Hope Fault Research Articles

Evolution of an earthquake-induced landslide complex in the South Island of New Zealand: How fault damage zones and seismicity contribute to slope failures

Abstract Tectonic deformation within fault damage zones can influence slope stability and landslide failure mechanisms due to rock mass strength effects and the presence of tectonic structures. Here, we used detailed site investigations to evaluate controls on deformation within the Half Moon Bay landslide complex, located ~1 km from the surface trace of the Hope fault in the South Island of New Zealand. During the 2016 Mw 7.8 Kaikōura earthquake, the slope experienced up to ~13 m of displacement and partially transitioned into a rock avalanche (with a volume of ~350,000 m3). Deep-seated deformation of the entire slope predated the 2016 earthquake. Results of geomorphological analysis, field mapping, geophysical surveys, slope displacement, and a 60-m-deep borehole in the incipient portion of the landslide indicated the presence of a subvertical tectonic fabric and intense fracturing and weathering of the rock mass, which gradually decrease with depth. Based on these results, we established a conceptual model wherein the landslide failure mechanism is a combination of flexural toppling along the subvertical structures coupled with joint-step-path sliding along preexisting, closely spaced discontinuities within the graywacke rock mass. Coseismic slope displacements revealed a large area of incipient failure behind the headscarp of the 2016 rock avalanche, which will likely result in further avalanching at the site. This case study demonstrates that inherited tectonic structures (combined with seismicity and weathering in an oversteepened coastal slope) play an important role in the evolution of hillslopes near active faults.

Composition and Miocene deformation of the lithospheric mantle adjacent to the Marlborough Fault System in North Canterbury

ABSTRACT Mantle xenoliths in a nephelinite in the Little Lottery River provide insight into the Miocene mantle adjacent to the Australia-Pacific plate boundary in N Canterbury. The xenoliths comprise peridotite and pyroxenite extracted from depths of ∼ 40 to 60 km. The olivine Mg# < 89, a lack of spinel and occurrence of ilmenite, elevated bulk Cr and Al, light rare Earth element (REE)-enriched clinopyroxene, and 87Sr/86Sr15 Ma clinopyroxene populations (0.7029–0.7047) in most harzburgite and dunite samples, and in all lherzolite, wehrlite, olivine websterite and orthopyroxenites, indicate that most are the product of reaction of depleted peridotite with Fe, Ti, Al and light REE-bearing silicate melts of basaltic or similar composition. Available isotopic data indicate that the xenoliths could be derived from mantle lithosphere beneath the Hikurangi Plateau, in which case the reactive melts may have been associated with the Cretaceous plateau formation. Extensive recrystallisation of olivine indicates that portions of this lithosphere mantle were affected by the deformation close to the time of entrainment. Since the eruption occurred at ∼ 15 Ma, these textures require that the mantle lithosphere in this area was deforming before formation of today's expression of the proximal Hope Fault strand of the Australia-New Zealand plate boundary.

Fault slip-rates and Coulomb stress interactions in the intersection zone of the Hope, Kelly and Alpine Faults, South Island, New Zealand

