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Multidisciplinary Quaternary Deformation Analysis in a Complex Low Tectonic Setting–The Example of SW Portugal, Europe

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems II

Type: Oral

Date: 4/21/2021

Presentation Time: 02:45 PM Pacific

Description: 

Studies of active tectonics can be challenging in areas with low strain rates and long recurrence periods. Increased difficulty can arise from complex surface processes that mask or obliterate deformation. Nonetheless, these are tectonically active areas capable of infrequent moderate to large magnitude seismicity that can impact and disrupt society. One such case is the SW of Portugal, close to theAfrica-Eurasia plate boundary (4-5 mm/yr) which drives the Quaternary reactivation of several inherited structures. Individual slip-rates are low, ranging up to a few 0.1 mm/yr with recurrence periods of tens of ka, however some structures are large enough to produce large magnitude events like the Mw ≥8 1755 Lisbon EQ. Erosion processes are dominant, affecting preservation of Q sediments and landforms. To overcome the challenges, we performed a multidisciplinary analysis combining and cross-correlating different tools and approaches. Long and short term deformations were investigated primarily by geologic and geomorphologic analyses complemented with geophysics, remote sensing and geodesy. The dominance of erosion constraint applying geochronology methods and led to difficulties to interpret distribution of deformation in time and space. To overcome this, we did a regional morphotectonic analyses built on a set of morphotectonic indices. As expected, different indices show different sensibilities to the landscape and by themselves may not provide sufficient information. However, their cross-correlation allowed an adequate interpretation for a tectonic forcing, even in a low tectonic rate setting. Results demonstrate that SW Portugal is undergoing uplift at higher rates than neighboring areas and is delimited by major active structures. A geodetic analysis based on ~20 years data suggests that SW Portugal is accommodating deformation differently, behaving as a tectonic block. A careful “geo” multidisciplinary approach is crucial to validate observations and recognize “non-obvious” yet hazardous "slow" active structures.

Presenting Author: Paula M. Figueiredo

Student Presenter: No

Authors