Comparison of Paleoearthquake Elapsed-Times and Mean Interevent-Times for a Global Data Set of Active Faults: Implications for Future Earthquakes and Seismic Hazard

Abstract

The timing and size of successive prehistoric earthquakes on individual active faults are key for understanding seismic processes and time-dependent seismic hazards. Here, we analyze interevent and elapsed times for 890 large prehistoric and historic earthquakes on 210 normal, reverse and strike-slip faults from five active tectonic regions globally (Japan, Greece, New Zealand and the California & Basin-and-Range provinces in the US). Most faults (∼80%) have mean interevent times greater than the elapsed time (open-interval) since their last recorded earthquake. We also find that 85%–100% of closed interevent times, defined by 64 historic ruptures and their penultimate events on these faults, occurred within a factor of two of their mean recurrence-interval, with 75% less than the mean. These observations hold for a variety of tectonic settings and fault parameters, with faster slip-rate faults (>10 mm/a) being consistently more “advanced” in their seismic-cycle than slower moving faults. The entire global population of closed interevent-times is consistent with a Weibull probability density function (PDF), while stochastic modeling tailored to closed-interval parameters indicates that open recurrence-interval data sets are best “predicted” by positively skewed elapsed time distributions (52%–78% overlap integral) for all regions, except California. Thus, the rarity of elapsed times exceeding mean interevent-times on individual faults may be due to skewed recurrence PDFs (i.e., Brownian Passage Time, lognormal, etc.), in which the median and mode are less than its mean, while California is an outlier potentially because its open-intervals derive from a single geometrically interconnected fast-moving (>10 mm/a) fault system that is presently experiencing an earthquake-hiatus.