MODEXSIS Project -

Modeling Strike-slip fault seismic cycle and Earthquake Dynamics

By Yannick Caniven

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 the active fault seismic cycle. However, the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquakes and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years.

Figure 1: General view of the strike-slip fault experimental set-up at the Geosciences Montpellier Analog Modeling Lab. (LMA). The experimental device consists of a rigid aluminum structure supporting two compartments mounted on two horizontal linear-guided systems controlled by a computerized motoreductor. Both compartments have similar sizes of 1.2m× 0.7m× 0.12m and are in contact along their longest dimension. They represent the two compartments of a strike-slip fault and move in the opposite directions at a constant velocity ranging from 1 to 7 μm/s (0.35 cm/h to 2.5 cm/h). Compartment displacements are measured using a laser telemeter and image processing analysis.

To overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters, we have developed a new experimental model allowing for the simulation of strike-slip fault earthquakes and analyzing in detail hundreds of successive seismic cycles (Caniven et al., 2015).

Figure 2: a) Schematic cross-section of the experimental device showing its internal mechanical structure, the geometry of analog material layers, and how boundary conditions (initial normal stress and loading rate) are controlled. b) Model surface horizontal displacements are monitored using the sub-pixel image correlation technique. Numerical modeling tools are used to analyze model deformation at the surface and at depth. From Caniven et al., (2015).

Model rheology is made of multi-layered visco-elasto-plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle/ductile coupling, post-seismic deformation phase, and far-field stress transfers. The kinematic evolution of the model surface is monitored using an optical system, based on sub-pixel spectral correlation of high-resolution digital images (Figure 2).

Figure 3: Example of analog interseismic, coseismic, and postseismic phases (from left to right). Top: Amplitude of horizontal fault parallel surface displacements. Bottom: Fault perpendicular displacement profiles. The insets show comparisons to examples of geodetic velocity profiles acquired for natural cases. From Caniven et al., (2015).

Time-lapse extract of a typical strike-slip fault experiment. Each stage is separated from the previous one by 5s. Upper left and lower left illustrations show incremental horizontal displacements (vector field and amplitude). The upper right is an InSAR-like representation and the lower left graphic shows surface motions along the fault.

The model succeeds in reproducing the deformation mechanisms and surface kinematics associated with the main phases of the seismic cycle indicating that model scaling is satisfactory (Figure 3 and Time Lapse). This is also supported by the analyses of relationships between earthquake parameters (e.g. maximum vs average displacement vs rupture length) and comparisons to available earthquake scaling laws (Figure 4). 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.

Figure 4: a) Fault parallel horizontal displacements vs normalized distance along the fault (half profiles). b) Maximum displacement (Dmax) vs average displacement (Dmean) from profiles of the graph (a). c) Half maximum fault parallel displacements (Dmax1, Dmax2) vs half rupture length (L1, L2). d) Surface displacements aspect ratio (Sar): major (Le) vs minor (We) axis of average displacement (Dmean) isocontour. From Caniven et al., (2015).

Using this strike-slip experimental model, we especially investigated the role played by along-fault non-uniform and asymmetric applied normal stress on both coseismic slip and long-term fault behavior (Caniven et al., 2017). Uniform or heterogeneous applied normal stress along the fault plane is imposed and maintained constant during the whole experiment duration. Our results suggest that coseismic slip patterns are strongly controlled by variations in fault strength and subsequent accumulated shear stress along fault strike. Major microquakes occur preferentially in zones of major shear stress asperities (Figure 5).

Figure 5: a) 64 fault slip profiles (fault parallel component of horizontal surface displacements) that occurred successively during the studied period and respective maximum slip Dmax (colored points) for Strong Coseismic (SC) events (red), Post-Seismic (PS) events (green), Low-to-Moderate Coseismic (LMC) events (blue). Dashed black line shows normalized syy distribution along the fault trace b) Dmax along the fault vs Time. c) Locations of Dmax along the fault vs Time. Red ellipses and red arrows indicate sequences of left-ward migration of events. Dotted black circles indicate single moderate events. The white-black shaded background indicates the syy distribution along the fault trace (from the dashed profile) with the highest compressions in white. From Caniven et al., (2017).

Coseismic slip distributions exhibit a pattern similar to the along-fault applied normal stress distribution. The occurrence of isolated low to moderate microquakes where residual stresses persist around secondary stress asperities, indicates that stress conditions along the fault also control the whole variability of fault slip events (Figure 6).

Figure 6: a) Evolution of the cumulated horizontal displacement (fault-parallel component) at two different sites located close to the fault trace. The zoom on top shows both curves over stacked, with cumulated fault displacement normalized to the maximum value (Norm. Displacement). This allows us to better compare the slip behavior at the two sites. The inset right-below shows the σyy distribution along the fault trace and locations of observation sites. b) Instantaneous horizontal displacement parallel to the fault at the two sites. From Caniven et al., (2017).

Moreover, our experiment suggests that the along-fault stress heterogeneity caused by local variations of the imposed normal stress influences the regularity of the seismic cycle and, consequently, long-term fault slip behavior. Uniform applied normal stress favors irregular seismic cycles and the occurrence of earthquake clustering, whereas non-uniform normal stress with a single high amplitude stress asperity generates strong characteristic microquake events with stable return periods. Our results strengthen the assumption that coseismic slip distribution and earthquake variability along an active fault may provide relevant information on long-term tectonic stress and could thus improve seismic hazard assessment.

Learn more:

-> Caniven, Y., Dominguez, S., Soliva, R., Cattin, R., Peyret, M., Marchandon, M., Romano, C., and Strak, V., 2015. A new multilayered visco-elasto-plastic experimental model to study strike-slip fault seismic cycle. Tectonics, 34: 232–264, https://doi.org/10.1002/2014TC003701

-> Caniven, Y., Dominguez, S., Soliva, R., Peyret, M., Cattin, R., 2017. Relationships between along-fault heterogeneous normal stress and fault slip patterns during the seismic cycle: Insights from a strike-slip fault laboratory model, Earth and Planetary Science Letters, Elsevier, 480, pp.147-157. https://doi.org/10.1016/j.epsl.2017.10.009

See also:

-> Caniven, Y., and Dominguez, S., 2021. Validation of a multilayered analog model integrating crust-mantle visco-elastic coupling to investigate subduction megathrust earthquake cycle, JGR, Accepted (In Press).