRACT OF THE THESIS OF
Russell J. Van Dissen for the degree of Master of Science in Geology presented on February 15, 1989.
Title: Late Quaternary Faulting in the Kaikoura Region,
Southeastern Marlborough, New Zealand Redacted for privacy Abstract approved: Dr. Robert 8.0eats
Active faults in the Kaikoura region include the Hope,
Kekerengu, and Fidget Faults, and the newly discovered
Jordan Thrust, Fyffe, and Kowhai Faults. Ages of faulted alluvial terraces along the Hope Fault and the Jordan Thrust were estimated using radiocarbon-calibrated weathering-rind measurements on graywacke clasts. Within the study area, the Hope Fault is divided, from west to east, into the Kahutara, Mt. Fyffe, and Seaward segments. The Kahutara segment has a relatively constant Holocene right-lateral slip rate of 20-32 mm/yr, and an earthquake recurrence interval of 86 to 600 yrs: based on single-event displacements of 3 to 12 m. The western portion of the Mt. Fyffe segment has a minimum Holocene lateral slip rate of
16 + 5 mm/yr .(southeast side up); the eastern portion has horizontal and vertical slip rates of 4.8+ 2.7 mm/yr and
1.7 + 0.2 mm/yr, respectively (northwest side up). There is no dated evidence for late Quaternary movementon the Seaward segment, and its topographic expression is much more subdued than that of the two western segments.
The Jordan Thrust extends northeast from the Hope
Fault, west of the Seaward segment. The thrust has horizontal and vertical slip rates of 2.2 + 1.3 mm/yr and
2.1 + 0.5 mm/yr, respectively (northwest side up), and a maximum recurrence interval of 1200 yrs: based on 3 events within the last 3.5 ka. Drainage-divide elevation and mountain-front morphology of the Seaward Kaikoura Range, abundant evidence for recent activity on the Jordan Thrust, and lack of activity on the Seaward segment indicate that the late Quaternary displacement on the Hope Fault is transferred northward, west of the Seaward segment. The low slip rates for the thrust, compared to the higher lateral slip rates along the Kahutara and Mt. Fyffe segments, suggest that displacement on the Jordan Thrust does not accommodate all the displacement transferred from the Hope Fault. The remaining displacement is accommodated by distributed shear within the Torlesse rocks behind the thrust, and folds in front of and behind the thrust, although the latter was not documented for the Holocene. Late Quaternary Faulting in the Kaikoura Region, Southeastern Marlborough, New Zealand
by
Russell J. Van Dissen
A THESIS
submitted to
Oregon State University
in partial fulfillment of the requirements for the degree of
Master of Science
Completed February 15, 1989
Commencement June 1989 APPROVED:
Redacted for privacy
Professor of Geology/in charge of major Redacted for privacy
n of depat-tment of Geology
Redacted for privacy Dean of Gradua0School (7
Date thesis is presented February 15, 1989
Typed by researcher for Russell J. Van Dissen ACKNOWLEDGMENTS
For logistical assistance in the office and in the field, I am indebted to the New Zealand Geological Survey, especially the Earth Deformation Section. R.I. Walcott,
Victoria University of Wellington, aided in the arrangements necessary in getting me to New Zealand. For help with various phases of field work I thank S. Beanland,
K.R. Berryman, L.J. Brown, G.H. Browne, H.N.C. Cutten, D.L.
Fellows, M.G. Laird, J. Pedersen, R. Williams, and P.R. Wood. Aerial photography of the field area was provided for by the New Zealand Geological Survey; I thank D.L.
Fellows, D.L. Homer, and P.R. Wood for their help. J. van
Berkel provided the use of the University of Canterbury field station at Kaikoura. I would also like to acknowledge the farmers and residents of the Kaikoura area, the Marlborough Catchment Board, especially D.A. Mackay, and the New Zealand Forest Service in Kaikoura, without their help and cooperation this project would have been much more difficult and much less enjoyable. I thank S. Beanland and R.S. Yeats for their discussions about and critical reviews of this manuscript. With deep gratitude I thank the New Zealand-United States Educational Foundation whose award of a Fulbright Study Grant to me made funding for this project possible. TABLE OF CONTENTS
INTRODUCTION 1
Location and Previous Work 5
Methods and Quaternary Geology 6
DESCRIPTION OF THE ACTIVE FAULTS IN THE KAIKOURA REGION 13
Hope Fault 13
Kahutara Segment 13 Mt. Fyffe Segment 20 Seaward Segment 28
Jordan Thrust 29
Kekerengu Fault 40
Fidget Fault 41
Fyffe Fault 42
Kowhai Fault 46
DISCUSSION 48
Slip Rate on Hope Fault 48 Comparison of Slip Rate on Hope Fault with Pacific-Indian Plate Motion 55
Earthquake Recurrence Interval 56
Transfer of Displacement on Jordan Thrust 57
CONCLUSIONS 67
REFERENCES CITED 69 LIST OF FIGURES
Figure Page
1. Active faults in the Kaikoura region 2
2. Marlborough faults and offshore deformation 3
3. Calibration curve for modal weathering-rind thickness of surface Torlesse rocks 9
4. Faulted alluvial terraces at Sawyers Creek, Kahutara segment of the Hope Fault 17
5. Weathering-rind data from Sawyers Creek 18
6. Faulted alluvial fan at Mt. Fyffe Gate, Mt. Fyffe segment of the Hope Fault 21
7. Faulted and warped alluvial terraces at Waimangarara River, Mt. Fyffe segment of the Hope Fault 23
8. Profiles P-P of deformed alluvial terraces, 1 Waimangarara River 24
9. Faulted alluvial terraces at Hapuku River, Mt. Fyffe segment of the Hope Fault 26
10. Profile of Seaward Kaikoura Range drainage divide 31
11. Faulted alluvial terraces at Clinton River, Jordan Thrust 32
12. Profiles Pi-P of faulted alluvial terraces, Clinton 33
13. Weathering-rind data from Clinton River 34
14. Jordan Thrust exposure in Happy Valley. 38
15. Fyffe Fault exposure at Big Hau 43 16. Fyffe Fault where it makes a 35° turn in strike north of Big Hau 45 17. Faulted alluvial terraces at Charwell River, Kahutara segment of the Hope Fault 49 LIST OF FIGURES - continued
Figure Page
18. Latest Pleistocene slip-rate for the Hope Fault 54 19. Idealized relation between Hope Fault, Jordan Thrust, and Puhi Puhi syncline 60 20. Schematic cross-section across the Inland and Seaward Kaikoura Ranges 62
21. Elevation of Seaward and Inland Kaikoura Ranges projected parallel to direction of tectonic transport 65 LIST OF TABLES
Table Page
1. Late Quaternary displacements and ages for faulted terraces in the Kaikoura region 14
2. Late Quaternary lateral and vertical slip- rates for the active faults in the Kaikoura region 15
3. Late Quaternary lateral slip-rates for the Hope and Kakapo Faults near Glynn Wye 52
4. Average recurrence interval of earthquakes on the Kahutara segment with varying single- event displacement and varying slip-rate 58 LATE QUATERNARY FAULTING IN THE KAIKOURA REGION,
SOUTHEASTERN MARLBOROUGH, NEW ZEALAND
INTRODUCTION
The present-day tectonic setting of New Zealand is
dominated by the diffuse transform boundary between the Indian and Pacific plates, a transform that links the east- facing Tonga-Kermadec Trench and the west-facing Puysegur
Trench and Macquarie Ridge (McKenzie and Morgan 1969). The
major element of this transform is the right-lateral
strike-slip Alpine Fault. The Alpine Fault includes a
restraining bend (inset of Fig. 1, and Fig. 2). Yeats and Berryman (1987) point out that there isa tendency to
straighten out a restraining bend by shifting the plate boundary onto new faults that are on trend with the
boundary on the opposite side of the bend. The plate motion east of the bend is taken up by the Marlborough
fault system (inset of Fig. 1, and Fig. 2) which is made up
of the Wairau, Awatere, Clarence, and Hope Faults. In the Marlborough region, the convergence rate of the Pacific plate with respect to the Indian plate is 47 mm/yr at an azimuth of 264 ± 2° (Walcott 1979).
The Wairau Fault, formerly the most important of the
Marlborough faults, shows all the separation of Paleozoic
and Mesozoic tectonostratigraphic terranes between Nelson
and south Westland (inset of Fig. 1). It thus predates the 2
Active thrust fault showing 173'451
dip direction. Teeth toward I upthrown side. .# k" 70 Active strike-slip fault showing GS 3\ir GR. dip direction.u, upthrown fid9e side. 70 Ae Middle MII M Possible active fault showing dip direction. Late Quaternary (905 m) displacement not documented. Te 00 i 4 Whekere 4 Drainage divide of Seaward (2596 ml # Kaikoura Range. &M(tm) Al exander , 0 kau.,...,./ 28 cy, (2610 rn)Ar. ee J *km `t .0 48 4.-C> N Sounders .,* 4e15' 5 Half Moon Soy mt. CA (215,1-79r .iir/40 illokAt 68 11... / 85 t ngNite. 1 / F It. 7 / 0,000men e i 0:` 11 se9 Mt. Fiffe AC, 6 4)(1602) /90# liluku 47 eSIA River CI\ Vt. col"to 000m tudy Area 044) ':41* APqe N 0°1 . . Oavhoi Chorwell 17330.E Riker River Location Mop
Figure 1. Map of active faults in the Kaikoura region. Localities and features discussed in the textare Big Hau (BH), Charwell River (CW), Clinton River (CR),Floodgate Creek (FC), George Saddle (GR), George Stream (GS), Goidmine Creek (GM), Happy Valley (HV), Hapuku River (HR), Jordan Stream (JS), Kowhai Saddle (KS), Luke Creek (LC), Mt. Fyffe Bends (MB), McLean Stream (MS), Puhi Puhi River (PPR), Upper Kowhai Fault (UK),Sawyers Creek (SC), Snowflake Stream (SF), and Waimangarara River (WR). Inset shows Alpine Fault, Marlborough faults (seealso Fig. 2), Southern Alps, and offset tectonostratigraphicterranes (dots). Arrow shows azimuth and rate, in mm/yr, of relative motion of the Pacific Plate with respectto the Indian Plate. 2000 m isobath off the coast of Marlborough locates the southwestern end of the Hikurangi Trench,area below isobath is shaded. 3
_Inland Kaikouro Range drainage divide Seaward Kaikoura Range drainage divide 40 Active Fault 440 °ore) Cape Offshore Fault, teeth poin Campbell down dip. Offshore Folds, Syncline -4. Anticline 42° S 0 50 KM
R
173 E
Figure 2. Map of Marlborough faults and offshore deformation. On-land active faults (solid lines) from Officers of the New Zealand Geological Survey (1983) revised for the Kaikoura region by this study. Offshore deformation (dashed lines) from Lewis and Bennett (1985). Also shown are the late Quaternary lateralslip-rates for the Marlborough faults, in mm/yr, (boldnumbers in parentheses; see text for references). Localities and features discussed in textare Charwell River (CW), Clinton River (CR), Glynn Wye (GW), Goldmine Creek (GM),Hanmer pull-apart basin (HB), Hapuku River (HR),Kakapo Brook (KB), Mount Manakau (M),Manuka Stream (MK), McLean Stream (MS), Sawyers Creek (SC),Mount Tapuaenuku (T), and Waimangarara River (WR). CR, CW, GM, HR, MS, SC, and WR are the same as in figure 1, and Table 2 summarizes the slip-rates calculated at these sites (excluding CW). Table 3 presents lateral offsets, andages reported by Knuepfer (1984, 1988) for GW, KB, andMK. 4
other faults in the system and may predate the restraining bend itself (Yeats and Berryman 1987). However, because the growth of the Marlborough fault system has distributed strain across the system, the Wairau Fault has become less important. The late Quaternary right-lateral slip-rate along the Wairau Fault is 4-5 mm/yr at Branch River (Lensen
1976, Knuepfer 1984) whereas the slip-rate is 20-32 mm/yr along the central portion of the Hope Fault (Knuepfer 1984, this study).
