# Comparison of Statistical Analysis Models for Susceptibility Assessment of Earthquake-Triggered Landslides: A Case Study from 2015 Earthquake in Lefkada Island

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

_{w}= 6.4). The epicenter of the earthquake was located in the south-western part of the island between the villages Athani and Agios Petros and, with a focal depth of 10.7 km, was felt in a significant part of western Greece. The main consequences were the loss of two human lives, as well as the occurrence of extensive landslides, which in turn caused serious damage to properties and the road network. These landslide events affected mainly the western part of the island, namely: (a) The villages of Komilio, Dragano, and Athani, (b) the coastal zone from Eggremni to Gialos, and (c) the road axis from Tsoukalades to Agios Nikitas, with an overall length of 6 km [19].

_{w}= 6.3) earthquake in 2003.

## 2. Study Area

^{2}, it is the fourth largest Ionian Island. Lefkada can be characterized as a mostly mountainous region (about 70% of the total area) with an average altitude of 500 m. Its climate includes mild and rainy winter, and hot summer. Because of these climatic conditions and its geomorphology, the island offers a variety of landscapes, a key element of which is the rich vegetation, narrow plateaus, white beaches, springs, and gorges.

## 3. Data

#### 3.1. Landslide Inventory

#### 3.2. Geo-Environmental Factors

## 4. Methodology

#### 4.1. Frequency Ratio (FR) Model

_{pix}(S

_{j}) is the number of landslide pixels in factor category j, and N

_{pix}(N

_{j}) is the number of pixels in the same factor category. A FR value of 1 (average value) means that the density of landslides in the category is proportional to the size of the category. If the value is greater than 1, then there is a high correlation, whereas a value of less than 1 means a lower correlation [37].

_{i,j}is the frequency ratio value for the category j of the factor i, and n is the total number of the factors.

#### 4.2. Logistic Regression (LR) Model

#### 4.3. Data Processing

#### 4.4. Implementation of Models

## 5. Results

#### Validation of Results

## 6. Discussion

## 7. Conclusions and Outlook

## Author Contributions

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**The landslide inventory map, including location map and images illustrating two landslide events triggered by the 17th November 2015 earthquake in the island of Lefkada: (

**a**) Earth slide on the Eggremni beach; (

**b**) Rock slide on the road axis from Tsoukalades to Agios Nikitas.

**Figure 2.**Geo-Environmental factors: (

**a**) Land cover; (

**b**) lithology; (

**c**) elevation; (

**d**) slope angle; (

**e**) slope aspect; (

**f**) distance to main road network; (

**g**) distance to faults; (

**h**) peak ground acceleration (PGA).

**Figure 5.**Map with coverage similarities between the landslide susceptibility categories of the two models.

**Table 1.**Human and economic effects due to landslides represented on a global scale (Data provided by EM-DAT: The Emergency Events Database, Universite catholique de Louvain-CRED, D. Guha-Sapir, www.emdat.be, Brussels, Belgium).

Year | Occurrence | Total Deaths | Injured | Affected | Homeless | Total Affected | Total Damage (US$) |
---|---|---|---|---|---|---|---|

1970–1979 | 45 | 7217 | 1041 | 94,019 | 3100 | 98,160 | 124,166 |

1980–1989 | 78 | 5647 | 4250 | 860,691 | 2,520,332 | 3,385,273 | 1,030,141 |

1990–1999 | 93 | 5104 | 977 | 590,027 | 1,170,860 | 1,761,864 | 1,695,190 |

2000–2009 | 147 | 6182 | 1276 | 1,119,597 | 193,539 | 1,314,412 | 288,107 |

2010–2019 | 126 | 6579 | 1304 | 2,543,562 | 84,378 | 2,629,244 | 1,633,414 |

**Table 2.**Values derived from the frequency ratio (FR) model for all factor categories, and multicollinearity checking indexes (tolerance (TOL) and variance inflation factor (VIF)) and coefficients derived from logistic regression (LR) model for all factors.

Factors and Their Categories | FR Model | LR Model | ||||
---|---|---|---|---|---|---|

Number of Total Pixels | Number of Landslide Pixels | FR Value | TOL | VIF | Coefficients | |

