Present-day surface deformation in the South West Seismic Zone (SWSZ) of Western Australia from three episodic GPS (EGPS) measurements of a dense GPS network  

Authors / CoAuthors

Hu, G. | Darby, D. | Leonard, M. | Dawson, J.

Abstract

Understanding the nature of intraplate earthquakes in the South West Seismic Zone (SWSZ) in Western Australia, one of the most seismically active areas in Australia, has long been the focus of many scientists and has important implications for seismic hazard assessment. In order to measure the present-day surface deformation and the strain distribution in the SWSZ, a dense GPS network of 48 sites with an average inter-station separation of 50 km was established. To date, three campaigns have been conducted and analysed. The measurements made in 2002 and 2006 included observations of all 48 sites within the SWSZ, while only the core stations were observed in the 2004 campaign. Each site was observed for a minimum of four days. The daily solutions have repeatabilities of about 1-2 mm and 3-4 mm, in the horizontal and vertical components respectively, in each campaign. The campaigns, spanning four years, show no statistically significant interior horizontal motions at the sites, at the 95% confidence level with respect to the stable Australian plate, which sets an upper bound of 0.46 mm/yr at the 95% confidence level on the horizontal motion in the SWSZ region. Analysis of the geodetic strain between sites indicates the maximum likely average regional linear strain rates to be between 1.0×10-9/yr and 1.0×10-8/yr across the around 200km width of the SWSZ, with the azimuth of the axis of relative contraction being 133±21 degrees (95% confidence level), which is nearly orthogonal to the NNE direction of the Australian plate velocity. These findings are in general agreement with the geological, geodetic and seismic evidences, which themselves are discrepant. Future repeat occupations are expected to reduce the uncertainties and shed light on the apparent inconsistency between seismic and geological evidence.

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nonGeographicDataset

eCat Id

65806

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Keywords

• GA PublicationAbstract

( Theme )

• deformation

( Theme )

• earthquakes

( Theme )

• geophysics

( Theme )

• geodesy

• AU-WA

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

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2008-01-01T00:00:00

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