Isabelle Ryder

The 2010 Mw 8.8 Maule, Chile earthquake: Nucleation and rupture propagation controlled by a subducted topographic high

Knowledge of seismic properties in an earthquake rupture zone is essential for understanding the factors controlling rupture dynamics. We use data from aftershocks following the Maule earthquake to derive a three-dimensional seismic velocity model of the central Chile forearc. At 36°S, we find a high v_p (>7.0 km/s) and high v_p/v_s (∼1.89) anomaly lying along the megathrust at 25 km depth, which coincides with a strong forearc Bouguer gravity signal. We interpret this as a subducted topographic high, possibly a former seamount on the Nazca slab. The Maule earthquake nucleated at the anomalys updip boundary; yet high co-seismic slip occurred where the megathrust is overlain by lower seismic velocities. Sparse aftershock seismicity occurs within this structure, suggesting that it disrupts normal interface seismogenesis. These findings imply that subducted structures can be conducive to the nucleation of large megathrust earthquakes, even if they subsequently hinder co-seismic slip and aftershock activity.

Coseismic Tectonic Surface Deformation during the 2010 Maule, Chile, M w 8.8 Earthquake

Tectonic deformation from the 2010 Maule (Chile) Mw 8.8 earthquake included both uplift and subsidence along about 470 km of the central Chilean coast. In the south, deformation included as much as 3 m of uplift of the Arauco Peninsula, which produced emergent marine platforms and affected harbor infrastructure. In the central part of the deformation zone, north of Constitución, coastal subsidence drowned supratidal floodplains and caused extensive shoreline modification. In the north, coastal areas experienced either slight uplift or no detected change in land level. Also, river-channel deposition and decreased gradients suggest tectonic subsidence may have occurred in inland areas. The overall north-south pattern of 2010 coastal uplift and subsidence is similar to the average crestal elevation of the Coast Range between latitudes 33°S and 40°S. This similarity implies that the topography of the Coast Range may reflect long-term permanent strain accrued incrementally over many earthquake cycles.