Many rainfall-induced damaging slope failures occur each year in the tectonically active Apennine Mountains (Italy), where weak lithologies are widespread. Moreover, several cases of recent moderate magnitude earthquakes and long-term historical records provide evidence for the seismic triggering of landslides and other ground failures. Such evidence is very scarce for the little-studied low elevation SE portion of the Apennines, the Daunia Mountains (Apulia region), which include 25 hilltop towns in an area of ~2000 km2. Made of clay-rich flysch formations (Late Cretaceous-Miocene) disrupted by the Apennine frontal thrusts, the Daunia Mts. are known to be prone to rainfall-induced landsliding. To investigate the susceptibility to earthquake-induced slope failures, we use the results of our multi-temporal landslide inventory, which revealed the presence of hundreds of ancient (of unknown cause) very large (>2X105m2) landslides in Daunia. They originate at upper slopes and their spatial distribution indicates possible links with the seismo-tectonics of the region, as the areas with the higher landslide frequency (NW and SE parts of Daunia) are located close to the known seismogenetic sources of M>6 events. These two areas are lithologically and topographically similar to the middle part of Daunia having fewer large landslides. To gather additional evidence for the possible seismic origin of the ancient large landslides, we selected two such failures from the NW part of Daunia, where we could benefit from our detailed geological-geomorphological mapping, as well as the geotechnical data needed for slope stability analysis. The location of the failures, within 25 km from the epicenter of the 6.7M 1627 earthquake, facilitated the choice of an appropriate seismic input for dynamic analysis. Numerical modeling indicated that the two slopes are unlikely to fail without earthquake loading even when improbably high groundwater levels are assumed. The dynamic analysis indicated that both slopes would have likely failed (Newmark displacement threshold exceeded) under seismic shaking comparable to that of the 1627 earthquake. The presented evidence is circumstantial, but the origin and age of the large slope failures in Daunia should be clarified within the ongoing Seismic Microzonation of the Apulia region.
Unravelling the origin of large ancient landslides in low elevation Daunia Mountains, Italy
J Wasowski;L Pisano;N L Fazio;D De Lucia;A Ugenti;V Zumpano;F Filice;D Casarano;F Santaloia;P Lollino
2022
Abstract
Many rainfall-induced damaging slope failures occur each year in the tectonically active Apennine Mountains (Italy), where weak lithologies are widespread. Moreover, several cases of recent moderate magnitude earthquakes and long-term historical records provide evidence for the seismic triggering of landslides and other ground failures. Such evidence is very scarce for the little-studied low elevation SE portion of the Apennines, the Daunia Mountains (Apulia region), which include 25 hilltop towns in an area of ~2000 km2. Made of clay-rich flysch formations (Late Cretaceous-Miocene) disrupted by the Apennine frontal thrusts, the Daunia Mts. are known to be prone to rainfall-induced landsliding. To investigate the susceptibility to earthquake-induced slope failures, we use the results of our multi-temporal landslide inventory, which revealed the presence of hundreds of ancient (of unknown cause) very large (>2X105m2) landslides in Daunia. They originate at upper slopes and their spatial distribution indicates possible links with the seismo-tectonics of the region, as the areas with the higher landslide frequency (NW and SE parts of Daunia) are located close to the known seismogenetic sources of M>6 events. These two areas are lithologically and topographically similar to the middle part of Daunia having fewer large landslides. To gather additional evidence for the possible seismic origin of the ancient large landslides, we selected two such failures from the NW part of Daunia, where we could benefit from our detailed geological-geomorphological mapping, as well as the geotechnical data needed for slope stability analysis. The location of the failures, within 25 km from the epicenter of the 6.7M 1627 earthquake, facilitated the choice of an appropriate seismic input for dynamic analysis. Numerical modeling indicated that the two slopes are unlikely to fail without earthquake loading even when improbably high groundwater levels are assumed. The dynamic analysis indicated that both slopes would have likely failed (Newmark displacement threshold exceeded) under seismic shaking comparable to that of the 1627 earthquake. The presented evidence is circumstantial, but the origin and age of the large slope failures in Daunia should be clarified within the ongoing Seismic Microzonation of the Apulia region.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
