Effect of Shallow Slip Amplification Uncertainty on Probabilistic Tsunami Hazard Analysis in Subduction Zones: Use of Long-Term Balanced Stochastic Slip Models

Abstract

The complexity of coseismic slip distributions influences the tsunami hazard posed by local and, to a certain extent, distant tsunami sources. Large slip concentrated in shallow patches was observed in recent tsunamigenic earthquakes, possibly due to dynamic amplification near the free surface, variable frictional conditions or other factors. We propose a method for incorporating enhanced shallow slip for subduction earthquakes while preventing systematic slip excess at shallow depths over one or more seismic cycles. The method uses the classic k-2 stochastic slip distributions, augmented by shallow slip amplification. It is necessary for deep events with lower slip to occur more often than shallow ones with amplified slip to balance the long-term cumulative slip. We evaluate the impact of this approach on tsunami hazard in the central and eastern Mediterranean Sea adopting a realistic 3D geometry for three subduction zones, by using it to model * 150,000 earthquakes with M w from 6.0 to 9.0. We combine earthquake rates, depth-dependent slip distributions, tsunami modeling, and epistemic uncertainty through an ensemble modeling technique. We found that the mean hazard curves obtained with our method show enhanced probabilities for larger inundation heights as compared to the curves derived from depthindependent slip distributions. Our approach is completely general and can be applied to any subduction zone in the world.

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

“…Although shallow low rigidity zones may permit surprisingly large tsunamis for their magnitude, tectonic constraints imply such events should occur less often than higher-rigidity events with similar magnitude and lower slip. A similar trade-off was identified by Scala et al (2019) who used a completely different 'slip-amplification' approach to represent the effect of depth-varying rigidity on earthquake slip. Our 'magnitude-relabelling' approach implies the rigidity model affects the hazard by changing our interpretation of the integrated slip released by historical earthquakes (which in turn affects the logic-tree weights for the magnitude-frequency distributions).…”

“…Our 'magnitude-relabelling' approach implies the rigidity model affects the hazard by changing our interpretation of the integrated slip released by historical earthquakes (which in turn affects the logic-tree weights for the magnitude-frequency distributions). Compared with slipamplification (Scala et al 2019), the magnitude-relabelling approach has the practical advantage of not requiring any re-computation of tsunami waveforms. However it is not obvious whether one-or-other approach should be preferred on theoretical grounds, or the extent to which their results differ.…”

“…3.3), which affects the resulting hazard. This is not specific to our magnitude-relabelling approach; for example, Scala et al (2019) propose a completely different treatment of depth-varying rigidity for PTHA which also requires scenario rate modifications.…”

Urgent Tsunami Computing

“…The local historical and geophysical knowledge, such as the proximity to a subduction zone and local seismicity, can be used constrain the likelihood of the faulting mechanism given the location and the magnitude of the earthquake. Furthermore, stochastic simulation methods can be used for predicting earthquake slip distributions [10].…”

Self-similar stochastic slip distributions on a non-planar fault for tsunami scenarios for megathrust earthquakes

“…Therefore, the choice of the function used to describe the SPDF depends on a priori knowledge or assumptions of the likely rst-order spatial distribution of slip. For example, in situations where there is no knowledge of preferential locations for slip, a uniform PDF could be used (Murphy and Herrero 2020); whereas if a speci c earthquake or a particular rupture feature is assumed to occur (e.g., shallow slip ampli cation) a more speci c function can be applied (Murphy et al 2016;Scala et al 2020).…”