Plate boundary faulting in New Zealand's South Island involves transfer of ∼50% of slip from the largest fault (Alpine Fault) onto the Hope-Kelly Fault system through a structurally complex fault intersection zone. The slip-rate contributions of faults within the Hope-Kelly system and possible role of static stresses in facilitating slip transfer are explored in this study. Lidar-based geomorphic and fault mapping combined with luminescence dating of fault-proximal sedimentary deposits constrain post-last glacial slip-rates on the Hope and Kelly faults. Dextral slip-rates on the central Hope Fault (12–15 mm/yr) decrease westward on the Taramakau section from 5.6 (+2.1/−0.7) mm/yr to 1.7 (+1.0/−0.5) mm/yr. Dextral slip-rates on the Kelly Fault range from 6.2 (+2.7/−1.0) mm/yr to 2.0 (+2.5/−0.7) mm/yr to 6.2 (+7.8/−1.4) mm/yr. Proposed causes of slip-rate spatial variations include (i) complex slip localization and transfer across the deformation zone, (ii) undocumented slip on obscured or unrecognized faults, and (iii) possible transience in slip behaviours. Paleoseismic trenching and radiocarbon ages constrain timing of most recent surface rupture on the western Hope Fault to ca. 1680–1840 CE, with a preferred age of ca. 1800–1840 CE. Coulomb fault stress modelling indicates central Alpine Fault ruptures impart positive stress changes on Hope-Kelly receiver faults >5–10 bars, while Northern Alpine Fault earthquakes reduce Coulomb stresses on Hope-Kelly receiver faults, and vice versa. These results suggest central Alpine Fault earthquakes may propagate onto or trigger ruptures of Hope-Kelly Faults, but Hope-Kelly ruptures reduce stress on the northern Alpine Fault, possibly making ruptures of that fault less likely. This system of stress perturbations provides a mechanism for slip transfer from the central Alpine Fault onto the Hope Fault system.

Bayesian Inference of Seismogenic Stress for the 2016 Mw 7.8 Kaikōura, New Zealand, Earthquake

ABSTRACT We use a Bayesian Markov chain Monte Carlo estimation strategy to estimate the state of pre-earthquake stress from eight published coseismic slip models (CSMs) of the 2016 Mw 7.8 Kaikōura, New Zealand, earthquake. Our estimation relies on the Wallace–Bott assumption, which equates the direction of slip and the orientation of maximum shear stress along a fault plane, and is analogous to methods that infer stress from focal mechanisms. We infer the orientations and relative magnitudes of the principal components of tensorial stress preceding the 2016 Mw 7.8 Kaikōura, New Zealand, earthquake as stress posterior probability density functions (PDFs). We find that the orientations of the principal stresses are well resolved, with weaker to no resolution of the relative magnitudes of the principal stresses. We form a nonmutually exclusive composite posterior PDF as an aggregate of the individual posterior PDFs estimated from each CSM, which allows for the true coseismic slip to be included in any or all of the CSMs. We find that the Kaikōura earthquake can be described by a homogeneous pre-earthquake tensorial stress, despite the complex pattern of slip on multiple fault segments. This state of crustal stress is best represented by an Andersonian thrust regime with a west-northwest–east-southeast trending, horizontal most compressive stress. In addition to describing the state of pre-earthquake stress, the nonmutually exclusive composite posterior PDF allows for the evaluation of the mechanical consistency of the features within CSMs, both individually and as an ensemble. The estimated stress posteriors allow for testing of the CSMs for consistency with known slip mechanisms on the Hope fault, as well as arbitration between differences in inferred slip presented by the CSMs.

Heterogeneous material properties—as inferred from seismic attenuation—influenced multiple fault rupture and ductile creep of the KaikouraMw 7.8 earthquake, New Zealand

