Shear Zone

Analysis of structural rift architecture shows that the graben formation is commonly controlled by the contemporaneous activity of two fault trends with an angular obliquity of approximately 40°. Inspection of the crustal basement and geophysical data reveals that these faults are parallel to inherited oblique crustal and lithospheric discrete fabrics, which are reactivated during the extension event. We conducted experiments

This study describes the seismo-tectonic evolution of Cameroon. It is noticed that seismic activity is largely related to the Cameroon volcanic line (CVL) and many of the tectonic phenomena follow the previous structural lines. Although the area is that of a relatively low seismicity, the effects of a given earthquake could be considerable. This study combines seismic records, from 1952 to 2002 and from 2005 to 2007, with the integration of existing structural information to better define the seismogenic zones. An important identified cluster of epicenters in S-W defines the first seismic source region where events' characteristics show a weak seismicity related to volcanic activity. The second seismogenic zone, in the north of Mount Cameroon volcano, illustrates the activity of Central Cameroon Shear Zone (CCSZ) faults; its seismicity is considered weak to moderate with maximum magnitude recorded which is 5.1 Mb. The area of " Sanaga Shear Zone " (SSZ) constitutes the third seismic source region with moderate seismicity in which maximum magnitude recorded is 5.8 Mb; Depth of its faults segments is evaluated at 33 km. The fourth Source Region follows the North boundary of Congo Craton; a characteristic event with magnitude of 6 M allows evaluating fault depth at 33 km. Also three zones define crustal structure: the South Domain with thick crust, the Center Domain characterized by thin crust, active tectonic and volcanic structures and the north domain with shallow Moho.

The Ribeira belt in southeastern Brazil was generated during the Brazilian Orogeny, the South American equivalent of the Pan-African Orogeny (∼ 700-450 Ma). The central sector of the belt is characterised by a series of northwest-vergent crustal-scale thrust stacks ...

The Serido Group is a deformed and metamorphosed metasedimentary sequence that overlies early Paleoproterozoic to Archean basement of the Rio Grande do Norte domain in the Borborema Province of NE Brazil. The age of the Serido Group has been disputed over the past two decades, with preferred sedimentation ages being either Paleoproterozoic or Neoproterozoic. Most samples of the Serido Formation, the upper part of the Serido Group, have Sm–Nd TDM ages between 1200 and 1600 Ma. Most samples of the Jucurutu Formation, the lower part of the Serido Group, have TDM ages ranging from 1500 to 1600 Ma; some basal units have TDM ages as old as 2600 Ma, reflecting proximal basement. Thus, based on Sm–Nd data, most, if not all, of the Serido Group was deposited after 1600 Ma and upper parts must be younger than 1200 Ma. Cathodoluminescence photos of detrital zircons show very small to no overgrowths produced during ca. 600 Ma Brasiliano deformation and metamorphism, so that SHRIMP and isotope d...

The Late IGbaran magmatism in Burundi is represented by 2 magmafic associations. Small alkaline granitoid plutons constitute the first one. In Central Burundi, they form a N-S alignment of 40 kin. A new Rb-Sr 7 WR age of 1137 + 39 M.a. (Ro = 0.7027 + 0.0011; MSWD = 2.0), considered to date the emplacement of the granitoids, conf'mns a

The still ongoing studies on the geology of the Apuan Alps
show the presence of a deformational event which is developed
in the late-metamorphic to post-metamorphic conditions (D3),
that has occurred on the previous structures and has created the
low-angle shear zones and high-angle faults, associated with both
right hand and left hand complicated movement systems. These
shear zones represent a new element in the geological landscape
of the Apuan Alps, and our knowledge about them is deducted
from the information obtained from the traditional geologicalstructural
surveys and photo-interpretation of data derived from
aerial LIDAR and optical proximal sensing. The effects of brittle/
ductile to ductile deformation which characterizes the Apuan
Metamorphic Complex, has established the development of shear
zones consisting the mylonitic marbles, such as the specific types
of Bianco, Bardiglio, Nuvolato and Arabescato marbles, which
are distinguished by their excellent physical and mechanical
characteristics, as well as having high commercial and aesthetic
value. These particular structures and their three-dimensional
architecture affect the geometry of the deposits of ornamental
stones and as the consequence, also on the planning of medium
and long-term mining activities.

This note shows a study on the seismic passive earth pressure behind a non-vertical cantilever retaining wall using pseudo-dynamic approach. A composite failure surface comprising of an arc of the logarithmic spiral near the wall and a straight line in the planar shear zone near the ground, has been considered behind the retaining wall. The effects of soil friction angle, wall inclination, wall friction angle, amplification of vibration, horizontal and vertical earthquake acceleration on the passive earth pressure have been explored in this study. The results available in the literature for passive pressure, on the basis of pseudo-static analysis are found to predict the passive resistance on the conservative side and the assumption of a planar failure surface is found to overestimate the passive resistance for higher wall friction. An attempt has been made in the present study to overcome both the limitations simultaneously. The present results are compared with the existing values in the literature and found a reasonable match among the values.

The Pinto shear zone is one of several Late Cretaceous shear zones within the eastern fringe of the Mesozoic magmatic arc of the southwest Cordilleran orogen that developed synchronous with continued plate convergence and backarc shortening. We demonstrate an extensional origin for the shear zone by describing the shear-zone geometry and kinematics, hanging wall deformation style, progressive changes in deformation