Chemical and Physical Characteristics of Pulverized Tejon Lookout Granite Adjacent to the San Andreas and Garlock Faults: Implications for Earthquake Physics

Rockwell, T.; Sisk, M.; Girty, Gary H.; Dor, O.; Wechsler, Neta; Ben‐Zion, Yehuda

doi:10.1007/978-3-0346-0138-2_9

Cited by 19 publications

(57 citation statements)

References 25 publications

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“…Our study shows that the pulverized rock accounts for half the damage zone width on the northeastern block, followed by variably fractured rock from 50 to 100 m toward the outer damage zone boundary (Figure ). At the outcrop scale, pulverized rocks of the study site show a powdered white texture when crushed in the hand, similar to samples from various other pulverized granite outcrops along the SAF, such as that of the Tejon Lookout granite in Tejon Pass [ Rockwell et al ., ; Wilson et al ., ]. In detail, our microstructural observations combined with the observed fairly systematic directional dependence of ultrasonic velocities of samples, suggest that microfractures and shear zones are in a fault‐parallel to subparallel orientation (Figures , , and ).…”

Section: Discussionmentioning

confidence: 99%

“…Only in recent years have pulverized rocks been reported along various sections of the SAF [ Brune , ; Dor et al ., ; Dor et al ., ; Dor et al ., ; Rockwell et al ., ; Wilson et al ., ], farther to the north on the Garlock fault [ Rockwell et al ., ], and to the west on the San Jacinto fault [ Rockwell et al ., ; Wechsler et al ., ]. Dor et al .…”

Section: Geology Fault Structure and Field Methodsmentioning

confidence: 99%

“…Pulverized fault zone rocks from along the San Andreas fault (SAF) and other large displacement faults such as the Arima‐Takatsuki Tectonic Line [ Mitchell et al ., ] and North Anatolian fault [ Dor et al ., ] have previously been investigated with respect to their distribution and unique physical characteristics [ Agosta and Aydin , ; Billi and Di Toro , ; Brune , ; Dor et al ., ; Dor et al ., ; Rockwell et al ., ; Wilson et al ., ]. Unlike typical fault zone rocks, such as cataclasites and breccias that reveal accommodation of deformation by localized shear, grain rolling, and grain size reduction [ Blenkinsop , ], pulverized rocks are characterized by pervasive micro‐scale damage due to fragmentation of grains down to the micron‐range while still maintaining the original grain boundaries and rock fabric.…”

Section: Introductionmentioning

confidence: 99%

“…Lacking indications for macroscopic shear strain, the fragmentation appears associated with a high density of opening mode microfractures. Such structures have previously been interpreted as a product of dynamic stress fluctuations, hence the occurrence of pulverized fault zone rocks has been associated with earthquake rupture [ Brune , ; Doan and d ' Hour , ; Doan and Gary , ; Dor et al ., ; Mitchell et al ., ; Rockwell et al ., ; Wilson et al ., ; Yuan et al ., ].…”

Section: Introductionmentioning

confidence: 99%

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Damage and seismic velocity structure of pulverized rocks near the San Andreas Fault

et al. 2013

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[1] A combination of seismic refraction tomography, laboratory ultrasonic velocity measurements, and microstructural observations was used to study the shallow velocity structure of a strand of the San Andreas fault (SAF) just south of Littlerock, California. The examined site has a strongly asymmetric damage structure with respect to the SAF core. The conglomerates to the southwest show little to no damage, whereas a~100 m wide damage zone exists to the northeast with a~50 m wide zone of pulverized granite adjacent to the fault core. Seismic P-wave velocities of the damaged and pulverized granite were investigated over a range of scales. In situ seismic velocity imaging was performed on three overlapping profiles normal to the SAF with lengths of 350 m, 50 m, and 25 m. In the laboratory, ultrasonic velocities were measured on centimeter-to decimeter-sized samples taken along the in situ profiles. The samples were also investigated microstructurally. Micro-scale fracture damage intensifies with increasing proximity to the fault core, allowing a subdivision of the damage zone into several sections. Laboratory-derived velocities in each section display varying degrees of anisotropy, and combined with microfracture analysis suggest an evolving damage fabric. Pulverized rocks close to the fault exhibit a preferred fault-parallel orientation of microfractures, resulting in the lowest P-wave velocity orientated in fault-perpendicular direction. Closest to the fault, pulverized rocks exhibit a gouge-like fabric that is transitional to the fault core. Comparison of absolute velocities shows a scaling effect from field to laboratory for the intact rocks. A similar scaling effect is absent for the pulverized rocks, suggesting that they are dominated by micro-scale damage. Fault-parallel damage fabrics are consistent with existing models for pulverized-rock generation that predict strong dynamic reductions in fault-normal stress. Our observations provide important constraints for theoretical models and imaging fault damage properties at depth using remote methods.