SUMMARYThe 2016 Mw 7.8 Kaikoura, New Zealand, earthquake occurred along the eastern margin of the transition region between active subduction in the North Island and oblique collision in the South Island. To infer crustal properties, we imaged Q (1/seismic attenuation) by combining selected M &amp;gt; 3.5 aftershocks with data from previous Q models. For 158 distributed aftershocks, we fit spectral decay on temporary stations and all Geonet stations, providing 6194 t*p and 19 497 t*s. Considering the varied rheology and faults, we also used 2.5-D numerical models to study ductile strain development. The complex earthquake ruptured an ∼180-km-long zone of multiple faults, which involved jumping around the complicated eastern end of the Hope fault, without significant slip on the Hope fault. The Qs and Qp results show features in the upper and lower crust which correlate to the distribution and types of fault rupture. This earthquake involved numerous faults over a region of greywacke crust, where the underlying high Q Cretaceous slab is about 30-km depth. It initiated with ∼5-m slip on the Humps fault in a region of background seismicity and low Q lower crust, adjacent to the Hope fault. The central region near Kaikoura shows a high Q crustal block, which appears to have inhibited rupture; as the rupture progressed over several small faults to jump offshore of the apparently strong block. Underlying the Kaikoura greywacke crust, below 20-km depth, there is a 40-km-long region of increased Vp, Qs and gravity, which likely represents an intraplate plutonic complex emplaced into the Hikurangi Plateau, forming an elevated section which influences deformation. In the northern section, in a region with relatively uniform moderate to low Q, the earthquake evolved into the relatively continuous ∼80-km-long major rupture along the Jordan, Kekerengu and Needles faults, with ∼6–20 m dextral slip at depth and surface displacements of ∼10 m dextral and ∼2 m vertical. The northern progression of the rupture stopped when it approached an abrupt change to high Q crust across Cook Strait. At 20–30-km depth northwest of the rupture, deeper zones with low Q are consistent with regions of distributed ductile shear and creep where the observed afterslip may have occurred, where the underlying slab is 25–40 km deep. The numerical model shows that ductile deformation localizes in this area of lower crust above the relatively strong slab, connecting outer faults (Kekerengu) to inland faults (Clarence, Awatere, Wairau), and demonstrates that no subduction thrust is required under the Marlborough region.

Structure and kinematics of active faulting in the Hope-Kelly and Alpine Fault intersection zone, South Island, New Zealand

Using lidar, photogrammetry and field studies, we investigate the structure and kinematics of the Hope, Kelly, and Alpine faults where they converge and intersect along the Australian-Pacific plate boundary in New Zealand. Approximately 50% of the reverse-dextral slip rate of the Alpine fault in the west transfers to the dextral central Hope Fault in the east via a horsetail splay zone of distributed oblique dextral-normal shear forming the Hope-Kelly fault system. The westernmost portion of the Hope fault is misoriented for dextral slip and is likely an extensional fault that accommodates the Alpine fault slip rate change across the intersection zone. As it transitions to an extensional fault, most of the strike-slip of the Hope fault is transferred southward onto Kelly fault strands via incipient, linking fault domains of coeval NE-SW and EW-striking dextral faults. The transition from the narrow zone defining the central Hope Fault to dispersed horsetail splays of the Hope-Kelly fault system is located immediately above the eastward down-dip projection of the Alpine Fault at the base of the seismogenic zone. This suggests that structural interactions among these faults within seismogenic depths control surface rupture geometries and kinematics. Coeval intermingling of surface rupture traces transecting latest Pleistocene to Holocene landforms indicates ongoing structural interactions in active faulting at the intersection of the Hope-Kelly fault splays with the Alpine fault. The transition from dextral to dextral normal kinematics on the horsetail splay accommodates differential orogenic growth through geometrically and kinematically efficient faulting that allows extension of the Alpine fault hanging wall parallel to strike, enabling the slip rate change between the central and northern Alpine fault sections.

Map-view restorations of the South Island, New Zealand: a reappraisal of the last 10 Myr of evolution of the Alpine and Wairau faults

ABSTRACT Retro-deformation of horizontal and vertical displacements is used to reconstruct the evolution of the South Island plate boundary faults since the Late Miocene. Finite dextral offset across the Alpine Fault is estimated from a system of N-S reverse faults displaced from Otago to the Glenroy-Matakitaki area, where the N-S tectonic trends are generally interpreted as a ‘bend’ of the Alpine Fault. Increasing dextral offset on the Alpine Fault was accompanied by a NE-migrating wave of exhumation and uplift of its hanging wall, tracked by syntectonic terrestrial deposits. Strike-slip and dip-slip components both decrease near the ‘bend’, where deformation is transferred to the Wairau and Marlborough faults. The Wairau Fault offsets dextrally by c. 50 km the N-S faults of the Glenroy-Matakitaki area, correlated with the Waimea-Flaxmore Fault System of Nelson. Finite dextral separation along the Alpine Fault is 410 km, and the N-S ‘bend’ is interpreted as a transpressive stepover between the Alpine and the Wairau faults. The lack of connection between the Alpine and Wairau faults, combined with slip transfer to the Hope Fault over the last 2 Myr, do not favour propagation of coseismic rupture from the Alpine Fault to the Wairau Fault across the ‘bend’.

