Similarly to the results shown for Gold, he occurrence of an earthquake appears to have minimal impact of the direction of S&P prices in the month following an incident as shown in the charts below. The S&P 500 is a number derived from the values of stocks of 500 large-cap U.S. companies. It is an index commonly used to gauge the health of US stock markets oveall. The results here show that, unlike the results for Gold, which are essentially flat, there does appear to be a small gain, averaging out to about a half a percent. The actual performances ranged between a loss of .085% and a gain of 5.15% after a month. The second chart shows the outcome for incidents in the continental United States. Given the small sample size (only 13 incidents since 1950), the results do not appear to have any significance.
NOTE: Data sourced from Yahoo!Finance