CONSTRUCTING FOREARC ARCHITECTURE WITH MEGATHRUSTS: GEOLOGICAL AND GEOPHYSICAL EXAMPLES FROM THE 2010 MAULE EARTHQUAKE REGION
In the Maule earthquake region as well as in others subduction zones, both geodetic and seismic data show an alternation of the forearc deformation style across the seimic cycle. Large coseismic normal faulting and extension parallel to the subduction rebound follows great subduction earthquakes. Generally minor reverse kinematics and convergence-parallel shortening are observed interseismically. Although smaller than the Pichilemu sequence, an interseismic Mw6.3 crustal reverse earthquake was recorded in the forearc 20 years prior to the Maule megathrust. Paleoseismological evidence in Japan and northern Chile indicates that the long-lived, forearc normal faults may have recurrence times an order of magnitude longer than the subduction cycle.
The shallow crustal normal faults reactivated by the 2010 Maule earthquake show a consistent kinematic history throughout thousands of subduction seismic cycles. We propose that the normal fault-dominated architecture of the forearc may have been constructed by repetition of megathrusts. Evidence for Quaternary reverse faulting suggests that the interseismic deformation signature may also be preserved in the structural grain. Analogous observations along the 2011 Tōhoku earthquake rupture in Japan imply that such link between the short- and long-term deformation patterns of the forearc are not exclusive of the Maule earthquake region.