Linkage of Co-seismic Failure Stress and Gravity Changes using Statistical Approach for the 2016 Mw7.8 Kaikoura earthquake, New Zealand

摘要

The objective of the paper is to establish a statistical relationship between Coulomb failure stress and gravity changes triggered by the 2016 Kaikoura Mw 7.8 earthquake, New Zealand. The changes were generated using PSGRN/PSCMP program at a layered gravitational half-space. The analysis assumed that the evolving stress level in the area is stable before the Kaikoura earthquake. The study area is extended over the main ruptures and surrounded regions in the South Island; the change patterns were estimated at six depths of 0 km, 5 km, 10 km, 15 km, 20 km and 25 km. Due to the stress and gravity models, the change patterns of the two models were numerically estimated and statistically analyzed using different methodologies viz.; Descriptive statistics, Regression, Correlation and ANOVA. These statistical methods were served at 95% confidence interval to expose the linkage between the two models under the umbrella of SPSS 23 program. The different results can be summarized as: (1) Descriptive analysis result revealed that the positive Coulomb stress change is ~17 MPa and located at 20 km depth, whereas the negative change (~59 MPa) observed at the depth of 10 km. Likewise, the maximum gravity change -7.67 mGal- was observed at 15 km and the minimum change value of 4.69 mGal occurred at 0 km depth, worth mentioning the epicenter located at ~15 km depth, i.e., the maximum gravity change happened near the epicenter and decreased away from the epicenter. (2) According to the regression model, if all variables are held constant, a unit change in the stress at 5 km depth is associated with 0.943 increase in the stress at 0 km. Also, we found that a unit change in gravity change associated with 0.930 increase in the gravity at 0 km. (3) The correlation results mostly showed positive strong correlations of stress or gravity models at adjacent depths and vice versa. (4) The final result from ANOVA method was obtained from two steps: the first, comparing the stress or gravity changes at different depths utilizing the omnibus F-test and post hoc results. The results demonstrate existing of significant difference in both stress and gravity models. Secondly, further analysis of the mean difference were done to provide specific group details. The research is a scientific basis for utilizing statistical analysis in this area, and it can be applied for similar research in other areas over the world.