Abstract
Rupture speed Vr and stress drop Δτ are two key parameters that can
characterize earthquake source and the associated potential for ground
shaking. Despite their importance, a controversy has emerged in recent
years regarding whether there is a positive or negative correlation
between Δτ and Vr. Here I attempt to reconcile the controversy by
presenting a context-based solution and a physics-based solution. The
first solution calls for attention to the specific context under which
Vr and Δτ are discussed, as their meanings and estimated values can vary
between different studies. It is noted that a negative correlation
between Δτ and Vr can result, at least partly, from a tradeoff effect
inherent to certain analysis method. For the second solution, it is
shown that the specific correlation between Δτ and Vr can depend on the
condition of fracture energy Gc. Constant Gc often favors a positive
correlation, whereas introducing a variability of Gc can lead to a
negative correlation. More efforts are needed to improve the methods for
estimating Vr and Δτ, and to explore other mechanisms that may explain
the correlation between the two parameters.