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This is a pre-copy-editing, author-produced PDF of an article accepted for publication in The Geological Society of America Special Papers following peer review. The definitive publisher-authenticated version: "Regalla, C., Rowe, C., Harrichhausen, N., Tarling, M. and Singh, J., 2018. Styles of underplating in the Marin Headlands Terrane, Franciscan Complex, California. GSA Special Publications no. 534" is available online at: http://rock.geosociety.org/Store/detail.aspx?id=spe534.

On Kodiak Island, Alaska, decimeterthick black fault rocks are at the core of foliated cataclasites that are tens of meters thick. The cataclasites belong to melange zones that are regarded as paleodecollements active at 12–14 km depth and 230–260 °C. Each black layer is mappable for tens of meters along strike. The black fault rocks feature a complex layering made at microscale by alternation of granular and crystalline micro textures, both composed of micronscale subrounded quartz and plagioclase in an ultrafi ne, phyllosilicate-rich matrix. In the crystalline microlayers, tabular zoned micro lites of plagioclase make up much of the matrix. No such feldspars have been found in the cataclasite. We interpret these crystalline microlayers as pseudotachylytes. The granular microlayers show higher grainsize variability, crushed microlites, and textures typical of fl uidization and granular fl ow deformation. Crosscutting relationships between granular and crystalline microlayers include fl ow and intrusion structures and mutual brittle truncation. This suggests that each decimeters-thick composite black fault rock layer records multiple pulses of seismic slip. In each pulse, ultracomminuted fl uidized material and friction melt formed and deformed together in a ductile fashion. Brittle truncation by another pulse occurred after solidifi cation of the friction melt and the fl uidized rock. X-ray powder diffraction (XRPD) and X-ray fl uorescence (XRF) analyses show that black fault rocks have similar mineral composition and chemical content as the cataclasites. The observed systematic chemical differences cannot be explained by bulk or preferential melting of any of the cataclasite components. The presence of an open, fl uidinfi ltrated system with later alteration of black fault rocks is suggested. The geochemical results indicate that these subductionrelated pseudotachylytes differ from those typically described in crystalline rocks and other tectonic settings.

1135 Seismology has provided records of earthquake shaking dating back centuries, but even the longest historical records cannot suffi cient to demonstrate the long-term patterns, as we learned from the 2011 Tohoku Earthquake (Liu and Zhou, 2012). A major challenge for the study of past earthquakes is that events on such time scales—seconds to minutes—are rarely preserved in the rock record. When they are, the records represent isolated moments, not the days to years before and after the event that would place them in context. “Earthquake geology” includes the study of rupture itself (on the fault surface), ground shaking and its effects, and stress and fl uid pressure changes both on- and off-fault, on geologic to human time scales (Sibson, 2011). Loope et al. (2013, p. 1131 in this issue of Geology) document an exceptionally well-preserved array of sand volcanoes in the Navajo Sandstone (southwest United States), capturing an ~1-yr-long Jurassic earthquake swarm. Radiating seismic waves cause transient changes in pressure conditions that may result in permanent damage. Examples include slope failure, intrusion, injection and extrusion of fl uidized sediments (liquefaction), folding and slumping, and autobrecciation (Montenat et al., 2007). Such deformed sediments, sometimes called “seismites,” record energetic disturbance of material at the earth’s surface. If the sediments are rapidly buried, they may be preserved and identifi able in the rock record. Earthquakes, however, are not the only source of energy that might deform soft sediments. Storms, landslides and rockfalls, currents, far-traveled tsunami waves, and impacts may also cause liquefaction and deformation. The stress perturbation caused by such a transient event might be required for