Earthquake precursors: activation or quiescence?

Abstract

S U M M A R YWe discuss the long-standing question of whether the probability for large earthquake occurrence (magnitudes m > 6.0) is highest during time periods of smaller event activation, or highest during time periods of smaller event quiescence. The physics of the activation model are based on an idea from the theory of nucleation, that a small magnitude earthquake has a finite probability of growing into a large earthquake. The physics of the quiescence model is based on the idea that the occurrence of smaller earthquakes (here considered as magnitudes m > 3.5) may be due to a mechanism such as critical slowing down, in which fluctuations in systems with long-range interactions tend to be suppressed prior to large nucleation events. To illuminate this question, we construct two end-member forecast models illustrating, respectively, activation and quiescence. The activation model assumes only that activation can occur, either via aftershock nucleation or triggering, but expresses no choice as to which mechanism is preferred. Both of these models are in fact a means of filtering the seismicity time-series to compute probabilities. Using 25 yr of data from the California-Nevada catalogue of earthquakes, we show that of the two models, activation and quiescence, the latter appears to be the better model, as judged by backtesting (by a slight but not significant margin). We then examine simulation data from a topologically realistic earthquake model for California seismicity, Virtual California. This model includes not only earthquakes produced from increases in stress on the fault system, but also background and off-fault seismicity produced by a BASS-ETAS driving mechanism. Applying the activation and quiescence forecast models to the simulated data, we come to the opposite conclusion. Here, the activation forecast model is preferred to the quiescence model, presumably due to the fact that the BASS component of the model is essentially a model for activated seismicity. These results lead to the (weak) conclusion that California seismicity may be characterized more by quiescence than by activation, and that BASS-ETAS models may not be robustly applicable to the real data.

Probabilities for large events in driven threshold systems

“…Following the results in Ref. [34], we concluded that a new model for earthquake probabilities was needed, leading to the model described in this paper.…”

“…Are large earthquakes more probable during times of increased seismic activity (activation) or during times of decreased seismic activity (quiescence)? We have considered this question at length [34] and find no compelling evidence for either assumption. We concluded that earthquake probabilities computed from rates of activity are not statistically significant as compared to Poisson probabilities.…”

Record-Breaking Intervals: Detecting Trends in the Incidence of Self-Similar Earthquake Sequences

“…This problem of false-positive indications, very common to hazards forecasting, is typically addressed by raising or lowering a detection threshold to optimize a probability gain metric (JOLLIFFE and STEPHENSON, 2003;RUNDLE et al, 2011;USGS-CSEP, 2013). As we will discuss, in addressing item 3, this ''threshold'' approach probably does not apply directly to the RBTS method, as there does not seem to be an obvious pattern to the amplitude or duration of periods in which r\1, from Eq.…”

Analyses of seismicity parameters of the August 11th, 2012, Ahar-Varzaghan earthquakes in north-western Iran

“…As mentioned above, besides b-value measurements, the seismicity-rate changes, which may be associated with the physical properties of the seismogenic zone, could be useful precursors for the main future shocks. Rundle et al [28] have discussed the longstanding question on the highest occurrence probability of large earthquake (M > 6:0) during the time periods of smaller event activation or smaller event quiescence. Their results led to the conclusion that California seismicity was more likely characterized by quiescence than activation.…”