Impact of sea-level rise on earthquake and landslide triggering offshore the Alentejo margin (SW Iberia)

Abstract

Earthquakes and submarine landslides are recurrent and widespread manifestations of fault activity offshore SW Iberia. The present work tests the effects of sea-level rise on offshore fault systems using Coulomb stress change calculations across the Alentejo margin. Large-scale faults capable of generating large earthquakes and tsunamis in the region, especially NE-SW trending thrusts and WNW-ESE trending dextral strike-slip faults imaged at basement depths, are either blocked or unaffected by flexural effects related to sealevel changes. Large-magnitude earthquakes occurring along these structures may, therefore, be less frequent during periods of sea-level rise. In contrast, sea-level rise promotes shallow fault ruptures within the sedimentary sequence along the continental slope and upper rise within distances of <100 km from the coast. The results suggest that the occurrence of continental slope failures may either increase (if triggered by shallow fault ruptures) or decrease (if triggered by deep fault ruptures) as a result of sea-level rise. Moreover, observations of slope failures affecting the area of the Sines contourite drift highlight the role of sediment properties as preconditioning factors in this region.

Orbital‐ and Millennial‐Scale Changes in Lake‐Levels Facilitate Earthquake‐Triggered Mass Failures in the Dead Sea Basin

“…Previously suggested mechanisms for mass failures promoted by sea‐level rise include (a) enhanced rapid sedimentation causing greater overburden on slope sediments (Nisbet & Piper, 1998; Trincardi et al., 2003), and (b) increased water load enhancing seismicity (Brothers et al., 2013; Neves et al., 2016; Smith et al., 2013). In the Dead Sea case, relatively low sedimentation rates are statistically correlated with lake‐level rises and high‐stands at both the millennial‐ and orbital‐scales (Figures 3b–3d and 4e) (Lu, Bookman, et al., 2020; Lu, Waldmann, Nadel, & Marco, 2017), and thus do not support mechanism “(i).” Regarding the enhanced seismicity hypothesis, a complete paleoearthquake ( M w ≥ 5) record that covers the Last Glacial is currently lacking and we are therefore unable to evaluate this model.…”

“…Previously suggested mechanisms for mass failures promoted by sea-level rise include (a) enhanced rapid sedimentation causing greater overburden on slope sediments (Nisbet & Piper, 1998;Trincardi et al, 2003), and (b) increased water load enhancing seismicity (Brothers et al, 2013;Neves et al, 2016;Smith et al, 2013).…”

“…Despite numerous investigations on this topic, several schools of opinion exist. Some researchers demonstrate that lowering sea‐level can promote mass failures (Blumberg et al., 2008; Huhn et al., 2019; McHugh et al., 2002), while others suggest the opposite (Brothers et al., 2013; Neves et al., 2016; Trincardi et al., 2003).…”