Measuring the seismic risk along the Nazca–South American subduction front Shannon entropy and mutability

摘要

Four geographical zones are defined along the trench that is formeddue to the subduction of the Nazca plate underneath the South Americanplate; they are denoted A, B, C and D from north to south; zones A, Band D had a major earthquake after 2010 (magnitude over 8.0), whilezone?C has not, thus offering a contrast for comparison. For each zone,a sequence of intervals between consecutive seisms with magnitudesgreater than or equal to 3.0 is set up and then characterized by Shannon entropy andmutability. These methods show a correlation after a major earthquake inwhat is known as the aftershock regime but show independenceotherwise. Exponential adjustments to these parameters reveal thatmutability offers a wider range for the parameters to characterize therecovery compared to the values of the parameters defining thebackground activity for each zone before a large earthquake. It isfound that the background activity is particularly high for zone?A,still recovering for zone?B, reaching values similar to those of zone?A in the case of zone?C (without recent major earthquake) andoscillating around moderate values for zone?D. It is discussed howthis can be an indication of more risk of an important future seismin the cases of zones A and C. The similarities and differencesbetween Shannon entropy and mutability are discussed and explained.