金曜セミナー（Yehuda Ben-Zion氏）
Systematic detection and classification of burst-type (traditional aftershock) sequences and swarm-type earthquake clustersYehuda Ben-Zion*
Department of Earth Sciences, University of Southern California
I review results on detection and classification of different types of seismicity clusters in different regions and scales (Zaliapin & Ben-Zion 2013a,b 2015, 2016a,b). The analysis connects every event in a seismic catalog to its nearest neighbor in space-time-magnitude domain referred to as parent. Observed nearest neighbor event distances follow a bimodal distribution that can be used to partition catalogs into background events having relatively large distances and earthquake clusters associated with relatively short distances (Zaliapin & Ben-Zion 2013a). Applications to various catalogs demonstrate the existence of two basic types of clusters, burst-type and swarm type, found generally in different spatial regions (Zaliapin & Ben-Zion, 2013b, 2016b). Burst-type clusters have a prominently large mainshock, small number of foreshocks and dominance of first-generation offspring. Such clusters reflect highly brittle failure process in areas with relatively cold crystalline rocks and low fluid content (relatively high effective viscosity). Swarm-type clusters lack a prominent mainshock, have increased foreshock activity, and abundance of secondary, tertiary, and higher generation offspring. Such clusters reflect mixed brittle-ductile failure in areas with increased heat flow and fluids and/or soft sediments (reduced effective viscosity). These results are consistent with theoretical expectations on properties of earthquake sequences in regions with different effective viscosity (Ben-Zion & Lyakhovsky, 2006) and previous observational works with different techniques (Kisslinger & Jones, 1991; Yang & Ben-Zion, 2009; Enescu et al., 2009). A dozen of cluster statistics commonly considered in aftershock studies (number of events, duration, area, time decay rate, etc.) are strongly coupled with a simple scalar topological cluster characteristic -- average leaf depth -- quantifying the number of generations within a cluster. Simulations with the ETAS model generally produce only the burst-type clusters, but not the swarm-type that are abundant in areas with reduced effective viscosity. The discussed methodology is robust (with proper analysis) to common catalog deficiencies and errors (Zaliapin & Ben-Zion 2015) and may be used to distinguish between natural and induced seismicity (Zaliapin & Ben-Zion 2016a).
*The studies are done in collaboration with Ilya Zaliapin (UNR)
References
Ben-Zion Y. and V. Lyakhovsky, Geophys. J. Int., 165, 197-210, 2006.
Enescu, B., S. Hainzl and Y. Ben-Zion, Bull. Seism, Soc. Am., 99, 3114-3123, 2009.
Kisslinger, C. and L. M. Jones, J. Geophys. Res., 96, 11,947-11,958, 1991.
Yang, W. and Y. Ben-Zion, Geophys. J. Int., 177, 481-490, 2009.
Zaliapin, I. and Y. Ben-Zion, J. Geophys. Res., 118, 2847–2864, 2013a.
Zaliapin, I. and Y. Ben-Zion, J. Geophys. Res., 118, 2865–2877, 2013b.
Zaliapin, I. and Y. Ben-Zion, Geophys. J. Int., 202, 1949–1968, 2015.
Zaliapin, I. and Y. Ben-Zion, Bull. Seism, Soc. Am., 106, 2016a.
Zaliapin, I. and Y. Ben-Zion, Geophys. J. Int., in review, 2016b.