Dynamic implications of Baja California microplate kinematics on the North America - Pacific plate boundary region

Many plate boundaries appear to be broad deformation zones,
composed of several smaller microplates (e.g. California, Alaska,
Mediterranean sea). To accurately address plate boundary
deformation, as needed for seismic hazard assessment, it is
important to study the motion of these microplates. Furthermore the
dynamics of microplates, such as their driving forces and the
implication of their motion on the surrounding plate boundary
region are not well understood. Following suggestions from previous
studies that Baja California is a microplate located within the
North America – Pacific plate boundary region, a kinematic study
using horizontal velocity data from Global Positioning System was
performed. Building on the kinematic results and using numerical
modelling techniques, a 2D mechanical model that simulates the
transport of the Baja California microplate by lithospheric
coupling with the Pacific plate was created. This model addresses
the transport forces, and necessary preconditions in the North
America – Pacific plate boundary region for rigid microplate
transport. In addition, this model provides insights on the
deformational response of western North America to Baja California
motion, in particular the kinematic response of neighbouring
microplates and the activation of passive fault systems. This
latter was examined in more detail by separating the contribution
of deformation from Baja California microplate motion and Sierra
Nevada microplate motion to the formation of the Eastern California
Shear Zone. Overall, it was found, that microplates play an
important role for plate boundary kinematics and that their motion
strongly influences the dynamics and fault evolution in plate
boundary regions.