Fault (geology)

About: Fault (geology) is a research topic. Over the lifetime, 26732 publications have been published within this topic receiving 744535 citations.

Mineralogical characterization of protolith and fault rocks from the SAFOD Main Hole

Abstract: [1] Washed cuttings provide a continuous record of the rocks encountered during drilling of the main hole of the San Andreas Fault Observatory at Depth (SAFOD). Both protolith and fault rocks exhibit a wide variety of mineral assemblages that reflect variations in some combination of lithology, P-T conditions, deformation mechanisms, and fluid composition and abundance. Regions of distinct neomineralization bounded by faults may record alteration associated with fluid reservoirs confined by faults. In addition, both smectites occurring as mixed-layer phases and serpentine minerals are found in association with active strands of the San Andreas Fault that were intersected during drilling, although their rheological influence is not yet fully known. Faults containing these mineralogical phases are prime candidates for continuous coring during Phase 3 of SAFOD drilling in the summer of 2007.

Factors controlling normal fault offset in an ideal brittle layer

Abstract: We study the physical processes controlling the development and evolution of normal faults by analyzing numerical experiments of extension of an ideal two-dimensional elastic-plastic (brittle) layer floating on an inviscid fluid. The yield stress of the layer is the sum of the layer cohesion and its frictional stress. Faults are initiated by a small plastic flaw in the layer. We get finite fault offset when we make fault cohesion decrease with strain. Even in this highly idealized system we vary six physical parameters: the initial cohesion of the layer, the thickness of the layer, the rate of cohesion reduction with plastic strain, the friction coefficient, the flaw size and the fault width. We obtain two main types of faulting behavior: (1) multiple major faults with small offset and (2) single major fault that can develop very large offset. We show that only two parameters control these different types of faulting patterns: (1) the brittle layer thickness for a given cohesion and (2) the rate of cohesion reduction with strain. For a large brittle layer thickness (> 22 km with 44 MPa of cohesion), extension always leads to multiple faults distributed over the width of the layer. For a smaller brittle layer thickness the fault pattern is dependent on the rate of fault weakening: a very slow rate of weakening leads to a very large offset fault and a fast rate of weakening leads to an asymmetric graben and eventually to a very large offset fault. When the offset is very large, the model produces major features of the pattern of topography and faulting seen in some metamorphic core complexes.

Fracturing and hydrothermal alteration in normal fault zones

Abstract: Large normal fault zones are characterized by intense fracturing and hydrothermal alteration. Displacement is localized in a slip zone of cataclasite, breccia and phyllonite surrounding corrugated and striated fault surfaces. Slip zone rock grades into fractured, but less comminuted and hydrothermally altered rock in the transition zone, which in turn grades abruptly into the wall rock. Fracturing and fluid flow is episodic, because permeability generated during earthquakes is destroyed by hydrothermal processes during the time between earthquakes.

Slip rates and recurrence intervals of the Longmen Shan active fault zone,and tectonic implications for the mechanism of the May 12 Wenchuan earthquake,2008,Sichuan,China

Abstract: The great Wenchuan earthquake of May 12,2008 occurs on the Longmen Shan fault zone which forms a prominent section of the seismically very active seismic belt called the North- South Trending Seismic Belt by Chinese seismologists.There have been 3 earthquakes with magmtudes from 6 to 61/2 along the Longmen Shan fault zone during more then 2000 year documented history of the Sichuan province.Previous active faulting studies indicate slow(less than 3 mm/yr)slip rate across the Longmen Shan fault zone.Why such a strong earthquake occurred in the Longmen Shah fault zone?What are the characteristics of the May 12 earthquake? What is the tectonic mechanism of the earthquake?On the basis of geological studies of the earthquake surface rupture zone and pre-earthquake GPS measurements in the region,we try to understand the questions mentioned above.The May 12 earthquake,2008 is caused by displacement along the Yingxiu-Beichuan fault along which a more than 200 km long surface ruptures was formed.Another strand of the Longmen Shan fault zone,Guanxian-Jiangyou fault also ruptured as indicated by more then 60 km long surface ruptures.GPS measurements before the earthquake suggest that slip rate across the entire Longmen Shan fault zone does not excess about 2 mm/yr,and does not excess 1 mm/yr across individual fault strand.These data agree with seismogeological studies and historical seismicity of the Sichuan province.Using maximum coseismic displacement obtained from seismogeological studies and inversions from seismic waves, the recurrence intervals of great earthquakes,such as the 2008 Wenchuan earthquake,can be estimated to be 2000～6000 years.The Longmen Shan fault zone has a high dipping angle(more than 50°～60°)near surface and low-angle at depth(15～20 kin).This kind of listric shape favors significant strain or energy accumulation to form great earthquake.The May 12 Wenchuan earthquake,2008 is characterized by slow strain accumulation,long recurrence interval,and significant damage power.It is a new type of earthquake event that deserves further studies.