Earthquake in Peru
On August 15 at 18:40 local time in Peru, a Richter magnitude 8 earthquake caused great damage and hundreds of deaths (late on the 16th estimates suggested more than 500 dead and 1500 injured). The quake was centered near the coast of Peru about 150 Km SSE of Lima. The hardest hit city was Pisco, with 200 people killed and 70% of the city destroyed.
The time for the formal hypothesis test was set for a 24 hour period beginning about an hour before the quake. This relatively long event time was suggested by noting that effects associated with the Indian Ocean Tsunami did not begin until some 20 hours after the temblor. The result is Chisquare 86613 on 86400 df, for p = 0.304 and Z = 0.514. This is a positive but modest deviation. The graph shows a sharp negative trend immediately after the quake, but some 10 or 11 hours later it takes on a fairly steady positive trend that continues for the rest of the 24 hours.
In the next figure, we see a bit more of the context, with 2 days surrounding the quake. Reminiscent of the Tsunami case, there is a huge spike roughly 12 hours before the primary temblor.
Continuing the exploration, we also looked at the variance over the two days surrounding the quake. The figure shows the cumulative deviation of the device variance relative to the mean of the variance. There is an impressive, steep reduction of variance reaching a minimum 11 to 15 hours before the main temblor, increasing to a normal level by the time of the quake, then continuing at the expected level. For comparison, the cumulative deviation of variance on September 11 2001 is shown.