A Tectonophysical Analysis of Earthquake Frequency-Size Relationship Types for Catastrophic Earthquakes in Central Asia

摘要

We performed a tectonophysical analysis of earthquake frequency-size relationship types for large Central Asian earthquakes in the regions of dynamical influence due to major earthquake-generating faults based on data for the last 100 years. We identified four types of frequency-size curves, depending on the presence/absence of characteristic earthquakes and the presence or absence of a downward bend in the tail of the curve. This classification by the shape of the tail in frequency-size relationships correlates well with the values of the maximum observed magnitude. Thus, faults of the first type (there are characteristic earthquakes, but no downward bend) with M (max) 8.0 are classified as posing the highest seismic hazard; faults with characteristic earthquakes and a bend, and with M (max) = 7.5-7.9, are treated as rather hazardous; faults of the third type with M (max) = 7.1-7.5 are treated as posing potential hazard; and lastly, faults with a bend, without characteristic earthquakes, and with a typical magnitude M (max) 7.0, are classified as involving little hazard. The tail types in frequency-size curves are interpreted using the model of a nonlinear multiplicative cascade. The model can be used to treat different tail types as corresponding to the occurrence/nonoccurrence of nonlinear positive and negative feedback in earthquake rupture zones, with this feedback being responsible for the occurrence of earthquakes with different magnitudes. This interpretation and clustering of earthquake-generating faults by the behavior the tail of the relevant frequency-size plot shows raises the question about the physical mechanisms that underlie this behavior. We think that the occurrence of great earthquakes is related to a decrease in effective strength (viscosity) in the interblock space of faults at a scale appropriate to the rupture zone size.