Evidence for right-lateral displacement on the Hope Fault was first reported by McKay (1890) following the 1888 earthquake. Three fence lines crossing the fault were offset up to about 3 m. Freund (1971) suggested a right- lateral offset of as much as 19 km for the central portion of the Hope Fault, and he noted that near the coast, the fault becomes less distinct as it branches into several discontinuous traces. Also, there may have been little significant lateral displacement across the main active trace of the Hope Fault near the coast, at Hapuku River (HR of Fig. 1), based on middle Cretaceous lithofacies which can be traced across the fault (M.G. Laird, pers com.,
1985). Along the east-central portion of the Hope Fault, at Charwell River (CW of Fig. 1), Knuepfer (1984) reported that right-lateral slip - rates have averaged about 35 mm/yr throughout the last 15 ka (1 ka.1000 yrs), yet at Hapuku
River, he reported a significantly lower slip-rate. These observations suggest that the right-lateral displacementon 5
the Hope Fault does not continue out to sea, but may be
taken up near the coast by reverse slip on more northerly
faults. This study was undertaken to address this
possibility and to determine the nature and the extent of
late Quaternary faulting along the northeastern part of the
Hope Fault. Field work was carried out in 1987 from March to July and October to mid-December.
Location and Previous Work
The study area (Fig. 1) is bordered on the northwest
by the Seaward Kaikoura Range, and on the southeast by the
Pacific Ocean. The area includes several branches of the Hope Fault, the Fidget Fault, and the more northerly
trending Jordan Thrust and Kekerengu Fault.
The study area is part of the Kaikoura 1:250 000
geological map sheet (Lensen 1962), and the southern part of the area was included in a neotectonic study of the Hope
Fault by Freund (1971). Using radiocarbon-calibrated weathering-rind measurements, and soil morphology and
chemistry, Knuepfer (1984, 1988) estimated the ages of, and reported slip-rates for the faulted alluvial terraces at
Charwell River, Hapuku River, and McLean Stream (CW, HR, and MS of Fig. 1). At Charwell River, Bull and Knuepfer
(1987) studied the river'sresponse to climatic change and uplift since the latest Pleistocene. Many workers have noted the distinct marine terraces on the Kaikoura 6
Peninsula (e.g., McKay 1886, Cotton 1914, Jobberns 1928,
Suggate 1965, Bull 1985). Bull (1985) inferred an uplift rate of 0.64 mm/yr for the Kaikoura Peninsula, based on the vertical spacing of the Kaikoura Peninsula marine terraces, and the correlation of these terraces with global marine
terraces. Chandra (1968) and Brown (1988) have mapped the
geomorphology and Quaternary geology of the Kaikoura Plain.
Methods and Quaternary Geology
Within the study area, there are several faulted river
terrace sequences that record progressive late Quaternary displacement. These sequences are characterized by a major aggradational terrace above several degradational terraces.
To use faulted terraces to determine slip-rates, formerly adjacent piercing points with known ages must be correlated across the fault. In this study it is presumed that displacement of a terrace riser records the amount of slip that has taken place since the river abandoned the terrace tread below it. Lateral offsets reported for risers were obtained by averaging the displacements measured from both the toe and the crest of the riser. Profiles of deformed alluvial surfaces were made with a Kern GK23 level, a 200 m measuring tape and a 3 m fiberglass staff, or with a
Sokkisha SDM3C theodolite/ EDM. Spot heights, where noted, were measured with a hand level and a 2 m staff. Age estimates of faulted terraces were made using radiocarbon- 7
calibrated weathering-rind measurements on surface Torlesse graywacke cobbles, discussed below.
In lieu of radiocarbon samples, relative dating techniques have proved useful in estimating ages and correlating glacial and terrace deposits in New Zealand
(e.g., Chinn 1981, Birkeland 1982, Whitehouse and others
1986, Knuepfer 1988). These techniques measure post-
depositional alteration of surficial deposits and include
rock weathering-rind thickness, height of quartz-veins,
surface oxidation and pitting of clasts, soil morphology, and soil chemistry. Apart from time, several factors
influence the rate at which weathering features develop;
these include parent material, precipitation, temperature,
topography, and vegetation. Much of the South Island is underlain by a relatively homogeneous rock type, the well-
indurated sandstone and mudstone of the Torlesse Supergroup and its metamorphic equivalents (Suggate and others 1978). East of the Main Divide of the Southern Alps the Torlesse sandstone is generally an arkosic graywacke of prehnite- pumpellyite metamorphic facies (Mackinnon 1983). Thus the majority of glacial and alluvial deposits east of the Main
Divide are composed of a relatively uniform parent material. In the South Island, weathering-rind thickness
of surface boulders of Torlesse sandstone is the most widely applicable of the above techniques because the rate
of rind formation seems to be independent of or only slightly affected by variations in precipitation, 8
temperature, and topography (Chinn 1981, Whitehouse and
others 1986, Knuepfer 1988). The effect of vegetation is more difficult to evaluate because many sites that are now
grassland may have been forest before widespread fires during early Maori occupation 600-900 years ago (Whitehouse and others 1986).
When relative-dating methods are calibrated at sites of known age, a relationship between degree of post-
depositional modification and age can be established, and the ages of surfaces of unknown age can be estimated
("calibrated-age" methods of Colman and others 1987).
Using radiocarbon-dated deposits as age control, Chinn (1981) found that-for surface boulders of medium-grained
Torlesse sandstone, ages of surface weathering were highly correlated (r2= 0.97, r is the correlation coefficient) with their greatest modal thickness. He expressed this relationship as A = (1030) R1.24 where A is theage of the surface in years and R is the modal rind thickness in millimeters of about 50 boulders on the surface of the deposit. Chinn stated that the uncertainty of the age estimate is about + 20%. Whitehouse and others (1986) and
Knuepfer (1988) expanded the work of Chinn by the inclusion of additional calibrated sites. Figure 3 presents Knuepfer's (1988) calibration curve, where14C age of the deposit is plotted against modal weathering-rind thickness of surface Torlesse clasts. From this plot, Knuepfer revised Chinn's equation to A= (973 + 70)R(1.33 ± 0.05). 9
105 1: 20% envelope
Ar-(973)1:R1.33
102 lo- 10 Rind Modal Thickness (mm)
Figure 3. Calibration curve for modal weathering-rind thickne99 of surface Torlesse rocks. Modal rind thickness versus ''C age of deposit. Also shown is + 20% uncertainty envelope around best fit line of Knuepfer T1988). Figure redrawn from figure 4a of Knuepfer (1988). 10
For latest Pleistocene and younger ages, the uncertainty of this equation is roughly + 10%. Also shown in figure 3 is a + 20% uncertainty envelope around Knuepfer's equation.
Within the uncertainty of the radiocarbon dates, all but two of the data points lie within this envelope.
Common throughout much of the South Island is a pronounced latest Pleistocene aggradation surface (Suggate
1965). At Charwell River, Knuepfer (1984) and Bull and Knuepfer (1987) estimated the age of this aggradation surface to be 14 + 2 ka old. The age estimate is based on weathering-rind, soil chemistry, and soil morphology data collected at Charwell River, and on radiocarbon dates that constrain the age of the latest Pleistocene aggradation surface elsewhere in the South Island. Bull and Knuepfer (1987) stressed that climatically-induced sediment-yield increases during full-glacial climates (25-16 ka ago)were the main factor responsible for aggradation at this site. Farther to the west, a major phase of aggradation is represented by the coalesced fans that form much of the
Kaikoura Plain (Cotton 1950, Chandra 1968). Based on soil profile development, Chandra (1968) and Brown (1988) mapped these fans as latest Pleistocene in age. The most pronounced fan on the Kaikoura Plain is the Hapuku River fan. At Hapuku River, a boulder bar on the highest
(oldest) inset degradational terracebelow the aggradational fan surface has a modal weathering-rindage of 5820 + 850 yrs (Knuepfer 1988). The Kaikoura Plain and 11
Charwell River sites are only 20 km apart, and it is
probable that the events responsible for the latest
Pleistocene aggradation of Charwell River also caused the
major fan building of the Kaikoura Plain. If so, it is
probable that the fans are roughly the same age as the aggradation surface at Charwell River. Where other evidence is lacking, the age of the latest Pleistocene aggradation surface in the study area is presumed to be 14
+ 2 ka old.
