Are Triggering Rates of Labquakes Universal? Inferring Triggering Rates From Incomplete Information

The acoustic emission activity associated with recent rock fracture experiments under different conditions has indicated that some features of event–event triggering are independent of the details of the experiment and the materials used and are often even indistinguishable from tectonic earthquakes. While the event–event triggering rates or aftershock rates behave pretty much identical for all rock fracture experiments at short times, this is not the case for later times. Here, we discuss how these differences can be a consequence of the aftershock identification method used and show that the true aftershock rates might have two distinct regimes. Specifically, tests on a modified Epidemic-Type Aftershock Sequence model show that the model rates cannot be correctly inferred at late times based on temporal information only if the activity rates or the branching ratio are high. We also discuss both the effect of the two distinct regimes in the aftershock rates and the effect of the background rate on the inter-event time distribution. Our findings should be applicable for inferring event–event triggering rates for many other types of triggering and branching processes as well.