Eric L. Bilderback

Previously Unknown Fault Shakes New Zealand's South Island

At 4:35 A.M. local time on 4 September (1635 UTC, 3 September), a previously unrecognized fault system ruptured in the Canterbury region of New Zealands South Island, producing a moment magnitude (Mw) 7.1 earthquake that caused widespread damage throughout the area. In stark contrast to the 2010 Mw 7.0 Haiti earthquake, no deaths occurred and only two injuries were reported despite the epicenters location about 40 kilometers west of Christchurch (population ˜386,000). The Canterbury region now faces a rebuilding estimated to cost more than NZ

Fault kinematics and surface deformation across a releasing bend during the 2010 MW 7.1 Darfield, New Zealand, earthquake revealed by differential LiDAR and cadastral surveying

4 billion (US

Map of the 2010 Greendale Fault surface rupture, Canterbury, New Zealand: application to land use planning

2.95 billion). On the positive side, this earthquake has provided an opportunity to document the dynamics and effects of a major strike-slip fault rupture in the absence of death or serious injury. The low-relief and well-maintained agricultural landscape of the Canterbury Plains helped scientists characterize very subtle earthquake-related ground deformation at high resolution, helping to classify the earthquakes basic geological features [Quigley et al., 2010]. The prompt mobilization of collaborating scientific teams allowed for rapid data capture immediately after the earthquake, and new scientific programs directed at developing a greater understanding of this event are under way.

Hillslope response to climate-modulated river incision in the Waipaoa catchment, East Coast North Island, New Zealand

Dextral slip at the western end of the east-west–striking Greendale fault during the 2010 M_W 7.1 Darfield earthquake transferred onto a northwest-trending segment, across an apparent transtensional zone, here named the Waterford releasing bend. We used detailed surface mapping, differential analysis of pre- and postearthquake light detection and ranging (LiDAR), and property boundary (cadastral) resurveying to produce high-resolution (centimeter-scale) estimates of coseismic ground-surface displacements across the Waterford releasing bend. Our results indicate that the change in orientation on the Greendale fault incorporates elements of a large-scale releasing bend (from the viewpoint of westward motion on the south side of the fault) as well as a smaller-scale restraining stepover (from the viewpoint of southeastward motion on the north side of the fault). These factors result in the Waterford releasing bend exhibiting a decrease in displacement to near zero at the change in strike, and the presence within the overall releasing bend of a nested, localized restraining stepover with contractional bulging. The exceptional detail of surface deformation and kinematics obtained from this contemporary surface-rupture event illustrates the value of multimethod investigations. Our data provide insights into strike-slip fault bend kinematics, and into the potentially subtle but important structures that may be present at bends on historic and prehistoric rupture traces.

Strike-slip ground-surface rupture (Greendale Fault) associated with the 4 September 2010 Darfield earthquake, Canterbury, New Zealand

Abstract Rupture of the Greendale Fault during the 4 September 2010, M W7.1 Darfield (Canterbury) earthquake produced a zone of ground-surface rupture that severely damaged several houses, buildings and lifelines. Immediately after the earthquake, surface rupture features were mapped in the field and from digital terrain models developed from airborne Light Detection and Ranging (lidar) data. To enable rebuild decisions to be made and for future land use planning, a fault avoidance zone was defined for the Greendale Fault following the Ministry for the Environment guidelines on ‘Planning for the Development of Land on or Close to Active Faults’. We present here the most detailed map to date of the fault trace and describe how this was used to define and characterise the fault avoidance zone for land use planning purposes.

Quantifying temporal variations in landslide‐driven sediment production by reconstructing paleolandscapes using tephrochronology and lidar: Waipaoa River, New Zealand

Quantifying how hillslopes respond to river incision and climate change is fundamental to understanding the evolution of uplifting landscapes during glacial-interglacial cycles. We investigated the interplay among uplift, river incision, and hillslope response in the nonglacial Waipaoa River catchment located in the exhumed inner forearc of an active subduction margin on the East Coast of the North Island of New Zealand. New high-resolution topographic data sets (light detection and ranging [lidar] and photogrammetry) combined with field mapping and tephrochronology indicate that hillslopes adjusted to rapid latest Pleistocene and Holocene river incision through the initiation and reactivation of deep-seated landslides. In the erodible marine sedimentary rocks of the Waipaoa sedimentary system, postincision deep-seated landslides can occupy over 30% of the surface area. The ages of tephra cover beds identified by electron microprobe analysis on 80 tephra samples from 173 soil test pits and 64 soil auger sites show that 4000–5000 yr after the initiation of river incision, widespread hillslope adjustment started between the deposition of the ca. 14,000 cal. yr B.P. Waiohau Tephra and the ca. 9420 cal. yr B.P. Rotoma Tephra. Tephrochronology and geomorphic mapping analysis indicate that river incision and deep-seated landslide slope adjustment were synchronous between main-stem rivers and headwater tributaries. Hillslope response in the catchment can include the entire slope, measured from river to ridgeline, and, in some cases, the interfluves between incising subcatchments have been dramatically modified through ridgeline retreat and/or lowering. Using the results of our landform tephrochronology and geomorphic mapping, we derive a conceptual time series of hillslope response to uplift and climate change–induced river incision over the last glacial-interglacial cycle.