Weathering-rind samples were collected from the faulted alluvial terraces at two sites within the study area, Sawyers Creek and Clinton River (SC and CR of Fig.
1). Calibrated ages for these terraces were estimated using Knuepfer's equation of A= (973)R1'33, and 20% uncertainty. The procedure used to collect and measure the weathering rinds follows those of Chinn (1981), Whitehouse and others (1986) and Knuepfer (1988). Rind thicknesses on chips from 30-50 exposed boulders and cobbles of medium- grained Torlesse sandstone were estimated to the nearest 0.1-0.2 mm by using a graduated 10X magnifying comparitor.
Measurements were made from the rock surface to the inner limit of white discoloration. The rind-thickness data were used to construct a histogram and were smoothed by a three- point weighted running mean. This was done to account for the uncertainty in measuring the thickness of a gradational rind boundary to an accuracy of 0.2 mm. The thickest (largest) "significant" modal rind thickness that comprises 12
more than 5% of the sample is chosen from the smoothed histogram. A modal value of rind thickness is chosen rather than the mean because the sampled rinds may also include rinds that date from or are influenced byyounger events such as partial burial or shattering of boulders by frost or fire, which would bias themean. Chandra (1968) and Brown (1988) mapped the Quaternary geology of the Kaikoura Plain. Based on relative position with respect to the elevation of the latest Pleistocene aggradation surface, and relative amount of weathering, Brown (1988) grouped the alluvial surfaces of the Kaikoura
Plain into six categories constrained by radiocarbon dates.
The alluvial surfaces range in age from early Otiran (45-70 ka) to the present. With slight modification, the
Quaternary geology of the Kaikoura Plain presented in Plate
1 was taken from Brown (1988). Using aerial photographs, Brown's alluvial surface classification was extended both west and northeast of the Kaikoura Plain. This mapping was additionally constrained by the modal weathering-rind ages calculated in this study at Sawyers Creek and Clinton River, and by those reported in Knuepfer (1988) for the
Charwell River, Hapuku River, and McLean Stream. 1 3
DESCRIPTION OF THE ACTIVE FAULTS IN THE KAIKOURA REGION
In the Kaikoura area, there is a system of active faults from the Kaikoura Plain to the southeast flank of the Seaward Kaikoura Range (Fig. 1). These include the Hope Fault, the Jordan Thrust, the Kekerengu Fault, the
Fidget Fault, the Fyffe Fault, and the Kowhai Fault. A
discussion of these faults follows. Tables 1 and 2 summarize the displacements, ages, and slip rates calculated from faulted terraces along these faults.
Hope Fault
The Hope Fault is divided into the Kahutara segment, the Mt. Fyffe segment, and the Seaward segment, based on topographic expression, amount of late Quaternary offset, and style of faulting (Fig. 1, Van Dissen 1987).
Kahutara Segment
The active Kahutara segment extends from the edge of the study area to the Kowhai River, where the Fyffe Fault branches from the Hope Fault. The continuity of the fault trace west of the study area (Freund 1971), and the high late Quaternary slip-rates reported by Knuepfer (1984) at
Charwell River suggest that this segment extends west past
Charwell River, possibly as far west as the Hanmer pull- 14
TABLE 1. Summary of Late-Quaternary Displacements and Ages for Faulted Terraces in the Kaikoura Region
Location Feature* Displacement Modal Source (m) Weathering- Lateral Vertical Rind Age (yrs)
Hope Fault
Sawyers Creek T 78+2 2780+560 (1) 4
T 150+20 11 4570+910 (1.) 3
Goldmine Creek Fan 230+20 14+2** (1)
Waimangarara T 18 14+2 (1) River 1
Hapuku River T 30+10 10-12 6290+950 (1) 2
Boulder 12.6+0.5 8.5+0.3 6290+950 (2) bar
Jordan Thrust
Clinton River T 3.3+1 3.2 1520+300 (1) 4
T 6+3 4.4 2290+460 (1) 3 T 0 20-30 14+2** (1)
Kekerengu Fault
McLean Stream Younger 5.6+2 980+60 (2) terrace
Older 11.2+3 1.8+0.1 1540+120 (2) terrace
* Terrace risers were used to measure lateral displacement. Terrace treads were used to measure vertical displacement.
** Maximum age estimate
Sources: (1) This study, (2) Knuepfer (1984, 1988) 15
TABLE 2. Summary of Late-Quaternary lateral and Vertical Slip -Rates for the Active Faults in the Kaikoura Region
Location Feature* Slip Rate Comment Source mm/yr Right- "Vertical Lateral (showing upthrown side)
Hope Fault
Sawyers Creek T4 28+8 Minimum (1)
T 33+13 2.4+0.6 NW (1) 3
Goidmine Creek Fan 16+5 SE Minimum (1)
Floodgate CreekHigh SE (1) level terraces
Waimangarara T 1.3+0.2 NW Minimum (1) River 1
HapUku River T 2 4.8+2.7 1.7+0.4 NW (1)
Boulder 2.0+0.4 1.4+0.2 NW (2) bar
Jordan Thrust
Clinton River T 2.2+1.3 2.1+0.5 NW (1) 4
T 1.9+0.5 NW (1) 3
TO 1.3-2.5 NW Minimum (1)
Kekerengu Fault
McLean Stream Younger 5.7+2.6 NW (2) terrace
Older 7.3+2.8 1.2+0.1 NW (2) terrace
* Terrace risers were used to measure lateral displacement. Terrace treads were used to measure vertical displacement.
Sources: (1) This study, (2) Knuepfer (1984, 1988) 16
apart basin (HB of Fig. 2). The Kahutara segment is
characterized by a relatively continuous and linear trace and large late Quaternary right-lateral displacements with
subordinate vertical displacement, up to the northwest.
This segment is a range-bounding fault between the Seaward
Kaikoura Range to the north and the alluvial plain to the
south. Its trend is 070°, and the fault plane at Charwell River dips about 70° NNW (Knuepfer 1984).
Along the west bank of Sawyers Creek, at grid
reference 548/7369371, (Fig. 4 and SC of Fig. 1) a flight of faulted alluvial terraces records progressive offset.
At this site, T1is the latest Pleistocene aggradational
surface, and T-T are younger degradational terraces. The 2 4 T tread is only 2.5 m above the modern flood plain, and 4 the T riser (riser above the Ttread) is offset right- 4 4 laterally by at least 78 + 2 m (Table 1). The corresponding upstream T riser has been eroded away by 4 Sawyers Creek. Weathering-rind samples from the T surface 4 have a modal thickness of 2.2 mm (Fig. 5). Using the equation presented in Knuepfer (1988), and a + 20% uncertainty, this corresponds to an age of 2780 + 560 yrs.
Using the above offset and age, a minimum slip rate of 28 +
8 mm/yr can be calculated for T (Table 2). Downstream 4 from the fault, the riser above the next oldest terrace,
1 Locations are given according to the grid from NZMS 1 topographic maps, scale 1:63 360. 17
= 2.3= z
Store
- 22.5 Top 5.3 Scarp: Heavy lines, Fault ?0
1 I-7- Light lines, Terrace Riser Base Numbers give scarp height in meters T 7. Probable fault or possible landslide. Landslide showing head scarp. ,100m 7,.-me Small drainage and gully (approximate) Rood
Figure 4. Map of faulted alluvial terraces at. Sawyers Creek (SC of Fig. 1), Kahutara segment ofthe Hope Fault. T corresponds to the latest Pleistocene aggradation 1 surface, T-T are younger degradational terraces. Map drawn from'figld studies and NZGS aerial photographs GS 705 5-9. Figure 5 presents weathering-rind data collected at this site. 18
A
(cg 8- Terrace 4 Terrace 3 0. E 6. E 6- a a cr) a 4_ -6
.0a) 2- .0CD 2- E - z o 00 0 2 4 6 2 41 6 Rind Thickness, mm Rind Thickness, mm
B
Terrace No. 3 4
0 2 4 Rind Thickness, mm
Figure 5. Weathering-rind data from surface Torlesse rocks, Sawyers Creek. Terrace T is older than terrace T . (a) Histograms of rind measurements.3 (b) Rind data 4 smoothed using weighted running mean. Large dots denote the modes chosen for age determinations. 19
T3, is 22m high, the largest riser at Sawyers Creek. This riser is offset right-laterally by 150 + 20 m, and vertically by 11 m, northwest side up. Weathering-rind samples from Thave a modal thickness of 3.2 mm (Fig. 5) 3 which corresponds to an age of 4570 + 910 yrs.
About 6 km west-southwest of Sawyers Creek, at
Charwell River, Bull and Knuepfer (1987) dated eight cut- and-fill terraces by weathering-rind measurements, soil morphology, and soil chemistry. They found that between 5-
7 ka ago there was a major phase of degradation. During this phase of degradation the largest terrace risers were cut at Charwell River.
Because of the similar geologic and climatic setting of Sawyers Creek and Charwell River, it is likely that the response of Sawyers Creek to climatic changes was similar to that of Charwell River. If this is the case, Sawyers
Creek cut the T riser between 5-7 ka ago. This age is 3 within the uncertainty of the weathering-rind age of T3, and is further support for a near 5 ka age for T3. Using the 150 + 20 m right-lateral offset of the T riser and an 3 age of 4570 + 910 yrs, a horizontal slip rate of 33 + 13 mm/yr can be calculated. The 11 m vertical offset of T 3 gives a vertical component of slip-rate of 2.4 + 0.6 mm/yr, up to the northwest. 20
Mt. Fyffe Segment
The active Mt. Fyffe segment of the Hope Fault is bounded on the west by the Kowhai River, where the Fyffe
Fault branches from the Hope Fault, and on the east by the Hapuku River, where the Jordan Thrust is close to the Hope
Fault (Fig. 1). This segment is a range-bounding fault
that runs along the base of Mt. Fyffe; its trace is slightly arcuate, concave to the northwest. The western portion of the segment has a general trend of 080° and is characterized by right-lateral strike-slip displacement with a minor vertical component, up to the southeast. The eastern portion of this segment has a general trend of 060° and is characterized by reverse displacement, up to the northwest, with subordinant strike -slip displacement. In
Luke and Middle Creeks (LC of Fig. 1). the fault plane dips
70° NNW.
