The Earthquake Potential Score (EPS)
A 0–100 index derived from natural time entropy that quantifies proximity to the next significant event.
What the EPS Measures
The Earthquake Potential Score is a numerical index ranging from 0 to 100 that reflects how close a specific region is to experiencing its next significant earthquake. It is derived from natural time entropy statistics applied to the current seismic catalogue.
A higher EPS indicates that the region has accumulated more seismic events since its last significant earthquake - meaning it is further through the seismic cycle and statistically closer to its next large event. A lower EPS indicates the region is early in its cycle.
How the EPS Is Calculated
The EPS is computed from the natural time representation of the seismic catalogue for a defined geographic region. The key steps are:
- Count all seismic events above a completeness threshold since the last significant (M≥6.0) earthquake in the region.
- Compute the natural time entropy κ₁ - the variance of the natural time probability distribution weighted by seismic energy.
- Compare the current κ₁ value against the distribution of κ₁ values observed at the end of past seismic cycles in the same region.
- Map the percentile rank of the current κ₁ onto the 0–100 EPS scale.
How the EPS Is Used in Predictions
The EPS is one of the primary input features to the LSTM neural network alongside spatial parameters, magnitude statistics, and energy release metrics. The model learns how patterns of EPS evolution - including the rate of change, not just the current value - correlate with the occurrence of significant events in its training data.
Each live prediction carries an EPS value representing the state of the seismic system at the time the prediction was generated. This value is published alongside the prediction record and is downloadable from the Data Downloads page.
What the EPS Is Not
The EPS is not a probability that an earthquake will occur within any specific time window. It should not be read as "EPS 80 means 80% chance of an earthquake today." It is an index of cycle progression relative to historical patterns - a relative measure, not an absolute probability.