31 March 2011

Swan's explanation for replacing Professor Warwick McKibbin doesn't add up

Federal Treasurer Wayne Swan cited the length of time Professor Warwick McKibbin and Don McGauchie served on the Reserve Bank Board in the justification he gave to Ross Greenwood on 2GB for replacing these vocal critics of the Labor government’s fiscal policy.

Can I just make this point about the two departing members. They’ve been there for 10 years. I don’t think there’s ever been a situation where someone has been on the board longer than 10 years.

This is not true. Jillian Broadbent has been a member of the Reserve Bank Board since 1998. Swan didn’t have a problem reappointing her for a third five year term in May 2008.

18 March 2011

Reality check: Facts about the threat posed by radiation from the Fukushima Daiichi plant

  • People are exposed to an average of 3.0 mSv/year.
  • People have a normal radiation acceptance level of 20 mS/year.
  • On 17 March at 10am, helicopters measured 87.7 mSv/h at 90 m and 4.13 mSv/h at 300 m above the Daiichi plant.
  • Other measurements of radiation levels taken within ~60 km of the Daiichi plant ranged from 0.7 to 170 μSv/h on 17 March.


6 March 2011

Fairfax paints a grossly distorted picture of earthquake sizes

An article by Fairfax on the magnitude 6.3 earthquake that devastated the city of Christchurch in New Zealand includes an interactive diagram of several earthquakes which are compared by the relative sizes of circles shown on a map.

The magnitude 7.9 earthquake that occurred in Sichuan, China on 12 May, 2008, appears nearly as large as the catastrophic magnitude 9.1 earthquake near northern Sumatra on 26 December, 2004. It is not a meaningful comparison, because earthquake magnitudes are measured on a logarithmic scale. An increase in magnitude by one unit represents a tenfold increase in the maximum amplitude of the seismic waves recorded by the seismograph and about 32 times the amount of energy released. Thus the magnitude 9.1 earthquake near northern Sumatra had an amplitude 109.1 - 7.9 = 15.8 times larger than the magnitude 7.9 earthquake in Sichuan, China, and 109.1 - 6.3 = 631 times larger than the magnitude 6.3 earthquake in Christchurch.

Comparison of earthquakes by amplitude on seismogram

According to an empirical relationship developed by Beno Gutenberg and Charles Richter, log10E is proportional to 1.5M, where E is the energy released by the earthquake and M is the magnitude. This means that in terms of energy released, the magnitude 9.1 earthquake was about 101.5(9.1 - 7.9) = 63.1 times stronger than the magnitude 7.9 earthquake, and about 101.5(9.1 - 6.3) ≈ 15800 times stronger than the magnitude 6.3 earthquake.