At Goldmine Creek, S49/977867, (GM of Fig. 1) near the Kowhai River, a small stream on the south flank of Mt.
Fyffe has deposited an alluvial fan. The western side of the toe of this fan is offset right-laterally by 230 + 20 m
(af of Fig. 6). Vertical displacement is about 1-2 m, up 3 to the southeast, but the topographic relief of the fan precludes an accurate determination of this displacement.
The af fan is younger than the latest Pleistocene 3 aggradation surface of the Kaikoura Plain, based on soil development (Brown 1988). Using the assumed 14 + 2 ka age 21
7 / .//7- /To rlesse// Mt Fyffe/Bedrock Gate/
../'ta w a G-1 ...
g,105644CgIti vo',14.4!..4, '<"fe ..,
4ks. 1:3*.°P$1., ;oo-0,1)c,t4sk4v.t...,,z,-$4,7c, 1911, 4,11:1d1,,14d;12-4. IOQin..,,;`*s.4ire:712* ,z 0V01,4,67P c> Vt,4:'cw..e4Pa..4.cidi,,,,-0,. .9.; , vo.o..--'''" iA.;-qhP;4249:kvw,0 .., I 11\1.,:.0.4Vo.id,Qe-fr4:4f.' G-,..'4:11.!.640:0,ev.P.i7?*.,;;.*b:g 1°0m ..o--'94g0. 117!;"0*1 r ..,),...i00! (approximate) -t =ate .,,,,,,,,i5 Top 78 -r-rSCARP: Heavy lines, Fault Base Light lines, Terrace Riser or Cut Bank Numbers give scarp height in meters .41".> Landslide showing Relative age of X head scarp Surf icial Deposits * *r Marsh area Alluvium Drainage ailall 0) CT Metalled Road af3aft Fans >9 afi
Figure 6. Map of faulted alluvial fan at Goldmine Creek (GM of Fig. 1) near the Kowhai River, Mt. Fyffe segment of the Hope Fault. Map drawn from field studies and NZGS aerial photographs GS 702 1-3. 22
of the aggradation surface as an estimate of the maximum
age of the af3 fan, a minimum slip rate of 16 + 5 mm/yr can be calculated.
The possible decrease in slip-rate from the Kahutara
to the Mt. Fyffe segment may in part be due to the minimum
slip-rate calculated at this site, and in part due to the
distribution of slip from the Kahutara segment onto the Kowhai and Fyffe Faults.
The alluvial surfaces east of Floodgate Creek, 849/ 893985, (FC of Fig. 1) are cut by two uphill-facing fault
scarps. Complex and modified topography makes the
correlation of displaced features difficult. An accurate
estimate of the total vertical and horizontal displacement was not made, but the vertical displacement is probably
several meters up to the southeast. These alluvial surfaces are probably early Otiran (45-70 ka; Chandra 1968, Brown 1988).
Along the west bank of the Waimangarara River, S49/
938005, a flight of alluvial terraces is warped and faulted
(Figs. 7 and 8, and WR of Fig. 1). Profiles P1 and P2 of
figure 8 show that both T1 andT2 are warped the same amount, each back-tilted to the north by 2.1° from the
horizontal. It is unclear whether T is back-tilted as 3 well (Profile P3 of Fig. 8). The T2 riser is warped over, and is continuous over, a large northeast-trending tectonic
warp (large arrows of Fig. 7), and shows no horizontal
displacement. Downstream from the tectonic warp the Ti 23
Top 3.7
Bose Top VBaseV Down-slope direction of warped terrace, showing extent of warping. Alluvial fan Drainage Pi QIs Landslide ...... Profilelocation
Figure 7. Map of faulted and warpedalluvial terraces at the Waimangarara River (WR ofFig. 1), Mt. Fyffe segment of the Hope Fault. T1 corresponds to the latest Pleistocene aggradation surface. T -T are younger degradational terraces. Map drawn frbm eield studies and NZGS aerial photographs GS 339 1-4. Figure 8 presents profiles of these deformed terraces. 24
N Profile P1
-----..Ti S P4 NN.N.. Fan
. i
N N Profile P2 ProfileP3 12 S 13
TP4 I III I 60 E W Profile E c 40 P4 Scale T2 a, 20 IP fP2
0 ' 1 0 100 Distance (m) Vertical exaggeration 2%1
Figure 8. Profiles P1 -PA of the deformed alluvial terraces at the Waimangarara Rive. See figure 7 for the location of these profiles. 25
surface is buried by an alluvial fan. The thickness of the
fan at the end of profile P1is not known, but it appears to be less than several meters. The height of the sharp tectonic warp is 18 m, and the minimum tectonic relief of
the warp on T1is 25 m (Profile P1of Fig. 8); the T1 surface downstream from the warp is buried by the alluvial
fan. Brown (1988) shows that the Tsurface is the latest 1 Pleistocene aggradation surface. Because T1 and T2 are
warped the same amount, the 18 m high warp of T1is
probably younger than T (younger than 14 + 2 ka). Using a 2 minimum vertical deformation of 18 m and a maximum age of 14 + 2 ka, the minimum vertical component of the slip-rate
is 1.3 + 0.2 mm/yr.
The alluvial surfaces west of the Hapuku River, 849/
873027, are offset by several traces of the Hope Fault
(Fig. 9 and HR of Fig. 1). The fault-scarp height across
the latest Pleistocene aggradation surface, T1,varies from
26 m to about 5 m, up to the northwest. Upstream from the
scarp, T1 and the next youngest terrace, T2, are in places back-tilted to the north and northwest. The T riser is 2 offset right-laterally across several fault traces. An accurate estimate of the total displacement of T2 is
difficult to make because the fault scarps intersect the
riser at oblique angles, making the projection of the riser across the fault scarps subject to large errors, and because in several places the T2 riser has beeneroded. Nevertheless, a crude estimate of the total right-lateral 26
\\\\\\ \ Cretaceous /Tertiary T2 ..,..4- \ \Bedrock \e.. .i.1 .10.. / 45-41 \ r, , , , f ,,, 51 9. Zit CD7), V",1ryi 18 ,V9qt 15 of EiED4 0 (14?0 0 Younger ',gvard Terraces 0 V-DI''' T2 Grange Rd 110 44.1,. tt$ '...u.,47t'* v. 110 rvi
47=0 0*, Top 21 SCARP: Heavy lines, Fault Light lines, Terrace Riser Base Numbers give scarp height inmeters Down-slope directionof warped terrace Active fault trace of Young alluvial fan Drainage = = = = Road
Figure 9. Map of faulted alluvial terraces at the Hapuku River (HR of Fig. 1), Mt. Fyffe segment of the HopeFault. T 1 corresponds to the latest Pleistocene aggradation surface. Map drawn from field studies and NZGS aerial photographs GS 703 9-12. 27
displacement is 30 + 10 m. At Hapuku River, Knuepfer
(1984) reported that a boulder bar is offset by several traces of the Hope Fault, with a lateral displacement of 12.6 + 0.5 m, and an apparent vertical displacement of 8.5
+ 0.3 m, northwest side up. This bar is on T2 and Knuepfer
(1988) reported a modal weathering-rind age of 6290 + 950 yrs for the bar. If the boulder bar is the same age as the
T 2 surface, a right-lateral slip-rate of 4.8 + 2.7 mm/yr can be calculated based on the offset of the T riser. 2 Using the offset of the boulder bar, Knuepfer (1984) reported a lateral slip-rate of 2.0 + 0.4 mm/yr. The discrepancy between these two slip-rates is explained by noting that the boulder bar does not extend far enough upstream or downstream to be cut by all the faults that cut the T riser (Fig. 9). Thus, the Triser has a greater 2 2 offset than the boulder bar even though they are presumed to be the same age. The vertical displacement of T2 varies between 10-12 m, which gives an average vertical component of slip-rate of 1.7 + 0.4 mm /y
The warping of the Waimangarara terraces and the large and variable vertical displacements at Hapuku River suggest that Holocene deformation in this area has had a significant compressional component, with vertical displacements being up to the northwest. The change in throw along the Mt. Fyffe segment, from up to the southeast at Kowhai River and Floodgate Creek toup to the northwest at Waimangarara River and Hapuku River, corresponds toa 28
gradual northward swing in trend of the Mt. Fyffe segment.
The northward turn in trend brings the fault into an orientation of greater compression.
Seaward Segment
As the Mt. Fyffe segment approaches the Waimangarara and Hapuku Rivers, much of the continuity of the fault trace is lost as a series of splays. The Seaward segment extends east from the Hapuku River out to Half Moon Bay.
East of the Puhi Puhi River (PPR of Fig. 1), this segment consists of two sub-parallel faults separated in the middle by a left step 1 km wide. Both faults are about 3 km long, dip 70° N and trend between 070° and 080°. A third fault associated with the left step is about 1.3 km long and trends 042°.
The topographic expression of the Seaward segment is much more subdued than the well-defined scarps and warped terraces of the two western segments. Unlike both the
Kahutara and Mt. Fyffe segments, there is little change in topographic elevation across the trace of the Seaward segment. Along this segment there is no dated evidence for late Quaternary movement. East of the Puhi Puhi River, the two longer faults are characterized by topographic lows, linear drainages, and saddles. The smaller northeast- trending fault is clearly expressed by a which offsets a bedrock gully 4-6 m right-laterally and 1m vertically, up 29
to the northwest. The age of this displaced gully is not known, but the distinctness of thescarp suggests that the fault has moved within the late Quaternary. Because the northeast-trending fault appears to connect the two longer traces, and it has probably been active in the late
Quaternary, the two longer faults, though showingno direct evidence of late Quaternary activity, are interpreted as active as well.
The subdued topography and lack of any significant late Quaternary displacement strongly suggests that the
Seaward segment has experienced only a minor percent of the total late Quaternary displacement seen on either the
Kahutara or Mt. Fyffe segments, and that the lateral slip- rate of the Seaward segment is less than that at Hapuku River, less than 5 mm/yr.
