Tremor signals during fluid injection are generated by fault slip.

Seismic tremor signals, also known as long-period, long-duration signals, have been reported in several locations where fluid injection for enhanced oil and gas exploration is taking place. However, the origin of these signals remains poorly constrained. We studied seismic tremor signals in Wellington Field, Kansas, using a seismic array during a carbon dioxide injection program. We show that these signals are generated below the surface during the time of carbon dioxide injection. They have a distinct spectral signature, similar to those observed in glacial and volcanic environments. The tremor sources are located near the injection site and aligned with preexisting faults. Modeling results imply that such tremors are generated by frictional slip on fault. These observations may reveal an important deformation mode, which is useful for studying associated stress, seismicity, and triggering, as well as for tracking fault activities during injection operations of all fluids, including supercritical carbon dioxide.

Effectiveness of anterior subcutaneous internal fixation (INFIX) in the management of potentially infected pelvis fractures.

BACKGROUND: Anterior plating is the treatment of choice in anterior pelvic ring fractures. In certain situations where pelvis fracture is associated with open wound, infection, abdominal injury or bladder injury - internal fixation with plate is contraindicated. Conventionally, external fixation is done in such cases. However, External Fixation is associated with pin tract infection, pin loosening, difficult wound care and less patient compliance. The present study was conducted to evaluate a possible 'middle path' between the two procedures. METHODS: A prospective study was conducted from July 2017 to December 2019.18 adult patients with risk of infection were treated with INFIX. The patients' data was collected on presentation, preoperatively, intra-operatively and post operatively. The patients were followed up with serial radiographs. Functional status was assessed using Iowa Pelvis Score. After radiological union, implant removal was performed. The patients were followed up for a minimum of 6 months after the removal surgery. RESULTS: The average age of patients in present study was 39.55 years with a male predominance. 16 out of 18 patients were polytrauma cases with ISS more than 15.50% patients had Lateral Compression type of fracture. Radiological union was seen at an average of 3.5 months. After removal, 78% patients had excellent outcome and 22% patients had good outcome. The complications observed were LFCN irritation (27.78%) and asymptomatic heterotopic ossification (22%). CONCLUSION: Present study concludes that INFIX produces excellent outcome in pelvis fractures with risk of infection where anterior plating is contraindicated.

The role of ridges in the formation and longevity of flat slabs.

Flat-slab subduction occurs when the descending plate becomes horizontal at some depth before resuming its descent into the mantle. It is often proposed as a mechanism for the uplifting of deep crustal rocks ('thick-skinned' deformation) far from plate boundaries, and for causing unusual patterns of volcanism, as far back as the Proterozoic eon. For example, the formation of the expansive Rocky Mountains and the subsequent voluminous volcanism across much of the western USA has been attributed to a broad region of flat-slab subduction beneath North America that occurred during the Laramide orogeny (80-55 million years ago). Here we study the largest modern flat slab, located in Peru, to better understand the processes controlling the formation and extent of flat slabs. We present new data that indicate that the subducting Nazca Ridge is necessary for the development and continued support of the horizontal plate at a depth of about 90 kilometres. By combining constraints from Rayleigh wave phase velocities with improved earthquake locations, we find that the flat slab is shallowest along the ridge, while to the northwest of the ridge, the slab is sagging, tearing, and re-initiating normal subduction. On the basis of our observations, we propose a conceptual model for the temporal evolution of the Peruvian flat slab in which the flat slab forms because of the combined effects of trench retreat along the Peruvian plate boundary, suction, and ridge subduction. We find that while the ridge is necessary but not sufficient for the formation of the flat slab, its removal is sufficient for the flat slab to fail. This provides new constraints on our understanding of the processes controlling the beginning and end of the Laramide orogeny and other putative episodes of flat-slab subduction.