Animal combat

When an up-and-coming chimp is deciding whether to challenge the alpha male to a fight, and when two antelopes size each other up before locking horns, each combatant must estimate his chances of winning.  If they overestimate their chances, they’ll regularly get a beating, and if they underestimate their chances, they’ll lose out on the rewards of success (which usually includes lots of sex).  So natural selection has probably honed a certain degree of risk intelligence in animals where males engage in violent forms of intraspecific competition.

Fighting antelopes

Two Gemsbok antelopes (“Oryx Gazella”) having a go at each other

I wonder if anyone has collected statistics about the outcomes of these fights.  If so, I’d be curious to know whether challengers win about half the fights they start.  If they win substantially more than half, or significantly fewer, this wouldn’t necessarily mean they were underestimating or overestimating their chances of winning, because we don’t know how the costs of losing and the benefits of winning stack up against each other.  If the benefits of winning outweigh the costs of losing, then a good utility maximizer would risk starting fights even when the odds were stacked against him.  The costs and benefits might be different for challengers and  incumbents, of course, which would make things even more complex.  Someone must have modeled this, and there’s probably some complex game-theoretic analysis of optimal behavior, but are there any empirical data?  If you know of any, please email me at dylan.evans@projectionpoint.com

An earthquake in Tokyo?

In 2010 we ran an online prediction game at Projection Point in which we asked people to estimate the probabilities of world events.  One of the possible events we asked people to think about was an earthquake in Tokyo.

Thankfully, it didn’t happen.  But it occurred to me that the recent earthquake in Japan might have reduced the chance of an earthquake happening in Tokyo in the near future. By releasing the stored strain energy which has built up around the fault line over the past few decades, I reasoned, the Tōhoku earthquake might have lowered the energy further along the fault plane.

But it turns out things aren’t this simple.  Although a quake dissipates the stored strain energy in one section of a fault line, only 10 percent or less of this energy is radiated as seismic energy. Most of the energy is used to power the fracture growth, and this can lead to greater strain energy accumulating further down the fault line.  To make matters even more complicated, the geology of the Kanto plain – on which Tokyo sits - is a mess. Kanto sits very close to a tectonic triple junction, and according to Ross Stein of the US Geological Survey (USGS) there are broken pieces of plate jammed under Tokyo “like a pill that won’t go down your throat.” And on top of that there are two different slabs of plates, so there’s really “a triple stack of faults beneath Tokyo.”

The USGS team has modeled the region around the triple junction to help gauge future risks.  Four years before the Tohoku, the group figured Tokyo had a 30% chance in the next 30 years of experiencing an event (M 7.0-plus) that produces the sort of severe shaking which would test even the walls and pillars of highly earthquake-resistant buildings.

The group is now trying to work out whether this assessment needs to be revised following the M 9.0 Tohoku tremor.  ”We calculate that there are modest increases in stress on some of the faults that lie just to the south of Tokyo,” Dr Stein told the BBC. ”So our judgement would be that the hazard is either unchanged or higher than it was beforehand.”

This is worrying.  The effects of an earthquake in Tokyo would dwarf those of the Tohoku quake.  The city is home to  a quarter of Japan’s population, as well as being the country’s administrative and commercial centre.  Big quakes struck the area in 1703, 1855 and 1923, with the last claiming the lives of 100,000 people.  Were any one of these events to occur today, the economic losses alone would be expected to top 80 trillion Yen ($1 trillion).  But the capital to back catastrophe risks isn’t supplied by insurers. It mainly comes from reinsurers, and the key players in the global reinsurance market are all European (Munich Re & Swiss Re in particular). An earthquake in Tokyo could cause them to become insolvent. Since these are systemically important institutions for the insurance industry, their insolvency would have severe consequences for the global financial system.  Such financial aftershocks would dwarf the geological ones.