In November 2013, a series of earthquakes began along a mapped ancient fault system near Azle, Texas. Here we assess whether it is plausible that human activity caused these earthquakes. Analysis of both lake and groundwater variations near Azle shows that no significant stress changes were associated with the shallow water table before or during the earthquake sequence. In contrast, pore-pressure models demonstrate that a combination of brine production and wastewater injection near the fault generated subsurface pressures sufficient to induce earthquakes on near-critically stressed faults. On the basis of modelling results and the absence of historical earthquakes near Azle, brine production combined with wastewater disposal represent the most likely cause of recent seismicity near Azle. For assessing the earthquake cause, our research underscores the necessity of monitoring subsurface wastewater formation pressures and monitoring earthquakes having magnitudes of ∼M2 and greater. Currently, monitoring at these levels is not standard across Texas or the United States.

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[1] In the southeast corner of the Caribbean, westward subduction of (Atlantic) oceanic South America beneath the Lesser Antilles transitions to east-west transform motion between continental South America and the Caribbean plate. This geometry requires negatively buoyant, subducting, oceanic South American lithosphere to progressively detach from positively buoyant, continental South American lithosphere. The most widely accepted model is slab break-off, with oblique arc-continent collision and northwest dipping, continental subduction precipitating narrow rifting in the subducting slab. In contrast, the subductiontransform edge propagator (STEP) model conceptualizes progressive detachment along a vertical, dip-slip tear through the lithosphere, with stress focused at the edge of the propagating transform boundary. We present four types of seismic data to resolve the ongoing lithospheric detachment: local seismicity, receiver functions, wide-angle seismic velocity inversion, and a regional, balanced cross section constrained by petroleum industry data. These four data sets image a near-vertical tear extending through the entire lithosphere, revealing a key mechanism for the structural evolution of Venezuela.Components: 5172 words, 4 figures.

In this paper, the CROP03-deep seismic reflection profile in the Northern Apennines is described and re-considered in light of new geophysical data and interpretations made available in the last five years (particularly from heat flow measurements, aeromagnetics, tomography, active stress determination and passive seismology). The crustal structure of the Northern Apennines is shown to be composed of two distinct domains. To the west is the Tyrrhenian domain and to the east is the Adriatic domain. These domains have distinctive geological and geophysical characteristics that exhibit distinct reflectivity patterns at all crustal levels. In the Tyrrhenian domain, the Upper Oligocene-Lower Miocene compressive structures are no longer recognizable, because they are dissected by subsequent extensional tectonic features. The seismic profile highlights the strong asymmetry of extensional deformation, and the upper crust is affected by a set of six major, east-dipping, low-angle normal faults. In the Adriatic domain, compressive tectonics have acted since the Middle-Miocene, and the pattern of shallow contractional structures is well preserved. The geological interpretation of the seismic data supports a thick-skinned style of deformation, where the basement is involved in the major thrust sheets. The good quality of seismic data also allows for determining the total shortening produced by the contractional structures. In the central part of the profile, at the border between the Tyrrhenian and Adriatic domains, seismic data shows the presence of an intermediate sector. The sector consists of a highly reflective window, where the refraction data indicate a local doubling of the crust for about 30 km. A scenario is presented that attempts to describe the geodynamics that drove the tectonic evolution of the Northern Apennines since the Upper Oligocene.