Tectonic stress distribution of New Zealand

Abstract

New Zealand is considered as one of the most active earthquake sources in the world, experiencing the deadly 2011 M6.3 at Christchurch, as well as more than 180,000 earthquakes from 1964 to 2016. One important parameter in earthquake statistics is the b value in the frequency magnitude distribution (Gutenberg and Richter, 1954). There have been a number of observations that indicate that changing in b value is inversely related to changes in the stress level. An earthquake is caused by sudden release of seismic waves. Hence, this study was conducted to evaluate the spatial distribution of b value at New Zealand, implicating for prospective areas of the upcoming earthquakes. In this study, we considered the large earthquake, Mw ≥ 7.0, because they can result more vulnerable to the country. By the retrospective test, the appropriate parameter to calculate b value was 50 fixed earthquake events. After we got the suitable condition for b-value calculation, we analyzed the most recent earthquake data (1964 – 2012) and mapped the spatial distribution of b value of New Zealand. The result revealed that there are 11 anomalous of low b-value areas. The study showed there are five areas that were hit by the large earthquake before. After that, the b value had been increasing because of stress releasing. However, the b values of these areas have been decreasing, which means the stress have been increasing and these anomalous areas may potentially generate large earthquake up to 7.0 MW.