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The effects of strong ground shaking on hillslope stability can persist for many years after a large earthquake, leading to an increase in the rates of post earthquake land sliding. The factors that control the rate of post‐earthquake land sliding are poorly constrained, hindering our ability to reliably forecast how landscapes and landslide hazards and risk evolve. To address this, we use a unique data set comprising high‐resolution terrestrial laser scans and airborne lidar captured during and after the 2010–2011 Canterbury Earthquake Sequence, New Zealand. This earthquake sequence triggered thousands of rock falls, and rock and debris avalanches (collectively referred to as "rockfall"), resulting in loss‐of‐life and damage to residential dwellings, commercial buildings and other infrastructure in the Port Hills of Christchurch, New Zealand. This unique data set spans 5 years and includes five significant earthquakes. We used these data to (a) quantify the regional‐scale "rockfall" rates in response to these earthquakes and the postearthquake decay in rockfall rates with time; and (b) investigate the site‐specific factors controlling the location of seismic and nonseismic rockfalls using frequency ratios and logistic regression techniques. We found that rockfall rates increased significantly in response to the initial earthquake that generated the strongest shaking in the sequence—The MW 6.2 22 February 2011 event—Compared to the long‐term background rates derived from the dating of pre‐2010 talus piles at the toe of the slopes. Non seismic rockfall rates also increased immediately after the 22 February 2011 earthquake and decayed with time following a power‐law trend. About 50% of the decay back to the pre‐earthquake rockfall rates occurred within 1–5 years after the 22 February 2011 earthquake. Our results show that the short‐term decay in rockfall rates over time, after the initial earthquake, was attributed to the subsequent erosion of seismically damaged rock mass materials caused by environmental processes such as rain. For earthquake‐induced rockfall at the regional‐scale, the peak ground accelerations is the most significant variable in forecasting rockfall volume, followed by the relative height above the base of the slope. For both earthquake and non‐seismic conditions at the site‐specific scale, the probability of rockfall increases when the adjacent areas have failed previously, indicating that accrued damage preconditions localized areas of the slope for subsequent failure. Such preconditioning is a crucial factor driving subsequent rockfalls; that is, future rockfalls are likely to cluster near areas that failed in the past. Plain Language Summary: Evidence from previous earthquakes suggests that the frequency of land sliding after a large earthquake is significantly higher than before it. Strong earthquakes cause slope cracking and generate landslide debris, which can be more readily remobilized post earthquake, creating new hazards, including further landslides and landslide dams. These hazards may persist for years and decades and represent a prolonged risk that the impacted communities must consider. Currently, the relative increase in land sliding and rate of decay during and after a major earthquake is rarely quantified, thus posing a knowledge gap for those rebuilding after a major earthquake. This paper explores high‐resolution terrestrial laser scan models of slope surfaces and how these surfaces changed during and after strong earthquake shaking during the 2010–2011 Canterbury Earthquake Sequence (CES) in New Zealand. These surface "change" models were used to quantify the volumes of debris–rock and soil–that fell from these slopes during and after the CES. These data were used to establish a regional‐scale, physical relationship between the volume of debris falling from the cliffs per earthquake or unit of time, per unit area of slope. Using the change models, we investigated the factors that control the temporal and spatial distribution of the rockfalls at the regional‐ and site‐specific scales. At the regional scale, we found that the size of the slope and the relative increase in rockfall rates above pre‐CES rates controlled the subsequent non‐seismic rockfall decay time. At the site‐specific scale, the main conclusions from this study are: (a) for earthquake triggers, the peak ground acceleration (a measure of earthquake ground shaking) was the most important variable in forecasting the probability of failure, followed by the relative elevation or height above the base of the slope; and (b) for both earthquake and nonseismic triggers, the probability of failure increases when the adjacent areas have failed previously, indicating that preconditioning of the slope to failure is a key factor driving subsequent rockfalls. Key Points: We quantify rock slope changes during and after a major earthquake sequence through repeat high‐resolution terrestrial laser scan surveysWe analyze landslide rates over 5 years, during and after the earthquakes at the regional‐ and site‐specific scalesNon seismic landslide rates are heightened immediately after the initial earthquake and decayed with time (1–5 years) following a power‐law trend [ABSTRACT FROM AUTHOR]

