ALBERT

Beschreibung: The slip rate along a fault controls the accumulation of strain that is eventually released during an earthquake. Along a 150-km-long stretch of the North Anatolian fault near Istanbul, Turkey, strain has been building up 2 since the last large earthquake in 1766. Estimates of the geodetic slip rates along the main Marmara fault vary widely, ranging between 17 and 27.9 mm yr-1 (refs 2-5). This slip rate is difficult to quantify because of the lack of satellite observations offshore and the complexity of the submarine fault system that includes the main Marmara fault2,6,7. Here we estimate the right-lateral slip rate on the main Marmara fault using a three-dimensional geomechanical model that incorporates these structural complexities. From our simulations we infer slip rates between 12.8 and 17.8 mm yr-1; our estimates are smaller and more variable than previous results, primarily because of slip partitioning and internal deformation. Our model results reconcile geodetic observations and geological fault slip rates8-10, which had been considered conflicting previously. We suggest that the inferred variability in slip rate on the main Marmara fault favours segmented release of seismic moment during consecutive events over the failure of the whole seismic gap in one large earthquake. © 2010 Macmillan Publishers Limited. All rights reserved.

Beschreibung: Constraints on the potential size and recurrence time of strong subduction-zone earthquakes come from the degree of locking between the down-going and overriding plates, in the period between large earthquakes. In many cases, this interseismic locking degree correlates with slip during large earthquakes or is attributed to variations in fluid content at the plate interface. Here we use geodetic and seismological data to explore the links between pore-fluid pressure and locking patterns at the subduction interface ruptured during the magnitude 8.8 Chile earthquake in 2010. High-resolution three-dimensional seismic tomography reveals variations in the ratio of seismic P-to S-wave velocities (V p /V s) along the length of the subduction-zone interface. High V p /V s domains, interpreted as zones of elevated pore-fluid pressure, correlate spatially with parts of the plate interface that are poorly locked and slip aseismically. In contrast, low V p /V s domains, interpreted as zones of lower pore-fluid pressure, correlate with locked parts of the plate interface, where unstable slip and earthquakes occur. Variations in pore-fluid pressure are caused by the subduction and dehydration of a hydrothermally altered oceanic fracture zone. We conclude that variations in pore-fluid pressure at the plate interface control the degree of interseismic locking and therefore the slip distribution of large earthquake ruptures. © 2014 Macmillan Publishers Limited. All rights reserved.

Beschreibung: Evaluating the transfer of stresses from megathrust earthquakes to adjacent segments is fundamental to assess seismic hazard. Here, we use a 3D forward model as well as GPS and seismic data to investigate the transient deformation and Coulomb Failure Stresses (CFS) changes induced by the 2010 Maule earthquake in its northern segment, where the Mw 8.3 Illapel earthquake occurred in 2015. The 3D model incorporates the coseismically instantaneous, elastic response, and time-dependent afterslip and viscoelastic relaxation processes in the postseismic period. We particularly examine the impact of linear and power-law rheology on the resulting postseismic deformation and CFS changes that may have triggered the Illapel earthquake. At the Illapel hypocenter, our model results in CFS changes of ∼0.06 bar due to the coseismic and postseismic deformation, where the coseismic deformation accounts for ∼85% of the total CFS changes. This is below the assumed triggering threshold of 0.1 bar and, compared to the annual loading rate of the plate interface, represents a clock advance of approximately only 2 months. However, we find that sixteen events with Mw ≥ 5 in the southern region occurred in regions of CFS changes 〉 0.1 bar, indicating a potential triggering by the Maule event. Interestingly, while the power-law rheology model increases the positive coseismic CFS changes, the linear rheology reduces them. This is due to the opposite polarity of the postseismic displacements resulting from the rheology model choice. The power-law rheology model generates surface displacements that fit better to the GPS-observed landward displacement pattern.