Jordan Thrust
The Jordan Thrust does not appear on Lensen's (1962) geologic map. However, Jobberns (1932) inferred a west- dipping reverse fault between the steep slopes of the Seaward Kaikoura Range to the west and the relatively gentle topography of the younger rocks to the east. The Jordan Thrust is named for the fault-plane exposure along the eastern bank of the north branch of Jordan Stream, S42
& S43/012134, (JS of Fig. 1) where the fault hasan attitude of 010o 28°28 W. The thrust has a map length of 25 30
km and extends north from its junction with the Hope Fault, between the Waimangarara and Hapuku Rivers, to its junction with the Fidget and Kekerengu Faults near George Stream (GS of Fig. 1). Its strike ranges between 337° and 050°, and its dip ranges between 28° and 48° W. The southern portion of the thrust is located at the break in slope between the alluvial surfaces of the Puhi Puhi Valley, northwest of the Puhi Puhi River, and the steep slopes of the Seaward
Kaikoura Range. To the north, it is marked by a relatively linear mountain front. The highest summits of the Seaward
Kaikouras are found adjacent to the Jordan Thrust (Fig.
10).
Late Quaternary activity is documented at several sites along the thrust. Along the south bank of the south fork of Clinton River, S49/999086, (CR of Fig. 1) there is a flight of five alluvial terraces, the oldest four of which have been offset vertically, up to the northwest, and right-laterally (Fig. 11). Profiles were made of the terraces both downstream and upstream from the fault
(Profiles P1 and P2 of Fig. 12), and ofscarp heights
(Profiles P3, P4, P5 andP6 of Fig. 12). Weathering-rind samples were collected from three surfaces upstream from the fault (Till, T2u, T3u) and from two surfaces downstream from the fault (T3, T4) (Fig. 13).
T and Tare vertically offset by 3.2 m (Profile P 4u 4 3 of Fig. 12), and the weathering-rind age of T4 is 1520+ 300 yrs (Fig. 13). This yields a vertical slip rate of 2.1 31
Active thrust fault Active strike-slip fault ams .1101. MIND Possible active Te ao fault Whekere Seaward Kaikoura Range drainage divide Mona kou
c ,./
Whekere (2596 ml 4M.Wexander. (1198m) Manokau (2610m)ftr
fs
Kaikoura Peninsula Kowhat River
Figure 10. Profile of the Seaward Kaikoura Range drainage divide plotted in relation to theactive faults of the Kaikoura region. Elevations were projected perpendicular to a line with an azimuth of 045°. See figure 1 for additional information pertaining to the faults shownon this figure. 32
Top SCARP, Heavy lines, Fault Profile Location Base Light lines, Terrace Riser or Cut Bank Landslide showing location of head scarp Drainage 37Strike and dip of Jordan Stream Farm track 1` Thrust.
Figure 11. Map of faulted alluvial terraces at Clinton River (CR of Fig. 1), Jordan Thrust. Map drawn from field studies and NZGS aerial photographs GS 341 3-5. Figure 12 presents profiles of faultscarp, and riser heights. Figure 13 presents weathering-rind data collected at this site. 33
S Profile P1 N Landslide T3
TP 5 11'6 5 4 ii,.I.1,1 T,;,1,1
S ProfileP2 T it, _ T2 A --,...__. u FpP 6 TP5 '-- it ------. T4 u jLLLJ,.._L,LZI:4 1123.
NW ProfileP3 NW Profile P4 SE T3u SE T4u TA 4 ItP2 --...... - P2 IP
NW_Profile P5 SE - T2u E ---._ Landslide c20- IP2 ------0 - t-> to-Scale II,I,I,,, I . T F.'. I . I , a, 0 ." I NW 0 10 20 Profile P6 I Ti Distance (m) SE Vertical exaggerationI:I Landslide 1,1,1,1,1,1P2 , ...11
Figure 12. Profiles P1_p6 of the faulted alluvial terraces at Clinton River. See figure 11for the location of these profiles. 34
A 12-
B 10
20 8 T4 Terrace Terrace Terrace E6 4 15-6 3 E 6 3u a o _ V) U, (r) 04 4-
a15 152 E 02 42 E _ u) 0 r ';. z0J, z0 1413 0 4 0 2 4 0 Tau "b" Rind ;10 TerraceNo. Thickness, mm iu lu - -- 2u 3u Terrace Terrace 3 E 6 2u 06 lu 4 0 0 7).4 04
1'2 E2 20 2 4 0 4 6 0 2 RindThickness, mm Rind Thickness, mm
Figure 13. Weathering-rind data from surface Torlesse rocks, Clinton River. Terrace Tiis oldest; terrace T is youngest. (a) Histograms of rind measurements. (b) Rind data smoothed using weighted running mean. Large dots denote the modes chosen for age determinations. 35
+ 0.5 mm/yr. The T riser has a right-lateral separation 4 of 4.5 + 1 m, and intersects the scarp at a75° angle. 150 m from this site, the fault plane dips 37oNW. How much of the lateral separation of the T riser is the result of 4 reverse faulting and the orientation of the riser with
respect to the scarp? Using the 3.2 m vertical offset of
T and assuming a 37° dip on the fault plane, about 1.2 m 4 of the total lateral separation is calculated to be the result of reverse displacement and the orientation of the riser with respect to the fault-scarp. Thus, the T riser 4 has been right - laterally displaced by about 3.3 + 1 m.
This corresponds to a lateral slip-rate of 2.2 + 1.3 mm/yr.
The scarp height between T3u and T3 is 4.4 m (profile
P4 of Fig. 12). The weathering-rind ages of T3u and T3 are 2450 + 490 yrs and 2130 + 430 yrs, respectively (Fig. 13).
Averaging the age of T and Tas 2290 + 460 yrs, a 3u 3 vertical slip-rate of 1.9 + 0.5 mm/yr can be calculated.
The construction of a farm track has obscured the lateral separation of the T riser, yet a rough estimate would be 6 3 + 3 m. Due to the large uncertainty in this measurement a lateral slip rate was not calculated.
The T riser is 1.4 m higher upstream from the fault 4 thanitisclownstreamfromthefault(lorofilesPlandP2of
Fig. 12). The difference in scarp height between T4u-T4, and T3u -T3 is 1.2m. These measurements suggests that, prior to the deposition of the T surface, there was a 1.2- 4 1.4 m high scarp separating T and T3, and that T has 3u 3 36
experienced at leastone additional faulting event than T4.
A landslide covers the downstream correlatives of T 1u and T and there is no evidence of the landslide on T 2u, 3 (Fig. 11). Thus the landslide postdates T2u and predates
T3. T2 is older than T3, so it must be vertically offset by at least 4.4 m (the offset of T3). The scarp separating
T and the landslide surface is 2.3 m high (Profile P of 2u 5 Fig. 12). If T was unfaulted prior to the landslide, the 2 difference in the T2 and T3 scarp heights suggest that T2 is buried by at least 2.1 m of landslide debris. Also, upstream from the fault the T 3uriser is 1.6 m high, whereas downstream from the fault the T riser is 3.6 m 3 high (Profiles P1 and P2 of Fig. 12). The difference in the T3 riser heights is 2 m, the presumed thickness of the landslide if Twas unfaulted prior to the landslide. If 2 T was faulted prior to the landslide, it would be buried 2 by more than 2 m. The weathering-rind age of T2u is 3120 + 620 yrs (Fig. 13).
The scarp separatingT1u and the landslide surface is 3.7 m high (Profile P of Fig. 12). If 2 or more meters of 6 landslide debris also buries the downstream equivalent of
T then the vertical offset of Ti 1u, uwould be at least 5.7 m. This suggests that T1 was faulted prior to the formation of T3. The weathering-rind age of Till is 3470 + 690 yrs (Fig. 13).
At this site, a minimum of 3 faulting events are documented since the formation of T about 3.5 ka ago. 1u' 37
Thus, the maximum earthquake recurrence interval for the
Jordan Thrust is 1200 yrs.
Along the north bank of the south fork of Clinton
River, S49/000088, the Jordan Thrust has an attitude of
050° 37° NW. At this site, the fault plane and hanging- wall rocks overlie alluvium and possible scarp-derived colluvium of unknown age. The alluvial surface that overlies this exposure is offset vertically by 20-30 m, up to the northwest (T0 of Fig. 11). When correlated with surfaces of known age on the Kaikoura Plain, the elevation of T above the Clinton River suggests that it is younger o than the latest Pleistocene aggradation surface. Using a maximum age of 14 + 2 ka for this surface, a minimum vertical slip-rate of 1.3-2.5 mm/yr can be calculated.
In Happy Valley, S42 & S43/020182, there is a spectacular exposure of the Jordan Thrust (Fig. 14 and HV of Fig. 1). The attitude of the fault plane is 030° 42°
NW. Southeast of the fault plane, crushed footwall
Torlesse is depositionally overlain by a basal alluvial unit, and two colluvial wedges that are in turn overlain, via a fault or landslide contact, by crushed hanging-wall
Torlesse and basal alluvium. This entire sequence is in fault contact with and overlain by crushed hanging-wall
Torlesse. A possible scenario for this locality is as follows: 1) Alluvium was deposited over the fault contact between footwall and hanging-wall Torlesse. 2) Reverse faulting brought hanging-wall Torlesse over the basal 38
NNW
Footwall Crush Zone
Figure 14. Jordan Thrust exposure in Happy Valley (HV of Fig. 1). Attitude of fault plane is 030 42° NW. 39
alluvial deposit, and formed a scarp. Colluvial material derived from the downhill- facing scarp formed a colluvial wedge downstream from the scarp. 3) Additional faulting resulted in the deposition of a second colluvial wedge.
4a) Continued faulting brought hanging-wall Torlesse and overlying basal alluvium over the upper colluvial wedge; conversely, 4b) a landslide from the northwest brought hanging-wall Torlesse and alluvium over the upper colluvial wedge. 5) Subsequent faulting cut through the upper hanging-wall Torlesse and alluvium, and brought crushed hanging-wall Torlesse over hanging-wall Torlesse and alluvium.
Since the deposition of the basal alluvium, there has been a minimum of 14 m of throw along this fault. If the hanging-wall rocks and alluvium are faulted over the upper colluvial wedge, additional throw has occurred.
