Off-fault Damage Associated with a Localized Bend in the North Branch San Gabriel Fault, California
MetadataShow full item record
Structures within very large displacement, mature fault zones, such as the North Branch San Gabriel Fault (NBSGF), are the product of a complex combination of processes. Off-fault damage within a damage zone and first-order geometric asperities, such as bends and steps, are thought to affect earthquake rupture propagation and energy radiation, but the effects are not completely understood. We hypothesize that the rate of accumulation of new damage decreases as fault maturity increases, and damage magnitude saturates in very large displacement faults. Nonetheless, geometric irregularities in the fault surface may modify damage zone characteristics. Accordingly, we seek to investigate the orientation, kinematics, and density of features at a range of scales within the damage zone adjacent to an abrupt 13 degree bend over 425 m in the NBSGF in order to constrain the relative role of the initiation of new damage versus the reactivation of preexisting damage adjacent to a bend. Field investigation and microstructural study focused on structural domains before, within, and after the fault bend on both sides of the fault. Subsidiary fault fabrics are similar in all domains outside the bend, which suggests a steady state fracture density and orientation distribution is established on the straight segments before and after the bend. The density of fractures within and outside the bend is similar; however, subsidiary fault orientations and kinematics are different within the bend relative to the straight segments. These observations are best explained by relatively low rates of damage generation relative to rates of fault reactivation during the later stages of faulting on the NBSGF, and that damage zone kinematics is reset as the host rock moves into the bend and again upon exiting the bend. Consequently, significant energy released during earthquake unloading can be dissipated by reactivation and slip on existing fractures in the damage zone, particularly adjacent to mesoscale faults. Thus, areas of heightened reactivation of damage, such as adjacent to geometric irregularities in the fault surface, could affect earthquake rupture dynamics.
SubjectEarthquake Rupture Energetics
North Branch San Gabriel Fault
Becker, Andrew 1987- (2012). Off-fault Damage Associated with a Localized Bend in the North Branch San Gabriel Fault, California. Master's thesis, Texas A&M University. Available electronically from
Showing items related by title, author, creator and subject.
Development of secondary faults between en echelon, oblique-slip faults: examples from basement controlled, small-fault systems in the Llano Uplift of central Texas Hedgcoxe, Howard Reiffert (Texas A&M University, 1987)Not available
Evaluation of faulting characteristics and ground acceleration associated with recent movement along the Meers Fault, Southwestern Oklahoma Burrell, Richard Dennis (Texas A&M University, 1997)Recent studies have shown that a 27 km section of the Meers Fault was reactivated during Holocene time. Although these studies have proven the occurrence of recent fault activity, many basic characteristics of the faulting ...
Cohrs, Frelynn Joseph Reese (2012-07-16)Independent sets of reflection seismic and seismoelectric data were collected, processed, and interpreted with the aim of generating and studying guided waves within a fault zone. While seismic surveys have recently been ...