Mark Quigley

Present-day stresses, seismicity and Neogene-to-Recent tectonics of Australia's 'passive' margins: intraplate deformation controlled by plate boundary forces

Abstract Neogene-to-Recent deformation is widespread on and adjacent to Australias ‘passive’ margins. Elevated historical seismic activity and relatively high levels of Neogene-to-Recent tectonic activity are recognized in the Flinders and Mount Lofty Ranges, the SE Australian Passive Margin, SW Western Australia and the North West Shelf. In all cases the orientation of palaeostresses inferred from Neogene-to-Recent structures is consistent with independent determinations of the orientation of the present-day stress field. Present-day stress orientations (and neotectonic palaeostress trends) vary across the Australian continent. Plate-scale stress modelling that incorporates the complex nature of the convergent plate boundary of the Indo-Australian Plate (with segments of continent–continent collision, continent–arc collision and subduction) indicates that present-day stress orientations in the Australian continent are consistent with a first-order control by plate-boundary forces. The consistency between the present-day, plate-boundary-sourced stress orientations and the record of deformation deduced from neotectonic structures implicates plate boundary forces in the ongoing intraplate deformation of the Australian continent. Deformation rates inferred from seismicity and neotectonics (as high as 10−16 s−1) are faster than seismic strain rates in many other ‘stable’ intraplate regions, suggestive of unusually high stress levels imposed on the Australian intraplate environment from plate boundary interactions many thousands of kilometres distant. The spatial overlap of neotectonic structures and zones of concentrated historical seismicity with ancient fault zones and/or regions of enhanced crustal heat flow indicates that patterns of active deformation in Australia are in part, governed, by prior tectonic structuring and are also related to structural and thermal weakening of continental crust. Neogene-to-Recent intraplate deformation within the Australian continent has had profound and under-recognized effects on hydrocarbon occurrence, both by amplifying some hydrocarbon-hosting structures and by inducing leakage from pre-existing traps due to fault reactivation or tilting.

Quaternary faults of south-central Australia: palaeoseismicity, slip rates and origin

Faults bounding the Flinders Ranges of South Australia and the Barrier Ranges of New South Wales display clear evidence of significant Quaternary displacements. Kinematic analysis of the Wilkatana, Burra and Mundi Mundi Faults indicates that reverse-oblique fault slip occurred in response to east – west compression, consistent with maximum compressive stress (SHMax) orientations derived from historical earthquake focal mechanisms. Surface-rupturing events resulted from a series of moment magnitude (M) ≥6.6 palaeo-earthquakes over the past ∼100 000 years. The timing of the most recent surface-rupturing events was determined on each fault from optically stimulated luminescence dating of faulted and post-faulting strata. The Wilkatana Fault has been the site of at least two major earthquakes since around 67 ka, making this one of the youngest prehistoric fault scarp exposures in Australia. Thickness estimates of faulted Pliocene and Quaternary footwall sediment imply minimum fault slip rates of 20 – 30 m per million years, while extrapolation of a domed planation envelope in the bedrock hangingwall to the fault plane yields fault slip rates of 36 – 51 m per million years. Movement at these rates over the Pliocene to Holocene interval accounts for a significant proportion of the contemporary relief in the Flinders Ranges. The relative intensity of neotectonic activity and historical seismicity in the Flinders Ranges reflects the role of structural and thermal heterogeneities in a regional stress field dominated by far-field plate-boundary forces.

Recurrent liquefaction in Christchurch, New Zealand, during the Canterbury earthquake sequence

Continuous observational monitoring of a study site in eastern Christchurch, New Zealand, following the 2010 M w 7.1 Darfi eld earthquake has recorded ten distinct liquefaction episodes in the mainshock‐aftershock sequence. Three nearby accelerometers allow calibration between the geological expressions of liquefaction and the intensity of earthquake-induced surface ground motion at the site. Sand blow formation was generated by M w 5.2‐7.1 earthquakes with M w 7.5‐normalized peak ground accelerations (PGA 7.5 ) of ≥ 0.057 g (acceleration due to gravity). Silt drapes between successive sand blow deposits provide markers for delineating distinct liquefaction-inducing earthquakes in the geologic record. However, erosion quickly modifi es the surface of sand blows into alluvial and aeolian forms that complicate geologic diagnosis. The two feeder-dike generations identifi ed in subsurface investigations signifi cantly underrepresent the number of liquefaction-inducing earthquakes due to extensive dike reactivation. New constitutive equations enable PGA 7.5 variations to be estimated from the thickness and areal extent of sand blows.