Space Imaging Geodesy Reveals Near Circular, Coseismic Block Rotation During the 2016 Mw 7.8 Kaikōura Earthquake, New Zealand

AbstractLarge earthquakes usually rupture plate boundary faults, releasing the accumulated stress as displacements localized along smooth, narrow faults. However, certain earthquakes initiate off main faults, rupturing adjacent, secondary faults. The mechanisms of such atypical stress release remain enigmatic, partly due to a lack of detailed geodetic evidence. Here using the 3D coseismic displacement field derived from space imaging geodesy, we detect 10‐km‐scale, nearly‐circular coseismic block rotation during the 2016 Mw 7.8 Kaikōura earthquake in New Zealand. Together, geodetic observations, longer term local paleomagnetic data, analytical, and discrete element modeling imply that localized block rotation occurred south of the Hope fault along weak, steep, bedding‐parallel boundaries within a narrow, ~20‐km‐wide dextral shear zone. That stress near plate boundary faults can be partially released in zones of distributed ruptures absorbing coseismic rotation may retard rupture along main faults. Our observations also suggest that coseismic rotation may help accomodate plate boundary propagation.

Holocene to latest Pleistocene incremental slip rates from the east-central Hope fault (Conway segment) at Hossack Station, Marlborough fault system, South Island, New Zealand: Towards a dated path of earthquake slip along a plate boundary fault

AbstractGeomorphic field and aerial lidar mapping, coupled with fault-parallel trenching, reveals four progressive offsets of a stream channel and an older offset of the channel headwaters and associated fill terrace–bedrock contact at Hossack Station along the Conway segment of the Hope fault, the fastest-slipping fault within the Marlborough fault system in northern South Island, New Zealand. Radiocarbon and luminescence dating of aggradational surface deposition and channel initiation and abandonment event horizons yields not only an average dextral rate of ∼15 mm/yr since ca. 14 ka, but also incremental slip rates for five different time periods (spanning hundreds to thousands of years) during Holocene to latest Pleistocene time. These incremental rates vary through time and are, from youngest to oldest: 8.2 +2.7/−1.5 mm/yr averaged since 1.1 ka; 32.7 +∼124.9/−10.1 mm/yr averaged over 1.61–1.0 ka; 19.1 ± 0.8 mm/yr between 5.4 and 1.6 ka; 12.0 ± 0.9 mm/yr between 9.4 and 5.4 ka, and 13.7 +4.0/−3.4 mm/yr from 13.8 to 9.4 ka, with generally faster rates in the mid- to late Holocene relative to slower rates prior to ca. 5.4 ka. The most pronounced variation in rates occurs between the two youngest intervals, which are averaged over shorter time spans (≤1700 yr) than the three older incremental rates (3700–4500 yr). This suggests that the factor of ∼1.5× variations in Hope fault slip rate observed in the three older, longer-duration incremental rates may mask even greater temporal variations in rate over shorter time scales.

For an education with no hope

Most of the literature in educational research, and in philosophy of education specifically, has been clearly appealing to hope in its various forms, in attempts to bring it back, improve it and have more of it. This paper wishes to explore a different terrain. I ask whether there can be a worthwhile education that does not require hope, and I suggest that even when hope remains a commendable attribute of education, the strict prohibition on hopelessness in education should be rejected for there is much to be gained from embracing hope's opposite—despair. Firstly, I discuss hope's faults and drawbacks, focusing on the reasons for its rejection in ancient Greece and on its privatisation and commodification in contemporary capitalist society. Here, hope's connection to transcendence and the secular attempts to overcome it will be examined. Secondly, following the conceptualisation of despair by political theorist Robyn Marasco (2015), I reassess the dialectics of hope and despair and highlight the role of hopelessness in energising and enlivening critique. Finally, reading in Martin Luther King's famous ‘I have a dream’ speech, I suggest that a pedagogy of despair can accommodate presentism and even, despite its name, bring about a particular dialectics of hope.