Unfortunately, the ages of the alluvial and colluvial units are not known; however, it is apparent that this site documents several, at least 4 or 5, late Quaternary faulting events.
The Torlesse rocks of the hanging-wall are highly fractured. The best developed and youngest of these fractures are characterized by centimeter-thick, northwest- dipping, throughgoing clayey gouge zones. The bedding dragged along these fractures is consistent with reverse movement. It is probable that some of the uplift and deformation of the Seaward Kaikouras is accommodated on 40
these and other small scale faults behind the master fault.
Kekerengu Fault
As shown on Lensen's (1962) geologic map, the
Kekerengu Fault branches northeast from the Hope Fault several kilometers west of the Kaikoura Plain. Lensen shows a linear trace up the Kowhai River Valley, northwest of Mt. Fyffe, to the Clarence River. However, the fault in the Kowhai River Valley does not connect with the fault that trends parallel to the Clarence River (Fig. 1).
Because these are different faults, the fault that trends up the Kowhai River Valley is renamed the Kowhai Fault, discussed in a later section. The name Kekerengu Fault is retained for the northeast to east-northeast trending fault that continues out to sea from its junction with the Fidget
Fault and the Jordan Thrust. The Jordan Thrust is given a separate name to emphasize the difference between the Kowhai Fault and the Kekerengu Fault as mapped by Lensen (1962), and to emphasize the predominantly thrust nature of the Jordan Thrust.
Faulted alluvial terraces at McLean Stream, S42 & S43/110295 (MS of Fig. 1), document late Quaternary displacement along the Kekerengu Fault. Profiling of these terraces confirmed the displacements reported by Knuepfer
(1984). Two young terraces are offset right-laterally by
11.2 + 3 m and 5.6 + 2 m, respectively. The older terrace 41
has a vertically offset of 1.8 + 0.1 m, and the younger terrace has a variable vertical offset, both up to the northwest. Knuepfer (1988) reported a modal weathering- rind age of 1540 + 120 yrs for the older terrace, and of
980 + 60 yrs for the younger terrace. Using the above displacements and ages, the older terrace has lateral and vertical slip-rates of 7.3 + 2.8 mm/yr and 1.2 + 0.1 mm/yr, respectively. The younger terrace has a lateral slip-rate of 5.7 + 2.6 mm/yr.
Fidget Fault
In the Clarence Valley, west of the Seaward Kaikoura Range, the Fidget Fault (Fig. 2) has been active within the late Quaternary (Lensen 1962). East of the range, the Fidget Fault extends through George Saddle and down the
George Stream Valley (GR and GS of Fig. 1). In George
Stream, S42 & S43/066277, the fault has an attitude of 080°
90°. Towards the mouth of George Stream, 3 km upstream from its confluence with the Clarence River, the, pattern of fault scarps clearly shows that the Fidget Fault turns northward out of the George Stream Valley into the
Kekerengu Fault. The higher lateral-slip rate at McLean
Stream, compared to that at Clinton River, may be because
McLean Stream is north of this junction of the Fidget Fault with the Kekerengu Fault.
Northeast across the Fidget Fault, the elevation of 42
the Seaward Kaikoura Range rapidly decreases (Fig. 10).
Also, the topography of the Seaward Kaikouras is more subdued to the north of the Fidget Fault than it is to the south. It is possible that the steeply-dipping Fidget
Fault separates a region of high uplift associated with the
Jordan Thrust to the south, from a region of lower uplift associated with the Kekerengu Fault to the north.
Fyffe Fault
The Fyffe Fault, not shown on Lensen's (1962) geologic map, branches from the Hope Fault near the Kowhai River and extends for 11 km along the northwest and north flank of
Mt. Fyffe (Fig. 1). The northeast-trending portion of the fault dips about 60° SE. As the fault turns to a more easterly trend, the dip increases to 80° S. The fault is characterized by a pronounced crush zone within Torlesse bedrock, but only at Big Hau, 849/896031, (Fig. 15 and BH of Fig. 1)is late Quaternary activity documented.
At Big Hau it must be determined whether the 5.5 m vertical separation of the colluvium/Torlesse contact records the displacement of a contact that was originally continuous and unfaulted, or whether the colluvium is just ponded behind and mantled over a pre-existing bedrock scarp. For the entire length of the fault contact between the colluvium and Torlesse, there'is a uniformly thick (15-
18 cm) layer of clayey fault gouge that shows no signs of 43
A SE NW
Inset B Torlesse
Fyffe Fault co. 50m
B SE NW Reddish brown clayey sand Angular gravel
Dyke Torlesse
Fyffe Fault/
Figure 15. Fyffe Fault exposure at the northeast side of Big Hau (BH of Fig. 1). 44
having been eroded. Several clasts next to this layer are oriented with their long axes parallel to the dip of the layer, suggesting that they have been rotated parallel to the fault plane during faulting. Also, no layer within the colluvium can be traced across the upward projection of the fault plane. The above observations suggest that the vertical offset of the colluvium/Torlesse contact took place entirely after the deposition of the basal colluvium. Ridge rents (gravity fault traces of Beck, 1968) are presumed to have predominantly dip-slip displacement, and they are common along the ridges throughout the Mt. Fyffe area. Could the Fyffe Fault be a ridge rent? Slickenside lineations measured at Big Hau and three other localities along the northeast-trending portion of the fault plunge between 30°-50° S. This suggests that recent movement has been about equal amounts dip-slip and strike-slip and argues against the possibility that the fault could be a ridge rent.
Figure 16 (MB of Fig. 1) shows the Fyffe Fault where it goes through a 35° change in strike. Close to the bend the single fault trace splays into three separate faults.
The inset of figure 16 shows the offset of locally distinct bedrock units across these faults. The rock units dip 40 °-
60° W. The apparent vertical offsets cannot be explained by purely normal dip-slip movement; however, the offsets can readily be explained by right-lateral movement across the Fyffe Fault. This also argues against the possibility 45
Fyffe Fault, showing dip of fault plane, and 50 os-' trend and plunge of 1070 slickenside-lineations
"T-40 Bedding attitude Contours in meters 0 250 m
Figure 16. Map of Fyffe Fault where it makes a 35° turn in strike north of Big Hau (MB of Fig. 1). Inset shows the apparent vertical displacement of locally distinct rock units across the Fyffe Fault. 46
that the Fyffe Fault is a large ridge rent.
The apparent vertical offset of the rock units in figure 16, the orientation of the slickenside lineations, and the offset of the colluvium/Torlesse contact at Big Hau are all consistent with the Fyffe Fault being a right- lateral strike-slip fault with a component of normal displacement, up to the northwest, along the northeast trending portion of the fault.
Kowhai Fault
The Kowhai Fault (Fig. 1) is characterized by an extensive crush zone (up to 50 m wide), and its trace occupies aligned major topographic lows. For roughly 10 km west of the Kowhai River, the fault trends sub-parallel to, but 3-4 km north of the Hope Fault. Near Kowhai Saddle (KS of Fig. 1), the fault makes the same 35° turn in strikeas the Fyffe Fault. No dated evidence for late Quaternary displacement along the Kowhai Fault has been found.
However, the sharpness of the offset topography northeast of Snowflake Stream, 549/869023, (SF of Fig. 1) such as right-laterally offset drainages, beheaded streams, and shutter ridges, strongly suggests movement along this fault during the late Quaternary.
Northwest of the Kowhai Fault, as it parallels the
Kowhai River, there are many steeply dipping northwest- trending faults. These faults are characterized as 47
throughgoing planar crush zones. The most pronounced of these faults, informally termed the Upper Kowhai Fault, branches from the Kowhai Fault near Snowflake Stream and extends through the Upper Kowhai River drainage. In the Upper Kowhai River valley, it is characterized by a crush zone several meters thick and a well-defined fault plane that dips 70° SE. At this locality, S49/895079, (UK of Fig. 1) the crush zone and fault plane are overlain by an unfaulted 20+ m thick sequence of colluvium or till. The elevation of the upper deposit above the river channel, more than 180 m, and the degree of weathering of this deposit suggest that it is older than early Otiran (older than 45-70 ka).
Between Mt. Snowflake and Mt. Saunders (Fig. 1), the ridges and streams on the southeast flank of the Seaward
Kaikoura Range generally trend southeast. Where they cross the Upper Kowhai Fault they change trend to roughly southwest. These are not shutter ridges or offset streams, as is the case when a ridge or stream is offset by movement on a single discrete fault, but the change in trend of the ridges and streams may be due to the distribution of shear across a zone several kilometers wide involving the Kowhai
Fault, the Upper Kowhai Fault, and the lesser faults in between. 48
DISCUSSION
Slip Rate on Hope Fault
At Sawyers Creek (Fig. 4) a right-lateral slip-rate of 33 + 13 mm/yr was calculated for a surface about 4.6 ka old, and a minimum slip-rate of 28 + 8 mm/yr was calculated
for a surface about 2.8 ka old (Tables 1 and 2). Six kilometers to the west, at Charwell River, an 11 ka old terrace has a minimum and maximum slip-rate of 17 and 48 mm/yr, based on the offsets and age reported by Knuepfer
(1984) and Knuepfer (1988), respectively. However,
Knuepfer (1984) reported that during the last 4.4 ka the slip-rate at Charwell River has decreased to about 4 mm/yr.
The lateral slip-rates at Sawyers Creek are in conflict with the slip-rate at Charwell River for the last 4.4 ka. Further work at Charwell River (Fig. 17), as part of this study, has confirmed Knuepfer's (1984) statement that lateral displacements of the Charwell River terraces are difficult to determine. There are several reasons for this. 1) Terrace remnants upstream from the fault are of very limited extent (Fig. 17), and the trend of the risers of several of these remnants suggest that the river was flowing sub-parallel to the fault when the risers were cut.
