Quaternary fault kinematics in the northwestern Espanola Basin, Rio Grande rift, New Mexico
— Karen E. Carter and Jamie N. Gardner

Rift -margin faulting in the northern part of the Española Basin, Rio Grande rill, appears in be migrating east toward the basin center, and is expressed as N-trending fault zones that show Holecene displacements.  This small pan of the rift, (170 km² area), has extended at least 5% in a general E-W direction Since 1.2 Ma. Extension has been accommodated on five major N-trending fault zones composed of NW- to NE-striking, high angle normal faults that terminate in diffuse fracture zones. Faults are concave toward the hanging wall, which is preferentially dissected by minor synthesis. and antithetic splays. At the western margin of the basin, two faults show down-to-the-west motion with displacement of Quaternary rooks increasing toward the south to a maximum of  34 m. East, toward the basing center, two faults show down-to-the-east motion with displacement of Quaternary rocks increasing toward the north to a maximum of 37 m. Therefore, from west to east, the looks have opposing dips, concavity, displacement gradients and sense of motion, suggesting that deformation is roughly symmetrically and homogeneously distributed across the area. This movement history, combined with microseismic activity on basin-center faults and ages of faulted and unfaulted Holocene sediments, suggests that ( I) faults a formed in response to approximately E- to NE-directed extension in the past 1.2 Ma; (2) faulting within the basin could he advancing toward the basin center; and (3) total extension across this part of the Española Basin has been 5% since 1.2 Ma.