# Aveiro Canyon Head (Portugal) Submarine Slope Instability Assessment
## 4 Data Acquisition and Processing
### Predisposing Factors
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{3}{*}{**Factors**} & \multirow{3}{*}{**Variables (X\({}_{\mathrm{i}}\))**} & \multirow{3}{*}{**Information Value (IV)**} & \multicolumn{2}{c}{**Logistic**} \\  & & & **S = 17,668 Pixels;** & \multicolumn{2}{c}{**Forward**} \\  & & & **N = 405,714 Pixels.** & \multicolumn{2}{c}{**Conditional (LR)**} \\  & & & & \(\varepsilon=-22.8423\) \\ \cline{3-5}  & & \(\mathbf{S_{\mathrm{i}}}\) & \(\mathbf{N_{\mathrm{i}}}\) & \(\mathbf{I_{\mathrm{i}}}\) & \(\mathbf{\beta}\) \\ \hline \multirow{9}{*}{Bathymetry (m)} & 2875–2400 & 1351 & 67,236 & \(-0.3359\) & \(0.0000\) \\  & 2400–2100 & 1802 & 43,209 & \(-0.0188\) & \(11.7773\) \\  & 2100–1800 & 3535 & 36,300 & 0.3495 & \(12.3096\) \\  & 1800–1500 & 2943 & 30,660 & 0.3433 & \(13.3058\) \\  & 1500–1200 & 4055 & 30,474 & 0.4851 & \(13.4463\) \\  & 1200–900 & 3569 & 38,720 & 0.3256 & \(13.9575\) \\  & 900–600 & 413 & 32,789 & \(-0.5387\) & \(13.6531\) \\  & 600–300 & 0 \({}^{*}\) & 22,924 & \(-2.9997\) & \(11.6683\) \\  & 300–0 & 0 \({}^{*}\) & 103,402 & \(-3.6539\) & \(6.2134\) \\ \hline \multirow{9}{*}{Mean slope (degrees)} & 0–5 & 1593 & 126,867 & \(-0.5401\) & \(1.1351\) \\  & 5–10 & 4196 & 65,889 & 0.1651 & \(1.2185\) \\  & 10–15 & 4440 & 67,270 & 0.1806 & \(0.8517\) \\  & 15–20 & 3325 & 54,280 & 0.1482 & \(0.5190\) \\  & 20–25 & 2042 & 42,099 & \(0.0468\) & \(0.1781\) \\  & 25–30 & 939 & 25,951 & \(-0.0805\) & \(-0.2529\) \\  & 30–35 & 446 & 11,472 & \(-0.0493\) & \(-0.2454\) \\  & 35–40 & 257 & 5250 & 0.0508 & \(0.0311\) \\  & 40–45 & 197 & 3078 & 0.1672 & \(0.3864\) \\  & 45–50 & 114 & 1704 & 0.1865 & \(0.2917\) \\  & 50–78 & 119 & 1854 & 0.1685 & \(0.0000\) \\ \hline \multirow{9}{*}{Aspect (slope face exposure)} & N & 821 & 18,354 & 0.0116 & \(0.2859\) \\  & NE & 1024 & 14,686 & 0.2044 & \(0.7079\) \\  & E & 386 & 4361 & 0.3080 & \(0.9623\) \\  & SE & 779 & 8720 & 0.3121 & \(0.9770\) \\  & S & 2914 & 39,312 & 0.2310 & \(0.7409\) \\  & SW & 3745 & 76,858 & 0.0488 & \(0.3921\) \\  & W & 4253 & 114,122 & \(-0.0676\) & \(0.4504\) \\  & NW & 2782 & 97,739 & \(-0.1847\) & \(0.0757\) \\  & N & 964 & 31,562 & \(-0.1541\) & \(0.0000\) \\ \hline \multirow{9}{*}{Curvature} & Concave & 8673 & 146,324 & 0.1339 & \(0.1545\) \\  & Flat & 1361 & 112,680 & \(-0.5570\) & \(0.1189\) \\  & Convex & 7634 & 146,710 & 0.0773 & \(0.0000\) \\ \hline \multirow{9}{*}{Sediment cover} & Coarse sand & 0 \({}^{*}\) & 8218 & \(-2.5542\) & \(0.2279\) \\  & Medium sand & 0 \({}^{*}\) & 45,612 & \(-3.2985\) & \(-00449\) \\  & Fine sand & 0 \({}^{*}\) & 42,355 & \(-3.2663\) & \(-3.2677\) \\  & Very fine sand & 0 \({}^{*}\) & 9272 & \(-2.6066\) & \(-5.4053\) \\  & Coarse silt & 0 \({}^{*}\) & 392 & \(-1.2327\) & \(-75024\) \\  & Medium silt & 6057 & 107,362 & 0.1124 & \(5.8967\) \\  & Fine silt & 10,803 & 125,013 & \(0.2976\) & \(6.1883\) \\  & Very fine silt & 808 & 63,718 & \(-0.5358\) & \(5.3359\) \\  & Rock & 0 \({}^{*}\) & 3772 & \(-2.2160\) & \(0.0000\) \\ \hline \hline \end{tabular} \({}^{*}\) No instabilities identified in the terrain unit of the variable. A value of \(0.999\) was assumed to avoid undetermined values and to prevent an excessive increase in the obtained negative score values (I).  
\end{table} 
Table 2: Information value (I\({}_{\mathrm{i}}\)) and logistic regression (constant \(\varepsilon\) and \(\beta\) values) results for each one of the variables. In general, IV scores for mean slope angle are distributed in a relatively narrow range of values (Table 2), indicating that the probability for the occurrence of movements does not have a large variation along the canyon slope. In a more detailed analysis, the 0\({}^{\circ}\) to 5\({}^{\circ}\) slope angle class, which corresponds to the area of the canyon head whose surface, is almost flat, unsurprisingly provided low susceptibility scores; the slope angles from 5\({}^{\circ}\) to 20\({}^{\circ}\) and above 40\({}^{\circ}\) were the more susceptible to instability.