Development Of Strike-slip Faults Research Articles

Late Miocene transition from extension to dextral transtension in the southern Coastal Sonora fault zone, Gulf of California rift, Mexico

The Coastal Sonora fault zone (CSFZ) in northwestern Mexico records the Pacific–North America plate boundary reorganization during the Miocene from subduction to a transform boundary. This study presents the structural architecture of the Sierra El Aguaje-San Carlos-Guaymas region along the southern part of the CSFZ. The study area shows a complex fault pattern divided into four tectonic domains: ENE–WSW left-lateral, normal, and oblique faults in the Sierra El Aguaje and Cerro El Vigía domains and N–S domino-type normal faults in the El Parral and San Carlos domains, which are separated by the NW-striking dextral San Carlos fault. Based on a new fault-slip dataset and K-Ar ages, we propose a structural evolution model in which deformation progressively evolved from extension to dextral transtension. The deformation history involved ∼E–W pure extension associated with N–S normal faults from ∼15.3 Ma to ∼11–10 Ma, followed by transtension and the development of strike-slip faults after ∼11–10 Ma. That change induced the reactivation of preexisting faults and local strain partitioning between normal, oblique, and strike-slip faults. Transtension became strike-slip dominated during the latest Miocene and the Pliocene, accumulating ∼8 km of post-6.3 Ma dextral slip along the San Carlos fault. Paleostress analysis demonstrates that during the extensional phase, σ2 and σ3 were horizontal and oriented ∼N–S and ∼E–W, respectively. The transition to transtension required that σ2 reached the lithostatic stress value, its magnitude approached σ1, and its orientation remained ∼N–S. These conditions implied a horizontal tectonic force directed towards the north began after ∼11–10 Ma in northwestern Mexico. We propose that this new stress regime was related to the end of the Farallon–North America convergence and the inception of the Gulf of California oblique rifting with σ1 oriented N–S.

The Strike-Slip Fault Effects on Tight Ordovician Reef-Shoal Reservoirs in the Central Tarim Basin (NW China)

The largest carbonate condensate field in China has been found in the central Tarim Basin. Ordovician carbonate reservoirs are generally attributed to reef-shoal microfacies along a platform margin. However, recent production success has been achieved along the NE-trending strike-slip fault zones that intersect at the platform margin. For this contribution, we analyzed the strike-slip fault effects on the reef-shoal reservoirs by using new geological, geophysical, and production data. Seismic data shows that some NE-trending strike-slip faults intersected the NW-trending platform margin in multiple segments. The research indicated that the development of strike-slip faults has affected prepositional landforms and the subsequent segmentation of varied microfacies along the platform margin. In addition, the strike-slip fault compartmentalized the reef-shoal reservoirs into multiple segments along the extent of the platform margin. We show that fractured reef-shoal complexes are favorable for the development of dissolution porosity along strike-slip fault damage zones. In the tight matrix reservoirs (porosity < 6%, permeability < 0.5 mD), the porosity and permeability could be increased by more than 2–5 times and to 1–2 orders of magnitude in the fault damage zone, respectively. This suggests that high production wells are correlated with “sweet spots” of fractured reservoirs along the strike-slip fault damage zones, and that the fractured reservoirs in the proximity of strike-slip fault activity might be a major target for commercial exploitation of the deep Ordovician tight carbonates.

Variation in fracture patterns in damage zones related to strike-slip faults interfering with pre-existing fractures in sandstone (Calcione area, southern Tuscany, Italy)

This paper deals with the effects of pre-existing fractures on the development of damage zones related to meter and decameter strike-slip faults, which affected Late Oligocene-Early Miocene sandstone in the Calcione area, southern Tuscany (Italy). Strike-slip faults dissected rock masses locally affected by pervasive, pre-existing fractures related to previous deformational events. Two different domains were identified: rock masses affected and unaffected (or relatively unaffected) by pre-existing fractures. Strike-slip faults affecting the two domains made it possible to compare the different configurations of fracture patterns related to isolated or interacting fault segments. New data is provided on scaling relations between: i) fault length and the length of related fractures; ii) mean step length and width for overstepping fault segments; iii) angular values at the intersection of the fault plane and related fractures. Scaling relations obeyed a positive power law for faults dissecting sandstone unaffected by pre-existing fractures. On the contrary, no scaling relations were recognized for faults dissecting sandstone affected by pre-existing fractures. The development of strike-slip faults on rock masses affected by pre-existing fractures can simulate splays apparently related to faulting. Three main points were categorized for detecting deceptive cases. There is a real chance of a deceptive fracture pattern if: i) the angular values at the intersection of the fault and its fractures (mode I opening fracture) exceed 50° in the wall damage zone; ii) the scaling relation between fault length and maximum fracture length does not fit a power law; iii) fractures acted as shear fractures. The resulting framework provides additional data for understanding the development and architecture of strike-slip faults.

