M. Peyret

A new multilayered visco-elasto-plastic experimental model to study strike-slip fault seismic cycle

Nowadays, technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle. However, the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years. To overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters, we have developed a new experimental approach allowing for the simulation of strike-slip fault earthquakes and analyze in detail hundreds of successive seismic cycle. Model rheology is made of multilayered visco-elasto-plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle/ductile coupling, postseismic deformation phase and far-field stress transfers. The kinematic evolution of the model surface is monitored using an optical system, based on subpixel spectral correlation of high-resolution digital images. First, results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory. These results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth, along the fault plane. Our analog modeling approach appears, then, as an efficient complementary approach to investigate earthquake dynamics.

Roughness Characteristics of Oceanic Seafloor Prior to Subduction in Relation to the Seismogenic Potential of Subduction Zones

We have developed a new approach to characterize the seafloor roughness seaward of the trenches, as a proxy for estimating the roughness of the subduction interface. We consider that abrupt elevation changes over given wavelengths play a larger role in the seismogenic behavior of the subduction interface than the amplitude of bathymetric variations alone. The new database, SubRough, provides roughness parameters at selected spatial wavelengths. Here we mainly discuss the spatial distribution of short‐ (12–20 km) and long‐wavelength (80–100 km) roughness, RSW and RLW, respectively, along 250‐km‐wide strips of seafloor seaward of the trenches. Compared with global trend, seamounts show distinct roughness signature of much larger amplitudes at both wavelengths, whereas aseismic ridges only differ from the global trend at long wavelengths. Fracture zones cannot be distinguished from the global trend, which suggests that their potential effect on rupture dynamics is not the consequence of their roughness, at least not at these wavelengths. Based on RLW amplitude, segments along subduction zones can be defined from rough to smooth. Subduction zones like the Solomons or the Ryukyus appear dominantly rough, whereas others like the Andes or Cascadia are dominantly smooth. The relative contribution of smooth versus rough areas in terms of respective lateral extents probably plays a role in multipatch rupture and thus in the final earthquake magnitude. We observe a clear correlation between high seismic coupling and relatively low roughness and conversely between low seismic coupling and relatively high seafloor roughness.

How Subduction Interface Roughness Influences the Occurrence of Large Interplate Earthquakes

The role of seafloor roughness on the seismogenic behavior of subduction zones has been increasingly addressed over the past years, although their exact relationship remains unclear. Do subducting features like seamounts, fracture zones, or submarine ridges act as barriers, preventing ruptures from propagating, or do they initiate megathrust earthquakes instead? We address this question using a global approach, taking into account all oceanic subduction zones and a 117-year time window of megathrust earthquake recording. We first compile a global database, SubQuake, that provides the location of a rupture epicenter, the overall rupture area, and the region where the largest displacement occurs (the seismic asperity) for M W ≥ 7.5 subduction interplate earthquakes. With these data, we made a quantitative comparison with the seafloor roughness seaward of the trench, which is assumed to be a reasonable proxy for the subduction interface roughness. We compare the spatial occurrence of megathrust ruptures, seismic asperities, and epicenters, with two roughness parameters: the short-wavelength roughness R SW (12-20 km) and the long-wavelength roughness R LW (80-100 km). We observe that ruptures with M W ≥ 7.5 tend to occur preferentially on smooth subducting seafloor at long wavelengths, which is especially clear for the M W > 8.5 events. At both short and long wavelengths, seismic asperities show a more amplified relation with smooth seafloor than rupture segments in general. For the epicenter correlation, we see a slight difference in roughness signal, which suggests that there might be a physical relationship between rupture nucleation and subduction interface roughness. Plain Language Summary Subduction zones are regions on Earth where an oceanic plate dives below another plate. Earthquakes that occur along the contact between plates in such regions are among the largest and most destructive on Earth. To better understand where these large earthquakes are most likely to occur, we look at the effect of seafloor roughness. A rough seafloor is often characterized by many topographic features, such as seamounts or ridges, while a smooth seafloor is generally more flat. On a global scale, we compared the roughness of the incoming seafloor of the downgoing plate, with the occurrence of large earthquakes in each subduction zone. We find that the seafloor in front of large earthquakes is generally smoother than in areas where no large earthquakes have occurred. This is the clearest for very large earthquakes, with magnitudes larger than 8.5. Investigating which parameters play a role in the location of earthquakes helps us to understand where future earthquakes are more likely to occur.

Reservoir Characterization Using Inversion of a Combine Set of Geodetic Data, from Salt to Unconventional Exploitation

Optimizing the resource extraction and limiting the environmental constraint motivate to accurately characterize reservoirs. The extraction of resources induces volume change of the reservoir causing displacements in the surrounding medium up to the surface. The resulting surface deformation is usually significant enough to be measurable by geodetic instruments (GPS, satellites, tiltmeters, strainmeters). However, the data needs to be associated to a reservoir model using an inverse scheme to allow the estimation of physical properties of the reservoir. Complete geodetic data including InSAR, GPS, tilt, strain and gravimetric data are uncommon for conventional, unconventional or mining exploitations. In this study, we work on the one site that gathers a wide range of geodetic data: the salt exploitation of Vauvert, France, operated by KemOne. Our approach aims at estimating the volume changes of the cavities created by the extraction combining all the available geodetic data. To do so, we minimize a global functional including weighting factors for each data type. The weighting factors are optimally estimated for our study and can be adapted depending on the issue. Hence, an optimal distribution of data can be suggested for a specific reservoir characterization.