• Thermal maturity varies from low to early oil window between 4.45 and 31.50 Ma. • Bulk geochemistry indicates low organic matter content in the samples. • The low hydrogen indices indicate mainly Type III and Type IV kerogen. • Tectonic activity influenced organic matter accumulation in the Canterbury Basin. • Sedimentary deposition was influenced by global sea-level variations. The various influences of global sea level (eustasy) and local tectonic changes on sedimentation processes in continental margin deposits are important topics in sedimentary research. International Ocean Discovery Program Expedition 317 to the Canterbury Basin, on the eastern margin of the South Island of New Zealand, provided an opportunity to study sediment geochemistry in contrasting depositional settings, from mid-shelf to upper continental slope sedimentary rocks from the Eocene to the Holocene. This paper provides the first examination of the organic geochemical record from Pliocene, Miocene, and Oligocene sediment samples recovered during the expedition from the U1351, U1352, and U1353 sites, using bulk geochemistry and hydrocarbon distributions, including biomarkers. The main aim of this research was to correlate changes in organic accumulation with local tectonic activity and global climate changes that occurred in the Miocene. There is good preservation of C 11 to C 35 n -alkanes, with varying predominance of odd-over-even chain length n -alkanes, and much variation in the terrigenous/aquatic ratio over the cores. Based on biomarker and Rock Eval parameters, thermal maturity varies from low in the Pliocene, to early oil window in the deeper Miocene and Oligocene sedimentary rocks. The pristane/phytane ratios for the three cores indicate anoxic to oxic depositional environments. Marine organic matter input is indicated by the high C 30 sterane index, whilst high relative amounts of oleanane, C 24 tetracyclic terpane, and C 29 steranes indicates major terrigenous organic matter input. Local tectonic activity is suggested to have had a significant influence on the accumulation of the organic matter in the Canterbury Basin. The influence of eustasy and global sea temperature variations are suggested for the periods < 14 Ma, 12–7 Ma, and ∼ 6 Ma. An increase in terrigenous organic matter input during the late Miocene correlates with the uplift of the Southern Alps and an increase in the continental slope angle for the South Island of New Zealand. [ABSTRACT FROM AUTHOR]

Landslide failure mechanisms are influenced by topography, lithology, structure and rock mass damage – factors that also control landslide susceptibility. Failure mechanisms, however, are rarely considered in regional-scale coseismic landslide susceptibility analyses. In this study, we use 3D pixel tracking in pre- and post-earthquake aerial imagery, geomorphic mapping, rock mass characterisation, and geophysical ground investigations to develop conceptual models for three earthquake-induced landslides triggered by the 2016 Mw 7.8 Kaikōura earthquake on New Zealand's South Island. Analysis of two incipient landslides in Cretaceous greywacke illustrates the failure stages of a rock mass comprising multiple sets of closely-spaced and low persistence discontinuities. Conversely, analysis of a landslide in Neogene massive siltstones illustrates the role of high-persistence bedding planes in generating large translational rockslides. These two distinct mechanisms typify failures in highly deformed basement and overlying massive sedimentary rocks respectively, and highlight the link between rock mass damage, failure mechanism, and initiation. In greywacke failures, the rupture plane initiated close to the ridgetop and propagated as a joint-step-path failure along pre-existing, but low-persistence joints whereas the landslide in Neogene siltstone initiated by sliding along weak, high persistence, bedding planes near the base of the slope where topographic stresses are highest. Analysis of landslide displacements furthermore points out that the evolution of landslides is closely related to rock mass characteristics. In highly jointed Cretaceous greywacke, relatively little displacement is needed for rock mass disintegration and avalanching to occur whereas in Neogene siltstone, the landslide displaces as a coherent body - even at large displacements. Our results suggest that (1) failure mechanisms and, as a result, coseismic landslide susceptibility factors, may vary fundamentally in different geological settings; (2) characteristic spatial landslide displacement patterns may be used to remotely identify relevant failure mechanisms; and (3) the amount of displacement that can be accommodated before a failure transitions from sliding to avalanching, is highly dependent on material characteristics and topographic constraints. • Conceptual models of three coseismic landslides triggered by the 2016 Mw 7.8 Kaikōura earthquake reveal failure mechanisms. • Slopes in greywacke rock mass with closely-spaced, low-persistent joints fail through a joint-step-path failure mechanism. • Landslide susceptibility factors vary between failures in highly jointed greywacke and weak, but massive siltstone. • Analysis of spatial displacement patterns may help to remotely identify failure mechanisms. • The amount of displacement required for rock mass disintegration to occur is smaller in greywacke than siltstone. [ABSTRACT FROM AUTHOR]

Catastrophic deep-seated rock slope failures (RSFs; e.g., rock avalanches) can be particularly useful proxies for fault rupture and strong ground motion, and currently represent an underappreciated hazard of earthquakes in New Zealand. This study presents observations of the previously undescribed Cascade rock avalanche (CRA), a c. 0.75 km single-event, long-runout, catastrophic failure interpreted to have been coseismically triggered by a large to great earthquake c. 660 AD on the Alpine Fault. Despite its size and remarkable preservation, the CRA deposit has been previously identified as a terminal moraine and fault-damaged outcrop, highlighting the common misinterpretation of similar rock avalanche deposits. Comparisons are drawn between the CRA and other Alpine Fault-attributed rock avalanches, such as the better-studied c. 860 AD Round Top rock avalanche, to re-assess coseismic rock avalanche hazard. Structural relationships indicate the rock mass comprising the CRA may have formerly been a portion of a larger (c. 3 km) RSF, before its catastrophic collapse on a deep-seated gravitational collapse structure (sackung). Sackungen and RSFs are common throughout the Southern Alps and other mountainous regions worldwide; in many cases, they should be considered potential precursors to catastrophic failure events. Two masses of rock in the Cascade River Valley show precursory signs of potential catastrophic failures of up to c. 2 km; a similar mass may threaten the town of Franz Josef. [ABSTRACT FROM AUTHOR]