Development of strike-slip faults from dikes, Sequoia National Park, California

Faults several kilometers long near Pear Lake in Sequoia National Park, California nucleated on preexisting dikes weakened by closely-spaced échelon joints. These joints essentially parallel much more widely spaced regional joints. Fault nucleation by dike fracturing can explain how a nearly planar fault can grow to lengths of several kilometers or more. We suggest that opening mode fractures, including dikes, might serve more commonly as nuclei for faults than is generally appreciated. The longest fault in the study area, the Pear Lake fault, has a trace length of ∼7 km and a maximum measured lateral separation of 86–98 m. A sharp decrease in slip occurs near the center of the trace of the Pear Lake fault where another fault branches from it. Mechanical analyses demonstrate that a sharp decrease in slip is expected where a fault branches. All the faults near Pear Lake show non-elliptical slip distributions. Based on our mechanical analyses, we infer that the observed slip distributions reflect a mechanical interaction among the faults. The geometry and distribution of structures that precede faulting (i.e. dikes and joints) control to a large extent the structure of a fault network and hence the ultimate slip distribution on faults in the network.

Development of strike-slip faults in the dolomites of the Sella Group, Northern Italy

The dolomites in the Sella Group, Northern Italy, were intensely jointed and faulted during the Alpine orogeny. Field observation of joints, joint-zones, and faults are the basis for a model for fault development in dolomite. We propose that joints developed parallel to the maximum compressive stress direction and were homogeneously distributed throughout the Sella Group before faults became localized (fault pre-nucleation stage). With ongoing deformation, the joints were localized into en-échelon arrays also called joint-zones. These joint-zones are incipient faults and are characterized by small dilation (≪1 mm) of the individual joints, narrow joint spacing (1–15 mm), a high number of joints in the array (up to thousands), high joint-overlap, and joint-array angles between 10° and 40°. The next stage in fault development involves the break up of the rock bridges in the joint-zones and the localization of shear. Joint-zones with pockets of breccia are the smallest faults encountered and accommodate strike-slip offsets of 5–7 mm, whereas joint-zones with a continuous breccia zone accommodate offsets of 1–3 cm. Faults with offsets of more than 1 m are characterized by a breccia zone 0.5–15 m wide, and high joint densities in the wall-rock. The absence of a distinct granular structure of the dolomites of the Sella Group and the shallow depth of burial during Alpine deformation (less than 1000 m) may have promoted the growth and localization of joints, their linking via cross-joints, and the formation of continuous faults.

Development of strike-slip faults: shear experiments in granular materials and clay using a new technique

A new experimental technique has been developed to study fault development in layers of moist granular materials (clay and fault gouge) in shear. Faults nucleated on pre-existing pores and on low-displacement protofaults in flaw-free areas. Only a small number of the protofaults developed significant displacement, forming conjugate simple fault sets. After nucleation, simple faults propagated in-plane. As these simple faults grew in length and new simple fault sets nucleated, they began to interact and coalesce. Simple faults linked up to form compound faults, and compound faults linked up to form even larger through-going strike-slip faults. The fault patterns produced in the shear experiments were integrated fault networks consisting of several sets of conjugate shears and tensile structures. Compound faults exhibited both releasing and restraining steps formed during fault coalescence. Displacement along such a compound strike-slip fault caused a mismatch of the two walls. A few points became resistant barriers while the remaining segments became pull-apart basins. Both releasing and restraining steps led to the development of pull-apart basins. Fault displacement and propagation rate were linear functions of fault length. The difference between the experiment described here and traditional Riedel experiments is that the new experiments do not have a pre-existing fault in the experimental setup. Therefore they are more suitable to study fault nucleation and evolution in a broad shear zone.

Effect of mechanical interaction on the development of strike-slip fault with echelon patterns

Effect of mechanical interaction on the development of strike-slip fault with echelon patterns

Effect of mechanical interaction on the development of strike-slip faults with echelon patterns

The overlapping geometry of echelon strike-slip faults is well-known. We have quantified this observation by measuring the amount of overlap and separation, and plotting them against each other for over 120 examples. Although there is large scatter, the data show a linear trend suggesting that the overlap increases proportionally with separation, up to a limiting value. We have analyzed this conspicuous relationship in terms of fault interaction by using a numerical model based on displacement discontinuity. The results show that fault interaction is, in fact, an important factor in contributing to the overlapping geometry of echelon strike-slip faults.