The 2015 landslide and tsunami in Taan Fiord, Alaska

Abstract This paper provides a photographic tour of the ground-surface rupture features of the Greendale Fault, formed during the 4 September 2010 Darfield earthquake. The fault, previously unknown, produced at least 29.5 km of strike-slip surface deformation of right-lateral (dextral) sense. Deformation, spread over a zone between 30 and 300 m wide, consisted mostly of horizontal flexure with subsidiary discrete shears, the latter only prominent where overall displacement across the zone exceeded about 1.5 m. A remarkable feature of this event was its location in an intensively farmed landscape, where a multitude of straight markers, such as fences, roads and ditches, allowed precise measurements of offsets, and permitted well-defined limits to be placed on the length and widths of the surface rupture deformation.

Patterns of debris flow initiation and periglacial sediment sourcing in the Colorado Front Range: Patterns of debris flow initiation in the Colorado Front Range

Hillslope response to climate-driven fluvial incision controls sediment export and relief generation in most mountainous settings. Following the shift to a warmer, wetter climate after the Last Glacial Maximum (LGM) (∼18 ka), the Waipaoa River (New Zealand) rapidly incised up to 120 meters, leaving perched, low-relief hillslopes unadjusted to that base level fall. In the Mangataikapua—a 16.5 km2 tributary principally composed of weak melange—pervasive post-LGM landslides responded to >50 m of fluvial incision by sculpting and denuding >99% of the catchment. By reconstructing LGM and younger paleosurfaces from tephra identified by electron microprobe analysis (EMPA) and lidar-derived surface roughness, we estimate the volume, timing, and distribution of hillslope destabilization in the Mangataikapua and the relative contribution of landslide-prone terrain to post-LGM landscape evolution. We calculate volume change between four paleosurfaces constrained by tephra age (Rerewhakaaitu, 17.5 ka; Rotoma, 9.4 ka; Whakatane, 5.5 ka; and Waimihia, 3.4 ka). From the paleosurface reconstructions, we calculate the total post-LGM hillslope sediment contribution from the Mangataikapua catchment to be 0.5 ± 0.06 (s.d.) km3, which equates to a subcatchment averaged erosion rate of ∼1.6 mm yr−1. This is double the previous hillslope volume when normalized by study area, demonstrating that landslide-prone catchments disproportionately contribute to the terrestrial post-LGM sediment budget. Finally, we observe particularly rapid post-Waimihia erosion rates, likely impacted by human settlement.

Surface rupture during the 2010 Mw 7.1 Darfield (Canterbury) earthquake: Implications for fault rupture dynamics and seismic-hazard analysis

Glacial retreat in recent decades has exposed unstable slopes and allowed deep water to extend beneath some of those slopes. Slope failure at the terminus of Tyndall Glacier on 17 October 2015 sent 180 million tons of rock into Taan Fiord, Alaska. The resulting tsunami reached elevations as high as 193 m, one of the highest tsunami runups ever documented worldwide. Precursory deformation began decades before failure, and the event left a distinct sedimentary record, showing that geologic evidence can help understand past occurrences of similar events, and might provide forewarning. The event was detected within hours through automated seismological techniques, which also estimated the mass and direction of the slide - all of which were later confirmed by remote sensing. Our field observations provide a benchmark for modeling landslide and tsunami hazards. Inverse and forward modeling can provide the framework of a detailed understanding of the geologic and hazards implications of similar events. Our results call attention to an indirect effect of climate change that is increasing the frequency and magnitude of natural hazards near glaciated mountains.

SURFACE RUPTURE OF THE GREENDALE FAULT DURING THE DARFIELD (CANTERBURY) EARTHQUAKE, NEW ZEALAND: INITIAL FINDINGS

During an extreme storm in the Colorado Front Range in September 2013, 11 debris flows initiated at high elevations in Rocky Mountain National Park. We characterized these debris flows to determine controls on their initiation and found that eight of the 11 initiated in areas of convergent topography, and eight initiated at elevations > 2800m. The high proportion of debris flows in areas of convergent topography emphasizes the importance of local topographic control on initiation. Debris flows at high elevations in the Front Range are atypical; this event broadens our understanding of debris flow regimes in the Front Range. Survey data (scarp dimensions, transport distance) suggest that transport is influenced by downslope processes rather than characteristics of the initiation site. At one site with evidence of multiple debris flows sourced from the same colluvial hollow, we obtained relative ages of debris flow deposits through geomorphic mapping and fan stratigraphy. We used radiocarbon and beryllium-10 (Be) analysis to age stratigraphic deposits and debris flow levees. Radiocarbon ages (n = 6) were highly variable and were interpreted to reflect secondary hillslope processes rather than debris flow ages. Large ranges in cosmogenic exposure age and anomalously old samples indicate that sampled boulders (n = 14) contained inherited Be concentrations. Beryllium-10 concentrations were likely acquired as exposed bedrock surfaces or during intermediate storage in the colluvial hollow. We suggest that Be inheritance limits the utility of cosmogenic exposure dating of debris flows with short transport distances (10 1 to 10 km). Despite these limitations, we documented field evidence for four to seven debris flows in the last 75 ka, including two in the last 8 ka. Considered collectively, Be sample ages from all levees suggest that greatest sediment production occurred during Quaternary glacial stages due to periglacial processes. Subsequent evacuation of the colluvial hollow likely occurred during wetter periods of the mid-Holocene.