A geometric model to estimate slip rates from terrace rotation above an offshore, listric thrust fault, Kaikōura, New Zealand

The Kaikōura Peninsula lies at the transition from subduction to continental collision at the southern end of the Hikurangi subduction system. This study uses a 2012 lidar survey over the Kaikōura Peninsula to re-map a flight of four uplifted Late Pleistocene marine terraces at high resolution. The lidar shows that the terraces are being progressively tilted landwards in a manner consistent with listric thrust faulting offshore. The fault, known as the Kaikōura Peninsula Fault, dips shallowly at c.30° to the northwest at depth and probably truncates the Seaward segment of the Hope Fault in the footwall of the Jordan Thrust. Geometric analysis of the tilt, using ages based on previous dating and a regional sea level curve, suggests that slip rates on the Kaikōura Peninsula Fault have ranged between 2.3 ± 1.5 mm/yr and 4.1 ± 1.3 mm/yr over the Late Pleistocene. The elevations of Late Holocene fringing beaches track regional sea level changes, apart from a departure indicating a single uplift event (penultimate earthquake) in the late 18th to earliest 19th century (1702–1838 CE), followed by uplift in the 2016 Kaikōura earthquake. The slip rate calculated from beach uplift, including the Kaikōura earthquake, is consistent with longer term rates. The accumulation of the slip over only c.220 years following >2000 years of quiescence suggests that the offshore thrust and associated faults exhibit clustered behavior, possibly as a result of keystone faulting.

River patterns reveal two stages of landscape evolution at an oblique convergent margin, Marlborough Fault System, New Zealand

Abstract. Here we examine the landscape of New Zealand's Marlborough Fault System (MFS), where the Australian and Pacific plates obliquely collide, in order to study landscape evolution and the controls on fluvial patterns at a long-lived plate boundary. We present maps of drainage anomalies and channel steepness, as well as an analysis of the plan-view orientations of rivers and faults, and we find abundant evidence of structurally controlled drainage that we relate to a history of drainage capture and rearrangement in response to mountain-building and strike-slip faulting. Despite clear evidence of recent rearrangement of the western MFS drainage network, rivers in this region still flow parallel to older faults, rather than along orthogonal traces of younger, active strike-slip faults. Such drainage patterns emphasize the importance of river entrenchment, showing that once rivers establish themselves along a structural grain, their capture or avulsion becomes difficult, even when exposed to new weakening and tectonic strain. Continued flow along older faults may also indicate that the younger faults have not yet generated a fault damage zone with the material weakening needed to focus erosion and reorient rivers. Channel steepness is highest in the eastern MFS, in a zone centered on the Kaikōura ranges, including within the low-elevation valleys of main stem rivers and at tributaries near the coast. This pattern is consistent with an increase in rock uplift rate toward a subduction front that is locked on its southern end. Based on these results and a wealth of previous geologic studies, we propose two broad stages of landscape evolution over the last 25 million years of orogenesis. In the eastern MFS, Miocene folding above blind thrust faults generated prominent mountain peaks and formed major transverse rivers early in the plate collision history. A transition to Pliocene dextral strike-slip faulting and widespread uplift led to cycles of river channel offset, deflection and capture of tributaries draining across active faults, and headward erosion and captures by major transverse rivers within the western MFS. We predict a similar landscape will evolve south of the Hope Fault, as the locus of plate boundary deformation migrates southward into this region with time.

