Multifractal analysis for the ULF geomagnetic data during the Guam earthquake

In our previous papers we have shown that the fractal (monofractal) dimension (D₀) showed a significant increase before the Guam earthquake occurred on August 8, 1993. In order to have a further support to this precursory effect, we have carried out the corresponding multifractal analysis (by means of detrended fluctuation analysis) for the same data to study the statistical self-similar properties in a wide range of scales. We have analyzed the ULF geomagnetic data (the must intense H component) observed at Guam observatory. As the result, we have found that we could observe significant changes in the multifractal parameters at Guam such that α_min showed a meaningful decrease about 25 days before the earthquake and correspondingly Δα increased because α_max exhibited no significant change at all. Correspondingly, the generalized multifractal dimension Dq(>1) showed a significant decrease (whereas Dq(q<0) showed no change) and D₀(=Dq(q=0) (as already found in our previous papers) is reconfirmed to increase before the earthquake. These multifractal characteristics seem to be a further support that these changes are closely associated with the earthquake as a precursor to the Guam earthquake.