An Alternative Hypothesis for Recent Earthquake Activity in the Ridgecrest Area

  Let's say our first hypothesis is that the stress index SI is an accurate indicator of earthquake activity, A, and an alternative hypothesis is that the activity is determined by the elapsed time from that of the M7.1 earthquake. We find that there is a negative correlation although it is quite good because its magnitude is close to unity. The correlations for the primitive hypotheses are approximately 0.9 for the same interval of time which excludes the M7.1 earthquake.

But the correlation is related to the slope of a straight line drawn through the data from which we can estimate the activity and the number of earthquakes since the means from which the correlation was determined are known. When we compare the alternative hypothesis with the first hypothesis we find that the observed number of earthquakes is within about two standard deviations of both curves so we don't have a valid reason for rejecting either hypothesis. We are still in suspense about their validity.

In a few days the two hypotheses will become mutually exclusive so it's likely one will have to be rejected. The alternative hypothesis can be interpreted as all the earthquakes since the M7.1 are aftershocks.

Supplemental (Jul 21): Note that the correlation is the slope in standardized coordinates. The black diagonal lines are A_std=±t_std.

Supplemental (Jul 21): Today's search of the USGS earthquake catalog of the Ridgecrest area gave 14 earthquakes for UTC doy 201. This is slightly outside the 2σ bounds but the σ used is for a normal distribution and equal to √n̄. The bounds are likely to be slightly larger since for smaller counts the spread is larger than that of a normal distribution. The number of earthquakes is probably inside 3σ bounds so at the risk of being over cautious we are still reluctant to reject the first hypothesis.