Transgranular Fractures in the Damaged Zone of the Punchbowl Fault
Abstract
Understanding faults is challenging but not impossible. Looking at the Punchbowl fault, an ancient trace of the San Andreas Fault in the Transverse Ranges of southern California, is one way to understand a fault that has been studied for years and still hasn’t been fully understood. I am interested in grasping the formation and structures of the damage zone of large displacement continental transform faults, in particular the San Andreas Fault. To do this, I characterized the fractures in the damage zone of the Punchbowl Fault. The fractures associated with the Punchbowl Fault include open mode fractures, transgranular cracks, transgranular filled cracks, calcite filled veins, hematite filled veins, shear fractures, and the list continues. The Punchbowl formation rock samples had already been gathered by other students and I went back and looked at new traits of the fracture system, specifically on the microscale. I separated the fractures into three categories; open fractures (OF), shear fractures (SF), and shear fractures with fill (SOF). Each of these rock samples were put on thin sections to observe on a microscale. Eventually I was able to count the number of fractures on a coarse grid and determine the fracture density. The fracture density data showed a decrease in fracture density the further away the samples were located. The primary focus was mainly on the shear fractures and open mode fractures these were the largest fractures in the thin sections. I focused on these to make sure that the fracture densities would follow those of other ancient traces of the SAF. I found that the damage zone of the San Gabriel Fault [Becker, 2012] and the San Andreas Fault at the San Andreas Fault Observatory at Depth [Ayyildiz, 2012] both matched the fracture density assortment I found for the Punchbowl fault.
Citation
Zambrano, Melissa (2013). Transgranular Fractures in the Damaged Zone of the Punchbowl Fault. Undergraduate Research Scholars Program. Available electronically from https : / /hdl .handle .net /1969 .1 /164404.