The 1979 Cadoux earthquake and intraplate stress in Western Australia

Denham, David B.; Alexander, L.G.; Everingham, I. B.; Gregson, P.J.; McCaffrey, Robert J.; Enever, J.R.

doi:10.1080/08120098708729429

Cited by 14 publications

(19 citation statements)

References 10 publications

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“…We find that the rupture area estimated by Dawson et al () is also only 16% of that expected from global scaling relationships for an earthquake of similar magnitude. Note that the magnitude of the compressive stress field in Western Australia is similar to that in southeastern Australia (Coblentz et al, ; Denham et al, ). These observations raise the question whether moderate‐sized seismic sources modulated by a high compressive stress magnitude in the Australian continent are self‐similar.…”

Section: Resultsmentioning

confidence: 73%

Interacting Intraplate Fault Systems in Australia: The 2012 Thorpdale, Victoria, Seismic Sequences

Attanayake

Sandiford

Schleicher³

et al. 2019

JGR Solid Earth

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Using a new seismic waveform data set, we locate 234 earthquakes and estimate source parameters (focal mechanisms, magnitude, and stress drop) of the two largest earthquakes (E1 and E2) in the 2012 seismic sequence in Thorpdale, Victoria. The focal mechanisms suggest thrust faulting, consistent with previous observations in southeast Australia. The estimated magnitudes are M w 4.9 ± 0.14 (E1) and 4.3 ± 0.1 (E2). The estimates of stress drop 57 ± 7.4 MPa (E1) and 28 ± 2.4 MPa (E2) reflect strength of faults in an intraplate environment. By analyzing spatiotemporal distribution of aftershocks, we show that E1 and E2 reflect two separate seismic sequences about a month apart. E1 and E2 ruptured two adjacent faults with orientations 218°/78°/78°(Fault 1) and 134°/27°/171°(Fault 2), respectively, where angles indicate strike/dip/slip rake. To test causal mechanism of fault interaction, we performed Coulomb stress modeling, which shows very weak unloading of E2 by E1. Thus, we infer that fault interaction might instead reflect remotely triggered fluid diffusion. Also, a local rotation of the stress field proceeding E1 might have favorably reoriented Fault 2 for failure. Finally, we identify an apparent correlation between high heat flow and seismicity in southeastern Australia, suggesting a combination of mechanisms including transient stress perturbations and lithospheric thermal weakening associated with high heat flow as the principal factors localizing intraplate seismicity.Plain Language Summary The 2012 earthquake sequence in Thorpdale is the most recent and significant seismic activity in southeast Australia, during which two moderate-sized earthquakes were felt in the region with the second earthquake thought to be an aftershock of the first. Using a newly assembled data set, we estimate source parameters of these earthquakes and locate 232 smaller earthquakes associated with this seismic sequence. In this study, we show that faults ruptured with thrust motion, the moment magnitude of the two largest earthquakes are 4.9 and 4.3, and the stress release per fault length (57 and 28 MPa) is larger than the global average. By locating aftershocks, we also show that the two largest earthquakes ruptured two separate faults rather than one. The absence of any plausible Coulomb stress loading suggests that these different faults interacted with each other through other mechanisms such as a fluid diffusion. Key Points:• The two largest earthquakes (M w 4.9 and 4.3) in the seismic sequence indicate thrust faulting in southeast Australia • Higher than average stress drop (57 and 28 MPa) suggests the rupture of strong faults with longer recurrence intervals • Adjacent fault planes ruptured, implying fault interaction through interplay between stress conditions and fluid diffusion Supporting Information:• Supporting Information S1

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Section: Resultsmentioning

confidence: 73%

Interacting Intraplate Fault Systems in Australia: The 2012 Thorpdale, Victoria, Seismic Sequences

Attanayake

Sandiford

Schleicher³

et al. 2019

JGR Solid Earth

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“…Prior to this period, within a 15 km radius, the area was essentially aseismic in the seismic recording history. Transient cluster seismicity is a feature of the SWSZ [ Denham et al , 1987] and while in some cases the enhanced local seismicity relates to aftershock sequences, other clusters are not associated with any previously known seismic events. The closest recorded moderate‐sized earthquake to the Kalannie cluster is the 1987 M6.2 Cadoux earthquake, which was located over 50 km to the south.…”

Section: Resultsmentioning

confidence: 99%

“…The SWSZ is located in the southwest of the Archean Yilgarn block, which was formed approximately 3.7–2.3 Ga [ Myers , 1993; Reynolds and Hillis , 2000] and consists of bedrock granites, gneisses, and greenstones [ Denham et al , 1987]. The area is generally characterized as having undulating topography.…”

Section: Settingmentioning

confidence: 99%

“…The South West Seismic Zone (SWSZ), located in the southwest region of Western Australia (WA), is an area of concentrated intraplate earthquake activity within a recognized stable continental region [ Crone et al , 1997]. In the last 40 yr, the area has experienced a number of damaging intraplate earthquakes, including the M6.9 1968 Meckering [ Everingham et al , 1969] and the M6.2 1979 Cadoux earthquakes [ Denham et al , 1987], as well as a number of other significant damaging earthquakes [ Leonard et al , 2002] (Figure 1). The SWSZ is near to the Perth population center of 1.5 million people.…”

Section: Introductionmentioning

confidence: 99%

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Shallow intraplate earthquakes in Western Australia observed by Interferometric Synthetic Aperture Radar

