Abstract
On August 16th, 2018, a Mw 5.1 earthquake struck the Molise region (central Italy), inducing 84 earthquake-triggered landslides that predominantly involved soil covers of clayey materials and flysch on gently dipping slopes. To quantify the spatiotemporal landslide activity in the months immediately after the earthquake, a differential SAR interferometry (DInSAR) analysis was performed for a time span from 2 years before to one year after the earthquake, recognising both first-time and reactivated landslides. The results showed a clear increase in landslide activity following the low-magnitude earthquake with respect to the activities recorded in the same months of the previous years. Several coherent landslides (earth slides and earth flows) were observed following seasonally recurrent rainfall events. Such increases were observed for both reactivated and first-time landslides, showing decreases in inactive periods and activity over longer periods. Furthermore, the spatial density distribution of the landslides was investigated in the postseismic time interval along transects perpendicular and parallel to the direction of the tectonic element responsible for the seismic event. An asymmetrical distribution was deduced parallel to the fault strike with a higher number of landslides located inside the compressional sector according to a strike-slip faulting mechanism.
Highlights
Earthquake-triggered landslides (EqTLs) represent one of the major geological hazards in mountainous and hilly areas and are one of the main seismically induced ground effects[1]
While increases in erosion and landslide rates were registered after strong earthquakes in recent decades on predisposed slopes featuring a weak soil cover or weakened substratum and high susceptibility to landslides, this effect could be relevant after relatively low-magnitude earthquakes, contributing as an acquired legacy to the aggravation of postseismic rainfall-induced landslide s usceptibility[18]
The inference of soil moisture and seasonal saturation of the involved debris covers requires a high number of episodes to perform a reliable statistical analysis of earthquake-induced effects
Summary
Earthquake-triggered landslides (EqTLs) represent one of the major geological hazards in mountainous and hilly areas and are one of the main seismically induced ground effects[1]. Postseismic ground effects are documented to be as effective as coseismic e ffects[2], inducing or promoting prolonged erosion and perturbations of stream network muss budgets by increasing the sediment load in r ivers[3–5] These conditions pertain to natural slopes in tectonically active areas, where seismic shaking can weaken rock masses or soils, leaving them free to be flushed and eroded from h illslopes[3]. Impulsive shaking plays a prominent role in increasing the landscape sensitivity of the involved areas to meteoclimatic forcing after e arthquakes[7], which can be quantified by a reduction in critical rainfall threshold[1,10–12] or a reduction in strength that reflects an increase in landslide rates This erosive response is proved to be linked to the character of seismic shaking[3] (i.e., usually expressed by the peak ground acceleration (PGA) or the Arias intensity) and is markedly effective in the epicentral areas, where most EqTLs are r egistered[13,14] and where the most effective tectonic and seismological control in the near-fault region is e xpected[15–17]. Control by tectonic and faulting mechanisms in the distribution of EqTLs in coseismic stages, reported in datasets of ground failures worldwide[1,19], has been evaluated postseismic stages, analysing the spatial density and directional distributions with respect to the strike-slip faulting mechanism
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