Authors / CoAuthors
Gaull, B.A. | Michael-Leiba, M.O.
Abstract
New earthquake risk maps of southwest Western Australia including continental margins have been prepared. The risk is depicted as contours of peak ground velocity, acceleration, and ground intensity with a 10 per cent probability of being exceeded in 50 years. The maps are based on the Cornell-McGuire methodology. Ten earthquake source zones have been thus defined and corresponding recurrence relations derived. The relation obtained, using a maximum-likelihood fit, for the primary zone to the east of Perth, is log N = 3.66-0.90 ML, where N is the number of events greater than or equal to the Richter magnitude, ML. Local intensity attenuation constants, a, b, and c, are derived for the expression I = aebMLR-c, where I is the estimated Modified Mercalli intensity at a hypocentral distance R km from an earthquake of magnitude ML. Using the relation log A= I/3.1-2.3 to convert the intensity to peak ground acceleration, A in m.s-2, the adopted constants were 0.025, 1.10 and 1.03 respectively. Similarly, using the empirical formula 21 = 7v/5 to convert intensity to peak ground velocity, v in mm.s-1, the corresponding values were 3.30, 1.04 and 0.96, respectively. The contour expressing the greatest risk in the area of interest is that of a peak ground velocity of 160 mm.s-1, and it encloses an area of about 2000 km2 centred on the most active source zone east of Perth. The value for Perth city is 48 mm.s-1. Increasing (i) the maximum magnitude from ML 7.5 to ML 8.5; (ii) the depth of earthquake foci from 5 km to 15 km; (iii) the b value from 0.90 to 0.94; and (iv) the attenuation constants to their estimated maximum value, in the primary source zone, changes the Perth velocity contour from 48 mm.s-1 to 56 mm.s-1 , 48 mm.s-1 , 42 mm.s-1 , and 58 mm.s-1, respectively. The omission of a suspected seismic gap 100 km east of Perth from the primary source zone changes the velocity contour from 48 mm.s-1 to 46 mm.s-1. Sensitivity to adopting another empirical relation between peak ground acceleration and intensity has been examined. This increases the risk at Perth from 0.44 m.s-2 to 0.65 m.s-2. We recommend a microzonation study of Perth and installation of more strong-motion instruments to improve our risk estimates, which should be updated in 5-10 years.
Product Type
document
eCat Id
81214
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
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2601
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Keywords
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- GA PublicationJournal
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- WA
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_External
Publication Date
1987-01-01T00:00:00
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geoscientificInformation
Series Information
BMR Journal of Australian Geology and Geophysics 10:2:145-151
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Unknown
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Extents
[-35.85, -18.76, 111.13, 130.29]
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