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Section: Discussionmentioning

confidence: 99%

Section: Geology Fault Structure and Field Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Damage and seismic velocity structure of pulverized rocks near the San Andreas Fault

et al. 2013

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“…Following several observations of PR along the SAF, Brune [2001], Wilson et al [2005], and Rockwell et al [2009] have studied in detail an outcrop of the pulverized Tejon Lookout granite in the Tejon Pass and from the Tejon Ranch on the Garlock fault [ Sisk et al , 2005]. Based on the analysis of particle size distributions (PSD) they argued that the energy dissipated during fracturing (and/or energy required to create the extremely fine grain gouge) may be considerably larger than prior estimates, and thus may have implications to the overall earthquake energy budget.…”

Section: Introductionmentioning

confidence: 99%

Origin of pulverized rocks during earthquake fault rupture

2011

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[1] The origin of pulverized rocks (PR) in surface outcrops adjacent to the fault cores of the San Andreas and other major faults in Southern California is not clear, but their structural context indicates that they are clearly associated with faulting. An understanding of their origin might allow inferences to be drawn about the nature of dynamic slip on faults, including rupture mechanisms and their speed during earthquakes. In the present study, we use split Hopkinson bar recovery experiments to investigate whether PR can be produced under dynamic stress wave loading conditions in the laboratory and whether PR is diagnostic of any particular process of formation. The results of the study indicate that in Westerly granite for transition from sparse fracture to pervasive pulverization requires high strain rates in excess of 250/s and that the formation of PR may be inhibited at the larger burial depths. The constraint imposed by field observations of the relatively low strains (1-3%) in PR recovered from the field and the laboratory derived threshold for the critical strain rate (∼250/s and higher) together indicate that a dynamic supershear-type rupture may be necessary for the origin of pulverized rocks at distances of tens of meters away from the fault plane as observed in the field for both large strike-slip-type and the relatively small dip-slip-type fault ruptures in nature.

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Dynamic fracturing by successive coseismic loadings leads to pulverization in active fault zones

et al. 2016

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Previous studies show that pulverized rocks observed along large faults can be created by single high‐strain rate loadings in the laboratory, provided that the strain rate is higher than a certain pulverization threshold. Such loadings are analogous to large seismic events. In reality, pulverized rocks have been subject to numerous seismic events rather than one single event. Therefore, the effect of successive “milder” high‐strain rate loadings on the pulverization threshold is investigated by applying loading conditions below the initial pulverization threshold. Single and successive loading experiments were performed on quartz‐monzonite using a Split Hopkinson Pressure Bar apparatus. Damage‐dependent petrophysical properties and elastic moduli were monitored by applying incremental strains. Furthermore, it is shown that the pulverization threshold can be reduced by successive “milder” dynamic loadings from strain rates of ~180 s−1 to ~90 s−1. To do so, it is imperative that the rock experiences dynamic fracturing during the successive loadings prior to pulverization. Combined with loading conditions during an earthquake rupture event, the following generalized fault damage zone structure perpendicular to the fault will develop: furthest from the fault plane, there is a stationary outer boundary that bounds a zone of dynamically fractured rocks. Closer to the fault, a pulverization boundary delimits a band of pulverized rock. Consecutive seismic events will cause progressive broadening of the band of pulverized rocks, eventually creating a wider damage zone observed in mature faults.

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Chemical and Physical Characteristics of Pulverized Tejon Lookout Granite Adjacent to the San Andreas and Garlock Faults: Implications for Earthquake Physics

Cited by 19 publications

References 25 publications

Damage and seismic velocity structure of pulverized rocks near the San Andreas Fault

Damage and seismic velocity structure of pulverized rocks near the San Andreas Fault

Origin of pulverized rocks during earthquake fault rupture

Dynamic fracturing by successive coseismic loadings leads to pulverization in active fault zones

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