Special seminar: Maxime HENRIQUET, CEREGE

"Seismic cycle of faults in the intra-continental domain: example of the Petrinja fault and earthquake (2020, Croatia) based on morphotectonic and geodetic analyses".

Summary :

On 29 December 2020, central Croatia was hit by an earthquake of Mw 6.4, causing extensive damage in the region of Petrinja, a small town located ~ 40 km southeast of the capital Zagreb. The earthquake was the strongest in Croatia in the last 100 years and among the largest in Europe on a strike-slip fault.

In order to better constrain the seismic cycle associated with young and reactivated unstripping faults in an intraplate context, the work I will present is based on the Petrinja fault and the 2020 earthquake. The focus is on the modalities of stress accumulation and release at complementary time scales, from coseismic rupture to topographically recorded cumulative deformation.

The coseismic surface deformation field associated with the 2020 earthquake is constrained by GNSS measurements from civilian near-field networks, as well as InSAR data and correlation of optical images (Pleiades and Worldview satellites). These geodetic data are inverted to characterise the seismic source, and compared with surface ruptures collected in the field to assess the location of the deformation. Elastic inversion of the geodetic benchmarks reveals that the rupture occurred on a sub-vertical fault, at shallow depth ( 70% of the slip is probably distributed at the surface. The joint inversion of geodetic landmarks, optical image correlation and InSAR data will enable us to strengthen our understanding of the source of the 2020 earthquake.

At the same time, morphotectonic analysis of the Petrinja fault is enabling us to quantify the cumulative deformation along this fault, and by dating certain geomorphological markers (alluvial cones and terraces) we are seeking to constrain its loading rate. Using field observations and high-resolution topographic data (LiDAR and Pleiades tri-stereo DTM), we have accurately mapped the fault trace, highlighted in several places by the offset of geomorphological markers (incisions, terraces and alluvial fans) which have recorded cumulative displacements ranging from 5 to > 50 m and potentially up to ~180 m. The mapped fault is discontinuous, with deformation absorbed by a series of small segments (< 5 km). This probably reflects recent transpressive deformation marked by an immature fault system, in agreement with the seismologically derived source parameters of the 2020 earthquake. Some markers have been dated (14C on coals and cosmogenic nuclide 36Cl for carbonate deposits) to estimate the slip rate of the fault, and preliminary results suggest a long-term slip rate of around 1 mm/yr in the central zone.

Finally, the 2020 surface rupture mainly affected the northern section of the Petrinja fault, while the cumulative displacements mapped appear to be greater along the southern section. A better understanding of the seismic history of the entire fault system is therefore crucial for assessing the seismic risk in this region.

This seminar is open to everyone and will also be accessible via zoom with the following link: https://univ-amu-fr.zoom.us/j/85025661948?pwd=K09LZGx5OWF6cm11UXYxSEFmVm9oZz09

This seminar is part of the series of seminars for candidates for the position of Senior Lecturer open in section 35 (Profile: Dynamics of continental surfaces in response to tectonic and/or climatic forcing) for CEREGE this year

Location: Room 205