Fault (geology)

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

Andean structural control on interseismic coupling in the North Chile subduction zone

Abstract: Segmentation can influence the extent of earthquake rupture and event magnitude: large megathrust earthquakes result from total rupture of relatively continuous segments of the subduction interface. Segmentation is attributed to variations in the frictional properties of the seismogenic zone or to topographic features on the down-going plate. Structures in the overriding plate may also influence segmentation but their importance has been dismissed. Here, we investigate the links between interface segmentation at the North Chile seismic gap and a crustal-scale fault structure in the overriding plate that forms a coastal scarp of about 1 km in height. We use satellite interferometric synthetic aperture radar (InSAR) and Global Positioning System (GPS) data to measure interseismic surface deformation between 2003 and 2009 and compare the deformation with rupture extent during well-documented earthquakes. From these data we infer the degree of coupling and segmentation at depth. We find that along a 500-km-long segment, the base of the strongly coupled seismogenic zone correlates with the line of the surface coastal scarp and follows the outline of the Mejillones Peninsula. This correlation implies that large-scale structures in the overriding plate can influence the frictional properties of the seismogenic zone at depth. We therefore suggest that the occurrence of megathrust earthquakes in northern Chile is controlled by the surface structures that build Andean topography.

Selection of Earthquake Scaling Relationships for Seismic‐Hazard Analysis

Abstract: A fundamentally important but typically abbreviated component of seismic‐hazard analysis is the selection of earthquake scaling relationships. These are typically regressions of historical earthquake datasets, in which magnitude is estimated from parameters such as fault rupture length and area. The mix of historical data from different tectonic environments and the different forms of the regression equations can result in large differences in magnitude estimates for a given fault rupture length or area. We compile a worldwide set of regressions and make a first‐order shortlisting of regressions according to their relevance to a range of tectonic regimes (plate tectonic setting and fault slip type) in existence around the world. Regression relevance is based largely on the geographical distribution, age, and quantity/quality of earthquake data used to develop them. Our compilation is limited to regressions of magnitude (or seismic moment) on fault rupture area or length, and our shortlisted regressions show a large magnitude range (up to a full magnitude unit) for a given rupture length or area across the various tectonic regimes. These large differences in magnitude estimates underline the importance of choosing regressions carefully for seismic‐hazard application in different tectonic environments.

Cohesive strengthening of fault zones during the interseismic period: An experimental study

Abstract: [1] There is widespread evidence indicating that faults regain a portion of their strength during the interseismic period. Here, we present experiments designed to understand and quantify the interseismic cohesive strengthening resulting from fluid-rock reactions in fault zones. The triaxial experiments consisted of fracturing cores of Fontainebleau sandstone under dry conditions, forming a localized shear failure zone (stage 1). The specimens were then reacted hydrothermally under isostatic conditions, allowing the fault damage zone to compact, consolidate and strengthen (stage 2). Following reaction, the specimens were then reloaded to failure under nominally dry conditions, so that the increase in cohesive strength of the fault could be measured (stage 3). Experiments show that cohesion increase is positively correlated to temperature and pore pressure during reaction. After 6 hours of reaction at the highest temperatures (927°C) and pore pressures (200 MPa), cohesion increases by as much as 35 MPa. Microstructural examination of the specimens showed that the gouge particles within the fault compacted and cemented together, exhibiting textures typical of pressure solution and that fractures in the surrounding damage zone had healed. A theoretical treatment of the data was conducted using these experiments in combination with results on time-dependent changes in fault cohesion presented by Tenthorey et al. (2003). We find that the rate-controlling process in our experiments has an activation energy (Q) of approximately 70 kJ mol−1. We use this information to develop a model for time-dependent cohesive strengthening in fault zones within the continental seismogenic regime. We conclude that significant cohesive strengthening of fault zones can occur during the interseismic period of medium to large earthquakes given the presence of reactive pore fluids.

Thickening of fault zones: A mechanism of melange formation in accreting sediments

Abstract: Sediments accreted at subduction zones undergo stratal disruption and form a type of melange. The thickness of the disrupted zones grows with progressive deformation. This suggests that initial fault surfaces are abandoned and deformation propagates into adjacent undeformed sediment. Factors causing the abandonment of fault surfaces during continuing deformation include (1) strengthening owing to porosity loss during consolidation, (2) localized drops in fluid pressure on fault surfaces that act as dewaterinig conduits, and (3) reorientation of fault surfaces. The disruptive processes occurring in accretionary prisms result principally from the deformation of a consolidating sediment mass.