Time-dependent recurrence of strong earthquake shaking near plate boundaries: A lake sediment perspective

Abstract

Accurate probabilistic seismic hazard analysis requires a good knowledge of the recurrence parameters of the strongest earthquakes in a region. Due to the typical short temporal span of instrumental and historical data, it is often unclear whether one should adopt a time-dependent or time-independent (Poissonian) recurrence model, the choice of which has large repercussions on the probability estimates for new strong events. The rapidly-growing discipline of lacustrine paleoseismology aims at producing long continuous records of strong seismic shaking, which integrate the activity of all significant seismic sources in a region and allow a reliable determination of recurrence patterns. The typical continuous sedimentation regime in lakes can lead to complete, sensitive paleoseismic records and a reduced temporal uncertainty in recurrence intervals. Here, I present a worldwide compilation of published long lacustrine paleoseismic records grouped per tectonic domain, and statistically explore the variability of their recurrence intervals expressed by the coefficient of variation (CoV). A CoV 1 indicates a time-independent process, whereas CoV <0.5 and 0.5–1 are interpreted as a quasi-periodic and weakly-periodic process, respectively. By resampling the data and applying different statistical tests, it is found that generally at least ~10 intervals are needed to allocate a paleoseismic record to the main recurrence models, and ~ 15 intervals are required to confidently reject the possibility of Poissonian behavior, if applicable. The compilation shows a wide range of CoVs (0.32–1.48), which do not seem to be controlled (on a global scale) by the mean interval, record time span, sedimentation rate, seismic intensity threshold or record type. Plate boundary settings generally exhibit a quasi-periodic to weakly-periodic recurrence behavior, characterized by a rising hazard function with elapsed time since the last event. In contrast, intraplate settings are characterized by a Poissonian or clustered model and either a constant hazard function with time or an enhanced hazard function shortly after an event. This general pattern seems to be modulated by the local distribution of seismic sources, where a CoV 0.3–0.4 can be interpreted as caused by a simple, isolated seismic source, and a CoV ~1 may indicate the additive effect of several seismic sources capable of leaving a sedimentary fingerprint in the lake. Most lacustrine records at subduction zones show a CoV ~0.4–0.8, representing a mixture of a dominant megathrust seismic cycle and other secondary sources. In contrast, transform settings present a larger variability in recurrence parameters, with CoV ranging between ~0.4 and ~ 1.4. A clustered recurrence (CoV >1) may be related to changes in the sensitivity of the lacustrine paleoseismograph or to real earthquake clustering due to e.g. stress transfer between neighboring faults. The most useful lacustrine paleoseismic records can be retrieved in high-seismicity settings where many paleoseismic events can be recorded in a relatively short time span (i.e. <10 kyr). Such records yield sufficient intervals to reach a stable CoV and to allow probability distribution fitting, but avoid large changes in seismicity and sediment dynamics, which can be caused by e.g. the direct and indirect effects of regional deglaciation.