Background and Meeting Strategy: 

Having surveyed the range of possible OEF uses at a previous Powell Center meeting, we now move on to identifying the best available science, both for near-term deployments and for more advanced capabilities anticipated in the future. Because all models are only an approximation of the system, best available science must be ascertained in the context of specific uses. Also, and as emphasized at our previous meeting, it is important to identify and work directly with a set of early adopters, which for our planning purposes can be considered as follows:

1. CEPEC and NEPEC

2. CalEMA

3. PG&E

4. California Earthquake Authority (perhaps through the commercial loss modeling companies they rely upon)

Table 1, on the following page, lists various potential OEF products, ranging from a magnitude-probability distribution, to a full earthquake-rupture forecast, to various risk estimates.

Because OEF aims to “to help communities prepare for potentially destructive earthquakes” (Jordan et al., 2014), usefulness will be dictated by reliability and skill at larger magnitudes (e.g., M≥6.5 in California). Table 2 lists various informational constraints that could be utilized in forecasting such events. As indicated therein, an explicit goal of UCERF3-ETAS has been to incorporate finite faults, elastic rebound, and characteristic magnitude frequency distributions. Interestingly, we find that you cannot combine ETAS with finite faults without also including elastic rebound, and adding the latter in turn implies a need for characteristic magnitude-frequency distributions on faults. Considerable time will be spent discussing UCERF3-ETAS at this meeting, especially given the complexity of the model. However, we will also review and discuss both simpler and more advanced approaches (e.g., physics-based simulators).

We currently plan to have two follow up Powell Center meetings, one to address operationalization challenges and one on verification and validation.

Table 1. Potential products that could be produced either directly by an operational earthquake forecast system, or by further processing in downstream risk calculations. Each of these will constitute an estimate in that uncertainties will need to be quantified (taken from the Potential Uses of OEF report).

Table 2. Some of informational constraints (observed or model inferred) that one might use to forecast the probability of triggered earthquakes (taken from the UCERF3-ETAS documentation).

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