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Just Some Nerd said:Perhaps Perth has been assigned 0.09 because part of the region would be across the 0.09 boundary? I do hate how this map has been drawn however, they're not really contours and are more similar to the borders of regions (think 1170.2 zones)
IDS said:human909 - I was going to post some text from the AS 1170.4 commentary, but I see you already posted it yourself on 20th Feb.
It seems to me that the commentary makes the intended application of the maps perfectly clear. It clearly states that the contours are the outer boundaries with a specified minimum Z value, and outside the Z = 0.09 contour the required value is Z = 0.08. I see no statement or implication that the Z value should be interpolated between the boundaries of the regions. The contours therefore delineate regions with a constant required Z value.
Excellent point. It highlights the conflicting messages very well.JustSomeNerd said:Perhaps Perth has been assigned 0.09 because part of the region would be across the 0.09 boundary? I do hate how this map has been drawn however, they're not really contours and are more similar to the borders of regions (think 1170.2 zones)
That is for a 50 year return period which is ridiculously low.SRL V1.0 said:whereas the corresponding NSHA18 calculated value is 0.031
human909 said:That is for a 50 year return period which is ridiculously low.
human909 said:Only three years ago Melbourne felt a 'decently' sized tremor. The epicentre at Mansfield 130km away has PEAK GROUND ACCELATION of 0.20g, so almost 7 times the figure above if you didn't notice the decimal shift. We had an after shock just 2 days ago.
Fair call.li0ngalahad said:I don't think that's correct. That's a 10% probability in 50 years, which is actually a 475y return period.
Exactly.li0ngalahad said:That's quite concerning actually, it goes to show how these assessments can be relied upon only to a certain extent, especially because of the limited historical data we have for Australia, and I'm glad the approach is somewhat conservative in keeping the old Z values for design.