Abstract: We describe remnants of large (107–1010 m3) Late Pleistocene to Holocene rockslides and rock avalanches that block(ed) rivers and are preserved in the Himalayas, the Tien Shan, and the New Zealand Southern Alps despite rates of uplift and erosion of up to 10 mm year−1. These natural dams control fluvial response on 101–104 year timescales by (a) storing and releasing sediment during forced alluviation and fluvial re-incision; (b) relocating river channels through diversion or seepage; (c) inhibiting river erosion into bedrock; (d) forming persistent long-profile knickpoints and knickslopes associated with steep high-energy (>103 W m−2) breach and epigenetic bypass gorges and fluvial hanging valleys; and (e) shaping valley-floor morphology. Sediments indicate that rockslide-dammed lakes may persist up to 104 years, before being drained or infilled. Several short-lived (100–102 year) historical rockslide dams in the Indian and Nepal Himalayas and the Southern Alps have had marked volumetric impacts on catchment sediment budgets shortly following failure. Therefore, we caution against the linear extrapolation of sediment delivery from prehistoric rockslide dams through time as a response variable. We find reach-scale changes to channel gradient to be prominent and persistent indicators of fluvial response to large rock-slope failures. [Copyright &y& Elsevier]

This study examines the geomorphic effects of large (>106 m³) rock-slope failures on long profiles of rivers in the Swiss Alps and the New Zealand Southern Alps. Regression of channel slope versus drainage basin area objectively highlights knickpoints separating incised from aggraded reaches that often correspond to locations of large rock-slope failures. For a fixed concavity index, the highest values of the steepness index and erosion index along a given profile spatially coincide with breach channels cut into formerly river-damming rockslide debris as old as 10 k.y. Assuming that the knickpoints do not predate slope failure, data show that high profile steepness and inferred specific stream power are not always the cause, but often a result, of large river-blocking rock-slope failure in mountain basins. Omission of rockslide data from slope-area plots lowers the steepness index and increases the concavity index on average, yet only in few cases more than one standard deviation. [ABSTRACT FROM AUTHOR]

Rock slope failure (RSF) occurs in different contexts but is typically reported either as (i) single-category inventories or (ii) single-site geotechnical monographs. Few studies have sought to evaluate the spatial incidence of all modes of RSF conjointly, and to infer scenarios of regional landscape evolution from observed patterns of cumulative rock slope overstressing. Here we present the results of a systematic inventory of rock avalanches, rockfalls, rockslides, and gravitational rock slope deformations in the Western Alps (France, Italy, Switzerland) conducted using satellite imagery made available in Google Earth as a detection tool, and aided by preliminary ground-truth checks. The inventory totals 1416 montane RSFs, impacting 9.1% of the study area. Underpinned by GIS tools, the study further examines the spatial distribution of RSF with consideration for (i) predisposing factors (typically: lithology, geological structure), and (ii) preparatory factors (geomorphological process regimes that drives a given slope segment to the point of failure). The latter encompass slower variables (e.g., long-term crustal stress regime, cumulative residence time above equilibrium line altitudes) and faster variables (e.g., short-span glacier-related stresses, permafrost thaw, seismicity). RSF density patterns helped to define seven RSF super-hotspots (large diversity of RSF modes, up to 50% of displaced rock masses/unit area), which define the most intensely overstressed areas of the Western Alps. These super-hotspots occur at sites where highly dynamic, thick, warm-based glaciers above the equilibrium line either intersected (middle Maurienne) or followed the strike of (middle Isère) N-S bands of highly susceptible lithologies and structures during the Quaternary. The widespread incidence of rock slope deformation (cumulative area: 1760 km2, i.e., nearly 3 times the total of the other three RSF categories combined) appears further correlated with the low tectonic activity of the orogen and with its areas dominated by an extensional tectonic regime west of the Penninic Frontal Thrust. This contrasts with seismically active orogens, e.g., New Zealand's Southern Alps, where rock slope deformation is scarce compared to rock avalanches and shallow landslides. • A new inventory of 1416 rock slope failures (RSF) in the Western Alps is presented. • RSF size and failure mode are analysed in relation to climatic and geological variables. • Regionally, hotspots of extreme slope stress are dominated by rock slope deformation. • Spatial patterns of slope overstressing put landscape evolution in a new perspective. • The slope evolution cycle is contrasted with that of New Zealand's Southern Alps. [ABSTRACT FROM AUTHOR]