Landslides Triggered by the 2016 Mw 7.8 Pedernales, Ecuador Earthquake: Correlations with ESI-07 Intensity, Lithology, Slope and PGA-h

Abstract

We provide a dataset of the landslides induced by the 2016 Pedernales megathrust earthquake, Ecuador (Mw 7.8, focal depth of 20 km) and compare their spatial distribution with mapped bedrock lithology, horizontal peak ground acceleration (PGA-h) and the macroseismic intensity based on earthquake-induced environmental effects (ESI-07). We studied 192 coseismic landslides (classified as coherent, disrupted and lateral spreads) located in the epicentral area, defined by the VII to IXESI-07 isoseismals. Based on our findings, lahar deposits, tuffs and volcanoclastic units are the most susceptible to landslides occurrence. Alluvial plains with fluvial loose fine sand are the most susceptible setting for lateral spreading, with a maximum intensity of IXESI-07. The coherent landslides are frequently found in altered shale and siltstone geological units with moderate slopes (8°–16°), with typical intensity ranging between VII and VIIIESI-07. Our analysis draws a typical framework for slope movements triggered by subduction earthquakes in Ecuador. The most dangerous setting is the coastal region, a relatively highly urbanized area located near the epicenter and where liquefaction can trigger massive lateral spreading events. Coherent and disrupted landslides, dominating the more internal hilly region, can be triggered also in moderate slope settings (i.e., less than 10°). Indeed, the regression analysis between seismic intensity, PGA-h and landslide occurrence shows that most of the events occurred at PGA-h values between 0.4 g and 1.2 g, at a distance of 30 to 50 km from the rupture plane. Our database suggests that lithology and hillslope geometry are the main geological/geomorphological factors controlling coseismic landslides occurrence; while the distance from the rupture plane plays a significant role on determining the landslide size. Finally, we underline that coseismically-triggered landslides are among the most common environmental effects occurring during large subduction events that can be effectively used to properly evaluate the earthquake macroseismic field. The landslide inventory we compiled is suitable for assessing the vulnerability of physical environment from subduction earthquakes in Ecuador, and offers a primary data source for future worldwide analysis.

The 1976 Guatemala Earthquake: ESI Scale and Probabilistic/Deterministic Seismic Hazard Analysis Approaches

“…The assessment of geological, hydrological, geomorphological, and vegetation features, once used only marginally to evaluate the seismic risk, plays a privileged and key role in the ESI scale approach. The ESI scale has also been applied to modern and paleo-earthquakes [24][25][26][27][28][29][30], providing significant input for a better evaluation of seismic hazards in different socio-economic contexts [31][32][33][34][35][36][37][38][39].…”

Earth Observation and GIS-Based Analysis for Landslide Susceptibility and Risk Assessment

“…The triggering mechanisms include a variety of external factors, such as intensive rainfalls, earthquakes (seismic-triggered landslides are classified as coherent, disrupted, and lateral spreads), speedy river erosion, landscape processes, and anthropogenic activities (deforestation and road construction in steep mountainous areas, uncontrollable irrigation, etc.) [12][13][14][15][16][17]. The designation of landslide risk areas can be achieved in one (or more) of the following ways: (a) landslide inventory maps, that display (at least) the geographical distribution of past events, followed by associated databases of landslide and terrain properties; (b) landslide susceptibility (LS) maps that refer to the tendency of an area to landslide occurrence-they depict the possibility of occurrence of a landslide event of a specific type at a particular place (where); (c) landslide hazard maps, which define the likelihood of occurrence of a potentially damaging landslide that may take place within a given area and period of time (where, how often, and how large)-this concept contains both spatial and temporal dimensions [8,18,19]; and (d) landslide risk maps that show potential damage or losses to individuals, infrastructure and property [20].…”

Comparison of Earthquake-Triggered Landslide Inventories: A Case Study of the 2015 Gorkha Earthquake, Nepal

“…Lekkas et al [33] used the ESI scale and its correlation with geological structures for seismic hazard estimation of the 2008 Mw 7.9 Wenchuan, China, earthquake. In another study by [34], correlations between ESI-07 intensity, slope, and lithology were discussed regarding landslides triggered by the 2016 Mw 7.8 Pedernales, Ecuador, earthquake.…”