Ground motion simulations of Hope fault earthquakes

This paper examines ground motions for a major potential Mw7.51 rupture of the Hope Fault using a physics based simulation methodology and a 3D crustal velocity model of New Zealand. The simulation methodology was validated for use in the region through comparison with observations for a suite of historic small magnitude earthquakes located proximal to the Hope Fault. Simulations are compared with conventionally utilised empirical ground motion models, with simulated peak ground velocities being notably higher in regions with modelled sedimentary basins. A sensitivity analysis was undertaken where the source characteristics of magnitude, stress parameter, hypocentre location and kinematic slip distribution were varied and an analysis of their effect on ground motion intensities is presented. It was found that the magnitude and stress parameter strongly influenced long and short period ground motion amplitudes, respectively. Ground motion intensities for the Hope Fault scenario are compared with the 2016 Kaik¯oura Mw7.8 earthquake, it was found that the Kaikoura earthquake produced stronger motions along the eastern South Island, while the Hope Fault scenario resulted in stronger motions immediately West of the near-fault region and similar levels of ground motion in Canterbury. The simulated ground motions for this scenario complement prior empirically-based estimates and are informative for mitigation and emergency planning purposes.

A 2000 Yr Paleoearthquake Record along the Conway Segment of the Hope Fault: Implications for Patterns of Earthquake Occurrence in Northern South Island and Southern North Island, New Zealand

Abstract Paleoseismic trenches excavated at two sites reveal ages of late Holocene earthquakes along the Conway segment of the Hope fault, the fastest-slipping fault within the Marlborough fault system in northern South Island, New Zealand. At the Green Burn East (GBE) site, a fault-perpendicular trench exposed gravel colluvial wedges, fissure fills, and upward fault terminations associated with five paleo-surface ruptures. Radiocarbon age constraints indicate that these five earthquakes occurred after 36 B.C.E., with the four most recent surface ruptures occurring during a relatively brief period (550 yr) between about 1290 C.E. and the beginning of the historical earthquake record about 1840 C.E. Additional trenches at the Green Burn West (GBW) site 1.4 km west of GBE reveal four likely coseismically generated landslides that occurred at approximately the same times as the four most recent GBE paleoearthquakes, independently overlapping with age ranges of events GB1, GB2, and GB3 from GBE. Combining age constraints from both trench sites indicates that the most recent event (GB1) occurred between 1731 and 1840 C.E., the penultimate event GB2 occurred between 1657 and 1797 C.E., GB3 occurred between 1495 and 1611 C.E., GB4 occurred between 1290 and 1420 C.E., and GB5 occurred between 36 B.C.E. and 1275 C.E. These new data facilitate comparisons with similar paleoearthquake records from other faults within the Alpine–Hope–Jordan–Kekerengu–Needles–Wairarapa (Al-Hp-JKN-Wr) fault system of throughgoing, fast-slip-rate (≥10 mm/yr) reverse-dextral faults that accommodate a majority of Pacific–Australia relative plate boundary motion. These comparisons indicate that combinations of the faults of the Al-Hp-JKN-Wr system may commonly rupture within relatively brief, ≤100-year-long sequences, but that full “wall-to-wall” rupture sequences involving all faults in the system are rare over the span of our paleoearthquake data. Rather, the data suggest that the Al-Hp-JKN-Wr system may commonly rupture in subsequences that do not involve the entire system, and potentially, at least sometimes, in isolated events.

Dynamic viability of the 2016 Mw 7.8 Kaik\u014dura earthquake cascade on weak crustal faults

We present a dynamic rupture model of the 2016 Mw 7.8 Kaikōura earthquake to unravel the event’s riddles in a physics-based manner and provide insight on the mechanical viability of competing hypotheses proposed to explain them. Our model reproduces key characteristics of the event and constraints puzzling features inferred from high-quality observations including a large gap separating surface rupture traces, the possibility of significant slip on the subduction interface, the non-rupture of the Hope fault, and slow apparent rupture speed. We show that the observed rupture cascade is dynamically consistent with regional stress estimates and a crustal fault network geometry inferred from seismic and geodetic data. We propose that the complex fault system operates at low apparent friction thanks to the combined effects of overpressurized fluids, low dynamic friction and stress concentrations induced by deep fault creep.