Elevation (m) | 0.615 | 1.627 | −0.015 | |||

(1) 0–134 | 96,907 | 315 | 2.78 | |||

(2) 135–306 | 86,741 | 111 | 1.09 | |||

(3) 307–501 | 95,228 | 4 | 0.04 | |||

(4) 502–754 | 58,042 | 4 | 0.06 | |||

(5) 755–1171 | 33,779 | 0 | 0 | |||

Slope Angle (Degrees) | 0.898 | 1.113 | 0.052 | |||

(1) 0–8 | 97,552 | 56 | 0.49 | |||

(2) 9–16 | 100,441 | 102 | 0.87 | |||

(3) 17–25 | 85,991 | 95 | 0.94 | |||

(4) 26–35 | 58,647 | 93 | 1.35 | |||

(5) 35–65 | 28,066 | 88 | 2.68 | |||

Slope Aspect | 0.670 | 1.493 | 4.709 | |||

(1) North | 34,034 | 9 | 0.22 | |||

(2) North-East | 40,218 | 6 | 0.12 | |||

(3) East | 56,505 | 0 | 0 | |||

(4) South-East | 49,155 | 3 | 0.05 | |||

(5) South | 34,312 | 4 | 0.10 | |||

(6) South-West | 41,160 | 19 | 0.39 | |||

(7) West | 60,759 | 243 | 3.35 | |||

(8) North-West | 46,861 | 150 | 2.68 | |||

Distance to Main Road network (m) | 0.850 | 1.177 | −0.004 | |||

(1) 0−347 | 179,992 | 166 | 0.79 | |||

(2) 348−846 | 111,966 | 218 | 1.66 | |||

(3) 847−1,648 | 63,214 | 50 | 0.68 | |||

(4) 1,649−3,231 | 12,889 | 0 | 0 | |||

(5) 3,232−5,530 | 2611 | 0 | 0 | |||

Distance to Faults (m) | 0.627 | 1.595 | −0.002 | |||

(1) 0−324 | 162,088 | 425 | 2.24 | |||

(2) 325−765 | 101,455 | 6 | 0.05 | |||

(3) 766−1,354 | 62,190 | 1 | 0.01 | |||

(4) 1,355−2,163 | 29,937 | 2 | 0.06 | |||

(5) 2,164−3,752 | 15,002 | 0 | 0 | |||

PGA (g) | 0.704 | 1.420 | 60.946 | |||

(1) 0,08 | 10,895 | 0 | 0 | |||

(2) 0.09–0.12 | 238,830 | 35 | 0.13 | |||

(3) 0.13−0.16 | 98,023 | 398 | 3.47 | |||

(4) 0.17−0.20 | 22,924 | 1 | 0.04 | |||

Land Cover | 0.816 | 1.225 | 2.948 | |||

(1) Artificial Surfaces | 14,182 | 9 | 0.54 | |||

(2) Permanent Crops | 60,462 | 7 | 0.10 | |||

(3) Pastures | 8997 | 0 | 0 | |||

(4) Heterogeneous Agricultural Areas | 114,705 | 45 | 0.34 | |||

(5) Forests | 48,515 | 83 | 1.46 | |||

(6) Scrub/Herbaceous Vegetation | 107,438 | 241 | 1.92 | |||

(7) Open Spaces with Little/No Vegetation | 12,907 | 49 | 3.24 | |||

(8) Water | 3466 | 0 | 0 | |||

Lithology | 0.822 | 1.216 | 2.274 | |||

(1) Alluvium Deposits | 12,059 | 41 | 2.89 | |||

(2) Limestones | 209,228 | 381 | 1.55 | |||

(3) Marls | 47,455 | 6 | 0.11 | |||

(4) Conglomerates | 25,303 | 0 | 0 | |||

(5) Scree-Talus Cones | 6466 | 0 | 0 | |||

(6) Flysch | 12,736 | 1 | 0.07 | |||

(7) Metamorphic Rocks | 55,804 | 5 | 0.08 |

**Table 3.**Coverage cross-comparison for the landslide susceptibility categories between both the FR and LR models.

FR | LR | ||||
---|---|---|---|---|---|

VL (%) | L (%) | M (%) | H (%) | VH (%) | |

VL | 21 | 1 | – | – | – |

L | 29 | 4 | 1 | – | – |

M | 19 | 4 | 3 | 2 | 1 |

H | 5 | 2 | 1 | 2 | 2 |

VH | 1 | – | – | – | 2 |

ROC Analysis Results | FR | LR |
---|---|---|

Number of Cases | 216 | 216 |

Number Correct | 169 | 201 |

Positive Cases Missed | 0 | 2 |

Negative Cases Missed | 47 | 13 |

Accuracy (%) | 78.2 | 93.1 |

Sensitivity (%) | 100 | 98.1 |

Specificity (%) | 56.5 | 88 |

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**MDPI and ACS Style**

Polykretis, C.; Kalogeropoulos, K.; Andreopoulos, P.; Faka, A.; Tsatsaris, A.; Chalkias, C.
Comparison of Statistical Analysis Models for Susceptibility Assessment of Earthquake-Triggered Landslides: A Case Study from 2015 Earthquake in Lefkada Island. *Geosciences* **2019**, *9*, 350.
https://doi.org/10.3390/geosciences9080350

**AMA Style**

Polykretis C, Kalogeropoulos K, Andreopoulos P, Faka A, Tsatsaris A, Chalkias C.
Comparison of Statistical Analysis Models for Susceptibility Assessment of Earthquake-Triggered Landslides: A Case Study from 2015 Earthquake in Lefkada Island. *Geosciences*. 2019; 9(8):350.
https://doi.org/10.3390/geosciences9080350

**Chicago/Turabian Style**

Polykretis, Christos, Kleomenis Kalogeropoulos, Panagiotis Andreopoulos, Antigoni Faka, Andreas Tsatsaris, and Christos Chalkias.
2019. "Comparison of Statistical Analysis Models for Susceptibility Assessment of Earthquake-Triggered Landslides: A Case Study from 2015 Earthquake in Lefkada Island" *Geosciences* 9, no. 8: 350.
https://doi.org/10.3390/geosciences9080350