T. Stahl

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.

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

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

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.

Late Quaternary faulting in the Sevier Desert driven by magmatism

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.

Tectonic geomorphology of the Fox Peak and Forest Creek Faults, South Canterbury, New Zealand: slip rates, segmentation and earthquake magnitudes

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.

Field estimate of paleoseismic slip on a normal fault using the Schmidt hammer and terrestrial LiDAR: Methods and application to the Hebgen fault (Montana, USA): Schmidt hammer-derived paleoseismic slip on a normal fault

Seismic hazard in continental rifts varies as a function of strain accommodation by tectonic or magmatic processes. The nature of faulting in the Sevier Desert, located in eastern Basin and Range of central Utah, and how this faulting relates to the Sevier Desert Detachment low-angle normal fault, have been debated for nearly four decades. Here, we show that the geodetic signal of extension across the eastern Sevier Desert is best explained by magma-assisted rifting associated with Plio-Pleistocene volcanism. GPS velocities from 14 continuous sites across the region are best-fit by interseismic strain accumulation on the southern Wasatch Fault at c. 3.4 mm yr−1 with a c. 0.5 mm yr−1 tensile dislocation opening in the eastern Sevier Desert. The characteristics of surface deformation from field surveys are consistent with dike-induced faulting and not with faults soling into an active detachment. Geologic extension rates of c. 0.6 mm yr−1 over the last c. 50 kyr in the eastern Sevier Desert are consistent with the rates estimated from the geodetic model. Together, these findings suggest that Plio-Pleistocene extension is not likely to have been accommodated by low-angle normal faulting on the Sevier Desert Detachment and is instead accomplished by strain localization in a zone of narrow, magma-assisted rifting.

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

ABSTRACT The Fox Peak and Forest Creek Faults in South Canterbury show evidence for segmentation based on the surface expression of late Quaternary faulting. Slip rates were calculated at over 100 sites along the Fox Peak Fault from (a) global positioning system (GPS) and total station fault scarp profiles; (b) field measurements of fault geometry and kinematics; and (c) age data from infrared stimulated luminescence, Schmidt hammer exposure-age dating and regional map correlations. Near the centre of fault segments, maximum slip rates for the Fox Peak Fault reach c. 1.6–1.7 mm yr−1, whereas an average slip rate of c. 1–1.5 mm yr−1 summed across the Forest Creek and Fox Peak Faults falls below rates derived by geodetic models. The geomorphology and single event displacements suggest segment-breaching ruptures of the Fox Peak Fault during late Quaternary earthquakes with moment magnitudes (MW) of 7.0–7.2. This study highlights the role that evaluations of landscape evolution in reverse faulting regimes can play in assessing seismic hazard.

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

The weathering characteristics of bedrock fault scarps provide relative age constraints that can be used to determine fault displacements. Here, we report Schmidt hammer rebound values (R-values) for a limestone fault scarp that was last exposed in the 1959 Mw 7.3 Hebgen Lake, Montana earthquake. Results show that some R-value indices, related to the difference between minimum and maximum R-values in repeated impacts at a point, increase upward along the scarp, which we propose is due to progressive exposure of the scarp in earthquakes. An objective method is developed for fitting slip histories to the Schmidt hammer data and produces the best model fit (using the Bayesian Information Criterion) of three earthquakes with single event displacements of ≥ 1.20m, 3.75m, and c. 4.80m. The same fitting method is also applied to new terrestrial LiDAR data of the scarp, though the LiDAR results may be more influenced by macro-scale structure of the outcrop than by differential weathering. We suggest the use of this fitting procedure to define single event displacements on other bedrock fault scarps using other dating techniques. Our preliminary findings demonstrate that the Schmidt hammer, combined with other methods, may provide useful constraints on single event displacements on exposed bedrock fault scarps. Copyright