Three‐Dimensional Surface Deformation in the 2016 MW7.8 Kaikōura, New Zealand, Earthquake From Optical Image Correlation: Implications for Strain Localization and Long‐Term Evolution of the Pacific‐Australian Plate Boundary

AbstractWe generated dense, high‐resolution 3‐D ground displacement maps for the 2016 MW7.8 Kaikōura, New Zealand earthquake—the most geometrically and kinematically complex rupture yet recorded—from stereo WorldView optical satellite imagery using a new methodology that combines subpixel image correlation with a ray‐tracing approach. Our analysis reveals fundamental new details of near‐field displacement patterns, which cannot easily be obtained through other methods. From our detailed correlation maps, we measured fault slip in 3‐D along 19 faults at 500‐m spacing. Minimum resolvable horizontal slip is ~0.1 m, and vertical is ~0.5 m. Net slip measurements range from &lt;1 to ~12 m. System‐level kinematic analysis shows that slip on faults north of the Hope fault was oriented primarily subparallel to the Pacific‐Australian plate motion direction. In contrast, slip on faults to the south was primarily at high angle to the plate motion and secondarily parallel to plate motion. Fault kinematics are in some locations consistent with long‐term uplift patterns, but inconsistent in others. Deformation within the Seaward Kaikōura Range may indicate an attempt by the plate boundary fault system to geometrically simplify. Comparison of published field measurements along the Kekerengu fault with our correlation‐derived measurements reveals that ~36% of surface displacement was accommodated as distributed off‐fault deformation when considering only field measurements of discrete slip. Comparatively, field measurements that project previously linear features (e.g., fence lines) into the fault over apertures &gt;5–100 m capture nearly all (~90%) of the surface deformation.

Surface Rupture of Multiple Crustal Faults in the 2016 Mw 7.8 Kaikōura, New Zealand, Earthquake

Multiple (>20 >20 ) crustal faults ruptured to the ground surface and seafloor in the 14 November 2016 M w Mw 7.8 Kaikōura earthquake, and many have been documented in detail, providing an opportunity to understand the factors controlling multifault ruptures, including the role of the subduction interface. We present a summary of the surface ruptures, as well as previous knowledge including paleoseismic data, and use these data and a 3D geological model to calculate cumulative geological moment magnitudes (M G w MwG ) and seismic moments for comparison with those from geophysical datasets. The earthquake ruptured faults with a wide range of orientations, sense of movement, slip rates, and recurrence intervals, and crossed a tectonic domain boundary, the Hope fault. The maximum net surface displacement was ∼12 m ∼12 m on the Kekerengu and the Papatea faults, and average displacements for the major faults were 0.7–1.5 m south of the Hope fault, and 5.5–6.4 m to the north. M G w MwG using two different methods are M G w MwG 7.7 +0.3 −0.2 7.7−0.2+0.3 and the seismic moment is 33%–67% of geophysical datasets. However, these are minimum values and a best estimate M G w MwG incorporating probable larger slip at depth, a 20 km seismogenic depth, and likely listric geometry is M G w MwG 7.8±0.2 7.8±0.2 , suggests ≤32% ≤32% of the moment may be attributed to slip on the subduction interface and/or a midcrustal detachment. Likely factors contributing to multifault rupture in the Kaikōura earthquake include (1) the presence of the subduction interface, (2) physical linkages between faults, (3) rupture of geologically immature faults in the south, and (4) inherited geological structure. The estimated recurrence interval for the Kaikōura earthquake is ≥5,000–10,000 yrs ≥5,000–10,000 yrs , and so it is a relatively rare event. Nevertheless, these findings support the need for continued advances in seismic hazard modeling to ensure that they incorporate multifault ruptures that cross tectonic domain boundaries.

