Insights from the geological record of deformation along the subduction interface at depths of seismogenesis

Subduction interfaces are loci of interdependent seismic slip behavior, fluid flow, and mineral redistribution. Mineral redistribution leads to coupling between fluid flow and slip behavior through decreases in porosity/permeability and increases in cohesion during the interseismic period. We investigate this system from the perspective of ancient accretionary complexes with regional zones of mélange that record noncoaxial strain during underthrusting adjacent to the subduction interface. Deformation of weak mudstones is accompanied by low-grade metamorphic reactions, dissolution along scaly microfaults, and the removal of fluid-mobile chemical components, whereas stronger sandstone blocks preserve veins that contain chemical components depleted in mudstones. These observations support local diffusive mass transport from scaly fabrics to veins during interseismic viscous coupling. Underthrusting sediments record a crack porosity that fluctuates due to the interplay of cracking and precipitation. Permanent interseismic deformation involves pressure solution slip, strain hardening, and the development of new shears in undeformed material. In contrast, coseismic slip may be accommodated within observed narrow zones of cataclastic deformation at the top of many mélange terranes. A kinetic model implies interseismic changes in physical properties in less than hundreds of years, and a numerical model that couples an earthquake simulator with a fluid flow system depicts a subduction zone interface governed by feedbacks between fluid production, permeability, hydrofracturing, and aging via mineral precipitation. During an earthquake, interseismic permeability reduction is followed by coseismic rupture of low permeability seals and fluid pressure drop in the seismogenic zone. Updip of the seismogenic zone, there is a post-seismic wave of higher fluid pressure that propagates trenchward.

Land Motion Offers Insights into Cascadia Earthquake Cycle

Comparing recent GPS data with a longer record of sea level along the western coast of North America allows researchers to home in on interseismic deformation above the Cascadia megathrust.

Interseismic Deformation in the Gulf of Aqaba Inferred from GPS Measurements

<p>The Dead Sea Transform fault forms the boundary between the Arabian plate and the Sinai-Levant subplate. Several aspects of this fault system have been extensively studied during the last century. However, the present-day kinematics and deformation along its southern end in the Gulf of Aqaba remain poorly understood. Here we present a crustal motion velocity field based on three GPS surveys conducted between 2015 and 2019 at 30 campaign sites, complemented by 12 permanent stations operating near the gulf. We constrained a pole of rotation for the Sinai-Levant subplate based on five selected stations on the Sinai Peninsula. This Euler pole predicts a left-lateral slip rate of ~4.5 mm/yr on the fault system in the gulf, consistent with earlier findings. We find that standard models of interseismic deformation, such as back-slip and screw dislocation models do not provide a reasonable constraint on fault locking depths due to limited near-fault measurements. Despite this, our results reveal a small (~1 mm/yr) but systematic left-lateral residual motion across the gulf that cannot be resolved by elastic models of strain accumulation. We further find that the orientation of these residuals agrees with modelled postseismic transient motions caused by the 1995 M<sub>W</sub> 7.2 Nuweiba earthquake in the NE and SW quadrants relative to the gulf trend. Combined, these observations suggest that postseismic deformation caused by the Nuweiba earthquake may still be ongoing. We anticipate our findings to be a starting point for future geodetic studies in the northern Red Sea region where large-scale infrastructure mega-projects, such as the NEOM city and the King Salman bridge across the gulf are being developed. Future studies would benefit from incorporating additional GPS stations on the Sinai side of the gulf, refined finite-fault models, seafloor geodetic measurements and better information about past earthquakes.</p>