Long-Delayed Aftershocks in New Zealand and the 2016 M7.8 Kaikoura Earthquake
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We study aftershock sequences of six major earthquakes in New Zealand, including the 2016 M7.8 Kaikaoura and 2016 M7.1 North Island earthquakes. For Kaikaoura earthquake, we assess the expected number of long-delayed large aftershocks of M5+ and M5.5+ in two periods, 0.5 and 3 years after the main shocks, using 75 days of available data. We compare results with obtained for other sequences using same 75-days period. We estimate the errors by considering a set of magnitude thresholds and corresponding periods of data completeness and consistency. To avoid overestimation of the expected rates of large aftershocks, we presume a break of slope of the magnitude–frequency relation in the aftershock sequences, and compare two models, with and without the break of slope. Comparing estimations to the actual number of long-delayed large aftershocks, we observe, in general, a significant underestimation of their expected number. We can suppose that the long-delayed aftershocks may reflect larger-scale processes, including interaction of faults, that complement an isolated relaxation process. In the spirit of this hypothesis, we search for symptoms of the capacity of the aftershock zone to generate large events months after the major earthquake. We adapt an algorithm EAST, studying statistics of early aftershocks, to the case of secondary aftershocks within aftershock sequences of major earthquakes. In retrospective application to the considered cases, the algorithm demonstrates an ability to detect in advance long-delayed aftershocks both in time and space domains. Application of the EAST algorithm to the 2016 M7.8 Kaikoura earthquake zone indicates that the most likely area for a delayed aftershock of M5.5+ or M6+ is at the northern end of the zone in Cook Strait.
This work was supported by Russian Science foundation, project No. 16-17-00093. We acknowledge the New Zealand GeoNet project and its sponsors EQC, GNS Science and LINZ, for providing data used in this study. We thank an anonymous reviewer for reading the paper and suggesting useful improvements.
- Aki, K. (1965). Maximum likelihood estimate of b in the formula log N = a − b M and its confidence limits. Bulletin of the Earthquake Research Institute, University of Tokyo, 43, 237–239.Google Scholar
- Bender, B. (1983). Maximum likelihood estimation of b-values for magnitude grouped data. Bulletin of the Seismological Society of America, 73, 831–851.Google Scholar
- Cattania, C., Hainzl, S., Wang, L., Roth, F., & Enescu, B. (2014). Propagation of Coulomb stress uncertainties in physics-based aftershock models. Journal of Geophysical Research: Solid Earth, 119(10), 7846–7864.Google Scholar
- Gardner, J. K., & Knopoff, L. (1974). Is the sequence of earthquakes in southern California, with aftershocks removed, Poissonian? Bulletin of the Seismological Society of America, 64, 1363–1367.Google Scholar
- Gutenberg, B., & Richter, C. F. (1954). Seismicity of the Earth and associated phenomena (Vol. ix, p. 310). Princeton: Princeton University Press.Google Scholar
- Rhoades, D. A., Christophersen, A., & Gerstenberger, M. C. (2016). Multiplicative earthquake likelihood models based on fault and earthquake data. Bulletin of the Seismological Society of America, 105(6). doi: 10.1785/0120150080.
- Rhoades, D. A., Gerstenberger, M. C., Christophersen, A., Zechar, J. D., Schorlemmer, D., Werner, M. J., et al. (2014). Regional earthquake likelihood models II: Information gains of multiplicative hybrids. Bulletin of the Seismological Society of America, 104(6), 3072–3083. doi: 10.1785/0120140035.CrossRefGoogle Scholar
- Shebalin, P. N. (2004). Aftershocks as indicators of the state of stress in a fault system. Doklady Earth Sciences, 398, 978–982.Google Scholar
- Utsu, T. (1961). A statistical study on the occurrence of aftershocks. Geophysical Magazine, 30, 521–605.Google Scholar
- Wells, D. L., & Coppersmith, K. J. (1994). New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bulletin of the Seismological Society of America, 84(4), 974–1002.Google Scholar
- Werner, M., Marzocchi, W., Taroni, M., Zechar, J., Gerstenberger, M., Liukis, M., et al. (2015). Retrospective evaluation of time-dependent earthquake forecasting models during the 2010–12 Canterbury, New Zealand, earthquake sequence. SECED 2015 Conference: Earthquake Risk and Engineering towards a Resilient World 9–10 July 2015, Cambridge UK. http://www.seced.org.uk/images/newsletters/WERNER,%20MARZOCCHI,%20et%20al.pdf.