Southward propagation of the Marlborough Fault System: Fault linkage and blind faults in North Canterbury

摘要

Geomorphological and paleoseismic studies provide insight into the fault geometry and kinematics of a series of dextral northeast striking faults, including the Porters Pass, Hawdon, Bullock Hill, and Esk faults, in the South Island of New Zealand. These faults show post-glacial offsets that are significantly larger than predicted from co-seismic displacement - surface rupture length regressions derived from empirical relationships. Geomorphological mapping reveals slip rates as high as 9 mm/year for the Hawdon fault and Bullock Hill fault over an expected fault length of c. 140 km. Surface expressions of some parts of the studied faults are obscured by glacial gravels, indicating that blind faults are present in parts of the Sourthern Alps and may be the source for a component of a reported slip deficit in North Canterbury. Concluding from comparing scalingrelationship results for the individual faults I hypothesize that the Porters Pass, Hawdon, Bullock Hill and Esk faults are segments of an incipient fault system that stretches from the western tip of the Porters Pass fault to the Hope fault, east of Hanmer Springs. Considering the location, similar strike and dextral deformation mode, I suggest that this 140 km long dextral strike-slip fault system marks the southernmost extension of the Marlborough Fault System resulting from the ongoing southward propagation of the Pacific-Australian plate boundary in New Zealand's South Island.