2) A graben in the middle of the site disrupts the continuity of the terrace risers close to the fault. Thus, in order to measure offset, non-parallel risers must be 49
tir
Terrace riser or landslide T2 scarp T. ofAlluvial Fan TrUndifferentiated Terrace Remnant Top Scarp: Heavy lines, Fault 44'4 Marsharea Light lines, Terrace Riser r.-% Sma IIDrainage Bose or Cut Bank T T T Landslide or fault scarp 50 m
Figure 17. Map of faulted alluvial terraces at Charwell River (CW of Fig. 1), Kahutara segment of the Hope Fault (modified from figure 52 of Knuepfer 1984). 50
projected as much as 120 m across the graben. 3) A young fan upstream from the graben buries portions of high terrace remnants, making it difficult to correlate these features downstream from the fault. 4) In the lower terrace area, the river terrace is parallel to the fault trace (Knuepfer 1984). Thus, the river may have eroded away the downstream correlatives of young terraces upstream from the fault, and formed younger terraces downstream from the fault that have no upstream correlatives. 5) Slope failure has probably disrupted the location and shape of several of the remnants.
To illustrate the difficulties in measuring lateral offsets at Charwell River, two examples are given.
Upstream from the fault, the T3u riser of Knuepfer (1984) trends subparallel to the fault and almost perpendicular to the T riser downstream from the fault (Fig. 17). The 3 farthest south T 3ucan be traced is more than 100 m upstream from T3. Thus, it would be difficult to measure any meaningful displacement for these two nearly perpendicular risers without first making an assumption as to the shape of the river channel while the T riser was 3 cut. In Knuepfer's preferred terrace correlations, he reported that the T10 riser (inset of Fig. 17) has a 4 m greater offset than the older T riser. These examples 9a illustrate the ambiguity involved in measuring lateral displacements at Charwell River.
Is there evidence elsewhere along the Hope Fault to 51 suggest a drastic decrease in lateral slip-rate over the last 4-5 ka? Near Glynn Wye, Knuepfer (1984) calculated slip-rates at two locations along the Hope Fault (GW and MK of Fig. 2), and one location along the Kakapo Fault (KB of Fig. 2). During the present study, these sites were not investigated, and the following site descriptions, measured lateral displacements, and age estimates are from Knuepfer
(1984, 1988). Table 3 summarizes slip rates calculated at these sites.
Near the Glynn Wye homestead (GW of Fig. 2), a moraine and two early post-glacial degradation terraces are cut by the Hope Fault. The depositional east face of the moraine is offset right-laterally by 348 + 7 m, and it has a modal weathering-rind age of 18 680 + 3780 years. This corresponds to a slip-rate of 19 + 5 mm/yr. The younger of the two terraces is offset right-laterally by 135 + 6 m, and has a modal age of 8490 + 1380 yrs, which yields a slip-rate of 16 + 4 mm/yr.
At Manuka Stream (MK of Fig. 2), three young terraces are cut by the Hope Fault. The riser of the youngest terrace has a lateral offset of 18.1 + 3.5 m and a channel on this terrace has an offset of 25.4 + 2.0 m. The age of this young terrace is estimated at 1250 + 90 yrs which gives a slip-rate of about 14-20 mm/yr.
At Kakapo Brook (KB of Fig. 2), the Kakapo Fault displaces a late-glacial moraine and six terraces; however, the age of only one of the terraces was reported. Its 52
TABLE 3. Summary of Late-Quaternary lateral Slip -Rates for the Hope and Kakapo Faults near Glynn Wye
Location Feature Modal Weathering- Displacement Slip Rate Rind Age (yrs) * (mm/yr)
Hope Fault
Glynn Wye Moraine 18 680+3780 348+7 19+5
Riser 8490+1380 135+6 16+4
Mantka Riser 1250+90 18.1+3.5 14+4 Stream Channel 1250+90 25.4+2.0 20+3
Kakapo Fault
Kakapo Riser 5260+730 32+6 6.1+2.3 Brook
* froth Knuepfer (1988) X from Knuepfer (1984) 53
displacement and modal weathering-rind age are 32 + 6 m and
5260 + 730 yrs, respectively, which yields a lateral slip- rate of 6.1 + 2.3 mm/yr.
In summary, the Hope Fault, near Glynn Wye, has a lateral slip-rate of 19 + 5 mm/yr calculated from a 19 ka old moraine, and at Manuka Stream, it has a slip-rate of
14-20 mm/yr calculated from a 1.3 ka old terrace. The slip-rate data indicate that, for this part of the Hope Fault, there has been little if any decrease in lateral slip-rate in the last 4-5 ka (Table 3). Also, when the slip-rate on the Kakapo Fault is added to that on the Hope
Fault at Glynn Wye or Manuka Stream, the combined slip-rate of 16-32 mm/yr is compatible with those at Sawyers Creek, and probably Charwell River, within the uncertainties given.
Based on the minimum and maximum slip-rates of 17 mm/yr and 48 mm/yr, respectively, for an 11 ka old surface at Charwell River (modified from Knuepfer 1984), the 33 + 13 mm/yr slip-rate fora 4.6 ka old surface at Sawyers
Creek, the 28 +-8 mm/yr minimum slip-rate for a 2.8 ka old surface also at Sawyers Creek, and the combined Hope-Kakapo slip-rate near Glynn Wye, it would appear that the Hope Fault has had a relatively constant lateral slip-rate of
20-32 mm/yr throughout the last 19 ka (Fig. 18). It is probable that the low slip-rate at Charwell River for surfaces younger than 4.4 ka reflects more the difficulty in correlating terraces and measuring their offset across 54
Hope FaultSlip Rate
50 Pacific-Indian Plate Rate 40 T-
30
20-32 mm/yr %:::::* 20
10
GW,MK CW SC GM HR KB
Figure 18. Latest Pleistocene slip-rate for the Hope Fault. CW, GM, GW, HR, KB, MK, and SC are locatedon figures 1 and 2. 55
the fault, than it documents a drastic decrease in lateral slip-rate.
Comparison of Slip Rate on Hope Fault with
Pacific-Indian Plate Motion
In the northern South Island, the relative motion between the Pacific and Indian plates is 47 mm/yr at an azimuth of 264° + 2° (Walcott 1979). The latest Pleistocene lateral slip-rate on the Hope Fault is 20-32 mm/yr; thus, accounting for one-half to two-thirds of the calculated plate rate in the Marlborough region.
Furthermore, the sum of the late Quaternary lateral slip- rates across the Marlborough fault system is 45 + 12 mm/yr (Fig. 2): based on 4-6 mm/yr for the Wairau Fault (Lensen
1976, Kieckhefer 1979, Knuepfer 1984, Yeats and Berryman
1987); 5-10 mm/yr for the Awatere Fault (Knuepfer 1984, J.
McCalpin in prep.); 4-8 mm/yr for the Clarence Fault (Knuepfer 1984, Yeats and Berryman 1987); and 20-32 mm/yr for the Hope Fault (Knuepfer 1984, this study). Thus, in Marlborough, essentially all the motion between the Indian and Pacific plates is accommodated by right slip on the Marlborough faults (Knuepfer 1984). Multiple triangulation surveys over the past 100 years confirm the conclusion based on the latest Pleistocene slip-rates that all the plate motion in the northern South Island is absorbed on land, and there is little or no motion at the southern end 56
of the Hikurangi trench (Bibby and others 1986).
Earthquake Recurrence Interval
The Kahutara segment of the Hope Fault has a right- lateral slip-rate of roughly 20-32 mm/yr. If the slip is all released seismically, an earthquake recurrence interval on a given segment of the fault can be calculated by assuming an average amount of slip per event based on coseismic fault slip measured for other strike-slip faults.
Lateral displacements on major strike-slip faults generally range between 3 to 12 m per event. For example: roughly 3 m of lateral offset accompanied the 1888 earthquake along the Hope Fault near Glynn Wye (McKay 1890); single-event displacements of 8-9 m have been documented for sections of the Alpine Fault (Berryman and others 1986); offsets of 3 to 12 m have been attributed to the 1855 earthquake on the
Wairarapa Fault (Lensen and Vella 1971, Grapes and Wellman 1988); along the San Andreas Fault, slip associated with the 1857 Fort Tejon earthquake varied from 3 to 9.5 m (Sieh 1978), offsets of up to 6.7 m accompanied the 1906 San
Francisco earthquake (Reid 1910), and at Wallace Creek, slip associated with the last three large earthquakes ranged from 9.5 to 12.3 m per event (Sieh and Jahns 1984); in China, displacement along the Haiyuan Fault associated with the 1920 Haiyuan earthquake averaged 8 m (Zhang and others 1987), and roughly 6 m of lateral displacement 57 resulted from the 1932 earthquake along the western part of the Chang Ma Fault (Peltzer and others 1988). Table 4 presents average recurrence intervals for slip-rates of 20,
25, 30, and 35 mm/yr and single-event displacements of 3 to
12 m. A slip-rate of 30 mm/yr released at a rate of 6 m per event yields a recurrence interval of 200 yrs. A recurrence interval as long as 600 yrs, or as short as 85 yrs results from a slip-rate of 20 mm/yr released at a rate of 12 m per event, or a slip-rate of 35 mm/yr released at a rate of 3 m per event, respectively. A longer recurrence interval would result if some of the slip is released as creep; however, there are no examples of the Hope Fault displacing man-made features by creep. Also, three triangulation surveys in the Kaikoura area incorporate much of the Mt. Fyffe segment. Bibby (1981) included these networks to geodetically determine strain across the southern end of the Tonga-Kermadec-Hikurangi subduction zone. He reported no discontinuity in shear strain across any of the Marlborough faults, but the large scale of the networks makes it difficult to detect strain at the fault.
Transfer of Displacement on Jordan Thrust
Latest Pleistocene lateral displacements of greater than 150 m have been documented along the Kahutara and Mt.
Fyffe segments of the Hope Fault. However, the subdued topography and the lack of late Quaternary displacement 58
TABLE 4. Average Recurrence Interval of Earthquakes on the Kahutara Segment with Varying Single-Event Displacement and Varying Slip-Rate, in Years
single-event slip rate, mm/yr displacements, meters 20 25 30 35
3 150 120 100 86
6 300 240 200 171
9 450 360 300 257
12 600 480 400 343 59
along the Seaward segment, the mountain-front morphology of the Seaward Kaikoura Range, and the abundant evidence for late Quaternary faulting along the Jordan Thrust indicate that most of the late Quaternary displacement on the Hope
Fault is transferred northward and does not reach the
Seaward segment. A result of this northward transfer of displacement is the uplift of the Seaward Kaikoura Range on and behind the Jordan Thrust. The drainage-divide elevation of the Seaward Kaikoura Range reflects this uplift. The elevation of the Seaward Kaikouras increases from about 1400-1700 m adjacent to the Hope Fault, to over
2600 m northwest of the thrust (Fig. 10).