Dawson¹,

Cummins²,

Tregoning³

et al. 2008

J. Geophys. Res.

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We investigate two intraplate earthquakes in a stable continental region of southwest Western Australia. Both small‐magnitude events occur in the top ∼1 km of crust and their epicenters are located with an accuracy of ∼100 m (1σ) using satellite Interferometric Synthetic Aperture Radar (InSAR). For the Mw 4.7 Katanning earthquake (10 October 2007) the average slip magnitude is 42 cm, over a rupture area of ∼1 km2. This implies a high static stress drop of 14–27 MPa, even for this very shallow earthquake, which may have important implications for regional seismic hazard assessment. The earthquake rupture extends from a depth of around 640 m to the surface, making it a rarely observed intraplate, surface‐rupturing event. Using InSAR observations, we estimate the coseismic slip distribution of the shallow earthquake, such estimates being rarely available for small magnitude events. For the Mw 4.4 composite Kalannie earthquake sequence (21–22 September 2005), we use a long‐term time series analysis technique to improve the measurement of the co‐seismic signal, which is a maximum of 27 mm in the line‐of‐sight direction. Double difference seismic analysis shows some relocated cluster seismicity which corresponds in timing, location, and source parameters to the InSAR‐observed deformation. This earthquake is the smallest magnitude seismic event to have been investigated using InSAR and demonstrates the capability of the technique to provide important constraints on small‐magnitude coseismic events. The shallow depth of both these events adds weight to the suggestion that earthquakes associated with tectonic processes in this area of Western Australia often initiate in the upper 1 km of crust.

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“…Previous investigations have relied on aftershock locations determined with sparse regional or national networks for which the focal depths were not sufficiently constrained to determine the faulting geometry (e.g. Stewart & Denham 1974;Denham et al 1987).…”

Section: Introductionmentioning

confidence: 99%

Aftershocks of the 1988 January 22 Tennant Creek, Australia Intraplate Earthquakes: Evidence For A Complex Thrust-Fault Geometry

Bowman

Gibson²,

Jones

1990

Geophysical Journal International

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SUMMARY On 1988 January 22 three earthquakes of Ms 6.3‐6.7 occurred in a 12‐hr period near Tennant Creek (Northern Territory) in the Proterozoic North Australian Craton and produced 32 km of surface rupture on two main scarps. the Lake Surprise scarp is shaped like a boomerang with the east arm trending ESE and the west arm, WSW. the Kunayungku scarp lies 7 km to the northwest and trends ESE. Locations of 211 aftershocks determined using data from portable seismograph arrays define a 10‐km by 40‐km aftershock zone elongated parallel to the trend of the surface ruptures. In the western and eastern part of the fault zone, aftershocks occur only south of the Kunayungku and eastern Lake Surprise scarps, respectively. In the central section, in contrast, aftershocks lie primarily to the north of the western arm of the Lake Surprise scarp. Focal depths range from the surface to 8km. In all sections the shallowest earthquakes lie closest to the scarps, whereas deeper events lie further away. In cross‐section, the aftershocks lie in three distinct inclined zones, which delineate fault surfaces ruptured by the main shocks. Aftershocks are concentrated near the edges of the inferred fault surfaces suggesting that stress was relieved in the centre of the faults by rupture during the main shocks. the inferred fault‐plane dips are: 45° to the SSW for the Kunayungku fault, 55° to the NNW for the western Lake Surprise fault and 35° to the SSW for the eastern Lake Surprise fault. These dip directions are consistent with the sense of thrust movement inferred from surface deformation. the reversal of fault dip and sense of movement between the central and end segments requires a complicated fault geometry. the aftershock data would allow a second, south‐dipping plane in the central section that does not intersect the surface. This blind fault may be responsible for much of the moment release interpreted from the modelling of broad‐band teleseismic waveforms (Choy & Bowman 1989). Rupture of the north‐dipping plane may have been controlled by a pre‐existing fault marked at the surface by a quartz ridge 5‐km long and may be of secondary importance. Although the quartz ridge suggests previous faulting, the absence of significant topographic relief together with estimates of erosion rates suggest an average repeat time in excess of 104yr. Preliminary interpretation of water withdrawal histories and water‐level data from a borefield adjacent to the eastern Lake Surprise scarp does not support a causal relationship between the borefield and the occurrence of the earthquakes. The nearby Warramunga (WRA) seismic array provides a record of local earthquake activity from 1965 to the present. the fault area was essentially aseismic until two small earthquakes in 1986 February and a series of six magnitude 4‐5 earthquakes in 1987 January, which were followed by more than 1000 aftershocks. the frequency of occurrence of aftershocks declined very slowly in 1987, with p= 0.2 in the modified Omori formula, whereas for the 1988 aftershock sequence,...

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The 1979 Cadoux earthquake and intraplate stress in Western Australia

Cited by 14 publications

References 10 publications

Interacting Intraplate Fault Systems in Australia: The 2012 Thorpdale, Victoria, Seismic Sequences

Interacting Intraplate Fault Systems in Australia: The 2012 Thorpdale, Victoria, Seismic Sequences

Shallow intraplate earthquakes in Western Australia observed by Interferometric Synthetic Aperture Radar

Aftershocks of the 1988 January 22 Tennant Creek, Australia Intraplate Earthquakes: Evidence For A Complex Thrust-Fault Geometry

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