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.

The energy released during earthquake rupture is partly radiated as seismic waves and mostly dissipated by frictional heating on the fault interface and by off‐fault fracturing of surrounding host rock. Quantification of these individual components is crucial to understand the physics of rupture. We use a quasi‐static rock fracture experiment combined with a novel seismic tomography method to quantify the contribution of off‐fault fracturing to the energy budget of a rupture and find that this contribution is around 3% of the total energy budget and 10% of the fracture energy Gc. The off‐fault dissipated energy changes the physical properties of the rock at the early stages of rupture, illustrated by the 50% drop in elastic moduli of the rock near the fault, and thus is expected to greatly influence later stages of rupture and slip. These constraints are a unique benchmark for calibration of dynamic rupture models.

Inconsistent polarity patterns in sediments are a common problem in magnetostratigraphic and paleomagnetic research. Multiple magnetic mineral generations result in such remanence ''haystacks.'' Here we test whether end-member modeling of isothermal remanent magnetization acquisition curves as a basis for an integrated rock magnetic and microscopic analysis is capable of isolating original magnetic polarity patterns. Uppermost Miocene-Pliocene deep-marine siliciclastics and limestones in East Timor, originally sampled to constrain the uplift history of the young Timor orogeny, serve as case study. An apparently straightforward polarity record was obtained that, however, proved impossible to reconcile with the associated biostratigraphy. Our analysis distinguished two magnetic endmembers for each section, which result from various greigite suites and a detrital magnetite suite. The latter yields largely viscous remanence signals and is deemed unsuited. The greigite suites are late diagenetic in the Cailaco River section and early diagenetic, thus reliable, in the Viqueque Type section. By selecting reliable sample levels based on a quality index, a revised polarity pattern of the latter section is obtained: consistent with the biostratigraphy and unequivocally correlatable to the Geomagnetic Polarity Time Scale. Although the Cailaco River section lacks a reliable magnetostratigraphy, it does record a significant postremagnetization tectonic rotation. Our results shows that the application of well-designed rock magnetic research, based on the end-member model and integrated with microscopy and paleomagnetic data, can unravel complex and seemingly inconsistent polarity patterns. We recommend this approach to assess the veracity of the polarity of strata with complex magnetic mineralogy.

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Postseismic recovery within fault damage zones involves slow healing of coseismic fractures leading to permeability reduction and strength increase with time. To better understand this process, experiments were performed by long‐term fluid percolation with calcite precipitation through predamaged quartz‐monzonite samples subjected to upper crustal conditions of stress and temperature. This resulted in a P wave velocity recovery of 50% of its initial drop after 64 days. In contrast, the permeability remained more or less constant for the duration of the experiment. Microstructures, fluid chemistry, and X‐ray microtomography demonstrate that incipient calcite sealing and asperity dissolution are responsible for the P wave velocity recovery. The permeability is unaffected because calcite precipitates outside of the main flow channels. The highly nonparallel evolution of strength recovery and permeability suggests that fluid conduits within fault damage zones can remain open fluid conduits after an earthquake for much longer durations than suggested by the seismic monitoring of fault healing.

Summary We present a new type of transducer capable of measuring local pore fluid pressure in jacketed rock samples under elevated confining pressure conditions. The transducers are passive (strain-gauge based), of small size (7 mm in diameter at the contact with the rock and around 10 mm in length), and have minimal dead volume (a few mm3). The transducers measure the differential pressure between the confining fluid and the internal pore pressure. The design is easily adaptable to tune the sensitivity and working pressure range up to several hundred megapascals. An array of four such transducers was tested during hydrostatic pressurisation cycles on Darley Dale sandstone and Westerly granite. The prototypes show very good linearity up to 80 MPa with maximum deviations of the order of 0.25 MPa, regardless of the combination of pore and confining pressure. Multiple internal pore pressure measurements allow us to quantify the local decrease in permeability associated with faulting in Darley Dale sandstone, and also prove useful in tracking the development of pore pressure fronts during transient flow in low permeability Westerly granite.

Elastic strain energy released during shear failure in rock is partially spent as fracture energy Γ to propagate the rupture further. Γ is dissipated within the rupture tip process zone, and includes energy dissipated as off‐fault damage, Γoff. Quantifying off‐fault damage formed during rupture is crucial to understand its effect on rupture dynamics and slip‐weakening processes behind the rupture tip, and its contribution to seismic radiation. Here, we quantify Γoff and associated change in off‐fault mechanical properties during and after quasi‐static and dynamic rupture. We do so by performing dynamic and quasi‐static shear failure experiments on intact Lanhélin granite under triaxial conditions. We quantify the change in elastic moduli around the fault from time‐resolved 3‐D P wave velocity tomography obtained during and after failure. We measure the off‐fault microfracture damage after failure. From the tomography, we observe a localized maximum 25% drop in P wave velocity around the shear failure interface for both quasi‐static and dynamic failure. Microfracture density data reveal a damage zone width of around 10 mm after quasi‐static failure, and 20 mm after dynamic failure. Microfracture densities obtained from P wave velocity tomography models using an effective medium approach are in good agreement with the measured off‐fault microfracture damage. Γoff obtained from off‐fault microfracture measurements is around 3 kJ m2 for quasi‐static rupture, and 5.5 kJ m2 for dynamic rupture. We argue that rupture velocity determines damage zone width for slip up to a few mm, and that shear fracture energy Γ increases with increasing rupture velocity.