Ground Motion and Seismic Source Aspects of the Canterbury Earthquake Sequence

This paper provides an overview of the ground motion and seismic source aspects of the Canterbury earthquake sequence. Common reported attributes among the largest earthquakes in this sequence are complex ruptures, large displacements per unit fault length, and high stress drops. The Darfield earthquake produced an approximately 30 km surface rupture in the Canterbury Plains with dextral surface displacements of several meters, and a subordinate amount of vertical displacement, impacting residential structures, agricultural land, and river channels. The dense set of strong ground motions recorded in the near-source region of all the major events in the sequence provides significant insight into the spatial variability in ground motion characteristics, as well as the significance of directivity, basin-generated surface waves, and nonlinear local site effects. The ground motion amplitudes in the 22 February 2011 earthquake, in particular, produced horizontal ground motion amplitudes in the Central Business District (CBD) well above those specified for the design of conventional structures.

Tectonic geomorphology of Australia

Abstract The Australian continent is actively deforming in response to far-field stresses generated by plate boundary interactions and buoyancy forces associated with mantle dynamics. On the largest scale (several 103 km), the submergence of the northern continental shelf is driven by dynamic topography caused by mantle downwelling along the Indo-Pacific subduction system and accentuated by a regionally elevated geoid. The emergence of the southern shelf is attributed to the progressive movement of Australia away from a dynamic topography low. On the intermediate scale (several 102 km), low-amplitude (c. 100–200 m) long-wavelength (c. 100–300 km) topographic undulations are driven by (1) anomalous, smaller-scale upper mantle convection, and/or (2) lithospheric-scale buckling associated with plate boundary tectonic forcing. On the smallest scale (101 km), fault-related deformation driven by partitioning of far-field stresses has modified surface topography at rates of up to c. 170 m Ma−1, generated more than 30–50% of the contemporary topographic relief between some of Australias highlands and adjacent piedmonts, and exerted a first-order control on long-term (104–106 a) bedrock erosion. Although Australia is often regarded as tectonically and geomorphologically quiescent, Neogene to Recent tectonically induced landscape evolution has occurred across the continent, with geomorphological expressions ranging from mild to dramatic.

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

Tectonic framework for the Cenozoic cratonic basins of Australia

4 billion (US

Holocene climate change in arid Australia from speleothem and alluvial records

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.

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

Variations in the extent of Cenozoic marine inundation of Australia, as revealed by the distribution of marine and nearshore deposits, points to a tectonic regime involving three distinct modes of deformation. At the longest wavelengths (order 103 km), the continent has experienced southwest-up, northeast-down tilting with an amplitude of ∼300 m since the Late Eocene. We attribute this tilting to the dynamic topographic response to the northward motion of Australia towards the subduction realm of Indonesia and the western Pacific, as well as its passage across a complexly structured mantle. At short wavelengths (order 101 km), variations in elevation are associated with cumulative fault movements up to the order of 100 m. Fault-slip vectors are generally compatible with the prevailing in situ stress field and therefore can be allied to distant plate-boundary forcing. At intermediate wavelengths (order 102 km), undulations with amplitudes of the order of ∼100 m reflect, at least in part, lithospheric buckling due to relatively high levels of intraplate stress arising from plate-boundary forcing. Understanding the patterns of surface deformation associated with each of these deformation modes provides a tectonic framework against which the broader significance of the Australian Cenozoic record for such things as eustasy must be evaluated.

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

New high-resolution MC-ICPMS U/Th ages and C and O isotopic analyses from a Holocene speleothem in arid south-central Australia provide evidence for increased effective precipitation (EP) relative to present at c. 11.5 ka and c. 8—5 ka, peak moisture at 7—6 ka, and onset of an arid climate similar to present by c. 5 ka. δ18O and δ13C time-series data exhibit marked (>+1‰) contemporaneous excursions over base-line values of −5.3‰ and −11.0‰, respectively, suggesting pronounced moisture variability during the early middle Holocene ‘climatic optimum’. Optically stimulated luminescence and 14C ages from nearby terraced aggradational alluvial deposits indicate a paucity of large floods in the Late Pleistocene and at least five large flood events in the last c. 6 kyr, interpreted to mark an increased frequency of extreme rainfall events in the middle Holocene despite overall reduced EP. Increased EP in south-central Australia during the early to middle Holocene resulted from (1) decreased El Niño-Southern Oscillation (ENSO) variability, which reduced the frequency of El Niño-triggered droughts, (2) the prevalence of a more La Niña-like mean climatic state in the tropical Pacific Ocean, which increased available atmospheric moisture, and (3) a southward shift in the Intertropical Convergence Zone (ICTZ), which allowed tropical summer storms associated with the Australian summer monsoon (ASM) to penetrate deeper into the southern part of the continent. The onset of heightened aridity and apparent increase in large flood frequency at c. 5 ka is interpreted to indicate the establishment of an ENSO-like climate in arid Australia in the late Holocene, consistent with a variety of other terrestrial and marine proxies. The broad synchroneity of Holocene climate change across much of the Australian continent with changes in ENSO behavior suggests strong teleconnections amongst ENSO and the other climate systems such as the ASM, Indian Ocean Dipole, and Southern Annular Mode.