## 4 Comparisons Between Algorithms  
The results generated by the VEFA are compared with those derived from the BETEF v2.0 application. The BETEF tool was developed by [PERSON], [PERSON], and [PERSON] of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and is freely available via the internet. It employs the statistical processing methodology described in [7,9]. To use the tool, unique statistical models must be developed for each volcano being monitored. This means each instance of the application uses a set of assumptions and statistical models that are valid only for a specific volcano. These models are non-transportable and have no defined false positive rate or optimized detection threshold. All model weighting coefficients and detection thresholds used by this application are selected subjectively by the user at the time of their development. The models used for each example were trained using monitoring and modeling data acquired from the most recent unrest episode preceding the event under test. Modeling results (\(X_{MM}\)) were included in the BETEF training set to determine their influence on its forecasting capability. Since eruption history is built directly into the BETEF model during the design process, the \(X_{ERH}\) parameter is not required as a real time input. Weighting coefficients for all BETEF input parameters (\(X_{NE}\), \(X_{CSM}\), \(X_{MM}\), and \(X_{DAYS}\)) were set to 1. All VEFA and BETEF forecasts are based on the same input data to ensure the comparability of results. The median value of the BETEF forecast is used for comparison purposes in all examples shown below. Error estimates were excluded from the comparisons since they are large and typically span the entire probability range. Forecasts for Grimsvotn and three other volcanoes were compared. The additional volcanoes are located in the western portion of North America and frequently exhibit varying forms of unrest. Okmok is an active shield volcano located on the northern portion of Umnak Island in the center of the Aleutian Arc. Comparison forecasts precede Okmok's 2008, VEI 4, eruption. Mount Saint Helens is an active stratovolcano that is situated in the Cascade Mountain Range in the southwestern section of Washington State and last erupted in 2004. Forecasts for Mount Saint Helens are generated over a period of seismic activity in February 2011 that was not due to volcanic unrest. The Yellowstone caldera is located in the Snake River Valley in the northwestern portion of Wyoming and last erupted several thousand years ago. Forecasts for Yellowstone are derived over an unprecedented episode of volcanic unrest that occurred in late 2010. The outcome of each test event and its associated seismicity level, in terms of low or high, is listed in Table 5. \begin{table}
\begin{tabular}{c c c c c} \hline
**Volcano** & **Intrusion** & **Eruption** & **Intensity (VEI\(>\)1)** & **High Seismicity** \\ \hline Grimsvötn & 1 & 1 & 1 & 1 \\ Mount Saint Helens & 0 & 0 & 0 & 0 \\ Okmok & 1 & 1 & 1 & 0 \\ Yellowstone & 1 & 0 & 0 & 1 \\ \hline \end{tabular}
\end{table} 
Table 5: Test event outcome for each algorithm stage and associated seismicity level, where 1 or 0 indicates whether the event occurred or not and if seismicity levels were high or low. Intrusion forecast comparisons for each example are shown in Figure 17A-D. Intrusion probability estimates for the Grimsvotn and Yellowstone episodes are in very good agreement with one another. However, both of these episodes have a significant amount of associated seismicity which is likely driving the BETEF's predictions. There are substantial differences between the forecasts for Okmok and Mount Saint Helens. In both cases, the results provided by the VEFA are driven by source modeling results since there is little seismicity associated with these episodes. The supplied modeling information does not appear to influence the BETEF forecasts for Okmok and Mount Saint Helens. Eruption forecast comparisons are shown in Figure 18A-D.