Figure 19 presents an idealized relation between the
Hope Fault, the Jordan Thrust, and the Puhi Puhi syncline.
If the slip-rate on the Hope Fault is considered to be 20- 32 mm/yr west of the Jordan Thrust, and a maximum of 5 mm/yr east of it, then roughly 15-27 mm/yr of slip is directed onto the Jordan Thrust (Fig. 19). Assuming that the thrust has a 35° NW dip at depth, upward ramping on the thrust would result in an uplift rate of 7-12 mm /yr. However, the vertical and horizontal slip-rates for the Jordan Thrust at Clinton River (CR of Fig. 19) are only 2.1 mm/yr, and 2.2 mm/yr, respectively (Table 2). If the slip- rates at Clinton River are representative of the activity along the thrust throughout the latest Pleistocene, it is apparent that they are not large enough to accommodate the lateral slip-rate along the western segments of the Hope 60
Active strike-slip fault t tc,-* 0C.f IT - / 11....a. Active thrust fault 4, cc
I N'19 Minor northwest-dipping Fid et F reverse fault 4
-,---15--4 Overturnedsyncline
0 10 KM
Se°41(116
Figure 19. Idealized relation between the Hope Fault, the Jordan Thrust, the small-scale minorreverse faults behind the thrust, and the Puhi Puhi syncline. Also shown are Clinton River (CR), and McLeanStream (MS). 61
Fault. Similarly, if displacement along the Hope Fault was concentrated entirely on the Jordan Thrust and transferred northward onto the Kekerengu Fault, a much higher lateral slip-rate, than the 3-10 mm/yr calculated at McLean Stream
(MS of Fig. 19), would be expected.
If most of the displacement on the Hope Fault is transferred northward to the Jordan Thrust, why is there such a discrepancy of displacement rates between the two faults? Some displacement is transferred to the Kowhai, and Fyffe Faults. However, a minimum slip rate on the Hope Fault of 16 + 5 mm/yr, east of these faults, indicates that the slip rate on these two lesser faults is low.
The importance of folding of the Inland and Seaward
Kaikoura Ranges was recognized by Cotton (1913), and
Jobberns (1932). Figure 20 presents a schematic cross- section across the Inland and Seaward Kaikoura Ranges based largely on the work of Cotton (1913), and Jobberns (1932). This cross section is perpendicular to strike, not parallel to the direction of Pacific-Indian plate motion. Using the terminology of Cotton (1913), this section shows the "covering strata", including the distinctive Amuri Limestone of Cretaceous/ Tertiary age, folded over the two
Kaikoura ranges, with the tectonic relief of the covering strata greater than the vertical displacement on the northwest-dipping faults that bound both ranges. This relationship is well documented across the Seaward Kaikoura Range and more speculative across the Inland Kaikoura Range 62
Figure 20. Schematic cross-section across the Inland Kaikoura Range (IKR) and the Seaward Kaikoura Range (SKR; modified from diagram on p. 227 of Cotton 1913, and section 3 of Jobberns 1932; not to scale). Also shown are the Puhi Puhi syncline (PPS), the Jordan Thrust (JT), the Clarence Fault (CF), and the Awatere Fault (AF). Torlesse is shaded, and (C) is the "covering strata" of late Cretaceous to Miocene age. 63
where the "covering strata" are less well preserved along the Awatere Fault (Lensen 1962). The Seaward Kaikoura
Range is composed of complexly folded and faulted Torlesse
(Lensen 1962). Reconnaissance mapping in these rocks did not document folds associated with the Jordan Thrust.
However, numerous small-scale throughgoing northwest- dipping reverse faults were noted. The relatively low slip-rates at Clinton River suggest that offset alone on the Jordan Thrust cannot account for all the late
Quaternary displacement transferred northward from the Hope
Fault. It is probable that most of the remaining displacement is expressed as surface folding of the Seaward
Kaikoura Range supplemented by distributed shear within the
Torlesse underlying the range. The location and sense of vergence of the overturned and tightly folded Puhi Puhi syncline suggest that convergence north of the Hope Fault was in part accommodated by folding in front of the thrust
(Figs. 19 and 20). It was not determined whether this folding has continued into the present.
The Clarence Fault, east of its eastern junction with the Elliot Fault, turns to a northeasterly trend (Fig. 2). The highest summits of the Inland Kaikoura Range are adjacent to this northeast-trending portion of the Clarence
Fault; the same relationship as seen for the Seaward
Kaikoura Range and the Jordan Thrust (Fig. 10). This relationship between the high elevations of the Kaikoura Ranges, and the Jordan Thrust and the northeast-trending 64
portion of the Clarence Fault is brought out by projecting the elevations of the Seaward and Inland Kaikoura Ranges onto a profile constructed perpendicular to the direction of tectonic transport (Fig. 21). By way of analogy with the Hope Fault and the Jordan Thrust, it is suggested that the northeast-trending portion of the Clarence Fault may be a northwest-dipping, oblique-slip reverse fault, and that the recent uplift of the Inland Kaikoura Range results from the northward transfer of displacement from the easterly- trending portion of the Clarence Fault, having predominantly strike-slip motion (Berryman 1979), onto and behind the northeast-trending portion of the Clarence
Fault.
The highest mountains and uplift rates in New Zealand are in the Southern Alps, where convergence between the
Indian and Pacific Plates, across the Alpine Fault, is oblique (inset of Fig. 1). Yet at the restraining bend of
the Alpine Fault (inset of Fig. 1 and Fig. 2), where convergence is head-on, there is no strong topographic, seismic, or gravity evidence of convergence across the bend (Yeats and Berryman 1987). Wellman (1979) estimated that the uplift rate of the Southern Alps is 10 mm/yr, but the uplift rate of the Spenser Mountains, east of the restraining bend, is only about 4 mm/yr. Why this paradox?
In Marlborough, late Quaternary slip on the Hope and
Clarence Faults accommodates most of the motion between the
Indian and Pacific Plates. Because of the distribution of 65
Elevations 0- -0 Seaward Kaikoura Range -`t Inland Kaikoura Range
4 3000 1.9'34$`\I ttzi\e' A-. "o A c 2000
0 -0 irj 1000
SSE NNW Jordan Thrust Clarence Fault (NE trending portion) Distance (km) V.E. 6.5 110 km
Figure 21. Profiles of the Seaward and Inland Kaikoura Ranges projected onto a cross section oriented perpendicular to the direction of tectonic transport. 66
strain across the Marlborough fault system, most of the plate motion passes south of the restraining bend. One- hundred km east from the restraining bend, in the Kaikoura region, lateral displacement along the Hope Fault is transferred northward onto and behind the Jordan Thrust. A similar situation may exist along the Clarence Fault where it turns to a northeasterly trend. Thus, the restraining bend need only account for the slip on the Wairau Fault (4- 6 mm/yr), whereas most of the plate slip has been transferred to the Hope and Clarence Faults, and the main topographic effect of plate convergence is uplift of the
Seaward and Inland Kaikoura Ranges. Wellman (1979) estimated that uplift rates of the Inland and Seaward
Kaikoura Ranges could be as high as 7 and 10 mm/yr, respectively. Also, the high elevations and uplift rates of the Southern Alps are present only south of the Hope Fault, where the motion between the Indian and Pacific Plates is no longer distributed over the Marlborough fault system, but concentrated as oblique convergence on the
Alpine. Fault. 67
CONCLUSIONS
The Hope Fault, one of the Marlborough faults, is part of the transform fault system at the Pacific-Indian plate boundary: the Marlborough faults and the Alpine Fault link the Tonga-Kermadec-Hikurangi and Puysegur subduction zones.
Throughout the late Quaternary, the Hope Fault has been the most active of the Marlborough faults, accommodating at least one-half and possible two-thirds of the predicted motion between the Indian and Pacific Plates. Within the study area, the Hope Fault is divided into the Kahutara, Mt. Fyffe, and Seaward segments; based on topographic expression, amount of late Quaternary offset, and style of faulting. The Kahutara segment has a relatively constant lateral slip-rate of 20-32 mm/yr, and an earthquake recurrence interval of 86 to 600 yrs; based on 3 to 12 m of slip per coseismic event. The subdued topography and the lack of late Quaternary displacement along the Seaward segment indicate that most of the large late Quaternary displacement on the Kahutara and Mt. Fyffe segments is not transferred onto the Seaward segment. At Clinton River, the Jordan Thrust has horizontal and vertical slip-rates of 2.2 + 1.3 mm/yr and 2.1 + 0.5 mm/yr, respectively, northwest side up, and a maximum recurrence interval of 1200 yrs: based on a minimum of 3 events within the last 3.5 ka. Mountain-front morphology and drainage- divide elevation of the Seaward Kaikoura Range, and 68
abundant evidence for recent activity along the Jordan
Thrust indicate that the late Quaternary displacement along the Hope Fault is transferred northward, west of the
Seaward segment. The low slip-rates for the Jordan Thrust, compared to the higher lateral slip-rates along the
Kahutara and Mt. Fyffe segments of the Hope Fault, suggest that the displacement transferred from the Hope Fault is accommodated over a wide zone involving the Jordan Thrust, small-scale northwest-dipping faults behind the thrust, and possibly folds in front of and behind the thrust, although the latter was not documented in this study. A result of the northward transfer of displacement from the Hope Fault is the uplift of the Seaward Kaikoura Range on and behind the Jordan Thrust.
The region of the highest mountains and uplift rates in New Zealand, the Southern Alps, is south of both the
Alpine restraining bend and the Hope Fault, where convergence between the Indian and Pacific Plates is oblique, rather than at the restraining bend itself, where convergence is head-on. The growth of the Marlborough Fault system has distributed strain over the entire system, with most of the plate slip accommodated on the Hope Fault. Thus, the majority of plate motion bypasses the restraining bend, and only south of the Hope Fault is it concentrated as oblique convergence on the Alpine Fault. 69
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