## 4 Results
### Susceptibility Assessment
#### 4.2.2 Susceptibility Calculation
\begin{table}
\begin{tabular}{c c} \hline \hline
**Evidence and Indicator** & **Description** & **Weight** \\ \hline Gas hydrate samples & Crystals or aggregates of gas hydrates observed in gravity cores. & 1 \\ Degassing structures & Bubbles and/or vacuoles (porosity) in sediment liquefactions observed in gravity core samples. & 1 \\ Pore water anomalies & Chemical and isotopic pore water anomalies that are caused by hydrate dissociation (e.g., downward chlorinity decrease combined with \(\delta\)18O increase). & 0.9 \\  & Only bottom-simulating reflectors generated by the impedance contrast between the gas-hydrated sediment above and a free gas layer below. Opal BSRs & 0.9 \\  & are excluded. & \\ High resistivity & Anomalous high electrical resistivity in logs due to the presence of & 0.9 \\  & massive hydrates. & \\ Velocity anomalies & Anomalous seismic propagation velocity in the sediment due to the presence of & 0.8 \\ Acoustic blanking facies & Zones devoid of reflections in seismic profiles because of the presence of free gas in the sediment. & 0.8 \\  & Local low-amplitude seismic attribute anomalies that may indicate the presence & 0.8 \\ Dim spots & of hydrocarbons. & 0.8 \\  & Seismic amplitude or high-amplitude anomalies that may indicate the presence & 0.8 \\ Bright spots & of hydrocarbons. & 0.8 \\ Gas chimneys & Areas of poor data quality or push-downs caused by subsurface leakage of gas & 0.8 \\ Seabed features & Geomorphological features related to seabed fluid flow. & 0.8 \\  & Steady or episodic, slow or rapid, visible or invisible flow of gaseous & 0.8 \\ Gas seepage: pockmarks, mud & hydrocarbons from subsurface sources to the Earth’s surface. Pockmarks are & 0.8 \\ volcanoes, gyrophons & craters in the seab caused by fluids erupting and streaming through the sediments. Mud volcanoes are positive cone-shaped reliefs created by the & 0.8 \\  & extrusion of mud, water and gases, mainly hydrocarbon fluids. & 0.8 \\ Mud diapirs & Positive, cone-shaped reliefs created by intrusion inside the sediment column of mud, water and gases, mainly hydrocarbon fluids. & 0.8 \\ HDAC & Hydrocarbon-derived authigenic carbonate formed as a consequence of the & 0.8 \\  & anaerobic oxidation of methane by consortia of microbes. & 0.8 \\ Gas flares & Acoustic artefacts in the water column caused by gas bubbles. & 0.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Weights given to each hydrate-related item of evidence or indicator for the development of the density map of evidence/indicators. The first step for the development of the density map was to create a lattice of evidence and indicators at a resolution of the work scale (\(5\times 5\) km), which will be the final resolution of the susceptibility assessment map. In this lattice, each geographical feature of evidence and indicators was weighted according to Table 3.  
A hypothesis was then established that considered the database of ground evidence for sites that have been sampled, but occurrences of gas hydrates might not be restricted to these point locations. If a given pixel were located between a ground evidence and an indicator, the likeliness of that pixel containing gas hydrates would be greater than that of a pixel located far from either. Given the discrete nature of the features described within the database and the relative concept of this likeliness, a regionalization technique was applied following a smoothed saturated algorithm of kernel density. Here, the weighting of the features represents an abstract concept of the confidence of having gas hydrates. This technique consists of a kernel density estimation, which fits a smoothly tapered surface to each point or polyline. The search radius (default option) was calculated on the basis of the spatial configuration and the number of input points. This approach corrects for spatial outliers (input points that are very far from the rest), so they will not make the search radius unreasonably large.