Mantle exhumation at magma-poor rifted margins controlled by frictional shear zones.

The transition zone from continental crust to the mature mid-ocean ridge spreading center of the Iberia-Newfoundland magma-poor rifted margins is mostly composed of exhumed mantle characterized by highs and domes with varying elevation, spacing and shape. The mechanism controlling strain localization and fault migration explaining the geometry of these peridotite ridges is poorly understood. Here we show using forward geodynamic models that multiple out-of-sequence detachments with recurring dip reversal form during magma-poor rifting and mantle exhumation as a consequence of the strength competition between weak frictional-plastic shear zones and the thermally weakened necking domain beneath the exhuming footwall explaining geometry of these peridotite ridges. Model behaviour also shows that fault types and detachment styles vary with spreading rate and fault strength and confirm that these results can be compared to other magma poor passive margins such as along Antarctica-Australia and to ultra-slow mid-ocean spreading systems as the South-West Indian Ridge.

Earthquake statistics changed by typhoon-driven erosion.

Tectonics and climate-driven surface processes govern the evolution of Earth's surface topography. Topographic change in turn influences lithospheric deformation, but the elementary scale at which this feedback can be effective is unclear. Here we show that it operates in a single weather-driven erosion event. In 2009, typhoon Morakot delivered ~ 3 m of precipitation in southern Taiwan, causing exceptional landsliding and erosion. This event was followed by a step increase in the shallow (< 15 km depth) earthquake frequency lasting at least 2.5 years. Also, the scaling of earthquake magnitude and frequency underwent a sudden increase in the area where mass wasting was most intense. These observations suggest that the progressive removal of landslide debris by rivers from southern Taiwan has acted to increase the crustal stress rate to the extent that earthquake activity was demonstrably affected. Our study offers the first evidence of the impact of a single weather-driven erosion event on tectonics.

Intraoperative severity assessment of coronary artery stenosis in patients at risk: the role of transesophageal echocardiography.

A 71-yr-old male was scheduled for infrarenal abdominal aortic aneurysm repair. Although he had only minor clinical predictors for increased perioperative cardiovascular risk with >4 estimated metabolic equivalents for activities, intraoperative transesophageal echocardiography revealed an abnormal maximal-to-prestenotic blood flow velocity ratio in the left main coronary artery. Postoperatively, a severe distal left main coronary artery stenosis was confirmed with coronary angiography. Understanding the flow velocity patterns in the coronary arteries helps the anesthesiologist to detect coronary lesions with transesophageal echocardiography.