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The development of multiple paleotemperature proxies over the last twenty years has led to an increasing number of coseismic temperature measurements collected across a variety of faults. Here we present the first compilation of coseismic temperature rise measurements and frictional energy estimates to investigate the contribution of frictional heating to the earthquake energy budget and how this varies over different fault and earthquake properties. This compilation demonstrates that there is no clear relationship between coseismic temperature and displacement or thickness of the principal slip zone. Coseismic temperature rise increases with the depth of faulting until ~5 km and below this depth temperature rise remains relatively constant. Frictional energy, similarly, increases with depth until ~5km. However, frictional energy is remarkably similar across all of the faults studied here, with most falling below 45 MJ/m2. Our results suggest that dynamic weakening mechanisms may limit frictional energy during coseismic slip. We also demonstrate a basic difference between small and large earthquakes by comparing frictional energy to other components of the earthquake energy budget. The energy budget for small earthquakes (<1-10 m of displacement) is dominated by frictional energy, while in large events (>1-10 m of displacement), frictional, radiated, and fracture energy contribute somewhat equally to the earthquake energy budget. 

Basal slip along glaciers and ice streams can be significantly modified by external time-dependent forcing, although it is not clear why some systems are more sensitive to tidal stresses. We have conducted a series of laboratory experiments to explore the effect of time varying load point velocity on ice-on-rock friction. Varying the load point velocity induces shear stress forcing, making this an analogous simulation of aspects of ice stream tidal modulation. Ambient pressure, double-direct shear experiments were conducted in a cryogenic servo-controlled biaxial deformation apparatus at temperatures between −2°C and −16°C. In addition to a background, median velocity (1 and 10 μm/s), a sinusoidal velocity was applied to the central sliding sample over a range of periods and amplitudes. Normal stress was held constant over each run (0.1, 0.5 or 1 MPa) and the shear stress was measured. Over the range of parameters studied, the full spectrum of slip behavior from creeping to slow-slip to stick-slip was observed, similar to the diversity of sliding styles observed in Antarctic and Greenland ice streams. Under conditions in which the amplitude of oscillation is equal to the median velocity, significant healing occurs as velocity approaches zero, causing a high-amplitude change in friction. The amplitude of the event increases with increasing period (i.e. hold time). At high normal stress, velocity oscillations force an otherwise stable system to behave unstably, with consistently-timed events during every cycle. Rate-state friction parameters determined from velocity steps show that the ice-rock interface is velocity strengthening. A companion paper describes a method of analyzing the oscillatory data directly. Forward modeling of a sinusoidally-driven slider block, using rate-and-state dependent friction formulation and experimentally derived parameters, successfully predicts the experimental output in all but a few cases. 

Abstract Creeping faults are difficult to assess for seismic hazard because they may participate in rupture even though they likely cannot nucleate large earthquakes. The creeping central section of the San Andreas fault in California (USA) has not participated in a historical large earthquake; however, earthquake ruptures nucleating in the locked northern and southern sections may propagate through the creeping section. We used biomarker thermal maturity and K/Ar dating on samples from the San Andreas Fault Observatory at Depth to look for evidence of earthquakes. Biomarkers show evidence of many earthquakes with displacements >1.5 m in and near a 3.5-m-wide patch of the fault. We show that K/Ar ages decrease with thermal maturity, and partial resetting occurs during coseismic heating. Therefore, measured ages provide a maximum constraint on earthquake age, and the youngest earthquakes here are younger than 3 Ma. Our results demonstrate that creeping faults may host large earthquakes over longer time scales. 

Abstract Observations of glacier slip over till beds, across a range of spatial and temporal scales, show abundant seismicity ranging from Mw∼−2 microearthquakes and tremor (submeter asperities and millisecond duration) to Mw∼7 slow-slip events (∼50  km rupture lengths and ∼30  min durations). A complete understanding of the mechanisms capable of producing seismic signals in these environments represents a strong constraint on bed conditions. In particular, there is a lack of experimental confirmation of velocity-weakening behavior of ice slipping on till, where friction decreases with increasing velocity—a necessity for nucleating seismic slip. To measure the frictional strength and stability of ice sliding against till, we performed a series of double-direct-shear experiments at controlled temperatures slightly above and below the ice melting point. Our results confirm velocity-strengthening ice–till slip at melting temperatures, as has been found in the few previous studies. We provide best-fit rate-and-state friction parameters and their standard deviations from averaging 13 experiments at equivalent conditions. We find evidence of similar velocity-strengthening behavior with 50% by volume debris-laden ice slid against till under the same conditions. In contrast, velocity-weakening and linear time-dependent healing of ice–till slip is present at temperatures slightly below the melting point, providing an experimentally supported mechanism for subglacial seismicity on soft-beds. The stability parameter (a−b) decreases with slip velocity, and evolution occurs over large (mm scale) displacements, suggesting that shear heating and melt buildup is responsible for the weakening. These measurements provide insight into subglacial stiffness in which seismicity of this type might be expected. We discuss glaciological circumstances pointing to potential field targets in which to test this frozen seismic asperity hypothesis. 

Biomarker thermal maturity is widely used to study burial heating of sediments over millions of years. Heating over short timescales such as during earthquakes should also result in measurable increases in biomarker thermal maturity. However, the sensitivity of biomarker thermal maturity reactions to short, higher-temperature heating has not been established. We report on hydrous pyrolysis experiments that determine the kinetic parameters of methylphenanthrene maturation at timescales and temperatures relevant to earthquake heating. Samples of Woodford Shale were heated at temperatures up to 343 °C over 15–150 min. The thermal maturity of the samples as measured by the methylphenanthrene index-1 (MPI-1) increased with heating time and temperature. We find that MPI-1 increases with time and temperature consistent with a first-order kinetic model and Arrhenius temperature relationship. Over the timescales tested here, MPI-1 is strongly affected by maximum temperature and less sensitive to heating duration. Production of new phenanthrene isomers and expulsion of a liquid pyrolyzate also occurred. Differential expulsion of methylphenanthrene isomers affected the apparent maturity of the rock at lower temperatures and may need to be considered for organic-rich fault rocks. Our results demonstrate that the overall MPI-1 reaction extent in both the rock and pyrolyzate are a useful measure of thermal maturity and reflect temperature history during rapid heating. 

We determine the trace element stratigraphy of Site C0019, drilled during the Japan Fast Trench Drilling Project (JFAST) International Ocean Discovery Program (IODP) Expedition 343, to illuminate the structure of the plate boundary following the Tohoku-Oki earthquake of 2011. The stratigraphic units at the JFAST site are compared to undeformed Western Pacific sediments from two reference sites (Ocean Drilling Program (ODP) Site 1149 and Deep Sea Drilling Project (DSDP) Site 436). The trace element fingerprints in these reference sedimentary units can be correlated to individual JFAST samples. At the JFAST site, we find that the accretionary wedge and downgoing plate sediments in the core are composed primarily of Holocene to Eocene sediments. There are several age reversals and gaps within the sequence, consistent with multiple faults in the bottom 15 m of the JFAST core. Our results point to several candidate faults that could have slipped during the 2011 Tohoku-Oki earthquake, in addition to the pelagic clay layer that has been proposed as the main décollement fault.