Temporal slip-rate stability and variations on the Hope Fault, New Zealand, during the late Quaternary

The Hope Fault transfers slip from Hikurangi subduction to the Alpine Fault in the northern South Island of New Zealand. It accommodates mainly dextral strike slip and currently carries the highest slip rate in the Marlborough Fault System. Displacements, displacement rates and earthquake recurrence intervals have been determined using a combination of high resolution LiDAR for 59 dextral displacements (~2.5–200 m) together with calibrated radiocarbon ages (~130 yr to 13,000 yr) for abandoned stream channels, terrace risers and alluvial fans. Mean single-event displacement (SED) of 3 ± 0.6 m (2.2 to 4.6 m for 21 measurements) and mean recurrence interval of ~266 ± 100 yr (range 128 to 560 yr) have been determined for the five most recent surface-rupturing earthquakes. On time scales ≥2300 yr the dextral slip rate is uniform at 12.2 ± 2.4 mm/yr, however, when averaged over time intervals of ~230 to 1700 yr slip rates range from ~4 to 46.4 mm/yr. This order-of-magnitude variability in slip rate over shorter timescales cannot be fully attributed to errors in displacement and age data, and is at least partly due to variations in earthquake recurrence interval and inferred SED. Short-term non-characteristic earthquake behaviour may be due to changes in fault loading arising from stress interactions between different segments of the Hope Fault and nearby faults.

Transpressional Rupture Cascade of the 2016 Mw 7.8 Kaikoura Earthquake, New Zealand

AbstractLarge earthquakes often do not occur on a simple planar fault but involve rupture of multiple geometrically complex faults. The 2016 Mw 7.8 Kaikoura earthquake, New Zealand, involved the rupture of at least 21 faults, propagating from southwest to northeast for about 180 km. Here we combine space geodesy and seismology techniques to study subsurface fault geometry, slip distribution, and the kinematics of the rupture. Our finite‐fault slip model indicates that the fault motion changes from predominantly right‐lateral slip near the epicenter to transpressional slip in the northeast with a maximum coseismic surface displacement of about 10 m near the intersection between the Kekerengu and Papatea faults. Teleseismic back projection imaging shows that rupture speed was overall slow (1.4 km/s) but faster on individual fault segments (approximately 2 km/s) and that the conjugate, oblique‐reverse, north striking faults released the largest high‐frequency energy. We show that the linking Conway‐Charwell faults aided in propagation of rupture across the step over from the Humps fault zone to the Hope fault. Fault slip cascaded along the Jordan Thrust, Kekerengu, and Needles faults, causing stress perturbations that activated two major conjugate faults, the Hundalee and Papatea faults. Our results shed important light on the study of earthquakes and seismic hazard evaluation in geometrically complex fault systems.

“3D_Fault_Offsets,” a Matlab Code to Automatically Measure Lateral and Vertical Fault Offsets in Topographic Data: Application to San Andreas, Owens Valley, and Hope Faults

AbstractMeasuring fault offsets preserved at the ground surface is of primary importance to recover earthquake and long‐term slip distributions and understand fault mechanics. The recent explosion of high‐resolution topographic data, such as Lidar and photogrammetric digital elevation models, offers an unprecedented opportunity to measure dense collections of fault offsets. We have developed a new Matlab code, 3D_Fault_Offsets, to automate these measurements. In topographic data, 3D_Fault_Offsets mathematically identifies and represents nine of the most prominent geometric characteristics of common sublinear markers along faults (especially strike slip) in 3‐D, such as the streambed (minimum elevation), top, free face and base of channel banks or scarps (minimum Laplacian, maximum gradient, and maximum Laplacian), and ridges (maximum elevation). By calculating best fit lines through the nine point clouds on either side of the fault, the code computes the lateral and vertical offsets between the piercing points of these lines onto the fault plane, providing nine lateral and nine vertical offset measures per marker. Through a Monte Carlo approach, the code calculates the total uncertainty on each offset. It then provides tools to statistically analyze the dense collection of measures and to reconstruct the prefaulted marker geometry in the horizontal and vertical planes. We applied 3D_Fault_Offsets to remeasure previously published offsets across 88 markers on the San Andreas, Owens Valley, and Hope faults. We obtained 5,454 lateral and vertical offset measures. These automatic measures compare well to prior ones, field and remote, while their rich record provides new insights on the preservation of fault displacements in the morphology.