Bayesian probabilities forM_w9.0+ earthquakes in the Aleutian Islands from a regionally scaled global rate

Abstract

We use the global rate of Mw ≥ 9.0 earthquakes, and standard Bayesian procedures, to estimate the probability of such mega events in the Aleutian Islands, where they pose a significant risk to Hawaii. We find that the probability of such an earthquake along the Aleutians island arc is 6.5% to 12% over the next 50 years (50% credibility interval) and that the annualized risk to Hawai'i is about $30 M. Our method (the regionally scaled global rate method or RSGR) is to scale the global rate of Mw 9.0+ events in proportion to the fraction of global subduction (units of area per year) that takes place in the Aleutians. The RSGR method assumes that Mw 9.0+ events are a Poisson process with a rate that is both globally and regionally stationary on the time scale of centuries, and it follows the principle of Burbidge et al. (2008) who used the product of fault length and convergence rate, i.e., the area being subducted per annum, to scale the Poisson rate for the GSS to sections of the Indonesian subduction zone. Before applying RSGR to the Aleutians, we first apply it to five other regions of the global subduction system where its rate predictions can be compared with those from paleotsunami, paleoseismic, and geoarcheology data. To obtain regional rates from paleodata, we give a closed‐form solution for the probability density function of the Poisson rate when event count and observation time are both uncertain.

Sensitivity of Probabilistic Tsunami Hazard Assessment to Far-Field Earthquake Slip Complexity and Rigidity Depth-Dependence: Case Study of Australia

“…Recently Shennan et al (2018) inferred the 1964 earthquake was the only event in the last 2000 years to rupture the entire region, by combining paleoseismic results at 22 sites. Our model's results near Alaska are most similar to Butler et al (2016), although the Wesson et al (2007Wesson et al ( , 2008 ARI's are within the 95% interval (Table 1). Wesson et al (2007Wesson et al ( , 2008 assumed M w !…”

“…The modelled ARIs are generally comparable to the range of estimates in other studies using longerterm historical or paleo data, and/or alternative moment conservation techniques ( Table 1). The credible intervals are wide, but this is also true of 95% intervals reported elsewhere (Table 1, Rong et al 2014;Butler et al 2016). The uncertainty is further emphasised by comparing ARIs from different studies at the same site (Table 1).…”

“…9 events have ARI ' 300-400 years by constraining the parameters of a tapered Gutenberg-Richter type model with tectonic convergence rates and earthquake catalogue data. In the same region Butler et al (2016) obtained an ARI of 1148 (490-3448) using the 'regionally scaled global moment rate' (RSGR) method, whereas our method suggests ARIs intermediate between these two estimates (Table 1).…”

“…The uncertainty is further emphasised by comparing ARIs from different studies at the same site (Table 1). For example on the relatively well studied Alaska megathrust (Kodiak to Prince William Sound), Wesson et al (2007Wesson et al ( , 2008 drew on multi-site Holocene stratigraphy to infer an ARI ' 650 years for earthquakes like the 1964 event (which had M w 9:2), whereas Butler et al (2016) estimated M w ! 9 ARI ' 1403 (447-9800) years using an expanded set of paleo data.…”

Extreme tsunami inundation in Hawai‘i from Aleutian–Alaska subduction zone earthquakes

“…We consider 'credible' to mean that the physical parameters of the earthquake (faulting and slip) have been observed-or inferred from analysis-in prior Mw 9? earthquakes (see Butler et al 2016 for probabilistic analysis). Since the largest tsunami experienced in Hawai'i is the 1946 event, we first validated our tsunami model forecasts with 1946 data, to link and corroborate knowledge of the earthquake with observed tsunami effects.…”